Direct Injection Spark Ignition Engine Research Articles

Combined impact of excess air ratio and injection strategy on performances of a spark-ignition port- plus direct-injection dual-injection gasoline engine at half load

Spark-ignition direct-injection gasoline engine is one of the main power of passenger cars. In this study, combined impact of excess air ratio (λ) and injection strategy on performances of a spark-ignition port- plus direct- injection (PI + DI) dual-injection gasoline engine at half load was investigated experimentally. Experimental results show that the brake mean effective pressure decreased with increasing λ at half load; the brake thermal efficiency first increased, then reached the highest value at approximately λ = 1.1 or 1.2 for different injection strategies, and finally decreased with increasing λ; the maximum cylinder pressure, maximum heat release rate and maximum cylinder temperature decreased with increasing λ, and their corresponding crank angles delayed; the starting of combustion (CA05) increased with increasing λ, the CA05 at PI0DI100 (0 % PI and 100 % DI per cycle), late DI mode and any λ values was the closest to top dead center; for early DI mode, combustion center (CA50) of PI0DI100 was greater or lower than that of PI50DI50 (50 % PI and 50 % DI per cycle) at roughly λ < 1.15 or λ > 1.15, respectively; combustion stability (COVimep) of early DI mode can be controlled within 2 %; the λ had a significant effect on brake-specific carbon monoxide (BSCO) emission at rich mixture and a little effect on BSCO emission at lean mixture; the brake-specific hydrocarbon (BSHC) emission of early DI mode was much higher than that of late DI mode, the injection strategy had an important effect on HC (hydrocarbon) emission; for early DI mode, the brake-specific nitrogen oxides (BSNOX) emissions first increased with increasing λ, then reached the highest value at λ = 1.1, and finally rapidly decreased with further increasing λ; for late DI mode, the BSNOX emissions decreased with increasing λ; the soot emission decreased with increasing λ; the soot emission of late DI mode was much higher than that of early DI mode; at a constant λ, sootPI50DI50,early DI mode ≈ sootPI0DI100, early DI mode ≪ sootPI50DI100, late DI mode < sootPI0DI100, late DI mode.

MACROSCOPIC SPRAY CHARACTERISTICS OF GASOLINE, METHANOL, AND ETHANOL IN DIRECT INJECTION SPARK IGNITION ENGINE-LIKE CONDITIONS

In recent decades, stringent emission norms have been enforced upon the engine research community and OEMs to encourage them to develop new spark ignition engine technologies, such as variable valve lifts, turbocharging, and direct injection spark ignition (DISI) engines. For further development, greater control of parameters such as in-cylinder air motion, spray characteristics, injection, and ignition events is required. Spray characterizations are crucial for understanding the mixing phenomena in heated and pressurized engine combustion chamber conditions. Spray pattern, fuel injection pressure (FIP), rate shape, and thermodynamic conditions of the combustion chamber play a vital role in the mixture preparation. The present study uses Mie-Scattering techniques to examine spray structures of fuels like methanol and ethanol and compare them to gasoline, which is of great interest to DISI engines. Three different temperatures of 50, 100, and 200&amp;deg;C and two chamber pressures, 4 and 8 bar, are considered to simulate typical engine-cylinder conditions. It is observed that the initial chamber conditions greatly influence the spray structure. Spray collapse is lesser for alcohol than gasoline. Three semi-empirical models for predicting spray penetration are analyzed: Dent, Hiroyasu and Arai, and Arr&amp;#232;gle. These models could not differentiate between the test fuels, particularly methanol and ethanol, for predicting spray penetration length. The degree of deviation in predictions is the lowest in the Hiroyasu and Arai model and the highest in the Dent model. Spray penetration length increased with an increasing FIP regardless of ambient conditions; however, the spray penetration length decreased with increasing chamber pressure.

Particulate Matter Emissions in Gasoline Direct-Injection Spark-Ignition Engines: Sources, Fuel Dependency, and Quantities

This study investigates sources of particulate matter (PM) from a direct-injected spark-ignition (DISI) engine, all of which are likely the result of poor mixture formation, although through varying mechanisms. Nine unique gasoline formulations, including both oxygenated and non-oxygenated fuels, with varying distillation curves and concentrations of different hydrocarbon classes were employed to investigate the effect of fuel on soot formation. The engine experiments were further supported by reacting and non-reacting experiments in a spray-chamber.The metal-engine experimental results indicated that engine-out PM emissions of the nine fuels generally conforms to their sooting tendency, here quantified by Particulate Matter Index (PMI). Discrepancies with the engine-out PM emissions and PMI were observed under transient operating condition, which is not reflective of the test conditions used to formulate the PMI. A diisobutylene surrogate blend and a high-olefin full-boiling range fuel were investigated further in the optically-accessible engine, showing soot generation from different sources. These differences came from the variation in their spray characteristics, as confirmed in the non-reactive spray-chamber experiments.While the earlier tests were conducted with a fouled injector, the injector was later cleaned and fuels were tested in the optical engine. High olefin fuel and diisobutylene blend showed significantly lower soot emissions with clean injector. E30 fuel exhibited spray impingement and subsequent diffusive combustion, known as pool fire, on the piston top characterized by a yellow flame due to soot luminosity. A final round of experiments in the spray-chamber mimic this pool fire mechanism. A stoichiometric flame was initiated after a spray has impinged on a wall and formed a film. Results showed a large time delay between the flame passing over the fuel film and the formation of soot mass. The slow soot formation via pyrolysis in spray-chamber suggest that pyrolysis may not be a dominating soot-production pathway in SI engines, even for conditions with significant wall wetting. The findings of this study highlight the many considerations which influence the effective design of a combustion system when the minimization of PM emissions is a goal, and the ways in which fuel formulation can change soot-production pathways in DISI engines.

Quantitative fluorescence-based imaging of in-cylinder fuel film thickness at kHz frame rates in a production-type direct-injection spark-ignition engine

Incomplete evaporation of liquid fuel films inside the combustion chamber is a major source of soot and particulate emissions in internal combustion engines. In this study, quantitative imaging of liquid fuel films on the cylinder wall is performed by laser-induced fluorescence (LIF) in a single cylinder engine with optical access to the cylinder liner. A four-component surrogate fuel mixed with 0.5% anisole as the fluorescent tracer was directly injected in a single injection into the motored engine. Fuel impinging on the cylinder wall is excited at 266 nm at kHz repetition rates and imaged by a high-speed camera coupled with an image intensifier. Simultaneously, lubricating oil doped with 0.01 mmol/l pyrromethene 567 is excited at 532 nm and imaged with a second camera. The fuel film thickness on the cylinder wall is compared for two different injections timings, 285 and 240°CA before top-dead center. The initial fuel film thickness is similar for both, but evaporation occurs faster for the later injection, such that the film thickness is similar at the time the piston rings reach the fuel films. When the rings scrape the fuel off the wall, it accumulates on top of the first piston ring and is partly transported downwards to the second and third ring. In the simultaneous oil image, washout of lubricating oil is seen.

Evaluation of the sample size requirements of machine learning models used in engine design and research

Machine Learning (ML) techniques have been effectively used to learn the intricate relationships between variables that play a significant role in the field of engine design. However, there are two challenges to this approach – (1) Identifying ML regression models that could capture the trends of a response variable, given a non-parametric training set of relatively small size, with an acceptable accuracy and response time, and (2) identifying the size of the dataset, with respect to the input parameters, to be used for training and validation of the ML models. There is not enough information in the literature to reach a consensus on the sampling size to be used for an engine design problem that would yield an acceptable measure of goodness-of-fit. This is evident from the varied size of the training/validation data size used within the engine research community, as will be elaborated on in the following sections. The objective of this paper is to provide an insight into the sampling size required by the different ML models to achieve an acceptable fit between the model and the data, to be used in three types of engine design/optimization problems – (1) conventional diesel combustion (CDC) engine performance over a wide range of speed and load, (2) cold-start operation of a direct-injected spark-ignition (DISI) engine, and (3) high-load performance of a dual-fuel reactivity-controlled compression ignition (RCCI) engine.

Large-eddy simulation of a natural gas direct injection spark ignition engine with different injection timings

This paper presents a large-eddy simulation (LES) study of a compressed natural gas (CNG) direct injection spark ignition (DISI) engine with different injection timings. Three cases with late, moderate and advanced injection timings are investigated to examine fuel/air mixing and combustion characteristics of a CNG DISI engine. A transition flame speed approach is used in which the flame propagates like a laminar flame until it reaches a specified kernel size and then develops as a turbulent flame. Changing the transition kernel size significantly affects both the in-cylinder pressure trace and the mass fraction burned (MFB) profile, highlighting the importance of correctly capturing the early stage of flame development. Different injection timings result in varying levels of mixing and homogeneity within the cylinder. Although more time is available for mixing in the most advanced injection case, the jet impingement on the piston crown increases the level of mixture in-homogeneity. It is shown that the variation of the laminar flame speed as a result of mixture in-homogeneity is the primary factor affecting flame propagation for different injection timings.

An experimental and modeling study of tetramethyl ethylene pyrolysis with polycyclic aromatic hydrocarbon formation

Iso-olefins, in the C5–C8 range can potentially be blended with renewable gasoline fuels to increase their research octane number (RON) and octane sensitivity (S). RON and S increase with the degree of branching in iso-olefins and this is a desirable fuel anti-knock quality in modern spark-ignited direct-injection engines. However, these iso-olefins tend to form larger concentrations of aromatic species leading to the formation of polycyclic aromatic hydrocarbons (PAHs). Thus, it is important to understand the pyrolysis chemistry of these iso-olefins. In this study, a new detailed chemical kinetic mechanism is developed to describe the pyrolysis of tetramethyl ethylene (TME), a symmetric iso-olefin. The mechanism, which includes the formation of PAHs, is validated against species versus temperature (700–1160 K) measurements in a jet-stirred reactor at atmospheric pressure and in a single-pulse shock tube at a pressure of 5 bar in the temperature range 1150–1600 K. Synchrotron vacuum ultraviolet photoionization mass spectrometer (SVUV-PIMS) and gas chromatography (GC) systems were used to quantify the species in the jet-stirred reactor and in the single-pulse shock tube, respectively. The mechanism derives its base and PAH chemistry from the LLNL PAH sub-mechanism. The predictions are accurate for most of the species measured in both facilities. However, there is scope for mechanism improvement by understanding the consumption pathways for some of the intermediate species such as isoprene. The formation of 1, 2, and 3-ring aromatic species such as benzene, toluene, naphthalene and phenanthrene measured experimentally is analyzed using the chemical kinetic mechanism. It is found that the PAH formation chemistry for TME under pyrolysis conditions is driven by both propargyl addition reactions and the HACA mechanism.

Experimental investigation of boundary layer flow near the cylinder wall in a direct-injection spark-ignition engine using particle image velocimetry

In a direct-injection spark-ignition (DISI) optical engine with a constant motored speed of 800 rpm, particle image velocimetry measurements on the in-cylinder bulk flow and the boundary layer flow near the cylinder wall were performed during the intake and compression strokes. Two different tumble flow levels were explored using a flap inserted in the intake port. The near-wall flow pattern under the effect of the bulk flow is more stable when the flap is fully closed with a higher intensity tumble. The serious optical distortion in the near-cylinder wall region under high magnification was addressed, and a high resolution of 76 μm × 76 μm within a field of view of 5 mm × 5 mm was achieved in six different measurement regions. Using inner scaling parameters (friction velocity uτ and viscous length-scale δυ), the dimensionless ensemble-averaged wall-tangential velocity profiles exhibit good consistency with the law-of-the-wall in the viscous sublayer but considerably departure in the logarithmic region. According to the low friction Reynolds number, the absence of the logarithmic layer was mainly attributed to the complete overlap between the viscosity-affected inner region and the outer region of the boundary layer. The near-wall velocity profiles were also normalized by three different outer scaling parameters. The collapse is significantly improved for y/ δ &gt;0.07 when the velocity profiles are normalized by δ/ δ*(1− u/ u∞). The fluctuation RMS velocity in the wall-normal direction is greater, particularly for the high tumble flow level condition.

Split Injection Strategy Optimization to Achieve Ideal Stratified‐Charge Mixture and Reinforce Ultralean Burn in a High Compression Ratio Direct Injection Spark Ignition Engine

Ultralean burn is considered an effective way to enhance the thermal efficiency of direct injection spark ignition engines. Herein, under ultralean burn condition, the split injection strategy is induced to investigate the in‐cylinder mixture distribution, combustion characteristics, and emissions by simulation in a high compression ratio engine model. First, the homogeneity index shows that compared with the single injection method, the split injection strategy shows better stratification of the mixture gas at the early stage of the compression stroke, which results in higher in‐cylinder pressure and heat release. Meanwhile, the results of heat balance show that split injection shows a slight effect on ignition delay, but significantly shortens combustion duration and advances CA50, and thus the exhaust loss is decreased. Second, with the decrease of a second injection fuel mass, the rich mixture is formed near the spark plug, thus reducing the ignition delay and combustion duration. Third, the split injection strategy presents faster flame kernel growth and propagation. A larger flame area is observed with the second injection mass decreasing. Finally, as the second fuel injection mass is reduced, NOx emissions increases continuously, while the soot emission decreases.

Potential of ozone addition on dethrottling of a gasoline/ethanol blend-fueled direct injection spark ignition engine in part load

Several efforts are required to improve engine efficiency and decrease global carbon dioxide (CO2) emissions and local pollutant products. In countries like Brazil, with a four-decade long experience with ethanol, the use of fossil fuels, although widespread, is being put under intense scrutiny. Governmental programs like ROTA 2030 stimulate engine research and development focused on environment-friendly fuels such as bioethanol-gasoline blends. Brazilian gasoline has about a quarter of ethanol, reducing the carbon footprint while maintaining suitable energy density. Regardless of the fuel, the load control method in part load operation of spark ignition engine causes a considerable penalty in fuel conversion efficiency. For these reasons, ozone addition was tested as an ignition enhancer that would allow higher de-throttling to reduce part-load pumping losses. The residual gas was used to dilute the mixture due to the possibility of keeping the three-way catalyst working properly with the stoichiometric mixture. An experimental investigation on efficiency, emissions and combustion related parameters was carried out in a downsized 1.0 l turbocharged direct-injected engine. Experimental tests were performed at 3 bar of indicated mean effective pressure (IMEP), 1500 rpm and stoichiometric air-fuel ratio. Spark timing (ST) was adjusted to achieve maximum indicated efficiency and the fuel used was Brazilian gasoline. Different ozone concentrations were used as a mixture with the intake air to overcome unstable engine operation by enhancing ignition. The results showed that it is possible to increase the gas exchange efficiency with ozone addition by promoting de-throttling operation with residual gases. Furthermore, the ozone addition exhibits the potential to promote autoignition of the end gas with spark assistance, even with a low compression ratio and residual gas fraction higher than 30%. However, the combustion efficiency is impaired by the higher residual gas fraction in some operation points that leave room for improvements.

Effects of injection pressure on the flame front growth in an optical direct injection spark ignition engine

• Optical diagnostics performed at wide open throttle and 1200 rpm conditions. • Elevated injection pressure does not monotonically increase engine output. • Higher spatial variation in turbulence measured for very high injection pressure. • Local overmixing and increased mixture inhomogeneity are likely causes. • Despite decreased power, soot is still lower at very high injection pressure. The fuel injection pressure of direct injection spark ignition (DISI) petrol engines has increased significantly to improve engine efficiency and reduce air-polluting emissions. The present study performs a detailed analysis of spray penetration, burn duration, flame front vectors and turbulence intensity to provide scientific explanations about the optimal injection pressure observed for the maximum power output/efficiency in a single-cylinder optically accessible DISI engine. Five injection pressures of 5, 10, 15, 20 and 25 MPa were tested based on an equal-split double injection strategy using a side-mounted six-hole direct injector. A high-speed camera with a 20 kHz frame rate was used to record spray development, propagating petrol flame and soot luminosity. The Mie-scattering technique was used to image the fuel dispersion under varied injection pressure and to calculate spray penetration. For time-resolved, two-dimensional flame front vector extraction, a newly developed flame image velocimetry (FIV) was applied to high-speed natural combustion luminosity movies. A spatial filtering method was also used for the flow decomposition to acquire flame front turbulence intensity. A total of 100 combustion cycles were FIV processed for each test pressure to tackle the inherent cyclic variations. The spray images showed that higher fuel injection pressure leads to faster spray tip penetration and enhanced spray evaporation for better air/fuel mixing. However, the in-cylinder pressure and power output do not continue to increase with an increase in injection pressure; they peak at 15 MPa and decrease at higher injection pressure. The spatially averaged flame front vector magnitude and turbulence intensity also peak at 15 MPa, indicating the optimal injection pressure was due to the maximum turbulent flame front growth. The distribution of turbulence intensity along the flame boundary shows increased variations at injection pressure higher than 15 MPa, because local over-mixing caused low turbulent flame growth regions. Although the highest turbulent flame front growth was not measured at 25 MPa, the soot luminosity was much lower than that of 15 MPa, which explains the development trend towards higher injection pressure.

Experimental and Numerical Study on the Effect of Nitric Oxide on Autoignition and Knock in a Direct-Injection Spark-Ignition Engine

&lt;div class="section abstract"&gt;&lt;div class="htmlview paragraph"&gt;Nitric Oxide (NO) can significantly influence the autoignition reactivity and this can affect knock limits in conventional stoichiometric SI engines. Previous studies also revealed that the role of NO changes with fuel type. Fuels with high RON (Research Octane Number) and high Octane Sensitivity (S = RON - MON (Motor Octane Number)) exhibited monotonically retarding knock-limited combustion phasing (KL-CA50) with increasing NO. In contrast, for a high-RON, low-S fuel, the addition of NO initially resulted in a strongly retarded KL-CA50 but beyond the certain amount of NO, KL-CA50 advanced again. The current study focuses on same high-RON, low-S Alkylate fuel to better understand the mechanisms responsible for the reversal in the effect of NO on KL-CA50 beyond a certain amount of NO. Experiments were conducted to measure the responses of KL-CA50 and trace-autoignition CA50, the latter being indicative of CA50 at which end-gas autoignition starts to become measurable from the apparent heat-release rate. Chemical-kinetics simulations were conducted to reveal the role of NO for end-gas autoignition, with a specific focus on sequential autoignition in a thermally stratified end-gas.&lt;/div&gt;&lt;div class="htmlview paragraph"&gt;The simulation results reveal that the magnitude of low-temperature heat release (LTHR) generally increases with NO. However, the relative importance of NO for enhancing LTHR diminishes when the LTHR inherent to a fuel’s chemistry is strong, such as at lower temperatures in a thermal boundary layer. This rendered more uniform LTHR within a hypothetical thermal boundary and led to a more sequential (&lt;i&gt;i.e.&lt;/i&gt; slower) autoignition event. It was also revealed that a change in compression ratio influences the importance of intermediate-temperature heat release (ITHR) due to changes of the temperature-pressure history of the end-gas. Together with the condition where end-gas autoignition occurs more sequentially, the shorter time spent in LTHR and ITHR regime can counter the increase in autoignition reactivity at high NO levels and allow KL-CA50 to advance.&lt;/div&gt;&lt;/div&gt;

Octane Requirements of Lean Mixed-Mode Combustion in a Direct-Injection Spark-Ignition Engine

This study investigates the octane requirements of a hybrid flame propagation and controlled autoignition mode referred to as mixed-mode combustion (MMC), which allows for strong control over combustion parameters via a spark-initiated deflagration phase. Due to the throughput limitations associated with both experiments and 3-D computational fluid dynamics calculations, a hybrid 0-D and 1-D modeling methodology was developed, supported by experimental validation data. This modeling approach relied on 1-D, two-zone engine simulations to predict bulk in-cylinder thermodynamic conditions over a range of engine speeds, compression ratios, intake pressures, trapped residual levels, fueling rates, and spark timings. Those predictions were then transferred to a 0-D chemical kinetic model, which was used to evaluate the autoignition behavior of fuels when subjected to temperature–pressure trajectories of interest. Finally, the predicted autoignition phasings were screened relative to the progress of the modeled deflagration-based combustion in order to determine if an operating condition was feasible or infeasible due to knock or stability limits. The combined modeling and experimental results reveal that MMC has an octane requirement similar to modern stoichiometric spark-ignition engines in that fuels with high research octane number (RON) and high octane sensitivity (S) enable higher loads. Experimental trends with varying RON and S were well predicted by the model for 1000 and 1400 rpm, confirming its utility in identifying the compatibility of a fuel’s autoignition behavior with an engine configuration and operating strategy. However, the model was not effective in predicting (nor designed to predict) operability limits due to cycle-to-cycle variations, which experimentally inhibited operation of some fuels at 2000 rpm. Putting the operable limits and efficiency from MMC in the context of a state-of-the-art engine, the MMC showed superior efficiencies over the range investigated, demonstrating the potential to further improve fuel economy.

Numerical investigation on combustion system optimization for direct injection of aviation kerosene in a two-stroke SI engine for unmanned aerial vehicle

In recent years, the transition from gasoline to heavy fuel has received more and more attention in the application of unmanned aerial vehicles (UAVs). This study aims to convert a two-stroke port fuel injection (PFI) gasoline engine as the prototype engine to a direct injection (DI) aviation kerosene engine by numerical simulations. The direct-injection combustion system was designed, and then the effects of fuel injection timing and ignition strategy on combustion and knock of a two-stroke direct injection spark-ignition (DISI) engine with aviation kerosene as fuel were evaluated. The results show that the direct-injection combustion system can increase the airflow velocity, thereby accelerating fuel diffusion and flame propagation. The knock intensity (KI) and indicated mean effective pressure (IMEP) all decrease with the retardation of the injection timing and spark timing. Injection timing has a greater impact on IMEP than spark timing. For different injection timings, spark timing has a more obvious impact on KI when injection timing is advanced. The coordinated control strategy of advancing injection timing and retarding spark timing can effectively suppress the tendency of knock and broaden its load range, which can make the power recovery rate reach 88.57% compared to the baseline engine.

Valve Vibration Induced Intake Air Flow Dynamics Analysis Using Near Valve Particle Image Velocimetry

Abstract The transient dynamics of air flow running through the moving intake valve gaps in combustion cylinders is crucial to the performance of spark-ignition direct-injection engines. However, research on the air flow behavior in the vicinity of valve exits is still limited. In this work, transient air flow characteristics of a custom-designed dual-valve system under the operating conditions of a fixed valve lift and a vibrating valve lift at two frequencies are experimentally investigated. The velocity vector field measured using planar particle image velocimetry (PIV) is first analyzed in time domain based on temporal mean and root-mean-square (RMS) values. Comparison of temporal mean flow fields reveals the difference in flow pattern while RMS represents the variation of intake air jet velocity along the inlet path of the vibration-affected jet. Instantaneous snapshots provide direct analysis of the valve vibration-induced intake air jet behavior. Furthermore, investigation in frequency domain extends insights into the dominant spectral components of flow structures. Fast Fourier transform (FFT) applied to every vector on the velocity field yields a vibration frequency affected zone (VFAZ), indicating the regions where the effect of valve vibration is significant. By employing dynamic mode decomposition (DMD) method, the spatio-temporal PIV results are decomposed into modes with specific frequencies. Reconstructed flow field using modes with the valve operating frequency visually unveils a cyclic vortex structure near the valve exit. In summary, this study elucidates the mechanism of near-valve intake air flow impingement and interaction behavior induced by the valve vibrating motion.

Optical Investigation of the Influence of In-cylinder Flow and Mixture Inhomogeneity on Cyclic Variability in a Direct-Injection Spark Ignition Engine

In this study, a single-cylinder direct-injection spark-ignition research engine with full optical access was used to investigate the influence of the flow field and fuel/air mixing on cyclic variability, in particular in the early flame propagation. The engine was operated under lean-burn conditions at 1500 rpm. Two different injection strategies were compared, port-fuel injection (PFI) and direct injection (DI), the latter with early and late injection split about 2:1 in fuel mass. High-speed particle image velocimetry captured the flow in the tumble plane in the compression stroke. The velocity fields and the movement of the tumble vortex are analyzed. Simultaneously, a second camera detected the chemiluminescence of the flame, and the projected area of the line-of-sight-integrated flame luminosity was extracted through morphological image processing. By combining pressure-based combustion analysis and high-speed optical diagnostics, the early flame propagation and the flow field are correlated. In separate experiments the equivalence ratio was imaged for the DI at selected crank angles and correlated with CA10 to learn about the influence of mixture inhomogeneity on early flame propagation. With PFI, the flow near the spark plug just before ignition is closely related to the subsequent speed of combustion. The combustion-relevant flow features can be traced back in time to about –90 °CA. In contrast, the chosen DI scheme results in a decorrelation of flow and flame, and the equivalence ratio distribution at ignition becomes more important. For both flow and mixture fields, regions of high correlation with early-combustion metrics are typically associated with gradients in the multi-cycle average fields.

Modeling of gaseous emissions and soot in 3D-CFD in-cylinder simulations of spark-ignition engines: A methodology to correlate numerical results and experimental data

In order to reduce development costs and time-to market, 1D and 3D CFD tools can support engine design providing reliable estimations of the tailpipe emissions. In particular, 3D-CFD in-cylinder simulations can evaluate formation of both soot and gaseous pollutants inside the combustion chamber. The main issue in such kind of simulations is the validation against experimental findings. In fact, the complexity of the emission measurements does not allow a straightforward one-to-one comparison between numerical and experimental results. Therefore the present paper aims at providing, on the one hand, a robust numerical framework for both gaseous and solid emissions, on the other hand a dedicated post-processing for a fair comparison between simulations and experiments. From a numerical standpoint, a simplified approach is dedicated to gaseous emissions, while a more detailed one is reserved to soot modeling. The latter is based on the Sectional Method, whose reaction rates are tabulated following 0D chemical kinetic simulations of a purposely designed surrogate in a constant pressure reactor. Simulations and experiments proposed in the present analysis are referred to a high-performance turbocharged direct-injection spark-ignition engine operated at part-load and low rpms. On equal performance, revving speed and mean mixture quality, different injection timings are investigated. The developed numerical approach and post-processing ensure a good agreement between simulations and experiments.

Multi-dimensional modeling of mixture preparation in a direct injection engine fueled with gaseous hydrogen

With the recent advances of direct injection (DI) technology, introducing hydrogen into the combustion chamber through DI is being considered as a viable approach to circumvent backfire and pre-ignition encountered in early generations of hydrogen engines. As part of a broader vision to develop a robust numerical model to study hydrogen spark ignition (SI) combustion in internal combustion (IC) engines, the present numerical investigation focuses on mixture preparation in a hydrogen DI SI engine. This study is carried out with a single hole injector with gaseous hydrogen injected at 100 bar injection pressure. Simulations are carried out for high and low tumble configurations and validated against optical data acquired from planar laser induced fluorescence (PLIF) measurements. Varying mesh configurations are investigated for the impact on in-cylinder mixture distribution. A particular emphasis is placed on the effect of nozzle geometry and mesh orientation near the wall. Overall, the computational model is found to predict the mixture distribution in the combustion cylinder reasonably well. The results showed that the alignment of mesh with the flow direction is important to achieve good agreement between numerical analysis and optical measurement data.

Spark-Induced Breakdown Spectroscopy In A Direct-Injected Natural Gas Spark-Ignition Engine

The purpose of this study is to investigate the fuel concentration around the spark plug obtained using spark-induced breakdown spectroscopy (SIBS) method with the spark plug with an optical fiber in the direct-injected natural gas SI engine. Effect of exposure duration on measurement accuracy of fuel concentration was discussed. Equivalence ratio around the spark plug in the direct-injected natural gas SI engine were measured under different natural gas injection timing. When the exposure duration is shortened, the emission of potassium elements near the emission wavelength of oxygen elements can be suppressed, and the measurement accuracy in the calculation of the emission intensity ratio can be improved. The relationship between the luminescence intensity ratio of hydrogen and oxygen (Hα/O) and the equivalence ratio of homogeneous mixture of natural gas and air was investigated and it was found that there was a positive correlation between the luminescence intensity ratio of hydrogen and oxygen (Hα/O) and the equivalence ratio. As a result of measuring the equivalence ratio around the spark plug of direct-injected natural gas SI engine using the SIBS method, an equivalence ratio of 0.67 was measured for a set value of 0.8 using the luminescence intensity ratio of hydrogen and oxygen.

Effect of ethanol blends, E10, E25 and E85 on sub-23 nm particle emissions and their volatile fraction at exhaust of a high-performance GDI engine over the WLTC

This study was aimed to characterize the effect of ethanol blends on sub-23 nm particles and on their volatile organic fraction from a turbocharged 1.8 L direct injection spark ignition engine. Tests were performed on the Worldwide Harmonized Light Vehicles Test Cycle. Engine was fueled with three different blends: 10, 25 and 85 %v/v of ethanol content, gasoline was used as reference fuel. An Engine Exhaust Particle Sizer was used to measure the particle number and size in the range 5.6–560 nm. Particle measure was carried out by diluting the sample gas through both a single diluter and the Dekati Engine Exhaust Diluter. The number and diameter of particles emitted from ethanol blends as well as the presence of volatiles are affected from both the specific phase of the cycle and the fuel properties. A large fraction of volatiles in the sub-23 nm range, especially in the low and extra-high phases of the test cycle, was observed whatever the fuel. Anyway, the percentage of sub-23 m particles increases as the ethanol content in the blends increases except for E85. For this blend, the greater decrease of temperature due to the stronger charge cooling effect ascribable to the larger ethanol content, deteriorates the combustion evolution contributing to the formation of large soot particles. The addition of ethanol to gasoline fuel increases the volatile organic fraction whatever the blend ratio.