Browse Topic: Gas engines

Items (1,900)

HELICOPTER TURBOSHAFT ENGINE IDLE POWER SCHEDULING

11/26/2025

The purpose of this AIR (Aerospace Information Report) is to provide aircraft and engine designers with a better understanding of helicopter turboshaft engine idle power characteristics and objectives to be considered in the design process. Idle is the lowest steady state power setting. At this setting, the engine typically does not produce enough power to obtain governed output shaft speed (i.e. the shaft speed is determined by the load imposed by the aircraft). In the aircraft, the engine is typically stabilized at this power setting after starting, prior to taxi and for some period of time after rotor shutdown for cool down prior to engine shutoff. Traditionally, the aircraft designer wants idle power scheduled as low as possible and of course, does not want any resulting aircraft operational difficulties such as overcoming the rotor brake. The engine designer, however, desires a higher scheduled power because of the reduced probability of engine operational problems. The attributes of conflicting idle desires are discussed. Other inputs are also considered to establish the engine idle power settings. The information contained herein will assist in the early design phase and ultimately will result in a more optimum match between engine and aircraft requirements.

S-12 Powered Lift Propulsion Committee

Investigation of a Second Exhaust Valve Lift to Improve Combustion in a Methane - Diesel Dual-Fuel Engine

2022-01-0466

3/29/2022

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

A Numerical Study on the Effect of a Pre-Chamber Initiated Turbulent Jet on Main Chamber Combustion

2022-01-0469

3/29/2022

To elucidate the complex characteristics of pre-chamber combustion engines, the interaction of the hot gas jets initiated by an active narrow throated pre-chamber with lean premixed CH4/air in a heavy-duty engine was studied computationally. A twelve-hole KAUST proprietary pre-chamber geometry was investigated using CONVERGE software. The KAUST pre-chamber has an upper conical part with the spark plug, and fuel injector, followed by a straight narrow region called the throat and nozzles connecting the chambers. The simulations were run for an entire cycle, starting at the previous cycle's exhaust valve opening (EVO). The SAGE combustion model was used with the chemistry modeled using a reduced methane oxidation mechanism based on GRI Mech 3.0, which was validated against in-house OH chemiluminescence data from the optical engine experiments. Two different piston geometries, a flat piston geometry, and a more realistic bowl piston geometry were studied to understand the influence of jet on main chamber combustion. Varying the piston geometries results in different free jet times and hence main chamber combustion characteristics. Pre-chamber fuel ratio (PCFR) 6% of the total amount of fuel was investigated while keeping the global excess air ratios (λ) condition a constant value of 2.0. Both piston cases resulted in similar pre-chamber pressurization, with almost the same pre-chamber discharge and the equal pressure difference between pre-and main-chamber (ΔP) at the start of jet ejection. Different combustion behaviors were observed on analysis of the heat release rate in the main chamber. The importance of turbulence generated by the pre-chamber-initiated jets was further studied. It was observed that free jet time is a critical factor in developing turbulence in the main chamber. This increase in turbulence helps in increasing the burning velocity causing faster combustion. The influence of the jet-piston interaction is also analyzed as that determines the combustion behavior in the later CAD.

Sanal, Sangeeth, Echeverri Marquez, Manuel, Silva, Mickael, Cenker, Emre, Im, Hong G.

Knock: A Century of Research

03-15-01-0004

7/28/2021

Knock is one of the main limitations on increasing spark-ignition (SI) engine efficiency. This has been known for at least 100 years, and it is still the case today. Knock occurs when conditions ahead of the flame front in an SI engine result in one or more autoignition events in the end gas. The autoignition reaction rate is typically much higher than that of the flame-front propagation. This may lead to the creation of pressure waves in the combustion chamber and, hence, an undesirable noise that gives knock its name. The resulting increased mechanical and thermal loading on engine components may eventually lead to engine failure. Reducing the compression ratio lowers end-gas temperatures and pressures, reducing end-gas reactivity and, hence, mitigating knock. However, this has a detrimental effect on engine efficiency. Automotive companies must significantly reduce their fleet carbon dioxide (CO2) values in the coming years to meet targets resulting from the 2015 Paris Agreement. One path towards meeting these is through partial or full electrification of the powertrain. However, the vast majority of automobiles in the near future will still feature a gasoline-fueled SI engine; hence, improvements in combustion engine efficiency remain fundamental. As knock has been a key limitation for so long, there is a huge amount of literature on the subject. A number of reviews on knock have already been published, including in recent years. These generally concentrate on current understanding and status. The present work, in contrast, aims to track the progress of research on knock from the 1920s right through to the present day. It is hoped that this can be a useful reference for new and existing researchers of the subject and give further weight to occasionally neglected historical activity, which can still provide important insights today.

Corrigan, Daire James, Fontanesi, Stefano

Model-Based Precise Air-Fuel Ratio Control for Gaseous Fueled Engines

02-13-03-0017

10/9/2020

In this article, an adaptive state estimation algorithm for precise air-fuel ratio (AFR) control is presented. AFR control is a critical part of internal combustion engine (ICE) control, and tight AFR control delivers lower engine emissions, better engine fuel economy, and better engine transient performance. The proposed control algorithm significantly improves transient AFR control to eliminate and reduce the amplitude of the lean and rich spikes during transients. The new algorithm is first demonstrated in simulation (using Matlab/SimulinkTM and GT-PowerTM) and then verified on a test engine. The engine tests are conducted using the European Transient Cycle (ETC) with HoribaTM double-ended dynamometer. The developed algorithm utilizes a nonlinear physics-based engine model in the observer and advanced control principles with modifications to solve real industrial control issues. This method dramatically reduces on-engine AFR transient calibration efforts, which was one of the objectives of this research. The developed algorithm is applicable for various fuel mixer configurations including pre-turbocharger, pre-throttle, and post-throttle. It also demonstrates robustness to engine to engine inconsistency. The novel algorithm is developed by following model-led design process. WoodwardTM natural gas engines and engine control modules are used for algorithm development and validation.

Han, Yi, Young, Peter

Simulation and Characterization of Variable-Voltage Hybrid-Electric Powertrains

F-0076-2020-16412

10/5/2020

A phenomenological simulation for a variable-voltage hybrid-electric powertrain was developed and compared with test data acquired on a 4 hp powertrain to understand the fundamental characteristics of such a system. The powertrain was modeled component by component, and compared with over 500 experimental data points, from the engine alone to the engine generator, to the engine-generator with four distributed propulsors. The principal conclusion of the predictive simulation and the experimental data was that generator voltage is a key parameter that needs careful control relative to rotor speed. For any operating state -- defined by rotor torque and RPM -- the generator voltage should be minimized to minimize engine specific fuel consumption. In general the system is influenced more by the engine generator than electric motors. Hence greater rotor torque and lower rotor RPM is desired. It was found that steady state performance can be confidently predicted with the engine model, if the thermal efficiency is calibrated with engine data. The overall understanding gained from this work is that the optimal operation of hybrid-electric powertrains in VTOL is closely coupled with controls and rotor aeromechanics as well as engine gas dynamics and thermodynamics, but can be captured with relatively simple phenomenological models.

Mills, Brent, Datta, Anubhav

Fuels in Ground Support Equipment (Other Than Gasoline or Diesel)

AIR5373A (Current)

9/23/2020

This SAE Aerospace Information Report (AIR) is intended as a source of comparative information and is subject to change to keep pace with experience and technical advances. This document describes currently used fuels and fuels which may be used in the future. Conventional gasoline and diesel fuels are intentionally omitted from this document.

AGE-3 Aircraft Ground Support Equipment Committee

Optical Characterization of the Combustion Process inside a Large-Bore Dual-Fuel Two-Stroke Marine Engine by Using Multiple High-Speed Cameras

2020-01-07884/14/2020

Dual-fuel engines for marine propulsion are gaining in importance due to operational and environmental benefits. Here the combustion in a dual-fuel marine engine operating on diesel and natural gas, is studied using a multiple high-speed camera arrangement. By recording the natural flame emission from three different directions the flame position inside the engine cylinder can be spatially mapped and tracked in time. Through space carving a rough estimate of the three-dimensional (3D) flame contour can be obtained. From this contour, properties like flame length and height, as well as ignition locations can be extracted. The multi-camera imaging is applied to a dual-fuel marine two-stroke engine, with a bore diameter of 0.5 m and a stroke of 2.2 m. Both liquid and gaseous fuels are directly injected at high pressure, using separate injection systems. Optical access is obtained using borescope inserts, resulting in a minimum disturbance to the cylinder geometry. In this type of engine, with fuel injection from positions at the rim of the cylinder, the flame morphology becomes asymmetric. The optical spatial mapping and tracking method is demonstrated to be well suited for the study of such an asymmetric combustion system. Spatial mapping and tracking of flame position is applied to both engine operating modes; normal diesel operation and dual-fuel operation with diesel pilot ignition of the gas. Similarities and differences between diesel and gas flame shape and development can thus be visualised directly. The effects of changing charge density, gas injection pressure and injection nozzle geometry on the flame geometry and development are also studied.

Hult, Johan, Matamis, Alexios, Baudoin, Eric, Mayer, Stefan, Richter, Mattias

Pre-design Investigation of Resonant Frequency Effects on Gas Exchange Efficiencies of a One-kW Natural-Gas Linear Engine Alternator

2020-01-04884/14/2020

Performance of a natural gas two-stroke engine incorporated in a 1-kW free-piston oscillating Linear Engine Alternator (LEA) - a household electricity generator - was investigated under different resonant frequencies for pre-design phase purposes. To increase the robustness, power density, and thermal efficiencies, the crank mechanism in free-piston LEA is omitted and all moving parts of the generator operate at a fixed resonant frequency. Flexure springs are the main source of the LEA’s stiffness and the mass-spring dynamics dominates the engine’s speed. The trade-off between the engine’s performance, mass-spring system limits, and power and efficiency targets versus the LEA speed is very crucial and demands a careful investigation specifically at the concept design stages to find the optimum design parameters and operating conditions. CFD modeling was performed to analyze the effects of resonant frequency on the engine’s gas exchange behavior. To take combustion effects into account, a semi-empirical method was employed to obtain the initial and boundary conditions during the gas exchange from experiments and imported into CFD simulation. The numerical results of the gas exchange were validated at the engine speed of 5400 RPM with the experimental results. The semi-empirical method eliminated the complicated combustion simulation and significantly reduced the computational time and well-matched with experiments within 1 % error. Results showed enhanced trapping efficiency of 7.1% per 1000 RPM, and reduced scavenging efficiencies of 5.5% per 1000 RPM as speed engine’s speed increased. Comparison of the trapping and scavenging efficiencies showed an improved fuel/power efficiency equal to about 1.45 % per each 15 Hz increase in the LEA resonant frequency.

Zamani Meymian, Nima, Darzi, Mahdi, Johnson, Derek, Famouri, Parviz

Piston Bowl Design Optimization to Improve Low End Rated Torque in BS-VI Diesel Engine Based on Multi-Dimensional Combustion Simulation

2020-01-02414/14/2020

In cylinder combustion and emission characteristics are dependent on piston bowl geometry design. In-cylinder fuel air mixing and flame front movement are influenced by piston bowl shape and design. These phenomena in turns affect the combustion behavior and the power developed by the diesel engine. In this study piston bowl geometry optimization of a LMD diesel engine is carried out to improve the torque and BSFC output at low end rated operating zones. The optimized bowl geometry is also incorporated in the engine and validated on the test bed. In this work, a commercially available CFD code AVL FIRE is used for combustion simulation and bowl geometry optimization. The validation of in-cylinder combustion simulation of a 2 liter Turbocharged LMD BS-VI diesel engine with base piston bowl geometry is carried out with the available test data. The validation of combustion simulation is performed for four engine operating speed points covering rated torque to rated power operating condition. Four key piston bowl geometry parameters were selected for the optimization study with the objective to improve the torque output at rated torque operation. Two bowl geometries from the optimization study were selected for further analysis at remaining engine operating points. Both the bowl geometries showed improvement in torque and BSFC at all the simulated operating zones. Based on the design feasibility one of the bowl geometry was selected for validation on physical engine. The results from test bed showed the optimized geometry gave torque improvement as predicted by the combustion simulation.

Appukuttan, Anish, Bisht, Jasvir, Kaundabalaraman, Kaarthic, Rathi, Hemantkumar

Experimental and Numerical Analysis of Passive Pre-Chamber Ignition with EGR and Air Dilution for Future Generation Passenger Car Engines

2020-01-02384/14/2020

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

Investigation of Reynolds Stress Model for Complex Flow Using CONVERGE

2020-01-11044/14/2020

The Reynolds stress turbulence model (RSM) has been developed to go beyond the Boussinesq hypothesis and to improve turbulence modeling of flows with significant mean streamline curvature and secondary flow. In this paper the RSM in commercial CFD software CONVERGE is tested for its performance and robustness when applying to complex flows. Several validation cases including flow over flat plate, vortex combustor, diesel engine spray and combustion were selected to test the RSM. The swirling flow in vortex combustor, non-reacting but vaporizing ECN Spray A (free jet) and Sandia small bore diesel engine case are used to demonstrate the benefits of the RSM over the widely used RNG k-epsilon model without model tuning. The vortex combustor case shows the RSM can provide good prediction for strong swirling flow. ECN spray A case was used to demonstrate that the RSM can accurately predict the liquid and vapor penetration lengths of a free jet under diesel engine conditions. Accurate spray-wall interaction is quite important for modern diesel engine combustion where piston bowls facilitate and rely on spray-wall interactions for better combustion efficiency and emission reduction. It is found that the RSM can improve the prediction of cylinder pressure compared to the RNG k-epsilon model using the small-bore diesel engine case. All test results show that the RSM is robust and its computational overhead compared to the RNG k-epsilon model ranges from 17% to 78% for test cases.

Liu, Zhenping, Wijeyakulasuriya, Sameera, Mashayekh, Alireza, Chai, Xiaochuan

The Potential of Gasoline Fueled Pre Chamber Ignition Combined with Elevated Compression Ratio

2020-01-0279

4/14/2020

Pre-chamber ignition is a method to simultaneously increase the thermal efficiency and to meet ever more stringent emission regulations at the same time. In this study, a single cylinder research engine is equipped with a tailored pre-chamber ignition system and operated at two different compression ratios, namely 10.5 and 14.2. While most studies on gasoline pre-chamber ignition employ port fuel injection, in this work, the main fuel quantity is introduced by side direct injection into the combustion chamber to fully exploit the knock mitigation effect. Different pre-chamber design variants are evaluated considering both unfueled and gasoline-fueled operation. As for the latter, the influence of the fuel amount supplied to the pre-chamber is discussed. Due to its principle, the pre-chamber ignition system increases combustion speeds by generating enhanced in-cylinder turbulence and multiple ignition sites. This property proves to be an effective measure to mitigate knocking effects. It is shown that less spark retard compared to conventional spark ignition allows to exploit the efficiency benefit of elevated compression ratios also in high load operation for stoichiometric mixtures. Furthermore, auxiliary fueling of the pre-chamber enables ultra-lean combustion (λ=2.0) with very low NOx emission levels. Apart from decreased throttling losses lean burn assists to further suppress knocking in case of elevated compression ratios. Finally, it is demonstrated that the combination of ultra-lean combustion and elevated compression ratio leads to a significant improvement of the indicated efficiency with peak values of about 43 %. Higher PN emissions in low load and increased heat losses remain challenges of the used pre-chamber ignition system.

Stadler, Andreas, Sauerland, Henning, Härtl, Martin, Wachtmeister, Georg

Experimental and 1D Numerical Investigations on the Exhaust Emissions of a Small Spark Ignition Engine Considering the Cylinder-by-Cylinder Variability

2020-01-05784/14/2020

This paper reports a numerical and experimental analysis on a twin-cylinder turbocharged Spark Ignition engine carried out to investigate the cylinder-to-cylinder variability in terms of performance, combustion evolution and exhaust emissions. The engine was tested at 3000 rpm in 20 different steady-state operating conditions, selected with the purpose of observing the influence of cylinder-by-cylinder A/F ratio variations and the EGR effects on the combustion process and exhaust emissions for low to medium/high loads. The experimental outcomes showed relevant differences in the combustion evolution (characteristic combustion angles) between cylinders and not negligible variations in the emissions of the single cylinder exhaust and the overall engine one. This misalignment resulted to be due to differences in the injected fuel amount by the port injectors in the two cylinders, mainly deriving from the specific fuel rail geometry. The experimental data were then used to validate a 1D engine model, integrated with refined sub-models of turbulence, combustion, heat transfer and emissions. The model takes into account the in-cylinder production of noxious species, and their propagation in the exhaust system, up to the three-way catalytic converter. A satisfactory accuracy was reached in reproducing the overall engine performance and the combustion process in the two cylinders. In particular, the emission sub-models confirmed that the variations of the cylinder-out exhaust emissions (NOx, HC and CO) were mainly due to the non-uniform effective in-cylinder A/F ratio. The proposed numerical methodology has the potential to highlight unexpected combustion non-uniformities among different cylinders and represents a powerful support to the engine design and development. It also allows for the prediction of the overall exhaust emissions at different engine operating conditions up to the entire domain, thus assisting the engine calibration phase and reducing the experimental efforts.

Marchitto, Luca, Teodosio, Luigi, Tornatore, Cinzia, Valentino, Gerardo, Bozza, Fabio

Simulation Analysis of Early and Late Miller Cycle Strategies Influence on Diesel Engine Combustion and Emissions

2020-01-06624/14/2020

Based on the working model of a diesel engine, the influence of 2 Miller cycle strategies-Early Intake Valve Closure (EIVC) and Late Intake Valve Closure (LIVC) on the combustion and emissions of diesel engine was analyzed. Then the working condition of each Miller cycle strategies on the engine under the rated speed was optimized through the adjust of the valve timing, boost pressure and the injection timing. The research found that both delaying and advancing the closure timing of the intake valve can decrease the pressure and temperature during compression stroke, prolonging the ignition delay. However, due to the decrease of the working media inside the cylinder, the average in-cylinder temperature and soot emissions will increase, which can be alleviated by raising the boost pressure and the resulting compensation of the intake loss. The study found that together with increasing boost pressure and delaying injection timing, both EIVC and LIVC can reduce the NOx and soot emissions simultaneously. The simulation results show that while keeping the peak firing pressure the same as the original machine, M-50 together with constant peak firing pressure boosting and a 6oCA injection delay can decrease the BSFC by 1.21%, the NOx emissions by 22%, and the soot emissions by 58.1%, while M100 together with constant peak firing pressure boosting and a 4oCA injection delay can reduce BSFC by 1.56%, the the NOx emissions by 12.96%, and the soot emissions by 54.75%.

Yang, Shuai, Yang, Xiaolin, Liu, Haifeng, Feng, Zhiwei, Li, Xiuyuan

Role of Lubricating Oil Properties in Exhaust Particle Emissions of an Off-Road Diesel Engine

2020-01-03864/14/2020

Particle number emissions from an off-road diesel engine without exhaust after-treatment were studied by using five different heavy-duty lubricating oils in the engine. The study extends understanding on how the properties of lubricating oil affect the nanoparticle emissions from an off-road diesel engine. The lubricants were selected among the performance classes of the European Automobile Manufacturers Association, at least one lubricant from each category intended for heavy-duty diesel engines. Particle size distributions were measured by the means of an engine exhaust particle sizer (EEPS), but soot emissions, gaseous emissions and the basic engine performance were also determined. During the non-road steady state cycle, the most of the differences were detected at the particle size range of 6-15 nm. In most cases, the lowest particle quantities were emitted when the highest performance category lubricant was used. Based on the results of this study, the low contents of Zn, P, and S in lubricating oil contributed to the reduced emission factors for engine-out nucleation mode particles at any load. In addition, the low content of sulfate ash was considered the main influential factor for the low particle number emissions.

Ovaska, Teemu, Niemi, Seppo, Sirviö, Katriina, Nilsson, Olav, Karjalainen, Panu, Rönkkö, Topi, Kulmala, Kari, Keskinen, Jorma

Control of Ignition Timing and Combustion Phase by Means of Injection Strategy for Jet-Controlled Compression Ignition Mode in a Light Duty Diesel Engine

2020-01-05554/14/2020

Controllability of ignition timing and combustion phase by means of dual-fuel direct injection strategy in jet-controlled compression ignition mode were investigated in a light-duty prototype diesel engine. Blended fuel with lower reactivity was delivered in the early period of compression stroke to form the premixed charge, while diesel fuel which has higher reactivity was injected near TDC to trigger the ignition. The effects of several important injection parameters including pre-injection timing, jet-injection timing, pre- injection pressure and ratio of pre-injection in the total heat value of injected fuel were discussed. Numerical Simulation by using CFD software was also conducted under similar operating conditions. The experimental results indicate that the jet-injection timing shows robust controllability on the start of combustion under all the engine load conditions. Pre-injection timing/pressure/ratio show little impact on the start of combustion due to low reaction activity of premixed charge. Early pre-injection timing and larger pre-injection pressure lead to wall-wetting and poor vaporization of pre-injected fuel especially at light duty conditions, as a result, combustion duration increases, and CO/THC emissions enhance. Larger pre-injection ratio in the total heat value of injected fuel prolongs combustion duration and enhances CO/THC emissions at lower engine load, reduces combustion duration and CO/THC emissions at higher engine load. The numerical simulation results demonstrate the two-stage combustion process described according to the experimental results. The two-stage combustion process of diesel jet JCCI mode is featured by the evolution of intermediate species such as H2O2 and OH, and the main emission products such as CO and NOx. At last, the effects of injection parameters on JCCI combustion characteristics are summarized.

Zhu, Jingyu, Bo, Li, Long, Wuqiang

Effects of Geometry on Passive Pre-Chamber Combustion Characteristics

2020-01-08214/14/2020

Towards a fundamental understanding of the ignition characteristics of pre-chamber (PC) combustion engines, computational fluid dynamics (CFD) simulations were conducted using CONVERGE. To assist the initial design of the KAUST pre-chamber engine experiments, the primary focus of the present study was to assess the impact of design parameters such as throat diameter, nozzle diameter, and nozzle length. The well-stirred reactor combustion model coupled with a methane oxidation mechanism reduced from GRI 3.0 was used. A homogeneous charge of methane and air with λ = 1.3 on both the PC and main chamber (MC) was assumed. The geometrical parameters were shown to affect the pre-chamber combustion characteristics, such as pressure build-up, radical formation, and heat release as well as the composition of the jets penetrating and igniting the main chamber charge. In addition, the backflow of species pushed inside the pre-chamber due to the flow reversal (FR) event was analyzed. It was found that the narrow throat type of pre-chamber is strongly influenced by the throat diameter, but weakly influence by nozzle length. A flow reversal pattern was observed, which promoted the accumulation of intermediate species in the PC, leading to a secondary heat release.

Silva, Mickael, Sanal, Sangeeth, Hlaing, Ponnya, Cenker, Emre, Johansson, Bengt, Im, Hong G.

Improving Heavy Duty Natural Gas Engine Efficiency: A Systematic Approach to Application of Dedicated EGR

2020-01-08184/14/2020

The worldwide trend of tightening CO2 emissions standards and desire for near zero emissions is driving development of high efficiency natural gas engines for a low CO2 replacement of traditional diesel engines. A Cummins Westport ISX12 G was previously converted to a Dedicated EGR® (D-EGR®) configuration with two out of the six cylinders acting as the EGR producing cylinders. Using a systems approach, the combustion and turbocharging systems were optimized for improved efficiency while maintaining the potential for achieving 0.02 g/bhp-hr NOX standards. A prototype variable nozzle turbocharger was selected to maintain the stock torque curve. The EGR delivery method enabled a reduction in pre-turbine pressure as the turbine was not required to be undersized to drive EGR. A high energy Dual Coil Offset (DCO®) ignition system was utilized to maintain stable combustion with increased EGR rates. High compression ratio, reduced squish pistons were designed to maintain MBT combustion phasing and fast burn rates along the torque curve. The final engine configuration was tested on the Heavy-Duty Supplemental Emissions Test (SET), a 13-mode steady-state engine dynamometer test. The engine was able to achieve a weighted average efficiency improvement of 12% over the baseline configuration with a peak BTE of 41.7%.

Kocsis, Michael C., Mitchell, Robert, Moiz, Ahmed Abdul, Kalaskar, Vickey, Williams, D. Ryan, Sjovall, Scott

Study on the Effect of Manifold Induction of Acetylene in a Dual-Fuelled CI Engine

2020-01-08174/14/2020

The utilization of gaseous fuels in internal combustion (IC) engines is receiving more significant greater interest in recent years because of their better fuel mixing characteristics. Apart from potential gaseous fuels such as liquefied natural gas (LPG), compressed natural gas (CNG), and hydrogen, other alternatives are being explored for their utilization in IC engines. The reason for this exploration is mainly because of the durability and robust nature of compression ignition (CI) engines, and more research focuses on the utilization of a variety of gaseous fuels in CI engines. However, gaseous fuels need to be used in CI engines on dual fuel mode only. In this investigation, a single-cylinder, four-stroke, air-cooled diesel engine was converted into Acetylene run dual-fuel CI engine by changing the intake manifold of the test engine. Acetylene at three flow rates viz., 2lpm, 4lpm, and 6lpm were introduced into the intake port by manifold induction technique while Jatropha biodiesel/diesel was injected directly into the cylinder. In this paper, the effect of manifold induction of Acetylene on the performance and emission characteristics of the test engine was assessed and compared with those of conventional diesel operation of the test engine.

Sahoo, Rakesh Kumar, Jaiswal, Akshat, Sivalingam, Murugan

Experimental and Numerical Assessment of Active Pre-chamber Ignition in Heavy Duty Natural Gas Stationary Engine

2020-01-08194/14/2020

Gas engines (fuelled with CNG, LNG or Biogas) for generation of power and heat are, to this date, taking up larger shares of the market with respect to diesel engines. In order to meet the limit imposed by the TA-Luft regulations on stationary engines, lean combustion represents a viable solution for achieving lower emissions as well as efficiency levels comparable with diesel engines. Leaner mixtures however affect the combustion stability as the flame propagation velocity and consequently heat release rate are slowed down. As a strategy to deliver higher ignition energy, an active pre-chamber may be used. This work focuses on assessing the performance of a pre-chamber combustion configuration in a stationary heavy-duty engine for power generation, operating at different loads, air-to-fuel ratios and spark timings. The engine was originally a 6-cylinder compression ignition engine which is here employed as a single cylinder engine and then suitably modified to host the pre-chamber (with its natural gas injection system and spark plug) with a new bowl piston to decrease compression ratio. A 0D model is built to make a thermodynamic analysis to characterize the local conditions in the pre-chamber before spark timing (temperature, pressure and composition), based on a compressible nozzle equation for the mass transfer between the chambers and a simplified Woschni model for the pre-chamber’s heat transfer. A mathematical expression was found to describe the relationship between the local conditions and the early stage of the combustion. Experimental results showed the beneficial effect of spark delay and mixture leaning for the reduction of NOx emissions, while CO, unburned hydrocarbons and engine performance see improvement with lower air-to-fuel ratios and spark advance.

Onofrio, Gessica, Li, Changle, Garcia Valladolid, Pablo, De La Morena, Joaquin, Garcia, Antonio, Tunestal, Per, Beatrice, Carlo

Assessment of the Ignition System Requirement on Diluted Mixture Spark Engines

2020-01-11164/14/2020

In order to face the new challenges, spark ignition engines are evolving by following some strategies and technologies. Among them, alternative combustion processes based on the dilution of the homogeneous mixture, either with fresh air or with Exhaust Gas Recirculation (EGR), are being explored. In a higher or lower extent, these changes modify in-cylinder thermodynamic conditions during the engine operation (pressure, temperature and gas composition) thus conditioning the spark ignition system requirements that will have to evolve to become more reliable and powerful. In this framework, an experimental study on the effect of the key in-cylinder conditions on the ignition system performance has been carried out in a single-cylinder spark-ignition (SI) research engine. The study includes EGR, lambda and energizing time sweeps to assess the behavior of the engine in different operating conditions. Furthermore, various Insulated-Gate Bipolar Transistors (IGBT) and spark plugs have been tested to assess the influence of these components on the ignition process at high diluted mixtures. Conclusions show that diluted mixtures (with EGR or lambda), even though they require more spark energy to achieve a stable combustion, have up to 4% benefit on indicated efficiency, providing that the combustion propagates adequately. However, at high diluted conditions the combustion is compromised, so two different approaches were explored to improve it. Whilst it was checked that increasing the clamping value of the IGBT does not necessarily imply a better combustion in all scenarios, the increment of the electrodes gap of the spark plug would require higher clamping voltage at the IGBT, and it would have a slight benefit on efficiency providing that the rest of components, in particular the coil, are adequate.

Molina, Santiago, Martin, Jaime, Novella, Ricardo, Gomez-Soriano, Josep, Padilla, Jose

On Maximizing Argon Engines' Performance via Subzero Intake Temperatures in HCCI Mode at High Compression Ratios

2020-01-11334/14/2020

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

Experimental Investigation of the Influence of Ignition System Parameters on Combustion in a Rapid Compression-Expansion Machine

2020-01-11224/14/2020

Lean burn combustion concepts with high mean effective pressures are being pursued for large gas engines in order to meet future stringent emission limits while maintaining high engine efficiencies. Since severe boundary conditions for the ignition process are encountered with these combustion concepts, the processes of spark ignition and flame initiation are important topics of applied research, which aims to avoid misfiring and to keep cycle-to-cycle combustion variability within reasonable limits. This paper focuses on the fundamental investigation of early flame kernel development using different ignition system settings. The investigations are carried out on a rapid compression-expansion machine in which the spark ignition process can be observed under engine-like pressure and excess air ratio conditions while low flow velocities are maintained. The schlieren setup for high-speed optical investigations of the area of the spark plug electrodes is described and a suitable post-processing routine is introduced. The influence of different spark current durations on early flame kernel formation is investigated using a modulated capacitive discharge ignition (MCDI) system. The outcomes reveal that a short spark current duration results in a slower increase and higher standard deviation of the flame area during the early phase of combustion. Moreover, stable flame initiation appears to require a minimum spark current duration. The methodology introduced in this paper will be applied in detailed investigations of other spark plug geometries and ignition settings in order to shed more light on the ignition of lean mixtures.

Kiesling, Constantin, Pirker, Gerhard, Tilz, Anton, Oppl, Thomas, Nickl, Andreas, Wimmer, Andreas, Meyer, Georg

Influence of Port Water Injection on the Combustion Characteristics and Exhaust Emissions in a Spark-Ignition Direct-Injection Engine

2020-01-02944/14/2020

It is well known that engine downsizing is still the main energy-saving technology for spark-ignition direct-injection (SIDI) engine. However, with the continuous increase of the boosting ratio, the gasoline engine is often accompanied by the occurrence of knocking, which has the drawback to run the engine at retarded combustion phasing. Besides, in order to protect the turbine blades from being sintered by high exhaust temperature, the strategies of fuel enrichment are often taken to reduce the combustion temperature, which ultimately leads to a high level of particulate number emission. Therefore, to address the issues discussed above, the port water injection (PWI) techniques on a 1.2-L turbocharged, three-cylinder, SIDI engine were investigated. Measurements indicate that the optimization of spark timing has a significant impact on its performance. The two factors of the water substance itself and spark advance caused by the knock mitigation are trade-offs, which eventually affect the combustion performance. Under knock limited spark advance (KLSA) condition, we find that the application of port water injection could effectively advance the combustion phasing and reduce exhaust gas temperature, which makes it possible to eliminate fuel enrichment and further enhances the fuel economy improvement at the maximum power point. As a result, about 5.2%-18.4% improvements in the fuel economy are obtained under different engine operating conditions. For the exhaust emissions, due to the increasing heat capacity of the mixture and the elimination of fuel enrichment, port water injection techniques cause an 85.3% reduction in particle number concentration. However, it shows that for a given λ, an increase in the water/fuel ratio would cause higher THC emissions, which is contributed to the occurrence of more quenching caused by higher peak combustion pressure. Finally, the potential of PWI on the engine combustion characteristics and emissions performance was revealed.

Fan, Yadong, Wu, Tianbao, Li, Xuesong, Xu, Min, Hung, David

Numerical Investigation of the Effects of Port Water Injection Timing on Performance and Emissions in a Gasoline Direct Injection Engine

2020-01-02874/14/2020

Port water injection is considered as a promising strategy to further improve the combustion performance of internal combustion engines for its benefit in knock resistance by reducing the cylinder temperature. A thorough investigation of the port water injection technique is required to fully understand its effects on the engine combustion process. This study explores the potential of the port water injection technique in improving the performance of a turbo charged Gasoline Direct Injection engine. A 3D computational fluid dynamics model is applied to simulate the in-cylinder mixing and combustion for this engine both with and without water injection. Different water injection timings are investigated and it is found that the injection timing greatly effects the mass of water which enters the combustion chamber, both in liquid and vapor form. Comparison have been given between the original engine and the water injection one and the results show that the water injection can reduce the cylinder temperature both in the compressing and combustion strokes. The pressure oscillation is also suppressed which indicates a better knocking resistance for water injection strategy. An optimized injection timings could be found for a particular load condition and also lead to a better combustion performance and emissions.

Yin, Peng, Li, Xuesong, Hung, David, Fan, Yadong, Xu, Min

Experimental Comparison of Biogas and Natural Gas as Vibration, Emission, and Performance in a Diesel Engine Converted to a Dual Fuel

04-13-01-00041/27/2020

Biogas, natural gas, and their usage in the diesel engine will be important in the future. For this purpose, the effects of biogas on engine performance, emissions, and engine vibrations of the diesel engines with dual fuel system are investigated in comparison with natural gas. It has also been included in evaluating the deformation of the engine oil due to hydrogen sulfide combustion reactions. In this study, a constant speed, naturally aspirated, and direct injection of the diesel engine with volume of 2.5 liter has been converted into a dual fuel system that can be included in gas fuels. In order to determine engine performance, exhaust emissions, engine vibration, and noise, the tests were carried out at load stages of 5, 10, 15, 20, and 25 kW and at a constant speed of 1500 rpm. The experiments were first performed in a mono operation condition of the conventional diesel fuel. Subsequently, tests were repeated under natural gas/diesel and biogas/diesel dual fuel operation conditions, respectively. As a result of the tests, it was observed that the vibration amount decreased and the noise emission was reduced by 3.5% in all stages where biogas was used as the main fuel. Depending on fuel or operation system change, no significant change was observed in cylinder block, cylinder heat, exhaust, and intake manifold temperature. The exhaust gas temperature is measured to be lower because of the carbon dioxide (CO2) content in the biogas. When approaching from the point view of engine emissions, it was determined that the carbon monoxide (CO) emission increased at all engine loads while a decrease of 50% in oxides of nitrogen (NOx) emission occurred.

Aytav, Emre, Koçar, Günnur, Teksan, Abdulhalik Emre

Development of a 3D-CFD Model for a Full Optical High-Pressure Dual-Fuel Engine

03-13-02-00171/27/2020

In times of ever stricter exhaust emission regulations, the importance of alternative combustion processes in internal combustion engines continues to grow. One approach to create a combustion progress which produces low CO2, soot, and methane emissions is the “High-Pressure Dual-Fuel” (HPDF)-combustion. Here, the direct-injected methane is ignited by a small amount of pilot-diesel and burns in a diffusive combustion mode. This study describes the development of a three-dimensional computational fluid dynamics (3D-CFD) model for the HPDF-combustion. A Reynolds-Averaged Navier-Stokes (RANS) approach with k-epsilon modelling for turbulence was chosen for the calculation of the flow field. The pilot fuel injection is implemented by using Lagrangian Particle Methods, whereas the gas injection is a mass flow boundary which is derived from measurements of the injector. The model is validated using data from a fully optically accessible single-cylinder research engine. The flow field is compared with particle image velocimetry (PIV) data taken before the start of injection (SOI). Concerning pilot injection, a grid convergence study is conducted and an optimization is developed to reduce computational costs. The penetration length of the liquid fuel spray is validated against Mie-scattering images which are taken during the “Pilot-Diesel-only” experiments in the fully optical single-cylinder research engine. The ignition and combustion is modeled via detailed chemistry, which is solved using the commercial Software CONVERGE and the SAGE chemistry solver. The flame liftoff length of the pilot-diesel and the ignition and combustion of the underexpanded gas jets are validated using high-speed imaging of flame luminosity and OH* chemiluminescence. It can be shown that the used n-heptane mechanism is capable of correctly reproducing the trends in the ignition and combustion process.

Frankl, Stephanie, Gleis, Stephan

High Efficiency by Miller Valve Timing and Stoichiometric Combustion for a Naturally Aspirated Single Cylinder Gas Engine

2019-32-05881/24/2020

Small-scale cogeneration units (Pel < 50 kW) frequently use lean mixture and late ignition timing to comply with current NOx emission limits. Future tightened NOx limits might still be met by means of increased dilution, though both indicated and brake efficiency drop due to further retarded combustion phasing and reduced brake power. As an alternative, when changing the combustion process from lean burn to stoichiometric, a three-way-catalyst allows for a significant reduction of NOx emissions. Combustion timing can be advanced, resulting in enhanced heat release and thus increased engine efficiency. Based on this approach, this work presents the development of a stoichiometric combustion process for a small naturally aspirated single cylinder gas engine (Pel = 5.5 kW) originally operated with lean mixture. To ensure low NOx emissions, a three-way-catalyst is used. In order to achieve high engine efficiency, measures implemented include Miller valve timing, optimized intake system, reduced engine speed and increased compression ratio. In the first step, a detailed 1D engine cycle simulation model was used to investigate the efficiency benefit of Miller valve timing and increased compression ratio. Within the numerical study, inlet valve closing timing and intake pipe length were varied, yet a closed-loop control was implemented to maintain a constant effective compression ratio of 14.66 by adjusting geometrical compression ratio for each configuration. Subsequently, the most expedient valve timing was designed using multi-body simulation of the inlet valve train, while increased compression ratio was achieved by modifying the series piston bowl geometry. Engine trials agree with simulation results and show highest efficiency for a Miller valve timing closing +15 °CA later to the series valve timing and geometrical compression ratio of 15.36. Compared to the series lean burn engine, indicated and brake efficiency increase by 3.2 %-points to 39.0 % and by 3.9 %-points to 34.4 %, respectively, while maintaining original brake power of Pe = 6.1 kW. Finally, an experimental study accompanied by 3D-CFD simulations was conducted to investigate the potential of optimized piston geometry to further increase efficiency. However, results reveal only minor effect of piston geometry on efficiency, what is likely stemming from interrelation of combustion efficiency, wall heat losses and heat release rate.

Judith, Jörn, Neher, Denis, Kettner, Maurice, Schwarz, Danny, Klaissle, Markus

Effects of Sub-Chamber Configuration on Heat Release Rate in a Constant Volume Chamber simulating Lean-burn Natural Gas Engines

2019-32-05511/24/2020

Sub-chamber is a useful device with regard to sustaining stable operation of compressed natural gas (CNG) engines under lean burn conditions. In our previous studies, we applied a sub-chamber injection system to CNG engines, in which a single injector and a spark plug are mounted in a small sub-chamber. The aim of this study is to investigate the effect of the sub-chamber configuration on heat release in the main combustion chamber. 11 types of sub-chamber with different nozzle number, nozzle diameter, and sub-chamber volume were examined under a condition that pressure is 2.3 MPa, and global equivalence ratio is 0.6. When the sub-chamber with smaller nozzles are used, the penetration velocity of burned gas jet increases. In addition, the velocity also increases with an increasing sub-chamber volume. The high-speed penetration of burned gas jet shortens the period of initial flame development. This is because the high-temperature burned gas quickly reaches to side wall of main chamber, and immediately ignites lean mixtures existing in the main chamber. Consequently, combustion duration time until heat release reaches 90 % is also shortened. On the other hand, the velocity difference between the jets from sub-chambers with different nozzle numbers is small. To predict the penetration velocity, we proposed an empirical formula based on the volume, nozzle diameter and nozzle number of sub-chamber. The jet intensity evaluated from the formula shows correlations with duration times of combustion periods as well as penetration velocities of burned gas jets.

Nada, Yuzuru, Kidoguchi, Yoshiyuki, Yamashita, Yuto, Furukawa, Ryo, Kaya, Ryu, Nakano, Hideaki, Kobayashi, Shinichi

Study on the decision process of basic specification in development of general purpose engine

2019-32-05801/24/2020

Social interest in global environmental issues has remained in the forefront during recent years, and as a result, internal combustion engines are expected to have further improved fuel efficiency and reduced exhaust emissions. General purpose engines are demanded for reduced cost in addition to various types of displacement developments. If optimum specifications are examined for each engine displacement and incorporated in the parts shapes, the number of dedicated parts for each engine displacement would increase, which is not desirable from a development/production cost-wise standpoint. It is considered important during the development of engines to efficiently and economically cope with market needs including improved specific power and fuel consumption. Therefore, it was considered necessary to improve combustion performance by enhanced in-cylinder flow and to commonize parts. Then, this study was designed to establish an approach for decision of engine specifications with the perspective of multiple displacement development after satisfying the target performance by combustion improvement. The long stroke and valve angle were adjusted so as to examine specifications that enable enhanced in-cylinder flow with multiple displacements. By confirming that combustion characteristic and fuel efficiency characteristic are correlated to turbulence intensity in cylinder as well as by focusing on Turbulent Kinetic Energy and stroke/bore ratio, engine specifications satisfying the target performance with multiple engine displacements was decided. By making stroke common, it has become possible configure engines of various displacements that satisfy the target performance while achieving reduction of the total number of parts and cost reduction. As a result of verification of the decided specifications by using prototype engines, it was found that the improvement of specific power and fuel efficiency was achieved in comparison to the base engine.

Aoki, Takayuki, Tsuchiyama, Takahiro

Influence of the Kind of Fuel Kind in the Ignition of Diesel Dual Fuel Operation with Introduced Natural Gas Combining EGR and Supercharging

2019-32-0581

1/24/2020

A number of studies in diesel dual fuel (DDF) operation which introduces natural gas from the intake pipe and ignites it by a diesel fuel injection in the combustion chamber have been conducted using conventional diesel engines. The present study investigated the influence of the ignition fuel on engine performance, combustion characteristics, and emissions with a combination of EGR and supercharging in DDF operation. The experiments employed iso-pentanol blended fuels for the ignition. Isopentanol is a next generation bio-alcohol fuel produced from cellulosic biomass, and actual use can be expected. The experiments were conducted at two CNG supply rates, 0% (ordinary diesel operation) and at a 40±4% (DDF operation) energy basis, and with EGR rates varied from 0 to 26%. The boost pressure was set at two conditions, 100 kPa (naturally aspirated, N/A) and 120 kPa (supercharged, S/C) with a supercharger. Four kinds of ignition fuels were used, JIS No.2 diesel fuel as a reference, neat methyl laurate (LME) which is a major component of coconut oil biodiesel, and two iso-pentanol blended fuels with 30% mass ratios, DiP30 (70% diesel and 30% iso-pentanol) and LiP30 (70% LME and 30% iso-pentanol). The results showed that regardless of the ignition fuel, the DDF operation with EGR and also supercharging resulted in substantial reductions in NOx and smoke emissions. However, the brake thermal efficiency decreased with increasing EGR rates, and with much longer ignition delays this tendency was more pronounced for the two iso-pentanol blends.

Yoshimoto, Yasufumi, Kinoshita, Eiji, Otaka, Takeshi

Design and Development of a High-Efficiency Single Cylinder Natural Gas-Fueled Jet Ignition Engine

2019-32-05651/24/2020

The current energy climate has created a push toward reducing consumption of fossil fuels and lowering emissions output in power generation applications. Combined with the desire for a more distributed energy grid, there is currently a need for small displacement, high efficiency engines for use in stationary power generation. An enabling technology for achieving high efficiencies with spark ignited engines for such applications is the use of jet ignition which enables ultra-lean (λ > ~1.6) combustion via air dilution. This paper provides a comprehensive review of the development of a 390cc, high efficiency single cylinder natural gas-fueled jet ignition engine operating ultra-lean. The engine was developed as part of the Department of Energy’s Advanced Research Projects Agency–Energy (DOE ARPA-E) GENSETS program. Design choices for minimizing friction are highlighted as well as test results showing further friction reduction through downspeeding. Extensive hardware optimization of the combustion system has been performed and results are presented for air-flow path optimization and the jet igniter. The efficiency benefits related to enleanment and downspeeding are analyzed using an efficiency loss breakdown based on the First Law of Thermodynamics. Through optimization efforts a peak brake thermal efficiency in excess of 34% was achieved, representing an increase of greater than 20% over the current state-of-the-industry for comparably sized CNG engines.

Peters, Nathan, Subramanyam, Sai Krishna Pothuraju, Bunce, Michael, Blaxill, Hugh, Pihl, Josh, Moses-Debusk, Melanie, Vishwanathan, Gokul, Tew, David

Impact of Intake Port Water Injection Timing on Mitigating the Tradeoff between Performance and NO _x Emissions for a Naturally Aspired Micro-CHP-Engine

2019-32-05761/24/2020

Small natural gas cogeneration engines usually operate with lean mixture and late combustion phasing to comply with NOx emission standards, leading to significant losses in engine efficiency. Owing to water evaporation heat and high specific heat capacity of the water vapor, leads the water injection to cooling the combustion chamber charge, which enables earlier combustion phasing, higher compression ratio and thus higher engine efficiency. Therefore, water injection enables mitigating the tradeoff between NOx emissions and engine performance, without loss in engine efficiency. The intake port injection represents, because of the low required injection pressure and the simple injector integration, a cost-effective way to introduce water into the engine. Hence, the purpose of this work is to adapt the intake port water injection timing to the charge mixture flow conditions in the intake port. For this purpose, a variation of the injection timing was experimentally carried out on the engine test bench. The combustion phasing and the NOx emissions were kept constant. At the same time, the engine power, engine efficiency, temperatures in the intake port and mass flow rates were recorded. To gain a deeper insight into the complex processes in the intake port, such as spray-flow interaction, wallfilm formation and evaporation, 3D CFD simulations were conducted for three selected cases with different injection timings. For the 3D CFD Simulations, the spray model used, was tuned with help of spray pictures, taken on the spray test bed. Experimental investigations have shown that an injection close to the intake valve opening allows an increase in engine performance at constant NOx emissions without loss of engine efficiency. In fact, early injection allows effective cooling of the intake port mixture and allows part of the injected water to enter the combustion chamber as liquid and to vaporize there. A disadvantage of an injection close to the intake port opening, shown by the 3D CFD simulations, is that the water vapor is distributed homogeneously in the combustion chamber with a slightly higher concentration in the prechamber area, which could lead to a significant slowdown of the combustion speed, if the injected amount of water is increased.

Beltaifa, Youssef, Kettner, Maurice, Eilts, Peter, Klaissle, Markus

Energy Release Characteristics inside a Spark-Ignition Engine with a Bowl-in-Piston Geometry

2020-01-5003

1/16/2020

The conversion of compression ignition (CI) internal combustion engines to spark-ignition (SI) operation by adding a spark plug to ignite the mixture and fumigating the fuel inside the intake manifold can increase the use of alternative gaseous fuels (e.g., natural gas) in heavy-duty applications. This study proposed a novel, less-complex methodology based on the inflection points in the apparent rate of heat release (ROHR) that can identify and separate the fast-burning stage inside the piston bowl from the slower combustion stage inside the squish region (a characteristic of premixed combustion inside a diesel geometry). A single-cylinder 2L CI research engine converted to natural gas SI operation provided the experimental data needed to evaluate the methodology, at several spark timings, equivalence ratios, and engine speeds. The results indicated that the end of the bulk combustion traditionally defined as the location of 90% energy release was not greatly affected by the change in operating conditions. Moreover, the actual duration of the rapid-burning stage was 60-80% shorter than the crank angle interval between 10% and 90% energy release. However, the fast-burning period (i.e., the start and the end of the rapid-burning stage) was well-characterized by the crank angle duration between the first and the second ROHR inflection points. Moreover, this novel methodology to characterize the combustion process suggested that the longer time interval between the end of fast-burn (i.e., the first ROHR inflection point) and the end of combustion was due to an important fuel fraction burning slower inside the squish region, which finally affects both efficiency and emissions of such converted engines.

Liu, Jinlong, Dumitrescu, Cosmin Emil