Browse Topic: Low temperature combustion (LTC)

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Water Injection for Combustion Phasing Control and Load Expansion on an Ethanol HCCI Engine2022-01-04513/29/2022
Homogeneous charge compression ignition (HCCI) combustion is low-temperature combustion (LTC) mode that offers an alternative to conventional combustion modes. The advantages of HCCI combustion include high conversion efficiency and low NOx emissions. On the other hand, a direct control mechanism for combustion phasing control is not attainable as in conventional SI (spark ignition) or CI (compression ignition) engines. This limits the HCCI operational range and provides one of the biggest challenges in HCCI mode commercial implementation. High heat release rates and knock initiation limit the high load operation, whereas combustion instabilities limit the low load operation. In this context, this paper explores the use of water injection technique to control the combustion phasing and expand the load of an ethanol HCCI engine. The experiments were conducted on a three-cylinder diesel engine, where all the exhaust gases from a diesel cylinder were used to achieve the HCCI combustion in another cylinder. The results showed that the water injection technique was effective in controlling the charge reactivity and consequently the combustion phasing while enabling higher engine load. The water injection reduced combustion speed and heat release rates, which led to higher combustion duration, better combustion phasing control, and a reduction of ringing intensity. It was possible to expand the initial engine load from 2.0 bar without water injection to 6.0 bar IMEP with water injection. In addition, the ethanol HCCI combustion achieved high indicated efficiencies, ranging from 34 to 39%, while maintaining good combustion stability and low emissions characteristics.
Telli, Giovani D., Rocha, Luiz A.O., Zulian, Guilherme Y., Lanzanova, Thompson D.M., Martins, Mario E.S.
Investigation of a Second Exhaust Valve Lift to Improve Combustion in a Methane - Diesel Dual-Fuel Engine2022-01-04663/29/2022
In recent years, the utilization of dual-fuel combustion has gained popularity in order to improve engine efficiency and emissions. With its high knock resistance, methane allows operation in high compression diesel engines with lower risk of knocking. With the use of diesel fuel as an ignition source, it is possible to exploit the advantages of lean combustion without facing problems to provide the high amount of ignition energy necessary to burn methane under such operating conditions. Another advantage is the variety of sources from which the primary fuel can be obtained. In addition to fossil sources, methane can also be produced from biomass or electrical energy.As the rate of substitution of diesel by methane increases, the trade-off between nitrogen oxide and soot is mitigated. However, emissions of carbon monoxide and unburned methane increase. Since carbon monoxide is toxic and methane has 25 times the global warming potential of carbon dioxide, these emission components pose a problem. Because of the stability of the molecule, methane catalysts require an exhaust gas temperature of over 500 °C in order to work effectively.In this work, the effect of conventional cooled external exhaust gas recirculation (EGR) and additional hot internal EGR are investigated for different substitution rates in a nonroad tractor engine converted to dual-fuel operation. The internal EGR rate is controlled by a variable second exhaust valve lift during the intake stroke - an approach which promises to benefit dual-fuel engines by increasing the in-cylinder gas temperature, thus favoring more complete combustion. A simulation model of the engine is used to determine the internal EGR rates and in-cylinder temperatures based on the experimental data. When internal EGR is used in combination with external EGR, the resulting emissions show additional reductions in nitrogen oxide (up to -51 %), carbon monoxide (up to -18 %) and methane (up to -28 %) with increasing internal EGR, while still maintaining low soot levels due to the substitution of diesel fuel for methane.
Mueller, Florian, Guenthner, Michael, Weigel, Alexander, Thees, Matthias
Infrared/Visible Optical Diagnostics of RCCI Combustion with Dieseline in a Compression Ignition Engine2020-01-05574/14/2020
Compression ignition engines are widely used for transport and energy generation due to their high efficiency and low fuel consumption. To minimize the environmental impact of this technology, the pollutant emissions levels at the exhaust are strictly regulated. To reduce the after-treatment needs, alternative strategies as the low temperature combustion (LTC) concepts are being investigated recently. The reactivity controlled compression ignition (RCCI) uses two fuels (direct- and port- injected) with different reactivity to control the in-cylinder mixture reactivity by adjusting the proportion of both fuels. In spite of the proportion of the port-injected fuel is typically higher than the direct-injected one, the characteristics of the latter play a main role on the combustion process. Use of gasoline for direct injection is attractive to retard the start of combustion and to improve the air-fuel mixing process. In this work, the influence of the direct-injected fuel properties on RCCI combustion mode is studied in an optical compression ignition engine. Gasoline fuel is injected in the intake manifold while a blend of gasoline and diesel (a.k.a. dieseline) is directly injected into the cylinder. Non-conventional optical diagnostics in the visible and infrared spectra are applied for the direct investigation of the in-cylinder phenomena during the injection and the combustion processes. A low-luminosity, mainly kinetically controlled combustion mode has been observed.
Sequino, Luigi, Mancaruso, Ezio, Monsalve-Serrano, Javier, Garcia, Antonio
The Use of Piezoelectric Washers for Feedback Combustion Control2020-01-11464/14/2020
The use of piezoelectric cylinder pressure sensors is very popular during engine testing, but cylinder pressure information is becoming mandatory also in several on-board applications, where Low Temperature Combustion (LTC) approaches require a feedback control of combustion, due to poor combustion stability and the risk of knock or misfire. Several manufacturers showed the capability to develop solutions for cylinder pressure sensing in on-board automotive and aeronautical applications, and some of them have been patented. The most straight-forward approach seems the application of a piezo-electric washer as a replacement of the original part equipping the spark plug; the injector could also be used to transfer the cylinder pressure information to the piezoelectric quartz, in diesel or Gasoline Direct Injections (GDI) engines. The paper describes the features of signals acquired using piezoelectric washers, discussing possible applications, highlighting the factors which impact the sensors accuracy, and proposing algorithms to compensate potential errors in the evaluation of combustion metrics. The sensors have been first tested on a press, then in two different gasoline engines: a naturally aspirated V12 and a turbocharged 2 cylinders with Variable Valve Lift system (VVL). Signals have been compared to those obtained with lab-grade cylinder pressure sensors, with particular attention to peak pressure, combustion phase and knock intensity. The main issue affecting the accuracy of cylinder pressure measurement using the piezoelectric spark plug washer is the effect of temperature variations both on the force transmitted by the thread to the washer and piezoelectricity properties.
Corti, Enrico, Abbondanza, Marco, Ponti, Fabrizio, Raggini, Lorenzo
The Effects of Thick Thermal Barrier Coatings on Low-Temperature Combustion2020-01-02754/14/2020
An experimental study was conducted on a Ricardo Hydra single-cylinder light-duty diesel research engine. Start of Injection (SOI) timing sweeps from -350 deg aTDC to -210 deg aTDC were performed on a total number of five pistons including two baseline metal pistons and three coated pistons to investigate the effects of thick thermal barrier coatings (TBCs) on the efficiency and emissions of low-temperature combustion (LTC). A fuel with a high latent heat of vaporization, wet ethanol, was chosen to eliminate the undesired effects of thick TBCs on volumetric efficiency. Additionally, the higher surface temperatures of the TBCs can be used to help vaporize the high heat of vaporization fuel and avoid excessive wall wetting. A specialized injector with a 60° included angle was used to target the fuel spray at the surface of the coated piston. Throughout the experiments, the equivalence ratio, ϕ, was maintained constant at 0.4; the combustion phasing was consistently matched at 6.8 ± 0.4 deg aTDC. It can be concluded that the thick TBC cases achieved 1 to 2 percentage points improvement in combustion efficiency, and generally, a ~2 percentage points increase in indicated engine efficiency. It is also noticed that applying a dense top sealing layer to the TBC further improves the UHC emissions compared to the TBC coated piston with an unsealed surface. From the heat release analysis, it can be concluded that the TBCs have no significant impact on the heat release process and knock intensity while matching the combustion phasing; however, it reduces the intake temperature requirement by up to 20 K. The exhaust gas temperatures were expected to increase for the TBC cases, but the expected increase in exhaust temperature was not conclusive from the results observed in this study.
Yan, Ziming, Gainey, Brian, Gohn, James, Hariharan, Deivanayagam, Saputo, John, Schmidt, Carl, Caliari, Felipe, Sampath, Sanjay, Lawler, Benjamin
Instantaneous PLII and OH* Chemiluminescence Study on Wide Distillation Fuels, PODE n and Ethanol Blends in a Constant Volume Vessel2020-01-03404/14/2020
The combustion characteristics and soot emissions of three types of fuels were studied in a high pressure and temperature vessel. In order to achieve better volatility, proper cetane number and high oxygen content, the newly designed WDEP fuel was proposed and investigated. It is composed of wide distillation fuel (WD), PODE3-6 mixture (PODEn) and ethanol. For comparison, the test on WD and the mixture of PODEn-ethanol (EP) are also conducted. OH* chemiluminescence during the combustion was measured and instantaneous PLII was also applied to reveal the soot distribution. Abel transformation was adopted to calculate the total soot of axisymmetric flame. The results show that WDEP has similar ignition delays and flame lift-off lengths to those of WD at 870-920 K. But the initial ignition locations of WDEP flame in different cycles were more concentrated, particularly under the condition of low oxygen atmosphere. Comparing with WD, the soot amount of WDEP decreased for 55% and 27% at 870 K and 920 K. For the case of 920 K and 15.8% of ambient oxygen, the soot amount in WDEP case decreased by 44%, indicating a more significant soot reduction effect at lower temperatures and EGR conditions.
Cui, Longxi, Ma, Yue, Liu, Dong, Ma, Xiao, Xu, Hongming, Shuai, Shijin
Effect of Split Injection and Intake Air Humidification on Combustion and Emission Characteristics of a Marine Diesel Engine in Partially Premixed Low-Temperature Combustion Mode2020-01-02984/14/2020
The objective of this study was to investigate combined effects of split injection strategies and intake air humidification on combustion and emissions of a partially premixed charge compression ignition (PCCI) marine diesel engine. In this research, a three-dimensional numerical model was established by a commercial code AVL-Fire to explore in-cylinder combustion process and pollutant formation factors in a four-stoke supercharged intercooled marine diesel engine under partial load at 1350 r/min. The novelty of this study is to combine different water-fuel ratios and fuel injection parameters (pilot injection timing and main injection timing) to find the optimized way to improve engine performance as well as NOx-soot emissions, thus meeting the increasingly stringent emissions restriction. The results indicate that as the main injection timing advances (-14°CA to -20°CA aTDC), the in-cylinder peak pressure increases by about 10%, the main injection ignition delay (MI ignition delay) becomes longer, the CA50 is advanced near the top dead center (TDC), which is effective to improve the indicated thermal efficiency (ITE). Meanwhile, soot emissions are reduced by about 50% compared with the original engine at the -20°CA aTDC main injection timing. The early pilot injection timing can form relatively uniform temperature field and concentration field in the cylinder before the start of main injection (SOMI) timing, which is advantageous to fuel-air mixing. The high level of water-fuel ratio is utilized to reduce overall combustion temperatures and achieve low temperature combustion of the diesel engine. NOx emissions significantly decrease by about 75% compared with the original engine when the water-fuel mass ratio is 2.0. All in all, the technical route to improve the NOx-soot trade-off relationship is found through the coupling optimization of split injection strategies and intake air humidification. Meanwhile, the indicated specific fuel consumption (ISFC) is reduced and NOx-ISFC trade-off relationship is improved.
Cai, Yujie, Wang, Ke, Kong, Shiru, Bian, Zhishang
Experimental and Numerical Analysis of Passive Pre-Chamber Ignition with EGR and Air Dilution for Future Generation Passenger Car Engines2020-01-02384/14/2020
Nowadays the combination of strict regulations for pollutant and CO2 emissions, together with the irruption of electric vehicles in the automotive market, is arising many concerns for internal combustion engine community. For this purpose, many research efforts are being devoted to the development of a new generation of high-performance spark-ignition (SI) engines for passenger car applications. Particularly, the PC ignition concept, also known as Turbulent Jet Ignition (TJI), is the focus of several investigations for its benefits in terms of engine thermal efficiency. The passive or un-scavenged version of this ignition strategy does not require an auxiliary fuel supply inside the PC; therefore, it becomes a promising solution for passenger car applications as packaging and installation are simple and straightforward. Moreover, combining this concept with lean burn is an interesting alternative for both improving the engine efficiency and maintaining low pollutant emissions as it enables Low Temperature Combustion (LTC) which ultimately reduces NOX emissions. EGR dilution is also an attractive approach as it is compatible with the three-way catalyst for NOX control. However, previous researches focused on developing the technology rather than understanding the governing physical phenomena. Consequently, the knowledge about the characteristics and limitations of the combustion process for this ignition concept is still limited. For this purpose, an experimental campaign combined with a computational study was performed in this research work to analyze the TJI combustion features in a turbocharged passenger car-size single-cylinder SI engine, sweeping EGR and λ levels. Single-cycle RANS simulations were carried out following a suitable methodology and the results were validated against experimental data keeping the same engine configuration and operating conditions. The simulation results were used to study in detail the combustion process and jet characteristics. The analysis of the results provided a detailed insight about the key aspects limiting the passive PC ignition concept compatibility with air/EGR dilution.
Novella, Ricardo, Pastor, Jose, Gomez-Soriano, Josep, Barbery, Ibrahim, Libert, Cedric, Rampanarivo, Fano, Panagiotis, Chistou, Dabiri, Maziar
Adaptive Optimal Management Strategy for Hybrid Vehicles Based on Pontryagin’s Minimum Principle2020-01-11914/14/2020
The energy management strategies (EMS) for hybrid electric vehicles (HEV) have a great impact on the fuel economy (FE). The Pontryagin's minimum principle (PMP) has been proved to be a viable control strategy for HEV. The optimal costate of the PMP control can be determined by the given information of the driving conditions. Since the full knowledge of future driving conditions is not available, this paper proposed a dynamic optimization method for PMP costate without the prediction of the driving cycle. It is known that the lower fuel consumption the method yields, the more efficiently the engine works. The selection of costate is designed to make the engine work in the high efficiency range. Compared with the rule-based control, the proposed method by the principle of Hamiltonian, can make engine working points have more opportunities locating in the middle of high efficiency range, instead of on the boundary of high efficiency range. Besides a hard and soft constraints of battery SOC are defined to balance the control of optimal costate and the working state of battery. Simulations based on the standard driving cycles are conducted to verify the FE performance. The results are compared with other control strategies to show the effect of proposed method in unknown driving condition.
Zhu, Mingliang, Wu, Xiaodong, Xu, Min
Numerical Investigation of the Combustion Kinetics of Partially Premixed Combustion (PPC) Fueled with Primary Reference Fuel2020-01-05544/14/2020
This work numerically investigates the detailed combustion kinetics of partially premixed combustion (PPC) in a diesel engine under three different premixed ratio fuel conditions. A reduced Primary Reference Fuel (PRF) chemical kinetics mechanism was coupled with CONVERGE-SAGE CFD model to predict PPC combustion under various operating conditions. The experimental results showed that the increase of premixed ratio (PR) fuel resulted in advanced combustion phasing. To provide insight into the effects of PR on ignition delay time and key reaction pathways, a post-process tool was used. The ignition delay time is related to the formation of hydroxyl (OH). Thus, the validated Converge CFD code with the PRF chemistry and the post-process tool was applied to investigate how PR change the formation of OH during the low-to high-temperature reaction transition. The reaction pathway analyses of the formations of OH before ignition time were investigated. It was found that in the case of PR0%, the second isomerization from C7H14OOH2-4O2 to NC7KET24 and the decomposition of NC7KET24 contributed 27.6% and 46.46% of OH formation respectively. The contribution of AC8H16OOH-B to the formation of OH was just 12.13%. It can be concluded that the low temperature oxidation reactions of n-heptane were key steps in producing OH. While in the cases of PR30% and PR50%, because of the higher in-cylinder temperature, most of OH derived from the decomposition reaction of H2O2 that contributed 54.47% and 54.63% of OH formation respectively. Besides, in the PR30% and PR50%, the oxidation reactions of IC4H7 contributed 31.95% and 33.84% of OH formation respectively, and the oxidation reaction of IC4H6OH contributed 19.08% and 22.22% of OH formation respectively, which indicated that the oxidation of iso-octane also contributed to the production of OH. In addition, the distributions of mass fraction, production rate and representative creation reaction (RCR) of OH showed that in the case of PR30% and PR50%, the formation of OH outside the spray periphery were dominated by the reactions R394 (H2O2 (+ M) <=> 2 OH (+ M)), while that in the spray periphery were predominantly controlled by the reaction R21 (NC7KET24 => NC3H7CHO + CH3COCH2 + OH) and R125 (IC4H6OH + HO2 <=> CH2CCH2OH + CH2O + OH). Premixed fuel from port injection changed the formation pathway of OH during the oxidation of direct injection fuel through the reaction R125.
Zhao, Yuanyuan, Wang, Hu, Liu, Xinlei, Liu, Daojian, Chenchen, Wang, Zhu, Hongyan, Zheng, Zunqing, Yao, Mingfa
Transition from HCCI to PPC: Investigation of the Effect of Different Injection Timing on Ignition and Combustion Characteristics in an Optical PPC Engine2020-01-05594/14/2020
The partially premixed combustion (PPC) concept is regarded as an intermediate process between the thoroughly mixed Homogeneous charge compression ignition (HCCI) combustion and compression ignition (CI) combustion. It’s a combination of auto-ignition mode, a fuel-rich premixed combustion mode, and a diffusion combustion mode. The concept has both high efficiency and low soot emission due to low heat losses and less stratified fuel and air mixtures compared to conventional diesel CI. The mechanisms behind the combustion process are not yet very well known. This work focuses on the efficiency and the in-cylinder process in terms of fuel distribution and the initial phase of the combustion. More specifically, double injection strategies are compared with single injection strategies to achieve different levels of stratification, ranging from HCCI to PPC like combustion as well as poor (43%) to good (49%) of gross indicated efficiency. The experiments were performed in an optical heavy-duty CI engine. To analyze how the efficiency was affected in a transition from HCCI to PPC, the natural luminosity (N.L.) was captured with high-speed video (HSV). To complement the HSV data, fuel, temperature, and oxygen distribution were explored by Computational fluid dynamics (CFD) simulation. The results show that the jet-jet and jet-piston interactions can be modified and can reshape the transition trends of gross indicated efficiency and ignition location compared to a single injection. In the transition region, these interactions can improve the efficiency by shaping the fuel-rich region away from cold areas, like the vertical wall of the piston and the squish region, to avoid fuel wetting and incomplete combustion. However, with double injections in the piston bowl (PPC region), jet-jet interaction can unfortunately inhibit the mixing process of the second fuel jet and oxygen due to interaction with the fuel rich region from the first injection, ending up with a lower combustion efficiency.
Zhang, Miao, Derafshzan, Saeed, Xu, Leilei, Bai, Xue-Song, Richter, Mattias, Lundgren, Marcus
Experimental Investigation of Combustion Stability and Particle Emission from CNG/Diesel RCCI Engine2020-01-08104/14/2020
This paper presents the experimental investigation of combustion stability and nano-particle emissions from the CNG-diesel RCCI engine. A modified automotive diesel engine is used to operate in RCCI combustion mode. An open ECU is used to control the low and high reactivity fuel injection events. The engine is tested for fixed engine speed and two different engine load conditions. The tests performed for various port-injected CNG masses and diesel injection timings, including single and double diesel injection strategy. Several consecutive engine cycles are recorded using in-cylinder combustion pressure measurement system. Statistical and return map techniques are used to investigate the combustion stability in the CNG-diesel RCCI engine. Differential mobility spectrometer is used for the measurement of particle number concentration and particle-size and number distribution. It is found that advanced diesel injection timing leading to higher cyclic combustion variations. Too advanced diesel injection results in a partial burn/misfire operating condition. The results indicate that the double diesel injection strategy has a relatively higher concentration of nucleation mode particles and it increases with advancing the diesel injection timings. Typical bimodal lognormal shape of particle-size and number distribution curve is shifted to uni-modal shape by increasing the mass of port-injected fuel.
Saxena, Mohit Raj, Maurya, Rakesh Kumar
On Maximizing Argon Engines' Performance via Subzero Intake Temperatures in HCCI Mode at High Compression Ratios2020-01-11334/14/2020
The improvement of the indicated thermal efficiency of an argon power cycle (replacing nitrogen with argon in the combustion reaction) is investigated in a CFR engine at high compression ratios in homogeneous charge compression ignition (HCCI) mode. The study combines the two effects that can increase the thermodynamic efficiency as predicted by the ideal Otto cycle: high specific heat ratio (provided by argon), and high compression ratios. However, since argon has relatively low heat capacity (at constant volume), it results in high in-cylinder temperatures, which in turn, leads to the occurrence of knock. Knock limits the feasible range of compression ratios and further increasing the compression ratio can cause serious damage to the engine due to the high pressure rise rate caused by advancing the combustion phasing. The technique proposed in this study in order to avoid intense knock of an argon cycle at high compression ratios is to cool the intake charge to subzero temperatures which leads to lower in-cylinder temperatures and hence, less possibility of having knock. The main variable in this study was the intake temperature which was investigated at 40.0 °C and -6.0 °C which corresponded to low and high compression ratios, respectively. Emission analysis shows that the low in-cylinder temperature of the cooled case led to less complete combustion, and so, lower combustion efficiency. Since nitrogen is replaced with argon, NOx was only formed in negligible amounts due to some nitrogen traces in the used gasses cylinders. Furthermore, the cooled charge required more work to be done in the gas exchange process due to the decrease in the intake pressure caused by cooling the intake which deteriorated the gas exchange efficiency. The heat losses factor was found to be the main parameter that dictated the improvement of the thermodynamic efficiency and it was found that the indicated thermal efficiency was deteriorated for the cooled case as a result of all the aforementioned factors. Although the values of the thermodynamic efficiency at high compression ratios did not meet the expectations based on the ideal Otto cycle due to the assumptions of the ideal cycle, the obtained values, in general, are relatively high.
Elkhazraji, Ali, Mohammed, Abdulrahman, Jan, Sufyan, Masurier, Jean-Baptiste, Dibble, Robert, Johansson, Bengt
Simulation-Based Evaluation of Spark-Assisted Compression Ignition Control for Production2020-01-11454/14/2020
Spark-assisted compression ignition (SACI) leverages flame propagation to trigger autoignition in a controlled manner. The autoignition event is highly sensitive to several parameters, and thus, achieving SACI in production demands a high tolerance to variations in conditions. Limited research is available to quantify the combustion response of SACI to these variations. A simulation study is performed to establish trends, limits, and control implications for SACI combustion over a wide range of conditions. The operating space was evaluated with a detailed chemical kinetics model. Key findings were synthesized from these results and applied to a 1-D engine model. This model identified performance characteristics and potential actuator positions for a production-viable SACI engine. This study shows charge preparation is critical and can extend the low-load limit by strengthening flame propagation and the high-load limit by reducing ringing intensity. The simulation results also suggest that under certain operating conditions, there can be a significant disparity between the autoignition sensitivity to temperature and pressure. This may dictate different load control or combustion phasing control strategies, and these results are likely fuel specific. The simulation also indicates that production-feasible control actuator positions can achieve SACI from about 2-10 bar BMEP within flammability, ringing intensity, and knock constraints.
Robertson, Dennis, Prucka, Robert
Impact of Multiple Injection Strategies on Efficiency and Combustion Characteristics in an Optical PPC Engine2020-01-11314/14/2020
Partially premixed combustion (PPC) is a promising way to achieve high thermal efficiency and low emissions, especially by using multiple injection strategies. The mechanisms behind PPC efficiency are still to be explained and explored. In this paper, multiple injections have been used to affect the gross indicated efficiency in an optical PPC engine modified from a Volvo MD13 heavy-duty diesel engine. The aim is both to improve and impair the gross indicated efficiency to understand the differences. The combustion natural luminosity is captured by a high-speed camera, and the distribution of fuel, oxygen, and temperature during the combustion process has been further explored by CFD simulation. The results show that with the right combination of the pilot, main, and post injection the gross indicated efficiency can be improved. Using a post injection in a triple-injection case show to have less effect on the combustion phasing than pilot injection in a double-injection case, while it can significantly affect combustion efficiency. The later of the double-injection cases tested (c30/16), has less heat transfer losses since the high-temperature region transported away from the cylinder head and piston bowl wall, which can be seen in the CFD-simulations. The highest gross indicated efficiency among the tested cases is given by the triple-injection case d38/24/6 as it reaches the best balance between the mixing and the local temperature through the jet-jet interactions and combustion-jet interactions.
Zhang, Miao, Xu, Leilei, Derafshzan, Saeed, Bai, Xue-Song, Richter, Mattias, Lundgren, Marcus
Varying Intake Stroke Injection Timing of Wet Ethanol in LTC2020-01-02374/14/2020
Computational Fluid Dynamics (CFD) modeling was used to investigate the effects of the direct injection of wet ethanol at various injection timings during the intake stroke in a diesel engine with a shallow bowl piston. Thermally Stratified Compression Ignition (TSCI) has been proposed to expand the operating range of Low Temperature Combustion (LTC) by broadening the temperature distribution in the cylinder prior to ignition. TSCI is accomplished by injecting either water or a water-fuel mixture with a high latent heat of vaporization like wet ethanol. This current study focuses on isolating the effects that injecting such a high heat of vaporization mixture during the intake stroke has on the distribution of temperature and equivalence ratio in the cylinder before the onset of combustion. A CONVERGE 3-D CFD model of a single cylinder diesel research engine using Reynolds Averaged Naiver Stokes (RANS) turbulence modeling was developed and validated against experimental data. Then, five cases of injection timing with an injector included angle of 60° were simulated from -330 CAD to -210 CAD BTDC in increments of 30 CAD and five cases with an injector included angle of 150° were simulated from -330 CAD to -240 CAD BTDC also in increments of 30 CAD with an additional case at -340 CAD BTDC. For each spray case, the temperature and equivalence ratio stratification in the cylinder 10 CAD before TDC were analyzed using joint probability density functions (jPDFs). Results show that a later injection timing yields a more stratified mixture as well as a stronger inverse relationship between local temperature and equivalence ratio. An injection of wet ethanol at specific timings also causes the fuel to experience different mixing profiles due to the injector included angle and the piston position at each injection timing. Wall wetting on the piston was another area explored under varying spray conditions due to the high heat of vaporization of the fuel mixture.
O'Donnell, Patrick C., Rahimi Boldaji, Mozhgan, Gainey, Brian, Lawler, Benjamin
Effects of Butanol Isomers on the Combustion and Emission Characteristics of a Heavy-Duty Engine in RCCI Mode2020-01-03074/14/2020
Butanol is an attractive alternative fuel by virtue of its renewable source and low sooting tendency. In this paper, three butanol isomers (n-butanol, isobutanol, and tert-butanol) were induced via port injection respectively and n-heptane was directly injected into the cylinder to investigate reactivity controlled compression ignition in a heavy-duty diesel engine. This work evaluates the potential of applying butanol as low reactivity fuel and the effects of reactivity gradient on combustion and emission characteristics. The experiments were performed from low load to medium-high load. Due to the different reactivities among the butanol isomers, the exhaust gas recirculation rate and the direct injection strategy were varied for a specific butanol isomer and testing load. Particularly, isobutanol/n-heptane can be operated with single direct injection and no exhaust gas recirculation up to medium load due to the high octane rating. As the load increases, all three butanol isomers displayed increased peak cylinder pressure and pressure rise rate. Especially, n-butanol cases yielded a pressure rise rate of 23.4 bar/oCA at medium-high load because of sub-optimal combustion phasing. It constrains the high load limit of n-butanol/n-heptane operation. While tert-butanol cases presented the slowest heat release rate and consequently the lowest pressure rise rates. Extremely low NOx emissions were achieved for all three isomers. Interestingly, tert-butanol/n-heptane operation stands out for showing ignorable engine-out soot mass in the whole testing range. N-butanol cases require the most direct fueling to phasing the combustion properly and displayed the highest soot mass and the highest number of particles in the accumulation mode. Among the isomers, tert-butanol/n-heptane operation achieved the highest gross indicated efficiency (above 52%) in most operating loads.
Han, Jinlin, Somers, Bart
Chemical kinetic mechanisms for HCCI combustion of wet ethanol with exhaust gas recirculation2019-36-02931/13/2020
This work compares the accuracy of in-cylinder pressure and apparent heat release rate (AHRR) diagrams to the experimental data and the use of different chemical kinetics models applied to the GT-Power® software. The engine computational model is based on a naturally aspirated diesel engine with three cylinders, one of them modified to operate with hydrous ethanol with port fuel injection and HCCI combustion achieved with hot exhaust gas recirculation (EGR) of the Diesel cylinders. Operating points chosen to perform the comparison to experimental tests were 1800 rpm, 300 kPa of indicated mean effective pressure and fuels with 10% and 20% of water-in-ethanol by volume. The kinetic mechanisms for ethanol oxidation evaluated were the detailed NUI Galway and a Skeletal model based on it. With either model, cylinder pressure diagrams were not very different from the experimental values. The detailed mechanism was, on average, 9 times slower to process each case than the Skeletal mechanism. The quality of data obtained with the Skeletal mechanism and its lower computational cost makes it a good solution for a quick analysis. However, when greater reliability is required, it is recommended to use the detailed NUI Galway kinetic mechanism, since it provides a better fit to the experimental data, with a more complete analysis of the chemical species involved in ethanol oxidation.
Herzer, Filipe A., Fagundez, Jean L. S., Martins, Mario E. S., Salau, Nina P. G.
Study on Characteristics of Combined PCCI and Conventional Diesel Combustion2019-01-216912/19/2019
The main objective of this study is to evaluate the characteristics of combustion that combine premixed charge compression ignition (PCCI)-based combustion with conventional mixing controlled combustion. In this type of combustion, it is supposed that the combustion duration is shortened due to the synchronization of the timing of two types of combustions. In addition, the cooling loss caused by spray impingement is expected to decrease by the reduction of the proportion of mixing controlled combustion. In this study, the effect of injection pressure, injection timing, and split injection on thermal efficiency and emissions were investigated in order to determine the appropriate injection parameters for PCCI-based combustion to realize the proposed combustion concept.
Bao, Zhichao, Pan, Weikang, Yokoyama, Takuji, Hirayama, Kazuki, Horibe, Naoto, Kawanabe, Hiroshi, Ishiyama, Takuji
Optimisation of Low Temperature Combustion Technology, for Future Drive Cycles, using a Factorial Design of Experiments2019-01-217112/19/2019
Automotive manufacturers are facing increased pressure to meet more stringent emissions legislation and new legislative driving cycles. One technology that has the potential to meet future legislation is Low Temperature Combustion (LTC), which has the potential to significantly reduce NOx over conventional diesel combustion. Most studies reported in the literature evaluating this technology only change ’one- factor-at-a-time’ at steady state conditions. This paper addresses these issues and presents a methodology utilising DoE analysis to optimise a validated multi- fidelity engine simulation for LTC over a transient cycle (WLTP) which makes the results more applicable to real world driving conditions. A validated simulation for a 2.4-litre compression ignition engine was developed in Ricardo WAVE. To increase the fidelity of the model, empirical data such as 3D scans of the inlet geometry were included. The simulation was validated against experimental engine emissions and performance data. A characterization study using a full factorial DoE was performed on the whole engine simulation to minimise vehicle emissions using LTC. The vehicle simulation was tested against the WLTP and the response of the emissions for different levels of exhaust gas recirculation (EGR), pilot start of injection (SOI) and main SOI timings and pilot injection duration were recorded. The results of the optimization showed that over the WLTP the NOx emissions decreased by approximately 85 % with an EGR of 47.5 %, retarding the pilot SOI and main SOI maps with 1 CAD compared to the default maps and increasing the pilot injection duration by 200 microseconds. NOx emissions were reduced by approximately 18 % with the use of 12 % EGR without exceeding the Euro 4 CO emissions limit. Further increase in EGR percentage significantly increased the CO emissions.
van Niekerk, A.S., Kay, P.J., Drew, B., Larsen, N.
Numerical study of wall heat transfer inside a combustion chamber under conventional diesel combustions and low temperature combustion conditions2019-01-231412/19/2019
The engine simulations using computational fluid dynamics (CFD) commercial code ANSYS-Forte is employed to study the effects of in-cylinder combustion on heat transfer through the combustion chamber walls. In this numerical study, three different combustion regimes are explored and compared. A conventional diesel combustion (CDC) and low temperature combustion (LTC) with early and late injection conditions are investigated. To simulate the velocity field in the computational domain, the renormalization group (RNG) k-ε turbulence model Is chosen. Also, a detailed chemistry CHEMKIN Pro package is implemented in a combustion model to calculate the reaction mechanism for the engine simulations. To obtain predicted heat flux results from three different combustion regimes, the available heat transfer wall model including temperature wall function and gas density variation is applied. To model validation, the simulated results is validated against experimental data from N14 engines which are operated with three different engine conditions. The predicted in-cylinder pressure and apparent heat release rate for three different modes of combustion performs reasonably well agreement with available experimental data. Three different points of interest on a piston surface are also investigated. The predicted heat fluxes through the walls provide the similar global trends for three combustion regimes. The magnitudes of simulated heat flux for a conventional diesel combustion (CDC) regime are in the normal range of typical measured values of diesel combustions and are the highest among all three combustion regimes, while the heat flux results of low temperature combustion with late injections are the lowest.
Kaewbumrung, Mongkol, Plengsa-ard, Chalermpol
Characterization of Low Temperature Reactions in the Standard Cooperative Fuel Research (CFR) Engine03-12-05-00389/24/2019
Abstract Many proposals for fuel rating in spark ignition (SI) engine have been suggested till date and still no consensus on this has been reached. The automobile industry is still using RON and MON tests for rating fuels, and still there exists a need to come up with new fuel rating systems. The fuel’s knocking tendency in SI engines is primarily governed by the end-gas autoignition. Another combustion mode, homogeneous charge compression ignition (HCCI), is also driven by autoignition of the complete charge inside the cylinder. Fundamentally, the combustion process in both combustion modes is driven by autoignition, and HCCI combustion mode can be used to understand the knocking behavior in SI engines. The lean combustion environment in HCCI mode provides a good platform to replicate the operating conditions of modern SI engines, which are operating at boosted pressures and low intake temperatures, and understanding of the fuel knocking behavior under such conditions is vital for achieving high-efficient engines. Therefore in this study, HCCI combustion will be used in the standard CFR engine to understand the autoignition behavior of the fuels for SI engines. For this purpose, three fuel blends were selected, which had the research octane number equal to 90. The standard CFR engine was operated with varying intake pressures and temperatures under HCCI combustion mode. The Lund-Chevron HCCI fuel number was used to rate the fuels and this was compared with RON and MON of the blends. It was found that HCCI combustion could be used to rate the fuels with the standard CFR engine with minor modifications to accommodate the boosted conditions without affecting the geometry and the flow inside the CFR engine. Low temperature reactions were observed and were correlated with the Lund-Chevron HCCI fuel numbers.
Waqas, Muhammad Umer, Hoth, Alexander, Kolodziej, Christopher P., Rockstroh, Toby, Gonzalez, Jorge Pulpeiro, Johansson, Bengt
Learning Based Model Predictive Control of Combustion Timing in Multi-Cylinder Partially Premixed Combustion Engine2019-24-00169/9/2019
Partially Premixed Combustion (PPC) has shown to be a promising advanced combustion mode for future engines in terms of efficiency and emission levels. The combustion timing should be suitably phased to realize high efficiency. However, a simple constant model based predictive controller is not sufficient for controlling the combustion during transient operation. This article proposed one learning based model predictive control (LBMPC) approach to achieve controllability and feasibility. A learning model was developed to capture combustion variation. Since PPC engines could have unacceptably high pressure-rise rates at different operation points, triple injection is applied as a solvent, with the use of two pilot fuel injections. The LBMPC controller utilizes the main injection timing to manage the combustion timing. The cylinder pressure is used as the combustion feedback. The method is validated in a multi-cylinder heavy-duty PPC engine for transient control.
Li, Xiufei, Yin, Lianhao, Tunestal, Per, Johansson, Rolf
Numerical Investigation of Methanol Ignition Sequence in an Optical PPC Engine with Multiple Injection Strategies2019-24-00079/9/2019
Methanol is a genuine candidate on the alternative fuel market for internal combustion engines, especially within the heavy-duty transportation sector. Partially premixed combustion (PPC) engine concept, known for its high efficiency and low emission rates, can be promoted further with methanol fuel due to its unique thermo-physical properties. The low stoichiometric air to fuel ratio allows to utilize late injection timings, which reduces the wall-wetting effects, and thus can lead to less unburned hydrocarbons. Moreover, combustion of methanol as an alcohol fuel, is free from soot emissions, which allows to extend the operation range of the engine. However, due to the high latent heat of vaporization, the ignition event requires a high inlet temperature to achieve ignition event. In this paper LES simulations together with experimental measurements on an heavy-duty optical engine are used to study methanol PPC engine. After a successful calibration of the pressure trace in terms of required intake temperature and combustion model, the optical natural luminosity data is used to validate prediction of ignition kernel and vapor penetration length. Moreover, it is shown that the inlet temperature requirement is reduced by 47 K degrees when applying multiple injection strategy. Changing the injection strategy also affects the average temperature of combustion and thus the emissions rates. Additionally, an ignition sequence analysis is performed to identify the mode of combustion and the heat release (HR) distribution depending on the local equivalence ratio, recognizing characteristics of PPC regime. Based on this analysis, a conceptual heat distribution model for PPC engine and other low temperature combustion (LTC) engine concepts is proposed.
Pucilowski, Mateusz, Fatehi, Hesameddin, Jangi, Mehdi, Lonn, Sara, Matamis, Alexios, Andersson, Oivind, Richter, Mattias, Bai, Xue-Song
Zero-Dimensional Heat Release Modeling Framework for Gasoline Compression-Ignition Engines with Multiple Injection Events2019-24-00839/9/2019
A zero-dimensional heat release model was developed for compression ignition engines. This type of model can be utilized for parametric studies, off-line optimization to reduce experimental efforts as well as model-based control strategies. In this particular case, the combustion model, in a simpler form, will be used in future efforts to control the combustion in compression ignition engines operating on gasoline-like fuels. To allow for a realistic representation of the in-cylinder combustion process, a spray model has been employed to allow for the quantification of fuel distribution as well as turbulent kinetic energy within the injection spray. The combustion model framework is capable of reflecting premixed as well as mixing controlled combustion. Fuel is assigned to various combustion events based on the air-fuel mixture within the spray. The mixing controlled combustion consists of two separate combustion events; one occurring within the fuel spray, which is characterized by rich fuel mixtures with a substantial level of turbulent kinetic energy and high combustion rates; the other one describes moderate combustion rates of lean fuel mixtures with less turbulent kinetic energy. Model constants were calibrated against experimental data from a 12.4L heavy-duty compression ignition engine operated on gasoline for various sweeps at 14bar BMEP and mostly at an engine speed of 1038rpm. A maximum prediction error in combustion phasing of 1.3CAD was found across the 30 calibrated sample points.
Pamminger, Michael, Hall, Carrie, Wang, Buyu, Wallner, Thomas, Rajkumar, M
Dual-Fuel Ethanol-Diesel Technology Applied in Mild and Full Hybrid Powertrains2019-24-01159/9/2019
The increasingly stringent emissions regulations together with the demand of highly efficient vehicles from the customers, lead to rapid developments of distinct powertrain solutions, especially when the electrification is present in a certain degree. The combination of electric machines with conventional powertrains diversifies the powertrain architectures and brings the opportunity to save energy in greater extents. On the other hand, alternative combustion modes as reactivity controlled compression ignition (RCCI) have shown to provide simultaneous ultra-low NOx and soot emissions with similar or better thermal efficiency than conventional diesel combustion (CDC). In addition, it is necessary to introduce more renewable fuels as ethanol to reduce the total CO2 emitted to the atmosphere, also called well-to-wheel (WTW) emission, in the transport sector. Therefore, the combination of these two growing technologies with the use of ethanol (E85) could be a potential way to achieve clean and efficient vehicles. In this work, numerical simulations of full hybrid electric vehicles (series, parallel and series-parallel) and mild hybrid vehicles were performed and compared versus the conventional powertrain in the WLTC driving cycle. The hybrid vehicles are simulated with both CDC and diesel-ethanol RCCI combustion engines as power source. Each powertrain was optimized in terms of electric components (battery capacity, electric motors...), internal combustion engine operating points, power management strategy and transmission/differential ratio to obtain the minimum fuel consumption and NOx emissions. The results show a significant reduction of the total mass consumption as the complexity of the hybrid system increases (more electrical devices needed). In this sense, the series-parallel architecture, which represents the most complex hybrid system, allows reducing the energy consumption around 20% compared to the conventional powertrain operating under CDC. In addition, the combined use of CDC and RCCI in the same engine map showed improvements in NOx, soot and CO2 emissions versus CDC. Moreover, the series hybrid powertrain obtained the lowest NOx and soot emissions values due to using fixed operating conditions in RCCI mode for the thermal engine. Lastly, the mild hybrid technology showed an acceptable balance between complexity and fuel consumption.
Benajes, Jesus, Garcia, Antonio, Monsalve-Serrano, Javier, Martinez, Santiago
Large Eddy Simulation of an Ignition Front in a Heavy Duty Partially Premixed Combustion Engine2019-24-00109/9/2019
In partially premixed combustion engines high octane number fuels are injected into the cylinder during the late part of the compression cycle, giving the fuel and oxidizer enough time to mix into a desirable stratified mixture. If ignited by auto-ignition such a gas composition can react in a combustion mode dominated by ignition wave propagation. 3D-CFD modeling of such a combustion mode is challenging as the rate of fuel consumption can be dependent on both mixing history and turbulence acting on the reaction wave. This paper presents a large eddy simulation (LES) study of the effects of stratification in scalar concentration (enthalpy and reactant mass fraction) due to large scale turbulence on the propagation of reaction waves in PPC combustion engines. The studied case is a closed cycle simulation of a single cylinder of a Scania D13 engine running PRF81 (81% iso-octane and 19% n-heptane). Two injection timings are investigated; start of injection at -17 CAD aTDC and -30 CAD aTDC. One-equation transported turbulence sub-grid closure is used for the unresolved momentum and scalar fluxes and the fuel spray is modelled using a Lagrangian particle tracking (LPT) approach. Initial flow conditions (prior to intake valve closing) are generated using a scale forcing method with a prescribed large-scale swirl mean flow motion. Fuel reactivity is modeled using finite rate chemistry based on a skeletal chemical kinetic mechanism (44 species, 140 reactions). The results are compared with optical engine experimental data and satisfactory agreement with the experiments is obtained in terms of the liquid spray length, cylinder pressure trace and ignition location. A majority of the fuel consumption is found to be in ignition fronts where small variations in temperature at low fuel concentrations are observed to cause large stratification in ignition delay time.
Ibron, Christian, Fatehi, Hesameddin, Jangi, Mehdi, Bai, Xue-Song
Experimental and Numerical Investigation of the Maximum Pressure Rise Rate for an LTC Concept in a Single Cylinder CI Engine2019-24-00239/9/2019
In the foreseeable future, the transportation sector will continue to rely on internal combustion engines. Therefore, reduction of engine-out emissions and increase in engine efficiency are important goals to meet future legislative regulations and restricted fuel resources. One viable option, which provides lower peak temperatures and increased mixture homogeneity and thus simultaneously reduces nitric oxide as well as soot, is a low-temperature combustion (LTC) concept. However, this might result in an increase of unburnt hydrocarbon, carbon monoxide, and combustion noise due to early combustion phasing and lower engine efficiency. Various studies show that these drawbacks can be compensated by advanced injection strategies, e.g. by employing multiple injections. The aim of this work is to identify the optimum injection strategy, which enables a wide range of engine operating points in LTC mode with reduced engine-out emissions. To achieve this goal, experiments with variations in the maximum pressure rise rate, injection pressure, intake pressure, and the EGR-rate are carried out and analyzed. Numerical investigation is carried out by three dimensional (3D) computational fluid dynamics (CFD) simulations in CONVERGE software for several multiple injection strategy conditions. CFD could predict ignition delay, pressure rise and heat release rate of each injection and hence overall injection rate shaping combustion process with good accuracy.
Korkmaz, Metin, Lakshmanan, Raghavan, Falkenstein, Tobias, Beeckmann, Joachim, Pitsch, Heinz
A Mixing Timescale Model for PDF Simulations of LTC Combustion Process in Internal Combustion Engines2019-24-01139/9/2019
Transported probability density function (PDF) methods are currently being pursued as a viable approach to model the effects of turbulent mixing and mixture stratification, especially for new alternative combustion modes as for example Homogeneous Charge Compression ignition (HCCI) which is one of the advanced low temperature combustion (LTC) concepts. Recently, they have been applied to simple engine configurations to demonstrate the importance of accurate accounting for turbulence/chemistry interactions. PDF methods can explicitly account for the turbulent fluctuations in species composition and temperature relative to mean value. The choice of the mixing model is an important aspect of PDF approach. Different mixing models can be found in the literature, the most popular is the IEM model (Interaction by Exchange with the Mean). This model is very similar to the LMSE model (Linear Mean Square Estimation). Other models are available in the literature, e.g. the MC model (Modified Curl model), the EMST model (Euclidian Minimum Spanning Tree) and the PMSR model (Pairwise Mixing Stirred Reactor). The IEM and the LMSE models relax scalar values in each particle to the mean with a characteristic time τt computed by the intensity of scalar mixing. These deterministic models are attractive for engine combustion process modeling, because they are easy to implement and give reliable results with a short computational time. However, the numerical solution of the system is strongly linked to particles number and scalar dissipation rate. This latter requires modeling in order to take into account the physical phenomena it stands for. In a previous study, an IEM model has been used to describe the mixing in a stochastic reactor model that simulates the HCCI process (LTC combustion). In this study, the turbulent time scale τt included in IEM model is modeled through the turbulent kinetic energy and its dissipation. Hence, a (k-ε) turbulence model based on zero-dimensional energy cascade applied during the compression and the expansion cycle is presented. On another hand, the confidence interval introduced in this approach related to the initial heterogeneities amplitude of temperature and of species mass has been described as a function of the turbulent Reynolds number. The in-cylinder pressure predicted by the model was validated against the experimental results by using two different single cylinder engines. One engine was equipped with an optical access in order to follow the evolution of HCCI combustion process. For both engines HCCI combustion was applied by using early injection timings in order to ensure homogeneity of the in-cylinder charge. For both engines a good agreement has been observed in terms of in-cylinder pressure traces. At varying engine operating conditions, the mean relative error levels are lower than 3%.
Maroteaux, Fadila, Mancaruso, Ezio, Vaglieco, Bianca Maria
Experimental Assessment of Ozone Addition Potential in Direct Injection Compression Ignition Engines2019-24-01189/9/2019
The potential of ozone addition in compression ignition engines is investigated experimentally in this paper. Experiments were carried out in an optically accessible single cylinder engine equipped with a common rail direct injection system. A commercially available ozone generator (P < 100W) was used to add to the intake flow a controlled amount of ozone. EU Diesel fuel (cetane number 52) and a Naphtha fuel (cetane number 33) were tested investigating the impact of Ozone in conventional diesel combustion and LTC cases (e.g. high exhaust gas recirculation rate). Minimal ozone concentration in the intake flow (100 ppm) demonstrated to reduce significantly the ignition delay. However, the impact observed strongly depends on the engine conditions tested and, in general, this effect observed becomes significant in conditions characterized by a long ignition delay: low intake temperature, high dilution, and low cetane number fuel. Significant practical benefits of ozone addition were found for engine cold-start, where ozone yields a significant reduction in misfire events during the first cycle and a faster stabilization of the combustion phasing and a reduction of the unburned hydrocarbons produced in the warm up phase. Also, a mild increase in the EGR tolerance for low load conditions was achieved (from 2 to5%). Optical diagnostics, such as CH2O planar laser induced fluorescence and natural chemiluminescence, were applied to understand the physics behind the ozone effects. The results demonstrated that O3 strongly affects the low temperature combustion phase, causing an earlier development of the chemical reactions. The impact on this phase is eventually reflected in a reduction of the second stage ignition delay, and in a more stable combustion.
Bardi, Michele, Pilla, Guillaume, Matrat, Mickaël
A Review of Spark-Assisted Compression Ignition (SACI) Research in the Context of Realizing Production Control Strategies2019-24-00279/9/2019
This paper seeks to identify key input parameters needed to achieve a production-viable control strategy for spark-assisted compression ignition (SACI) engines. SACI is a combustion strategy that uses a spark plug to initiate a deflagration flame that generates sufficient ignition energy to trigger autoignition in the remaining charge. The flame propagation phase limits the rate of cylinder pressure rise, while autoignition rapidly completes combustion. High dilution within the autoignited charge is generally required to maintain reaction rates feasible for production. However, this high dilution may not be reliably ignited by the spark plug. These competing constraints demand novel mixture preparation strategies for SACI to be feasible in production. SACI with charge stratification has demonstrated sufficiently stable flame propagation to reliably trigger autoignition across much of the engine operating map. A key controls challenge of SACI is the two regimes of combustion are near several constraints that may be competing. This work summarizes key findings from decades of research that can help enable production control strategies for SACI engines. A summary and analysis of the broad research of SACI is included, along with an examination of the relevant factors that must be considered while developing a control strategy. Additionally, a discussion of how production-intent SACI designs extend or innovate upon previous decades of research is included. Key control actuators and design parameters are synthesized along with their sensitivity on several SACI combustion metrics.
Robertson, Dennis, Prucka, Robert
Investigation of Fuel Condensation Processes under Non-reacting Conditions in an Optically-Accessible Engine2019-01-01974/2/2019
Engine experiments have revealed the importance of fuel condensation on the emission characteristics of low temperature combustion. However, direct in-cylinder experimental evidence has not been reported in the literature. In this paper, the in-cylinder condensation processes observed in optically accessible engine experiments are first illustrated. The observed condensation processes are then simulated using state-of-the-art multidimensional engine CFD simulations with a phase transition model that incorporates a well-validated phase equilibrium numerical solver, in which a thermodynamically consistent phase equilibrium analysis is applied to determine when mixtures become unstable and a new phase is formed. The model utilizes fundamental thermodynamics principles to judge the occurrence of phase separation or combination by minimizing the system Gibbs free energy. It is shown that thermodynamically unstable mixtures are formed during the late expansion stroke for the conditions of the experiments. Close agreement on the beginning of condensation is also observed between the simulations and available experiments.
Qiu, Lu, Reitz, Rolf, Eagle, Ethan, Musculus, Mark
Effect of Injection Timing on the Ignition and Mode of Combustion in a HD PPC Engine Running Low Load2019-01-02114/2/2019
This work aims to study the effect of fuel inhomogeneity on the ignition process and subsequent combustion in a compression ignition Partially Premixed Combustion (PPC) engine using a primary reference fuel (PRF) in low load conditions. Five cases with injection timings ranging from the start of injection (SOI) at -70 crank angle degrees (CAD) to -17 CAD have been studied numerically and experimentally in a heavy duty (HD) piston bowl geometry. Intake temperature is adjusted to keep the combustion phasing constant. Three dimensional numerical simulations are performed in a closed cycle sector domain using the Reynolds Averaged Navier-Stokes (RANS) formulation with k-ϵ turbulence closure and direct coupling of finite rate chemistry. The results are compared with engine experiments. The predicted trends in required intake temperature and auto-ignition location for a constant combustion phasing are consistent with experiments. The simulations show that the auto-ignition is critically dependent on both fuel and temperature stratification. The ignition occurs in fuel-lean regions but the mixing of the fuel with the cylinder gas and the cylinder gas temperature stratification (prior to injection) determines the ignition location. A higher heat release rate is observed in the later injection cases, which is attributed to the higher equivalence ratio of the mixture inside the bowl. Negative temperature coefficient (NTC) heat release behaviour of the studied fuel plays a role in shortening the ignition wave propagation but the impact of the effect varies among the injection cases. A sensitivity study of combustion efficiency with regard to the intake temperature is performed on two of the cases (SOI of -30 CAD and of -63 CAD). While the combustion phasing is slower and correctly predicted in the simulations of the advanced injection cases the combustion efficiency is found to be very sensitive to the intake temperature. This is attributed to the high sensitivity of the ignition delay time to equivalence ratio and temperature.
Ibron, Christian, Jangi, Mehdi, Lonn, Sara, Matamis, Alexios, Andersson, Oivind, Tuner, Martin, Richter, Mattias, Bai, Xue-Song
A Study on Kinetic Mechanisms of Diesel Fuel Surrogate n-Dodecane for the Simulation of Combustion Recession2019-01-02024/2/2019
Combustion recession, an end of injection (EOI) diesel spray phenomenon, has been found to be a robust correlation parameter for UHC in diesel LTC strategies. Previous studies have shown that the likelihood of capturing combustion recession in numerical simulations is highly dependent on the details of the low-temperature chemistry reaction mechanisms employed. This study aims to further the understanding of the effects of different chemical mechanisms in the prediction of a reactive diesel spray and its EOI process: combustion recession. Studies were performed under the Engine Combustion Network’s (ECN) “Spray A” conditions using the Reynolds-Averaged Navier-Stokes simulation (RANS) and the Flamelet Generated Manifold (FGM) combustion model with four different chemical mechanisms for n-dodecane that are commonly used in the engine simulation communities - including recently developed reduced chemistry mechanisms. The flamelet database for each of the chemical mechanism is generated using two methods: 0D homogeneous reactor (HR) ignition flamelets and 1D igniting counterflow diffusion (ICDF) flamelets. The effect of different tabulation approaches is investigated first following by the discussion of the impact of chemical mechanisms on the prediction of combustion recession. Further discussions include an evaluation of the performance of chemical mechanisms in predicting the most relevant reacting spray characteristics compared to the ECN experimental database: ignition delay time (IDT), flame lift-off length (LOL) and flame reactive region. Results show that the choice of both tabulation method and chemical mechanism play a significant role in initial flame stabilization and end of injection (EOI) transient processes. In general, both tabulation techniques were able to qualitatively capture the flame characteristics before EOI, however ICDF tabulation is better suited for the FGM approach in order to capture combustion recession. Furthermore, the chemical mechanisms studied indicate that mechanisms with stronger low temperature chemistry predictions are more likely to promote combustion recession under an FGM framework.
Fang, Xiaohang, Ismail, Riyaz, Davy, Martin
Numerical Parametric Study of a Six-Stroke Gasoline Compression Ignition (GCI) Engine Combustion2019-01-02074/2/2019
Numerical investigation of engine performance and emissions of a six-stroke gasoline compression ignition (GCI) engine combustion at low load conditions is presented. In order to identify the effects of additional two strokes of the six-stroke engine cycle on the thermal and chemical conditions of charge mixtures, an in-house multi-dimensional CFD code coupled with high fidelity physical sub-models along with the Chemkin library was employed. The combustion and emissions were calculated using a reduced chemical kinetics mechanism for a 14-component gasoline surrogate fuel. Two power strokes per cycle were achieved using multiple injections during compression strokes. Parametric variations of injection strategy viz., individual injection timing for both the power strokes and the split ratio that enable the control of combustion phasing of both the power strokes were explored. The computational results suggest that the operability limit of GCI combustion can be effectively expanded by controlling the mixture thermodynamic conditions and achieving optimum mixture stratification. It was uniquely found that the charge mixtures could burn in the mixing-controlled mode during the second power stroke with the injection timing control and result in substantial soot reduction while maintaining high combustion efficiency. Also, the variation of split ratio was found to be effective in controlling the combustion phasing and pressure rise rate for both the power strokes.
Rajput, Oudumbar, Ra, Youngchul, Ha, Kyoung-Pyo
Effect of Turbulence-Chemistry Interaction on Spray Combustion: A Large Eddy Simulation Study2019-01-02034/2/2019
Although turbulence plays a critical role in engines operated within low temperature combustion (LTC) regime, its interaction with chemistry on auto-ignition at low-ambient-temperature and lean-oxygen conditions remains inadequately understood. Therefore, it is worthwhile taking turbulence-chemistry interaction (TCI) into consideration in LTC engine simulation by employing advanced combustion models. In the present study, large eddy simulation (LES) coupled with linear eddy model (LEM) is performed to simulate the ignition process in n-heptane spray under engine-relevant conditions, known as Spray H. With LES, more details about unsteady spray flame could be captured compared to Reynolds-averaged Navier-Stokes equations (RANS). With LEM approach, both scalar fluctuation and turbulent mixing on sub-grid level are captured, accounting for the TCI. A skeletal mechanism is adopted in this numerical simulation, including 41 species and 124 reactions. Validations is carried out and numerical results show good agreement with experimental data. It is found that, Damköhler number (Da) at the onset of high temperature reaction evidently decreases as ambient temperature and oxygen reduces. Consequently, combustion mode varies from flamelet regime to slow chemistry regime, where the competitive effect between turbulent mixing and chemistry is more evident. Besides, scalar fluctuation has promoting effect on low temperature reaction, which is responsible for the over-prediction of ignition delay in low ambient temperature/oxygen condition without consideration of TCI. Further analysis of turbulence intensity on ignition is performed by using three different turbulence intensity. Contrary to what found in premixed combustion, ignition process in spray combustion will be promoted with enhanced small scale turbulence.
Cai, Junqian, Wang, Tianyou, Jia, Ming, Sun, Kai, Lu, Zhen, Xiao, Gang, Shen, Shiquan
Pathway to 50% Brake Thermal Efficiency Using Gasoline Direct Injection Compression Ignition2019-01-11544/2/2019
Continued improvement in the combustion process of internal combustion engines is necessary to reduce fuel consumption, CO2 emissions, and criteria emissions for automotive transportation around the world. In this paper, test results for the Gen3X Gasoline Direct Injection Compression Ignition (GDCI) engine are presented. The engine is a 2.2L, four-cylinder, double overhead cam engine with compression ratio ~17. It features a “wetless” combustion system with a high-pressure direct injection fuel system. At low load, exhaust rebreathing and increased intake air temperature were used to promote autoignition and elevate exhaust temperatures to maintain high catalyst conversion efficiency. For medium-to-high loads, a new GDCI-diffusion combustion strategy was combined with advanced single-stage turbocharging to produce excellent low-end torque and power. Time-to-torque (TT) simulations indicated 90% load response in less than 1.5 seconds without a supercharger. For cold starts, the engine is equipped with a fast 2.5kW electric air heater positioned upstream of the intake valves. No spark plugs are used. Dynamometer tests indicated excellent fuel efficiency over the operating map. Minimum BSFC of 194 g/kWh (BTE 43%) was measured at 1750rpm- 12bar IMEP with BSFC less than 210 (40% BTE) over a very wide operating region. The GDCI engine operates on US pump gasoline (RON91) and is ideal for down speeding and uploading for improved vehicle fuel economy. New simulations showed that potentially 48% BTE could be achieved through use of thermal barrier coatings and other improvements to the engine (Gen4X engine). Vehicle simulations were performed at Argonne using the Gen3X engine map for a midsize sedan, SUVs, and a pickup truck. Results indicated a 36 to 51% improvement in combined FTP fuel economy over a competitive 2015 1.6L turbocharged GDi engine equipped with intake variable valve lift. The simulations showed that the Gen3X engine with 12V start/stop or mild hybridization can compete with full hybrid powertrains in various vehicle segments.
Sellnau, Mark, Foster, Matthew, Moore, Wayne, Sinnamon, James, Hoyer, Kevin, Klemm, William
High-Load Compression-Ignition Engine Emissions Reduction with Inverted Phi-Sensitivity Fuel Using Multiple Injection Strategies2019-01-05544/2/2019
Inverted phi (ϕ)-sensitivity is a new approach of NOx reduction in compression-ignition (C.I.) engines. Previously, pure ethanol (E100) was selected as the preliminary test fuel in a single injection compression-ignition engine, and was shown to have good potential for low engine-out NOx emissions under low and medium load conditions due to its inverted ignition sequence. Under high load, however, the near-stoichiometric and non-homogeneous fuel/air distribution removes the effectiveness of the inverted ϕ-sensitivity. Therefore, it is desirable to recover the combustion sequence in the chamber such that the leaner region is burned before the near-stoichiometric region. When the combustion in near-stoichiometric region is inhibited, the temperature rise of that region is hindered and the formation of NOx is suppressed. To achieve the goal of homogenizing the mixture before combustion, thus switching ignition mode and lowering emissions when fueling with the target fuel, multiple direct-injection strategies are applied to this study. 3-D engine CFD simulations are conducted with different multiple injection strategies under high-load operations in a compression-ignition engine. The injection characteristics of optimized cases are examined in KIAV-3V coupled with a Genetic Algorithm(GA). An objective function is used to qualify the realization of optimized cases with minimized engine-out NOx, carbon monoxide (CO), soot and unburned hydrocarbon (UHC), while preserving engine performance. It is found that with multiply direct-injection strategies, the desired inverted ϕ-sensitivity dominated ignition can be regained under high-load engine operation conditions, uniform fuel-air mixture before combustion can be retrieved, and lower in-cylinder temperature and pressure are possible. Comparing to the double-injection strategy, the optimized triple-injection strategy shows more pronounced effects in terms of combustion quality and emission reduction.
Gao, Suya, Lee, Chia-Fon
Measurement of Gasoline Exhaust Particulate Matter Emissions with a Wide-Range EGR in a Heavy-Duty Diesel Engine2019-01-07614/2/2019
A large number of measurement techniques have been developed or adapted from other fields to measure various parameters of engine particulates. With the strict limits given by regulations on pollutant emissions, many advanced combustion strategies have been developed towards cleaner combustion. Exhaust gas recirculation (EGR) is widely applied to suppress nitrogen oxide (NOx) and reduce soot emissions. On the other hand, gasoline starts to be utilized in compression ignition engines due to great potential in soot reduction and high engine efficiency. New engine trends raise the need for good sensitivity and suitable accuracy of the PM measurement techniques to detect particulates with smaller size and low particulate mass emissions. In this work, we present a comparison between different measurement techniques for particulate matter (PM) emissions in a compression ignition engine running on gasoline fuel. A wide-range of EGR was used with lambda varied from 3 down to 1. The compared equipment includes AVL smoke meter, AVL Micro Soot Sensor, Pegasor and Cambustion Differential Mobility Spectrometer (DMS). The goal of this paper is to compare the recorded values and show the sensitivity of the instruments to soot properties altering, in both lean and stoichiometric combustion situations.
Shen, Mengqin, Shamun, Sam, Tunestal, Per, Tuner, Martin
Utilizing Static Autoignition Measurements to Estimate Intake Air Condition Requirements for Compression Ignition in a Multi-Mode Engine - Application of Chemical Kinetic Modeling2019-01-09554/2/2019
A multi-mode operation strategy, wherein an engine operates compression ignited at low load and spark-ignited at high load, is an attractive way to achieve better part-load efficiency in light duty, spark-ignition (SI) engines, while maintaining robust operation and control across the operating map. Given the sensitivity of compression ignition operation to in-cylinder conditions, one of the critical requirements in realizing such a strategy in practice is accurate control of intake charge conditions - pressure, temperature, as well as fuel loading, to achieve stable combustion and enable rapid mode-switches. A reliable way of characterizing fuels under such operating schemes is key. Towards this, this paper presents the second of a two-part study, comparing the reactivity trends for five, high octane gasolines in a modern SI engine operated in an advanced compression ignition mode to the behavior measured under similar thermodynamic conditions, but in the static environment of a rapid compression machine. In this work, a detailed chemical kinetic model is utilized with multi-component surrogates representing the full boiling-range gasolines to evaluate predicted autoignition behavior under the same scenario. While Shah et al. [1] demonstrated that the overall trends were found to be similar between the two experimental devices, when compared appropriately, this study finds that the model lacks adequate fidelity to properly distinguish chemical kinetic interactions between various fuel constituents. Important combustion metrics, including combustion timing and rates of heat release, are skewed. Additional work appears necessary in order to confidently apply kinetic models for multi-mode engine design / control, and fuel co-optimization.
Kang, Dongil, Shah, Ashish, Rockstroh, Toby, Goldsborough, Scott
Φ-Sensitivity for LTGC Engines: Understanding the Fundamentals and Tailoring Fuel Blends to Maximize This Property2019-01-09614/2/2019
Φ-sensitivity is a fuel characteristic that has important benefits for the operation and control of low-temperature gasoline combustion (LTGC) engines. A fuel is φ-sensitive if its autoignition reactivity varies with the fuel/air equivalence ratio (φ). Thus, multiple-injection strategies can be used to create a φ-distribution that leads to several benefits. First, the φ-distribution causes a sequential autoignition that reduces the maximum heat release rate. This allows higher loads without knock and/or advanced combustion timing for higher efficiencies. Second, combustion phasing can be controlled by adjusting the fuel-injection strategy. Finally, experiments show that intermediate-temperature heat release (ITHR) increases with φ-sensitivity, increasing the allowable combustion retard and improving stability. A detailed mechanism was applied using CHEMKIN to understand the chemistry responsible for φ-sensitivity. For fuels with NTC behavior, φ-sensitivity is greatest in the NTC region due to enhanced ITHR reactions, which explains the experimental correlation between φ-sensitivity and ITHR. Under engine conditions, higher intake pressure means lower intake temperature to balance the reactivity, and both effects increase the φ-sensitivity. However, φ-sensitivity remains almost constant if decreased oxygen concentration is used to control the reactivity increase with intake-pressure boost because pressure and oxygen have opposite effects. Finally, for fuels without an NTC region, φ-sensitivity is lower and almost constant as operating conditions vary. The potential of designing fuel blends that increase the φ-sensitivity compared to RD5-87 (regular E10 gasoline), while maintaining high RON and octane-sensitivity, was investigated. Higher φ-sensitivity and higher RON than RD5-87 can be reached with a 5-component blend that meets U.S. regulations. The fuel mixture is composed of a combination of 1-hexene, n-pentane, iso-octane, p-xylene and iso-butanol (which was recently approved for gasoline in the U.S.). This study shows that it is possible to have both high φ-sensitivity and high RON with high octane-sensitivity.
Lopez Pintor, Dario, Dec, John, Gentz, Gerald
Utilizing Static Autoignition Measurements to Estimate Intake Air Condition Requirements for Compression Ignition in a Multi-Mode Engine - Engine and RCM Experimental Study2019-01-09574/2/2019
A multi-mode operation strategy, wherein an engine operates compression ignited at low load and spark ignited at high load, is an attractive way of achieving better part-load efficiency in a light duty spark ignition (SI) engine. Given the sensitivity of compression ignition operation to in-cylinder conditions, one of the critical requirements in realizing such strategy in practice, is accurate control of intake charge conditions - pressure (P), temperature (T) and equivalence ratio (φ), in order to achieve stable combustion and enable rapid mode-switches. This paper presents the first of a two part study, correlating ignition delay data for five RON98 gasoline blends measured under engine-relevant operating conditions in a rapid compression machine (RCM), to the cylinder conditions obtained from a modern SI engine operated in compression ignition mode. The overall trend in reactivity for the fuels was found to be similar in the two devices, although the compressed charge in the engine did not correlate directly with the constant ignition delay trajectories in the P-T diagram. However, positive correlation was found between the compressed pressure at constant ignition delay in the RCM and the intake boosting requirement for the engine to maintain constant combustion phasing. This suggests that static auto-ignition delay measurements can be utilized to estimate intake manifold conditions towards enabling combustion phasing control in a gasoline compression ignition engine.
Shah, Ashish, Kang, Dongil, Goldsborough, Scott, Rockstroh, Toby
Effects of Compression Ratio and Water Vapor Induction on the Achievable Load Limits of a Light Duty Diesel Engine Operated in HCCI Mode2019-01-09624/2/2019
Among the various Low Temperature Combustion (LTC) strategies, Homogeneous Charge Compression Ignition (HCCI) is most promising to achieve near zero oxides of nitrogen (NOx) and particulate matter emissions owing to higher degree of homogeneity and elimination of diffusion phase combustion. However, one of its major limitations include a very narrow operating load range owing to misfire at low loads and knocking at high loads. Implementing HCCI in small light duty air cooled diesel engines pose challenges to eliminate misfire and knocking problems owing to lower power output and air cooled operation, respectively. In the present work, experimental investigations are done in HCCI mode in one such light duty production diesel engine most widely used in agricultural water pumping applications. An external mixture preparation based diesel HCCI is implemented in the test engine by utilizing a high-pressure port fuel injection system, a fuel vaporizer and an air preheater. With an existing compression ratio of 17.5, the engine could not be operated beyond 20% of rated BMEP owing to severe knocking. The existing bowl shaped piston is modified into a flat piston which is justified by the fact that fuel-air mixing has minimal or negligible role in HCCI combustion. In order to examine the effects of compression ratio on the achievable load range in HCCI, the geometric compression ratio is reduced in incremental steps from 17.5 to 11.5 with an interval of 2.5 by reducing the piston crown thickness. However, the compression ratio could not be reduced below 11.5 with the existing piston design. The results obtained show that the load range could be extended up to 57% by reducing the compression ratio to 11.5 without utilizing exhaust gas recirculation. It is also intended to examine the effects of water vapor induction on the achievable load range in HCCI. For this purpose, 20 ultrasonic atomizers with 1.7 MHz vibration frequency are utilized to produce water vapor which is inducted along with diesel vapor and air during the engine suction stroke. The homogeneous mixture of diesel vapor, water vapor and air is ignited during the engine compression stroke at a fixed compression ratio of 15. The water vapor concentration is varied from 0.8 mg/cycle to 2.4 mg/cycle by using a control valve. The results obtained shows that the load range could be extended up to 50% in HCCI by utilizing water vapor induction. At a fixed load condition, water vapor induction reduces NOx and smoke emissions, while unburned emissions are higher compared to the results obtained with reducing compression ratio because of lower temperatures and displacement of intake oxygen. Overall, the present work shows that either by reducing the geometric compression ratio or by utilizing water vapor induction, there is a greater potential to increase the load range of diesel HCCI engines.
M, Murugesa Pandian, Krishnasamy, Anand
Effects of Single versus Two-Stage Heat Release on the Load Limits of HCCI Using Primary Reference Fuels2019-01-09504/2/2019
Homogeneous Charge Compression Ignition (HCCI) enables combustion with high efficiency and low emissions. Control over the combustion process and its narrow operating range are still the biggest challenges associated with HCCI. To expand the operable load ranges of HCCI, this paper explores the effects of single versus two-stage ignition fuels by studying the Primary Reference Fuels (PRF) in a variable compression ratio Cooperative Fuel Research (CFR) engine. The PRF fuels, iso-octane and n-heptane, are blended together at various concentrations to create fuel blends with different autoignition characteristics. Experiments were conducted using these PRF blends to explore the extent to which the load range can be extended with two-stage ignition fuels at various compression ratios and intake temperatures. The reactivity of the PRF blends increases with the fraction of n-heptane and so does the amount of low temperature heat release (LTHR). Since the low PRF number fuels have a higher reactivity, they can be autoignited at very low compression ratios while maintaining comparable combustion phasing and equivalence ratios. At the lower compression ratios, the low load limits were found to be extended while maintaining high combustion efficiencies. Additionally, lower peak pressures and pressure rise rates were achieved at low PRF number fuels as a result of its two-stage heat release, which can be used to reach higher loads. In addition, the energy released from the LTHR can be used to delay the CA50 combustion phasing (i.e., the crank angle timing where 50% of the energy has been released) beyond what is possible with a single-stage ignition fuel, which allows further high load extension. However, using lower compression ratios has a negative impact on the thermal efficiency. The effects of the extended load, single- and two-stage heat release, combustion phasing, and equivalence ratios on combustion efficiency, thermal efficiencies, and combustion durations were also explored.
Hariharan, Deivanayagam, Yang, Ruinan, Mamalis, Sotirios, Lawler, Benjamin
Modeling the Effect of Thermal Barrier Coatings on HCCI Engine Combustion Using CFD Simulations with Conjugate Heat Transfer2019-01-09564/2/2019
Thermal barrier coatings with low conductivity and low heat capacity have been shown to improve the performance of homogeneous charge compression ignition (HCCI) engines. These coatings improve the combustion process by reducing heat transfer during the hot portion of the engine cycle without the penalty thicker coatings typically have on volumetric efficiency. Computational fluid dynamic simulations with conjugate heat transfer between the in-cylinder fluid and solid piston of a single cylinder HCCI engine with exhaust valve rebreathing are carried out to further understand the impacts of these coatings on the combustion process. For the HCCI engine studied with exhaust valve rebreathing, it is shown that simulations needed to be run for multiple engine cycles for the results to converge given how sensitive the rebreathing process is to the residual gas state. The effect of thermal barrier coatings on the piston surface is explored using the properties of Yttria-Stabilized Zirconia (YSZ) and Gadolinium Zirconate (GdZr) top coatings with two different thicknesses. Heat flux measurements from an experimental engine with an all metal piston and YSZ and GdZr thermal barrier coatings are compared to the simulation results and the simulation is found to under predict heat transfer. Reducing the conductivity of the coating advances combustion as does increasing the thickness of the coating.
Killingsworth, Nick, Powell, Tom, O'Donnell, Ryan, Filipi, Zoran, Hoffman, Mark
Experimental Investigations to Extend the Load Range of Premixed Charge Compression Ignited Light Duty Diesel Engine through Fuel Modifications2019-01-09534/2/2019
Premixed Charge Compression Ignition (PCCI) is one of the most promising low temperature combustion (LTC) strategies to achieve near zero oxides of nitrogen (NOx) and particulate matter (PM) emissions along with higher thermal efficiency. One of the major problems in diesel PCCI is a narrow operating load range because of very early ignition and knocking combustion at higher loads owing to higher reactivity of diesel fuel. Further, low volatile diesel resist vaporization, resulting in fuel spray wall wetting and higher unburned emissions in PCCI. Thus, high reactivity and low volatility of diesel fuel make it not suitable for PCCI combustion. The present work attempts to address these limitations, by blending diesel with high volatile and low reactive fuels, viz. gasoline and butanol at 10% and 20% blend levels by volume. A production light duty air cooled diesel engine most widely used in agricultural water pumping applications is modified to run in PCCI mode by replacing an existing mechanical fuel injection system with a flexible common rail injection system. The test engine is initially run in diesel PCCI mode to establish the baseline reference data. The direct injected (DI) diesel fuel timings and exhaust gas recirculation (EGR) concentration are optimized at each load conditions to achieve maximum brake thermal efficiency. The results obtained show that the engine could be operated only upto 40% of rated load in diesel PCCI mode beyond which it knocks severely. The engine is then operated with diesel-gasoline and diesel-butanol blends at 10% and 20% blend levels at similar operating conditions. Among the investigated fuel blends, 20% butanol with 80% diesel (DB20) perform better in terms of achievable load range and lower carbon monoxide emissions. Optimization of DI timings and EGR concentration with DB20 helps to extend the load range upto 60% of rated load. The NOx and smoke emissions are significantly lower in PCCI with all the tested fuels.
Gupta, Saurabh K, Krishnasamy, Anand
Simulation Based Investigation of Achieving Low Temperature Combustion with Methanol in a Direct Injected Compression Ignition Engine2019-01-11524/2/2019
Low temperature combustion concepts used in compression ignition engines have shown to be able to produce simultaneous reduction of oxides of nitrogen and soot as well as generating higher gross indicated efficiencies compared to conventional diesel combustion. This is achieved by a combination of premixing, dilution and optimization of combustion phasing. Low temperature combustion can be complemented by moving away from fossil fuels in order to reduce the net output of CO2 emissions. Alternative fuels are preferably liquid and of sufficient energy density. As such methanol is proposed as a viable option. This paper reports the results from a simulation based investigation on a heavy-duty multi-cylinder direct injection compression ignition engine with standard compression ratio. The engine was simulated using two different fuels: methanol and gasoline with an octane number of 70. The primary objective of the study was to find the optimal engine settings which maximized the brake efficiency for the engine. A secondary objective was to find the optimal injection strategy and combustion mode that would result if the brake efficiency was targeted. Comparing methanol with gasoline, the brake efficiency was on average 5.5% higher with methanol. This increase stemmed from a reduction of in-cylinder exhaust loss which was due to higher specific heats and favorable combustion phasing. Furthermore there was a significant difference in the optimal injection strategy comparing methanol and gasoline. Due to the higher octane number of methanol, all the fuel could be injected before the start of combustion. Consequently, an injection strategy typical for the low temperature combustion concept partially premixed combustion resulted. The injection strategy with gasoline, on the other hand, was similar to what is typically found in conventional diesel engines.
Svensson, Erik, Verhelst, Sebastian
Understanding Fuel Stratification Effects on Partially Premixed Compression Ignition (PPCI) Combustion and Emissions Behaviors2019-01-11454/2/2019
Fuel stratification effects on the combustion and emissions behaviors for partially premixed compression ignition (PPCI) combustion of a high reactivity gasoline (research octane number of 80) was investigated using the third generation Gasoline Direct-Injection Compression Ignition (Gen3 GDCI) multi-cylinder engine. The PPCI combustion mode was achieved through a double injection strategy. The extent of in-cylinder fuel stratification was tailored by varying the start of second fuel injection timing (SOIsecond) while the first fuel injection event was held constant and occurred during the intake stroke. Based on the experimental results, three combustion characteristic zones were identified in terms of the SOIsecond - CA50 (crank angle at 50% cumulative heat release) relationship: (I) no response zone (HCCI-like combustion); (II) negative CA50 slope zone: (early PPCI mode); and (III) positive CA50 slope zone (late PPCI mode). Across the three zones, Zone II produced the best overall performance. In addition, a wider spray inclusion angle (130° vs. 100°) was found to allow for more retarded SOIsecond, thereby resulting in stronger fuel stratification and enhanced control authority over CA50. Finally, closed-cycle combustion CFD analysis was performed to gain insight into the in-cylinder fuel-air mixing and combustion process in all three combustion zones. CFD analysis showed that a 130° spray inclusion angle led to improved fuel efficiency and emissions. It was also found that 350 bar fuel rail pressure helped reduce overmixing of the fuel, resulting in better ignitability of the gasoline and lower soot generated in the combustion chamber.
Cho, Kukwon, Zhao, Le, Ameen, Muhsin, Zhang, Yu, Pei, Yuanjiang, Moore, Wayne, Sellnau, Mark, Moore, Wayne, Sellnau, Mark
Comparative Study on the Effects of Inlet Heating, Inlet Boosting, and Double-Injection Strategy on Partially Premixed Combustion2019-01-11494/2/2019
Partially premixed combustion (PPC) is a low temperature combustion (LTC) concept which can relieve soot-NOx trade-off without sacrificing efficiency. However, at low load operating range, PPC with low reactivity fuel generally undergoes long ignition delay, which gives rise to high pressure rise rate, fast heat release and even misfires. To solve these problems and maintain high efficiency simultaneously, inlet heating, inlet boosting and double-injection strategy are experimentally investigated in a heavy-duty engine. BH80 (80vol% n-butanol and 20vol% n-heptane) are blended and tested at 8 bar gIMEP in PPC mode. Inlet heating (from 40oC to 100oC), inlet boosting (from 1.4 bar to 2.5 bar) and a double-injection strategy (pilot/main injection) are attempted to reduce the maximum pressure rise rate (PRRmax). The results show that all three methods can achieve negligible soot emissions. Moreover, a correlation between global temperature at TDC and ignition delay is noticed. In other words, high global temperature after compression stroke makes BH80 easier to ignite. As a consequence, the ignition delay shortens and the maximum pressure rise rate decreases. Compared to inlet heating and inlet boosting, the double-injection strategy shows more advantages in reducing pressure rise rates and obtaining high gross indicated efficiency (GIE). Specifically, with a well-tuned double-injection strategy, 3.6 bar/oCA PRRmax and 49.5% GIE are achieved. In addition, when more fuel is injected in the pilot injection pulse, NOx emissions are significantly decreased. However, a longer pilot pulse also produces more CO and HC emissions and leads to lower combustion efficiency.
Han, Jinlin, Wang, Shuli, Somers, Bart
Review of Combustion Indexes Remote Sensing Applied to Different Combustion Types2019-01-11324/2/2019
This paper summarizes the main studies carried out by the authors for the development of indexes for remote combustion sensing applicable to different combustion types, i.e. conventional gasoline and diesel combustions, diesel PCCI and dual fuel gasoline-diesel RCCI. It is well-known that the continuous development of modern Internal Combustion Engine (ICE) management systems is mainly aimed at complying with upcoming increasingly stringent regulations throughout the world, both for pollutants and CO2 emissions. Performing an efficient combustion control is crucial for efficiency increase and pollutant emissions reduction. Over the past years, the authors of this paper have developed several techniques to estimate the most important combustion indexes for combustion control, without using additional cylinder pressure sensors but only using the engine speed sensor (always available on board) and accelerometers (usually available on-board for gasoline engines). In addition, a low-cost sensor based on acoustic sensing can be integrated to support combustion indexes evaluation and other engine relevant information. The real-time calculation of combustion indexes is even more crucial for innovative Low Temperature Combustions (such as diesel PCCI or dual fuel gasoline-diesel RCCI), mainly due to the high instability and the high sensitivity to slight variations of the injection parameters that characterize this kind of combustions. Therefore, the authors of this paper have applied the developed techniques not only to conventional engines (gasoline and diesel combustion), but also to engines modified for Low Temperature Combustions, with promising results in terms of validation and applicability for real-time combustion control. The developed methodologies have been tested and validated through a large amount of experimental tests. To run the estimation algorithms in real-time, they have been all implemented in a specifically designed rapid control prototyping system, the goal being to quantify the accuracy of the estimations and optimize the strategy implementations for the extensive use (in the near future) in modern Engine Control Modules (ECM).
De Cesare, Matteo, Ravaglioli, Vittorio, Carra, Filippo, Stola, Federico
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