Browse Topic: HCCI engines

Items (1,156)

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

An Analytical Approach for Calculating Instantaneous Multilayer-Coated Wall Surface Temperature in an Engine

2020-01-01604/14/2020

Thermal swing coatings that have low volumetric heat capacity and low thermal conductivity are attractive because they have the potential to significantly reduce heat transfer to the combustion chamber walls. This paper presents an analytical method for determining the exact solution of the time-resolved wall temperature during the engine cycle for any number of coating layers and properties using the Laplace transformed heat diffusion equation. The method relies only on material properties and the past heat flux history, and represents the exact solution of the heat diffusion equation. The analytical nature of the solution enables fast computation and, therefore, application to system-level optimization calculations. The model relies on an assumption of one-dimensional heat flow, and constant material properties. The major advantage of this approach compared to the standard finite difference approach, wherein the wall is finely discretized, is that there is no approximation and the accuracy is guaranteed, i.e., it does not depend on nodal density. Results are presented for both a quasi-steady operating condition and for an engine transient event. In the latter case a 200-fold reduction in computation time relative to a finite difference code was realized.

Koutsakis, G., Ghandhi, J.B.

Combined Experimental/Numerical Study of the Soot Formation Process in a Gasoline Direct-Injection Spray in the Presence of Laser-Induced Plasma Ignition

2020-01-02914/14/2020

Combustion issued from an eight-hole, direct-injection spray was experimentally studied in a constant-volume pre-burn combustion vessel using simultaneous high-speed diffused back-illumination extinction imaging (DBIEI) and OH* chemiluminescence. DBIEI has been employed to observe the liquid-phase of the spray and to quantitatively investigate the soot formation and oxidation taking place during combustion. The fuel-air mixture was ignited with a plasma induced by a single-shot Nd:YAG laser, permitting precise control of the ignition location in space and time. OH* chemiluminescence was used to track the high-temperature ignition and flame. The study showed that increasing the delay between the end of injection and ignition drastically reduces soot formation without necessarily compromising combustion efficiency. For long delays between the end of injection and ignition (1.9 ms) soot formation was eliminated in the main downstream charge of the fuel spray. However, poorly atomized and large droplets formed at the end of injection (dribble) eventually do form soot near the injector even when none is formed in the main charge. The quantitative soot measurements for these spray and ignition scenarios, resolved in time and space, represents a significant new achievement. Reynolds-averaged Navier-Stokes (RANS) simulations were performed to assess spray mixing and combustion. An analysis of the predicted fuel-air mixture in key regions, defined based upon experimental observations, was used to explain different flame propagation speeds and soot production tendencies when varying ignition timing. The mixture analysis indicates that soot production can be avoided if the flame propagates into regions where the equivalence ratio (Φ) is already below 2. Reactive RANS simulations have also been performed, but with a poor match against the experiment, as the flame speed and heat-release rate are largely over estimated. This modeling weakness appears related to a very high level of turbulent viscosity predicted for the high-momentum spray in the RANS simulations, which is an important consideration for modeling ignition and flame propagation in mixtures immediately created by the spray.

Tagliante, Fabien, Sim, Hyung S., Pickett, Lyle M., Nguyen, Tuan, Skeen, Scott

Is the “K Value” of an Engine Truly Fuel Independent?

2020-01-0615

4/14/2020

The octane appetite of an engine is frequently characterised by the so-called K value. It is usually assumed that K is dependent only on the thermodynamic conditions in the engine when knock occurs. In this work we test this hypothesis: further analysis was conducted on experimental results from SAE 2019-01-0035 in which a matrix of fuels was tested in a single cylinder engine. The fuels consisted of a relatively small number of components, thereby simplifying the analysis of the chemical kinetic proprieties. Through dividing the original fuel matrix into subsets, it was possible to explore the variation of K value with fuel properties. It was found that K value tends to increase slightly with RON. The explanation for this finding is that higher RON leads to advanced ignition timing (i.e. closer to MBT conditions) and advanced ignition timing results in faster combustion because of the higher pressures and temperatures reached in the thermodynamic trajectory. The Livengood-Wu integral can be employed to show that for higher octane fuels, knock onset occurs at a higher temperature and pressure. Thus, the fuel octane quality can impact the thermodynamic trajectory in the engine.

Cracknell, Roger, Kassai, Masaharu, Shiraishi, Taisuke, Festa, Andrea, Gail, Sandro, Aradi, Allen, Shibuya, Masahiko

Nonlinear Identification Modeling for PCCI Engine Emissions Prediction Using Unsupervised Learning and Neural Networks

2020-01-05584/14/2020

Premixed charged compression ignition (PCCI) is an advanced combustion strategy, which has the potential to achieve ultra-low nitrogen oxide and soot emissions at high thermal efficiencies. PCCI combustion is characterized by a complex nonlinear chemical-physical process, which indicates that a physical description involves significant development times and also high computation cost. This paper presents a method to use cylinder pressure data and engine operations parameters for prediction of PCCI engine emissions by unsupervised learning and nonlinear identification techniques. The proposed method first uses principal component analysis (PCA) to reduce the dimension of the cylinder-pressure data. Based on the PCA analysis, a multi-input multi-out model was developed for nitrogen oxide and soot emission prediction by multi-layer perceptron (MLP) neural network. Before the training process, a second principal component analysis was done to reduce the input dimension with hyper-parameters thereby reducing memory requirements of the models. The algorithm is applied to an experimental data set from a single-cylinder light-duty engine with piezo injection system. By comparing the model predictions with experimental results, it is shown that the neural network coupling with the unsupervised learning method can successfully capture the nonlinear relationship between the state parameters and the emissions of PCCI combustion system.

Pan, Wang, Korkmaz, Metin, Beeckmann, Joachim, Pitsch, Heinz

Isobaric Combustion at a Low Compression Ratio

2020-01-07974/14/2020

In a previous study, it was shown that isobaric combustion cycle, achieved by multiple injection strategy, is more favorable than conventional diesel cycle for the double compression expansion engine (DCEE) concept. In spite of lower effective expansion ratio, the indicated efficiencies of isobaric cycles were approximately equal to those of a conventional diesel cycle. Isobaric cycles had lower heat transfer losses and higher exhaust losses which are advantageous for DCEE since additional exhaust energy can be converted into useful work in the expander. In this study, the performance of low-pressure isobaric combustion (IsoL) and high-pressure isobaric combustion (IsoH) in terms of gross indicated efficiency, energy flow distribution and engine-out emissions is compared to the conventional diesel combustion (CDC) but at a relatively lower compression ratio of 11.5. The experiments are conducted in a Volvo D13C500 single-cylinder heavy-duty engine using standard EU diesel fuel. The current study consists of two sets of experiments. In the first set, the effect of exhaust gas recirculation (EGR) is studied at different combustion modes using the same air-fuel ratio obtained from the preceding work. In the second set of experiments, different injection strategies are investigated for IsoL and IsoH combustion at constant and varying load conditions. From the results, it is found that isobaric combustion has similar or higher gross indicated efficiency than those of CDC. The exhaust losses are higher while the heat transfer losses are lower than CDC, which could be beneficial for DCEE concept. For isobaric cases, the NOx emissions were lower with higher uHC/CO/Soot emissions compared to CDC. From the injection strategy study, it was found that the gross indicated efficiency is highest with three injections i.e. at medium load. The efficiency is lower for both low and high load conditions due to increased exhaust and heat transfer losses, respectively. Also, the gross indicated efficiency is largely unchanged when more than one injection event is executed; however the IsoL yields higher overall emissions as compared to IsoH combustion.

Dyuisenakhmetov, Aibolat, Goyal, Harsh, Ben Houidi, Moez, Babayev, Rafig, Badra, Jihad, Johansson, Bengt

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

Exergy Based Optimal Controller Design of a Spark-Ignition Internal Combustion Engine

2020-01-02504/14/2020

Internal combustion engine (ICE) control techniques have been developed with only the first law of thermodynamics in mind, e.g. improving thermal efficiency, tracking specific load requirements, etc. The first law of thermodynamics does not account for the losses in work potential that are caused due to the in-cylinder high temperature thermodynamic processes irreversibilities. For instance, up to 25% of fuel exergy or fuel availability may be lost to irreversibilities during the combustion process. The second law of thermodynamics states that not all energy in an energy source is available to do work; its application evaluates the maximum available energy in that source after accounting for the losses caused by the irreversibilities. Therefore, including the exergy in an optimal engine control algorithm may lead to improved ICE thermal efficiencies. In this work, a model predictive controller (MPC) is developed based on the first and second laws of thermodynamics to control a detailed eight-cylinder ICE model developed in GT-Power. To make the controller practically applicable for eventual hardware in the loop (HiL) investigations, the GT-Power model is approximated with a single layer feedforward neural network (SLFN) that was trained on engine maps developed from a design of experiments. Two algorithms are used to solve the MPC optimization problem: sequential quadratic programing (SQP) and the continuation/forward difference generalized method of residuals (C/FDGMRES) for the purpose of comparing solution time and performance. Incorporating the second law of thermodynamics into the MPC design results in fuel savings of 6.8% and 3.2% for SQP and C/FDGMRES, respectively, when compared to controller MPC controller designs without exergy considerations. Comparing average solution times between the two MPC algorithms found C/FDGMRES solved the control problem on average four times faster than SQP.

Abotabik, Muataz, Meyer, Rick, Proctor, Christopher

Optimization of Intake Port and Pentroof Angle for Simultaneous Reduction of Fuel Consumption and Exhaust Emissions in a GDI Engine

03-13-03-00202/4/2020

This article aims to identify the best combination of intake port angle (IPA) and cylinder head pentroof angle (PA) of a gasoline direct injection (GDI) engine to achieve a simultaneous reduction in the fuel consumption and the exhaust emissions using computational fluid dynamics (CFD) and optimization techniques. The present study is carried out on a single-cylinder, four-stroke GDI engine. The design space is bound by the range of the IPA (35°, 80°) and the PA (5°, 20°). The initial data set consists of 80 design points, which are generated using the uniform Latin hypercube (ULH) algorithm. CFD simulations were carried out at all the points in the initial data set using CONVERGE at engine speed of 2,000 rev/min and the overall equivalence ratio of 0.7 ± 0.05. A prediction model based on the support vector machine algorithm is generated between the design inputs and the output parameters viz., indicated specific fuel consumption (ISFC), hydrocarbon (HC), nitric oxides (NOx), and soot. After sufficient validation of the prediction model, it is used for the optimization study. The optimization is carried out using the MOGA-II algorithm. The optimization study predicted that the IPA of 58° and the PA of 13.4° results best, in simultaneous reduction of the fuel consumption and the emissions. The results of the optimization study are further validated using the CFD analysis, which is carried out at the optimum design point. From the results, it is concluded that the optimization-driven design techniques could be effectively used to improve the engine performance and reduce the emissions simultaneously.

Saw, Om Prakash, Addepalli, Srinivasa Krishna, Mallikarjuna, J.M.

Effects of positive or negative dwell times of split injection on diesel spray development and mixture formation processes

2019-32-05961/24/2020

An investigation on the effect of dwell time of split injection on a diesel spray evolution and mixture formation process was carried out. A commercial 7-hole injector were used in the experiment to eliminate the possible discrepancies on the spray with single-hole research injector. Laser absorption scattering (LAS) technique was implemented for the measurement of the temporal evolution of fuel evaporation and mixture concentration. The diesel surrogate fuel consists of n-tridecane and 2.5% of 1-methylnaphthalene in volume basis was used. The total amount of fuel injected was initially fixed to 5.0 mg/hole. A split ratio of 9: 1 in mass basis was selected according to the results obtained from a previous study. The dwell time was varied from 120 µs to a negative value of −50 µs. The effects of negative dwell time was not ideal for lean mixture formation when compared to zero or positive dwell time conditions. The collision of the spray tail of the first injection and the head of the second injection created locally rich pockets at the vicinity of the nozzle. Finally, injection rate shaping through modulating the pulses consisted of several injections of negative dwell times was investigated. This rate shaping strategy which showed a gradual decrease of the injection rate at the EOI (end-of-injection) timing yielded positive effect on mixture formation. It also exhibited faster lean mixture formation than that of single injection.

Kim, Jaeheun, Kakami, Shinichi, Nishida, Keiya, Ogata, Yoichi

Study on Robust Fuel Performance with Differing Fuel Types in a 2-Stroke CAI Combustion Engine

2019-32-0573

1/24/2020

This study sought to achieve robust combustion with the differing fuel types and levels of fuel quality that are present in various areas of the world. The tests used the 2-stroke controlled auto ignition (CAI) engine from our earlier report [1], which was proven to have potential as an efficient, clean engine for diesel fuel. This study verified whether efficient, clean CAI combustion of gasoline fuel could be achieved with the same basic structure and engine system. Diesel and gasoline have very different volatility, viscosity and ignition characteristics, all of which significantly affect combustion in an engine. It is particularly necessary in CAI combustion to adjust the ignition timing according to the fuel used, as the difference in auto-ignition temperature from gasoline and diesel affects the CAI ignition timing. This issue was addressed by conducting experiments with a test engine to determine how the ignition timing is affected by the equivalent ratio, compression ratio and in-cylinder flow, and the ideal solution was verified. The results indicated that the ignition timing for CAI combustion can be effectively adjusted by changing the shape of the scavenging port to alter the in-cylinder flow. Computational fluid dynamics (CFD) analysis confirmed that the change in the scavenging port shape increased the in-cylinder flow velocity and the turbulence kinetic energy at the compression end. This indicates that the in-cylinder flow during the compression stroke affects the ignition timing for CAI combustion. The results produced by this study also indicated that equivalent thermal efficiency and emission levels can be achieved for both diesel and gasoline by setting an appropriate equivalent ratio, compression ratio, in-cylinder flow and exhaust valve lift profile for each type of fuel. In conclusion, this study confirmed that 2-stroke CAI is a combustion process with extremely robust fuel performance and the potential to be suitable for various fuel types with significantly different properties.

Kurata, Mashu, Okubo, Masami, Yamada, Yoshikazu, Kitano, Sho

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

Chemical kinetic mechanisms for HCCI combustion of wet ethanol with exhaust gas recirculation

2019-36-02931/13/2020

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.

Effects of ratio and dwell of split injection on fuel spray and mixture formation process under evaporating, non-reacting condition

2019-01-232312/19/2019

The effects of split injections of a diesel spray was evaluated in a constant volume chamber under evaporating, non-reacting condition. Laser absorption scattering (LAS) technique was utilized for the mixture concentration measurement, using a diesel surrogate fuel consists of n-tridecane and 2.5% of 1-methylnaphthalene in volume basis. While fixing the total injected fuel mass of 5.0 mg/hole, the effects of split ratio in mass basis and the dwell time (or injection interval) were investigated. Among the split ratios conducted in the current study (3,7, 5:5 and 7:3), the split ratio of 7:3 was the optimum for lean mixture formation regarding the overall distribution of the equivalence ratio at end-of-injection (EOI) timing. The air entrainment wave at the EOI timing of the first injection allowed the fuel at the vicinity of the nozzle to become leaner at a faster rate. It was thought that, the split ratio of 7:3 provided an adequate amount of fuel quantity and vapor penetration to fit into the fuel-lean region formed from the first injection. The increase of the dwell time provided longer time for leaner mixture formation of the first injection, but the improvement was small. Therefore, the shortest dwell of 120 μs was reasonable for lean mixture formation of the second spray. It showed similar equivalence ratio distribution compared to any other longer dwell time conditions under the absence of combustion.

Kim, Jaeheun, Kakami, Shinichi, Nishida, Keiya, Ogata, Yoichi

Spark Assisted Compression Ignition Engine with Stratified Charge Combustion and Ozone Addition

2019-01-225312/19/2019

Performance and emissions characteristics for stratified charge spark assisted compression ignition (SACI) with 30 ppm of added ozone (O3) were explored in a single-cylinder, optically accessible, spray-guided, research engine. For the present study, intake pressure and temperature were fixed at 1.0 bar and 42°C respectively, with a range of engine loads (1.5 – 5.5 bar indicated mean effective pressure) and speeds (800 – 1600 revolutions per minute) explored. Fuel stratification achieved by a late-cycle injection of ~ 10–25% of the total fuel was used to maintain stable operation at lower engine loads. For each condition spark timing, second injection SOI, and fuel split ratio between the main and second injection were optimized to maximize engine performance while maintaining nitrogen oxide emissions (NOx) below 5 g/kg-fuel. Ozone addition was found to decrease specific fuel consumption by up to 9%, with across the board improvement in combustion stability relative to similar conditions without O3. The effect of O3 addition was most substantial for the lowest loads. Moreover, because a higher fraction of the fuel burned was due to end-gas auto-ignition, specific NOx emissions likewise decreased by up to 30%. From complementary measurements of in-cylinder O3 decomposition acquired via an ultraviolet light absorption diagnostic, it was observed that rapid decomposition of O3 into molecular and atomic oxygen coincided with the onset of end-gas auto-ignition. The burst of resultant atomic oxygen was thought to accelerate low-temperature heat release (LTHR) reactions in the end gas. Optimal end-gas auto-ignition started between 20 and 30 crank angles before top dead center with temperatures at LTHR onset estimated to be between 575 and 700 K. An included analysis indicates that the spark deflagration was needed to add between 10 and 40 J of additional thermal energy to the end gas to achieve optimal auto-ignition.

Biswas, Sayan, Ekoto, Isaac

Effects of Piston Bowl Diameter on Combustion Characteristics of a Natural gas/Diesel Dual Fuel Engine

2019-01-217312/19/2019

Natural gas/diesel dual fuel engines have potential for a high thermal efficiency and low NOx emissions. However, they have the disadvantages of high unburned species emissions and lower thermal efficiencies at low loads (at low equivalence ratio). A way to solve this problem is to properly distribute the pilot fuel vapor in a natural-gas premixture. The combustion chamber geometry affects the combustion process since it influences the distribution of the pilot fuel vapor. This study investigates the influence of injection conditions and the piston bowl geometry on the performance and emissions of a dual fuel engine. Experiments were carried out using two pistons with different bowl diameters, 52 mm and 58 mm, at single-and two-stage diesel-fuel injection. The results show that the larger bowl provides lower hydrocarbon emissions at a lower equivalence ratio in the case of single-stage injection. For two-stage injection, the influence of the bowl diameter depends on the timing of the first injection. To elucidate the effects of pilot fuel distribution, computational fluid dynamics (CFD) calculations were conducted for non-reacting pilot fuel sprays under conditions equivalent to the experiments. As a result, the relative rich area of the pilot fuel in the case of the single injection in the large piston bowl do not impinge on the piston wall at the ignition timing of the experiment, which leads to higher heat release rate owing to the weak cooling effect.

Takizawa, Keigo, Tanaka, Hidetake, Horibe, Naoto, Ishiyama, Takuji, Sako, Takahiro

Evaluation of Cycle Variation of SWACER-like Knocking Using 3D SI Combustion Simulation

2019-01-220812/19/2019

Cyclic variation on heavy knocking was reproduced using 3D SI combustion simulation with RANS / LES turbulence models and detailed kinetic mechanisms. A 0.66 liter, inline 3 cylinder gasoline engine operated at 1200 rpm, WOT was mainly investigated. It was revealed that the combination of RANS, Liu mech. and calculation over multiple cycles worked well. Detailed process of heavy-knock was also suggested and it was thought that SWACER-like mechanism had concerned. RANS could describe typical behavior of heavy-knock within the first 3 cycle calculation and it showed good agreement with both the actual engine measurement and LES calculation result.

Kuroki, Tomonori, Shima, Yuta, Ono, Yasuhisa, Serizawa, Takeshi

Comparison of heat losses at the impingement point and in between two impingement points in a diesel engine using phosphor thermometry

2019-01-218512/19/2019

In-cylinder heat losses in diesel engines reduce engine efficiency significantly and account for a considerable amount of injected fuel energy. A great part of the heat losses during diesel combustion presumably arises from the impingement of the flame. The present study compares the heat losses at the point where the flame impinges onto the piston bowl wall and the heat losses between two impingement points. Measurements were performed in a full metal heavy-duty diesel engine with a small optical access through a removed exhaust valve. The surface temperature at the impingement point of the combusting diesel spray and at a point in between two impingement points was determined using phosphor thermometry. The dynamic heat fluxes and the heat transfer coefficients which result from the surface temperature measurements are estimated. Simultaneous cylinder pressure measurements and high-speed videos are associated to individual surface temperature measurements. Thus each surface temperature measurement is linked to a specific impingement and combustion events. An analysis of the surface temperature in connection with the high speed images reveals the great impact of flame impingement on instantaneous local heat flux at the impingement point. Absence of such an effect in between two impingement points implies an inhomogeneous temperature field.

Binder, Christian, Matamis, Alexios, Richter, Mattias, Norling, Daniel

Measurements and modeling of ozone enhanced compression ignition in a rapid compression machine and optically-accessible engine

2019-01-225412/19/2019

For the present study, an ultraviolet light absorption diagnostic was used to measure O3 concentration during the compression stroke of a rapid compression machine and an optically-accessible research engine. Charge oxygen concentration, initial temperature, and equivalence ratio were varied; neat iso-octane was used for fueled experiments. Measurements were compared to single-zone chemical kinetic simulation results. Rapid thermally induced O3 decomposition was observed near top dead center. Ozone decomposition advanced when the charge temperature was increased, oxygen concentration was reduced, or fuel was added. While the model well-captures the experimental trends, for unfueled conditions the temporal prediction of O3 decomposition is generally too far retarded.

Seignour, Nicolas, Ekoto, Isaac, Foucher, Fabrice, Moreau, Bruno

Detection of engine knock using speed oscillations in a single-cylinder spark-ignition engine

2019-01-220612/19/2019

In the present work, the possibility of engine knock detection is investigated based on in-cycle speed data, which is readily available to the ECU. Experiments were conducted at 3000 rpm with wide-open throttle condition in a single-cylinder, air-cooled, port-fuel-injection spark-ignition engine at different levels of knocking. It was found that amplitude of speed oscillations increased with the knock intensity for considered window with the size of 100 crank angle degree, starting from the top dead center of compression. The proposed knock indicators based on in-cycle speed oscillations were found to be able to identify the knock-limited spark timings at different operating conditions. Results showed that the amplitude of speed oscillations, derived from in-cycle speed data with resolution of six crank angle degree, could also be used to quantify the knock. The knock frequency based on speed oscillations also showed a sharp increase at the onset of knock. Cycle by cycle knock estimation was also done using the speed oscillations. Thus, methods based on in-cycle oscillations of speed have the potential for detecting the knock in small spark-ignition engines.

Bhaskar, Kiran, Jose, Jubin V, Mittal, Mayank, Ramesh, A

Study on Flame Characteristics under Conditions of Stratified Flame Ignition Hybrid Combustion

2019-01-231612/19/2019

In Spark Ignition (SI)-Controlled Auto Ignition (CAI) hybrid combustion, the in-cylinder temperature and total mass of dilution charge are usually increased compared to the traditional SI engine in order to achieve and control the auto-ignition combustion, which would in turn lead to the variations of the diluted flame propagation combustion. In this study, the optical measurements were performed to understand the flame characteristics at highly diluted conditions. The results showed that the decrease of the flame propagation speed of rich mixture was less than that of lean mixture at highly diluted conditions. However, the inhomogeneous distribution of residual gas led to asymmetric development of flame propagation. The high temperature, strong dilution and rich mixture created local auto-ignition sites which were located in front of the main flame and gradually merged with the main flame. This phenomenon could increase the flame propagation speed in a specific direction and improve the heat release stability effectively.

Niu, Jian, Chen, Tao, Xie, Hui, Yao, Yuan, Song, Kang, Wang, Xinyan, Zhao, Hua

A Study of Injection Directions on Improvement of Engine Performance and NOx Emission in A Low-speed Marine Engine

2019-01-232212/19/2019

A computational fluid dynamics (CFD) simulation model for a two-stroke low-speed marine engine has been established in CONVERGE software, to study the impact of different injection directions on fuel consumption and emissions of the engine. The goal of this research was to investigate injection angles in horizontal and vertical directions respectively. According to the simulation results, “trade-off” relationship was found in both directions between fuel consumption and NOx emission. Based on these results, 8° and -16° were considered as optimal injection angles in horizontal and vertical directions. With the optimized injection angles, lower NOx emission can be achieved with a little penalty on fuel consumption.

Sun, Qian, Ji, Wenxia, Huang, Zhen, Zhu*, Lei

Development of Non-equilibrium Plasma and Combustion Integrated Model for Reaction Analysis

2019-01-234912/19/2019

Control of self-ignition timing in a HCCI engine is still a major technical issue. Recently, the application of a non-equilibrium plasma using repetitively discharge has been proposed as the promising technology. However, non-equilibrium plasma reaction in higher hydrocarbon fuel mixture is very complicated. Hence, there have been few calculation reports considering a series of reactions from non-equilibrium plasma production to high temperature oxidation process. In this study, 0-dimensional numerical simulation model was developed in which both reactions of plasma chemistry and high temperature oxidation combustion was taken into account simultaneously. In addition, an ODEs solver has been applied for the reduction of calculation time in the simulation. By comparing calculation results with experiment such as self-ignition timing, the validity of the developed numerical model has been evaluated.

Horikoshi, Masahiro, Tanaka, Tatsuya, Okihama, Keisuke, Kon, Yohei, Takana, Hidemasa

Analysis of Reaction Mechanism Preparing Hot Ignition Observed in Homogeneous Compression of n-Heptane Air Mixture

2019-01-234812/19/2019

Multi-stage heat releases in homogenous charge compression ignition (HCCI) near the ignition threshold are analyzed in this study. Motored engine experiments are conducted with exhaust gas analysis by Fourier transform infrared spectrometer under hot ignition suppressed condition, in order to provide a deeper insight into the ignition mechanism of n-heptane. By increasing intake temperature from room temperature, heat release of low temperature oxidation (LTO) can be observed. Moreover, second heat release was observed after primary heat release of LTO, which increases rapidly with increasing intake temperature within narrow range below the high temperature oxidation (HTO) threshold. The mechanism of HTO preparation reaction is discussed.

Safwan bin Mazelan, Muhammad, Tezaki, Atsumu, Thapa, Sahadev

Numerical study of wall heat transfer inside a combustion chamber under conventional diesel combustions and low temperature combustion conditions

2019-01-231412/19/2019

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

A Study on Higher Thermal Efficiency and Lower Cooling Loss in Diesel Engine

2019-01-228312/19/2019

The purpose of this study is to achieve thermal efficiency improvement and cooling loss reduction of a diesel engine with a combustion concept of earlier evaporation, higher entrainment, and compact spray flame. In order to realize this concept, the paper focused on two-component fuel (nC5H12/nC10H22) with high evaporation. In this paper, the effects of two-component fuel on thermal efficiency and exhaust characteristics are examined by using single cylinder diesel engine. In addition, spray characteristics are revealed in an optically accessible chamber and combustion characteristics are revealed by using RCEM.

Fujikawa, Shoya, Arai, Naoyuki, Iwamoto, Seiya, Nishiura, Kohsuke, Matsumura, Eriko, Senda, Jiro

Wall Heat Transfer Modeling Based on the Energy Equation For Zero Dimensional Engine Simulation

2019-01-231312/19/2019

ABSTRACT It was important for predicting wall heat flux to apply wall heat transfer model by taking into account of the behavior of turbulent kinetic energy and density change in wall boundary layer. Although energy equation base wall heat transfer model satisfied above requirements, local physical amounts such as turbulent kinetic energy in near wall region should be applied. In this study, in order to predict wall heat transfer by zero dimensional analysis, how to express wall heat transfer by using mean physical amounts in engine combustion chamber was considered by experimental and numerical approaches.

Harada, Yuji, Uchida, Kenji, Yamashita, Hiroyuki

Learning Based Model Predictive Control of Combustion Timing in Multi-Cylinder Partially Premixed Combustion Engine

2019-24-00169/9/2019

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

Valve Flow Coefficients under Engine Operation Conditions: Piston Influence and Flow Pulsation

2019-24-00039/9/2019

Engine valve flow coefficients are used to describe the flow throughput performance of engine valve/port designs, and to model gas exchange in 0D/1D engine simulation. Valve flow coefficients are normally determined at a stationary flow test bench, separately for intake and exhaust side, in the absence of the piston. However, engine operation differs from this setup; i. a. the piston might interact with valve flow around scavenging top dead center, and instead of steady boundary conditions, valve flow is nearly always subjected to pressure pulsations, due to pressure wave reflections within the gas exchange ports. In this work the influences of piston position and flow pulsation on valve flow coefficients are investigated for different SI engine geometries by means of 3D CFD and measurements at an enhanced flow test bench. In the past, most research work on valve flow coefficients left aside possible piston influence and, for dynamic boundary conditions, it largely omitted subtraction of the gas inertia effects, which are already covered by 1D simulation. In this work, concerning piston influence, various valve overlap situations are investigated and compared with current 0D/1D simulation. It is shown that common piston shapes can cause masking effects for open valves and reduce their mass flow noticeably. Subsequently a modeling approach is presented to consider the piston influence in 0D/1D engine simulation. Besides this, the influence of flow pulsation on flow coefficients is investigated using pressure ratio profiles, which are derived from engine test bench measurements at different engine speeds. These profiles, one with, and one without change in flow direction, are applied to a 1D and a 3D CFD flow test bench model at various valve lifts. It is shown that 1D simulation can mainly provide a decent pulsation mass flow prediction, but it depends on the geometrical accuracy of the port model.

Fasse, Sven, Grill, Michael, Bargende, Michael

Possibilities of Wall Heat Transfer Measurements at a Supercharged Euro VI Heavy-Duty Diesel Engine with High EGR-Rates, an In-Cylinder Peak Pressure of 250 Bar and an Injection Pressure up to 2500 Bar

2019-24-01719/9/2019

A raise of efficiency is the strongest selling point concerning the total cost of ownership (TCO), especially for commercial vehicles (CV). Accompanied by legislations, with contradictive development demands, satisfying solutions have to be found. The analysis of energy losses in modern engines shows three influencing parameters. Wall heat transfer (WHT) losses are awarded with the highest optimization potential. Critical for the occurrence of these losses is the WHT, which can be described by representing coefficients. To reduce WHT accompanying losses a decrease of energy transfer between combustion gas and combustion chamber wall is necessary. A measurement of heat fluxes is necessary to determine the WHT relations of the combustion chamber in an engine. As this has not been done for a Heavy-Duty (HD) engine, with peak pressures up to 250 bar, an increased in-cylinder turbulence and high exhaust gas recirculation (EGR)-rates before, it is presented in the following. Different methods to determine wall heat flux, as well as data transfer variants for data measured at the piston, are presented and compared. The non-integer system identification method (NISI) and the data transfer with a specially manufactured printed circuit board (PCB) therefore represent explicit novelties for the usage in an internal combustion engine. Finally the application chosen for the measurements to determine heat fluxes is described in greater detail. The assembly method, the positioning of the thermocouples at the engine parts and the considerations behind it are shown as well. The applied evaluation process, including a Fourier transformation and the method for a holistic determination of the WHT relations of a HD engine are presented. [1, 2]

Hennes, Christian, Lehmann, Jürgen, Koch, Thomas

Numerical Simulation of Syngas Blends Combustion in a Research Single-Cylinder Engine

2019-24-00949/9/2019

Despite syngas is a promising alternative fuel for internal combustion engines (ICEs), its extensive adoption has not been adequately investigated so far. The dedicated literature offers several fundamental studies dealing with H2/CO blends burning at high pressure and room temperature, as well as preheated mixture at low pressure. However, these thermodynamic states are far from the operational conditions typical of ICEs. Therefore, it is essential to investigate the syngas combustion process at engine-like conditions to shed light on this fuel performance, in order to fully benefit from syngas characteristics in ICE application. One of the key properties to characterize a combustion process is laminar flame speed, which is also used by the most widespread turbulent combustion models. In the first part, a database of premixed laminar burning rates at engine-like conditions for different syngas (H2/CO) blends is created based on one-dimensional unstretched flame simulations using two validated chemical mechanisms. Then the resulting laminar flame speed values are fitted using a validated in-house method based on logarithmic correlations. In the second part of the paper, these are implemented in the G-equation combustion model and three-dimensional simulations of a four stroke Spark Ignition (SI) optical access engine fueled by syngas are carried out. The combustion characteristics of two H2/CO blends (50/50 and 75/25 volume fraction, respectively) are investigated and the simulation results are compared to the available experimental data for the same fuels. This joint numerical/experimental study allows to investigate and optimize the syngas combustion for ICEs and it provides general guidelines to further understand the feasibility of this alternative fuel in terms of ICE utilizations.

Pessina, Valentina, D'Adamo, Alessandro, Iacovano, Clara, Fontanesi, Stefano, Martinez, Santiago, Lacava, Pedro

Validation and Analysis of Heat Losses Prediction Using Conjugate Heat Transfer Simulation for an Internal Combustion Engine

2019-24-00919/9/2019

New technologies are required to improve engine thermal efficiency. For this it is necessary to use all the tools available nowadays, in particular computational tools, which allow testing the viability of different solutions at reduced cost. In addition, numerical simulations often provide more detailed information than experimental tests. Such is the case for the study of the heat transfer through the walls of an engine. Conjugate Heat Transfer (CHT) simulations permit precise calculations of the heat transfer from gas to walls throughout the whole engine cycle, and thus it is possible to know such details as the instantaneous heat losses and wall temperature distribution on the walls, which no experiment can give. Nevertheless, it is important to validate CHT calculations, either with some experimental measurements or with some other reliable tool, such as 0D-1D modelling known to work well. The proposed work is based on the CHT simulation of the heat transfer to the walls of an engine piston during an entire cycle to determine the parameters that permit obtaining good results. This will be ascertained by comparison with the results of a lumped model previously validated for many applications. Another objective of this work is also to determine if it is significant to take into account the spatial and temporal variations of the wall temperature for the prediction of the heat losses during the engine cycle, as generally a mean and constant wall temperature (isothermal walls) is assumed for CFD combustion calculations.

Broatch, Alberto, Margot, Xandra, Garcia-Tiscar, Jorge, Escalona, Johan

CFD Investigation of the Effects of Gas’ Methane Number on the Performance of a Heavy-Duty Natural-Gas Spark-Ignition Engine

2019-24-00089/9/2019

Natural gas (NG) is an alternative fuel for spark-ignition engines. In addition to its cleaner combustion, recent breakthroughs in drilling technologies increased its availability and lowered its cost. NG consists of mostly methane, but it also contains heavier hydrocarbons and inert diluents, the levels of which vary substantially with geographical source, time of the year and treatments applied during production or transportation. To investigate the effects of NG composition on engine performance and emissions, a 3D CFD model of a heavy-duty diesel engine retrofitted to NG spark ignition simulated lean-combustion engine operation at low speed and medium load conditions. The work investigated three NG blends with similar lower heating value (i.e., similar energy density) but different Methane Number (MN). The results indicated that a lower MN increased flame propagation speed and thus increased in-cylinder pressure and indicated mean effective pressure. In addition, a low MN increased the thermal efficiency despite the higher heat transfer to the surroundings. Also, a higher MN reduced the nitrogen-oxides emissions but increased unburned hydrocarbons (UHC) emissions. Moreover, while UHC emissions had a similar H/C ratio as the NG, there was no correlation between the carbon monoxide emissions and the fuel H/C ratio.

Ambrogi, Luca, Liu, Jinlong, Battistoni, Michele, Dumitrescu, Cosmin, Gasbarro, Lorenzo

Temperature Measurements of the Piston Optical Window in a Research Compression Ignition Engine to Set-Up a 1d Model of Heat Transfer in Transient Conditions

2019-24-01829/9/2019

The analysis of heat losses in internal combustion engines (ICEs) is fundamental to evaluate and to improve engine efficiency. Detailed and reliable heat transfer models are required for more complex 1d-3d combustion models. At the same time, the thermal status of engine components, like pistons, is needed for an efficient design. Measurements of piston temperature during ICEs operation represent an important and challenging result to get for the aforementioned purposes. In the present work, temperature measurements collected at different engine speeds and loads, both in motored and fired modes, have been performed and used to set-up a theoretical correlation and 1d model of heat transfer through the optical window of the piston. The in-cylinder gas and external ambient temperature, together with the thermodynamic and material properties are given. The model has been first calibrated in some selected operating conditions and then validated in the remaining. The aim of the 1d model is to simulate the transient of temperature during the engine warm up in motored, from the engine start up to the steady motored condition; and in fired mode, from motored up to steady fired condition. After tuning the model, a good agreement has been obtained in all the tested conditions; some refinements were needed when increasing the engine speed. The main peculiarity of the model is the possibility to get the steady temperature after long running time, not available from experiments because of technical limitations.

Mancaruso, Ezio, Sequino, Luigi, Vaglieco, Bianca Maria

Performance and Emissions of an Ammonia-Fueled SI Engine with Hydrogen Enrichment

2019-24-01379/9/2019

While the optimization of the internal combustion engine (ICE) remains a very important topic, alternative fuels are also expected to play a significant role in the reduction of CO2 emissions. High energy densities and handling ease are their main advantages amongst other energy carriers. Ammonia (NH3) additionally contains no carbon and has a worldwide existing transport and storage infrastructure. It could be produced directly from renewable electricity, water and air, and is thus currently considered as a smart energy carrier and combustion fuel. However, ammonia presents a low combustion intensity and the risk of elevated nitrogen-based emissions, thus rendering in-depth investigation of its suitability as an ICE fuel necessary. In the present study, a recent single-cylinder spark-ignition engine is fueled with gaseous ammonia/hydrogen/air mixtures at various hydrogen fractions, equivalence ratios and intake pressures. A small hydrogen fraction is used as combustion promoter and might be generated in-situ through NH3 catalytic or heat-assisted dissociation. The in-cylinder pressure and exhaust concentrations of selected species are recorded and analyzed. Results show that ammonia is a very suitable fuel for SI engine operation, since high power outputs could be achieved with indicated efficiencies higher than 37% by taking advantage of the promoting effects of supercharging and hydrogen enrichment around 10% by volume. High NOx and unburned NH3 exhaust concentrations were also observed under fuel-lean and fuel-rich conditions, respectively. While hydrogen enrichment promotes the NH3 combustion efficiency and helps reducing its exhaust concentration, it has a promoting effect on NOx formation, assumedly due to higher flame temperatures. Therefore, it is recommended to take advantage of the simultaneous presence of exhaust heat, NOx and NH3 in a dedicated after-treatment device to ensure the economic and environmental viability of future ammonia-fueled engine systems.

Lhuillier, Charles, BREQUIGNY, Pierre, Contino, Francesco, Rousselle, Christine

Compression Ratio and Intake Air Temperature Effect on the Fuel Flexibility of Compression Ignition Engine

2019-24-01109/9/2019

The effect of compression ratio (CR) and intake air temperature on the combustion characteristics of fuels with different octane ratings were investigated on a single-cylinder heavy duty engine. The study focused on Primary Reference Fuels (PRFs) and commercial grade diesel with octane numbers ranging from 0 to 100. The engine was configured at a CR of 11.5:1, which is lower than typical heavy-duty compression ignition CI engines. This aims to compare the fuels’ burning regime with recently reported measurements at CR17:1. Experiments were performed at different intake air temperatures of 20 to 80 °C and net indicated mean effective pressure (IMEPNet) of 5 to 20 bar. The injection rates have been characterized to determine the hydraulic delay of the injector and thus define the actual ignition delay time. At low loads, diesel-like fuels were found to burn in partially premixed combustion (PPC) mode whereas high octane fuels did not ignite. At high loads, fuels combustion becomes diffusion driven regardless of their RON or MON values. The effect of intake air temperature on the combustion characteristics depended on the combination of the octane ratings and the engine load. At high loads, fuels with low octane numbers were insensitive to the change of the intake air temperature. The ignition delay time was short enough to maintain a diffusion driven combustion. At lower loads, it is more challenging to reach conditions where the combustion characteristics are invariant regardless of the fuel’s RON and MON values (Fuel Flexible). At the low tested compression ratio of 11.5:1, the extent of fuel flexibility is limited to only high loads (IMEPNet = 20 bar) whereas it is extended to intermediate loads (IMEPNet = 10 and 15 bar) at CR17:1.

AlRamadan, Abdullah S., Ben Houidi, Moez, Aljohani, Bassam S. E., Eid, Hassan, Johansson, Bengt

Experimental Assessment of Ozone Addition Potential in Direct Injection Compression Ignition Engines

2019-24-01189/9/2019

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

Mazda finally ready with Skyactiv-D for U.S.

19AUTP06_146/1/2019

Mazda announced the long-awaited arrival of its Skyactiv-D diesel engine to the U.S. at April's New York International Auto Show. The 2.2L twin-sequential turbocharged 4-cylinder diesel is available for pre-order now in the highest AWD trim of Mazda's best-selling vehicle, the 2-row, 5-seat Mazda CX-5 SUV. The 2019 model with the diesel engine has a starting MSRP of $41,000-a $4K premium over the equivalent gasoline trim-with deliveries expected to begin this summer. Mazda also announced that the same Skyactiv-D engine will be available “soon” in the Mazda6 sedan, and confirmed that its Skyactiv-X homogeneouscharge gas engine will go on sale in Europe before the end of 2019. Mazda claimed that after the rollout in Europe, Skyactiv-X engines will then come to markets (including the U.S.), which already feature Mazda's Skyactiv-G highcompression gasoline engines.

Seredynski, Paul

Using Ducted Fuel Injection to Attenuate Soot Formation in a Mixing-Controlled Compression Ignition Engine

03-12-03-00215/10/2019

Ducted fuel injection (DFI) has been proposed as a strategy to enhance the fuel/charge gas mixing within the combustion chamber of a direct-injection mixing-controlled compression ignition engine. The concept involves injecting each fuel spray through a small tube within the combustion chamber to facilitate the creation of a leaner mixture in the autoignition zone, relative to a conventional free-spray configuration (i.e., a fuel spray that is not surrounded by a duct). While previous experiments demonstrated that DFI lowers both soot incandescence and soot mass in a constant-volume combustion vessel with a single-component normal-alkane fuel (n-dodecane), this study provides the first evidence that the technology provides similar benefits in an engine application using a commercial diesel fuel containing ~30 wt% aromatics. The present study investigates the effects on engine-out emissions and efficiency with a two-orifice injector tip for charge gas mixtures containing 16 and 21 mol% oxygen. The result is that DFI is confirmed to be effective at curtailing engine-out soot emissions. It also breaks the tradeoff between emissions of soot and nitrogen oxides (NOx) by simultaneously attenuating soot and NOx with increasing dilution.

Nilsen, Christopher W., Biles, Drummond E., Mueller, Charles J.

SI Engine Combustion and Knock Modelling Using Detailed Fuel Surrogate Models and Tabulated Chemistry

2019-01-02054/2/2019

In the context of today’s and future legislative requirements for NOx and soot particle emissions as well as today’s market trends for further efficiency gains in gasoline engines, computational fluid dynamics (CFD) models need to further improve their intrinsic predictive capability to fulfill OEM needs towards the future. Improving fuel chemistry modelling, knock predictions and the modelling of the interaction between the chemistry and turbulent flow are three key challenges to improve the predictivity of CFD simulations of Spark-Ignited (SI) engines. The Flamelet Generated Manifold (FGM) combustion modelling approach addresses these challenges. By using chemistry pre-tabulation technologies, today’s most detailed fuel chemistry models can be included in the CFD simulation. This allows a much more refined description of auto-ignition delays for knock as well as radical concentrations which feed into emission models, at comparable or even reduced overall CFD run-time. The FGM model has a high level of intrinsic predictive capability, as already demonstrated for many academic cases as well as for industrial burners, gas turbines and diesel engines. The application to gasoline engines has not been much investigated however, mainly due to the difficulty of model implementation and chemistry tabulation technology. In this work, the FGM combustion model is assessed on multiple operating points of a modern SI engine, using various levels of detail for the fuel chemistry, ranging from industry-standard reduced chemical schemes to state-of-the-art gasoline surrogate models. The investigated configuration represents a turbocharged gasoline engine with direct injection and homogeneous charge combustion. The engine simulation involved gas-exchange, fuel spray injection, spark ignition and combustion phases. The computational grid provides a mesh resolution in the range of 0.6-0.3 mm within the cylinder. CFD simulation has been started at the beginning of the exhaust stroke allowing to correctly predict the residual gas mass fraction, the mixture fraction as well as the temperature field - the parameters, which can directly affect the knocking effects. Firstly, the comparison between the simulated pressure curves and available experimental data for a spark timing sweep was discussed. The special attention was dwelled on an ability of the FGM based knock model to characterize the inherent knock combustion features including a knock probability and providing an information on knock cycle indicator.

Goryntsev, Dmitry, Tap, Ferry, Tvrdojevic, Mijo, Priesching, Peter

The Application of Controlled Auto-Ignition Gasoline Engines -The Challenges and Solutions

2019-01-09494/2/2019

Controlled Auto-Ignition (CAI) combustion, also known as Homogeneous Charge Compression Ignition (HCCI), has the potential to simultaneously reduce the fuel consumption and nitrogen oxides emissions of gasoline engines. However, narrow operating region in loads and speeds is one of the challenges for the commercial application of CAI combustion to gasoline engines. Therefore, the extension of loads and speeds is an important prerequisite for the commercial application of CAI combustion. The effect of intake charge boosting, charge stratification and spark-assisted ignition on the operating range in CAI mode was reviewed. Stratified flame ignited (SFI) hybrid combustion is one form to achieve CAI combustion under the conditions of highly diluted mixture caused by the flame in the stratified mixture with the help of spark plug. CAI combustion in two-stroke gasoline engine can be used to enhance the torque of a four-stroke gasoline engine with the same displacement at the same indicated mean effective pressure. Poppet-valved two-stroke gasoline engines with normal valve lift and variable valve timing device, and uniflow two-stroke engine with gas exchange process completed by intake ports on the bottom of cylinder wall and overhead exhaust poppet valves are promising to achieve CAI combustion in a wide operating range. Hence, CAI combustion in two-stroke gasoline engines is a feasible solution for its commercial application to vehicles.

Fu, Xue-Qing, He, Bang-Quan, Zhao, Hua, Zhang, Yan, Li, Yufeng, Bai, Honglin

Emissions from Advanced Ultra-Low-NO _x Heavy-Duty Natural Gas Vehicles

2019-01-07514/2/2019

The emissions of two ultralow NOx heavy-duty (HD) vehicles equipped with 0.02 g/bhp-hr low NOx natural gas (NG) engines were evaluated on a chassis dynamometer. This included a waste hauler and a city transit bus, each with a 0.02 g/bhp-hr NOx L9N near zero (NZ) natural gas engine. The vehicles were tested over a variety of different cycles, including the Urban Dynamometer Driving Schedule (UDDS), port drayage cycles, transit bus cycles, and a refuse truck cycle. For both vehicles, the NOx emissions results were below the 0.02 g/bhp-hr level for most cycles, with the exception of some cold start tests. For the waste hauler, NOx emissions averaged between 0.014 and 0.002 g/bhp-hr for the hot start tests, and from 0.043 to 0.014 g/bhp-hr for the cold start tests. This represented NOx emissions reductions from 97%-100% of compared with previous ISL G 8.9 engines. For the transit bus, the NOx emissions ranged from 0.0007 g/bhp-hr to 0.0042 g/bhp-hr for the warm tests and up to 0.04 g/bhp-hr for the cold start tests. The NOx results for the warm tests are 99% lower than the existing 2010 NOx diesel standard (0.2 g/bhp-hr) and 90% lower than the optional low NOx standard (0.02 g/bhp-h). In contrast, some elevation of ammonia emissions was observed for both vehicles, due to reactions that occur over the three way catalyst. Overall, the results suggest that ultralow NOx NG engines could play an important role in reducing NOx emissions from heavy-duty vehicles towards near zero levels in urban areas. The particle mass emissions were low and typically were more than 90% lower than the 2010 certification standard (10 mg/bhp-hr) for the L9N engine for both applications. Particle number (PN) emissions for the L9N (0.02 g/bhp-h) and other previous tests of ISL G 8.9 (0.2 g/bhp-h) engines both show higher PN emissions compared to diesel vehicles equipped with diesel particle filters (DPFs). Fuel economy, greenhouse gas and nitrous oxide (N2O) emissions are also reported in this paper.

Li, Chengguo, Han, Yuwei, Jiang, Yu, Yang, Jiacheng, Karavalakis, George, Durbin, Thomas D., Johnson, Kent

Laminar Flame Speeds of Premixed Iso-Octane/Air Flames at High Temperatures with CO ₂ Dilution

2019-01-05724/2/2019

Spherically expanding flames are employed to measure the laminar flame speed of premixed iso-octane/air mixtures at elevated temperatures through both experiments and numerical simulations. Iso-octane (2,2,4-trimethlypentane) is an important gasoline primary reference fuel (PRF). While most studies on laminar burning velocity of iso-octane focus on low temperatures (less than 400 K), the experiments here were conducted in an optically accessible constant volume combustion chamber between 373 K-473 K, at a pressure of 1 bar, and from ϕ=0.8 to ϕ=1.6. The effect of diluent is investigated through the addition of 15% CO2 dilution in order to simulate the effect of exhaust gas recirculation. The decreased reactivity with diluent addition reduces mixture reactivity, which can reduce the propensity for knock in spark ignition engines. All laminar flame speeds were calculated using the constant pressure method enabled via schlieren visualization of the spherically propagating flame front. Results show that laminar flame speeds of iso-octane/air mixtures at 1 bar increase by 46-51% with initial temperature increases from 373 K to 473 K. However, the addition of 15% CO2 dilution to the iso-octane/air mixtures at 1 bar and 473 K results in a 47-51% decrease in the laminar burning velocity. Numerical results obtained with CHEMKIN [1] using the kinetic mechanism of Chaos et al. [2] show excellent agreement with experimental data for ϕ=0.8-1.2; however, the kinetic mechanism slightly underestimates the experimentally observed laminar flame speeds between ϕ=1.3-1.6.

Duva, Berk Can, Chance, Lauren, Toulson, Elisa

Mixing-Limited Combustion of Alcohol Fuels in a Diesel Engine

2019-01-0552

4/2/2019

Diesel-fueled, heavy-duty engines are critical to global economies, but unfortunately they are currently coupled to the rising price and challenging emissions of Diesel fuel. Public awareness and increasingly stringent emissions standards have made Diesel OEMs consider possible alternatives to Diesel, including electrification, fuel cells, and spark ignition. While these technologies will likely find success in certain market segments, there are still many applications that will continue to require the performance and liquid-fueled simplicity of Diesel-style engines. Three-way catalysis represents a possible low-cost and highly-effective pathway to reducing Diesel emissions, but that aftertreatment system has typically been incompatible with Diesel operation due to the prohibitively high levels of soot formation at the required stoichiometric fuel-air ratios. This paper explores a possible method of integrating three-way catalysis with Diesel-style engine operation. The proposed concept utilizes a high-temperature combustion system-enabled by a combination of thermal insulation, reduced turbocharger aftercooling, and exhaust gas retention-to combust low-cetane “sootless” fuels like ethanol, methanol, and natural gas in a traditional Diesel-style combustion mode (i.e. mixing-limited diffusive combustion, rather than HCCI-like strategies). The proposed concept has demonstrated the ability to meet EPA 2010 soot emissions limits without a particulate filter, while also maintaining a stoichiometric exhaust composition that is compatible with three-way catalysis. Further, the proposed concept can meet, and even exceed, baseline Diesel engine efficiency by combining the high compression ratio Diesel engine design with reduced heat transfer losses. Finally, use of mixing-limited, Diesel-style combustion drastically simplifies combustion phasing, and limits rate of rise. These early results motivate additional work on this concept, further optimizing components for high-temperature operation on alcohol fuels, and integrating the results into a commercial multi-cylinder engine demonstration.