Direct Injection Spark Ignition Engine Research Articles

Unveiling the Potential of Hydrogen in a Downsized Gasoline Direct Injection Engine Performance and Emissions Experimental Study

<div>The transportation sector’s growing focus on addressing environmental and sustainable energy concerns has led to a pursuit of the decarbonization path. In this context, hydrogen emerges as a promising zero-carbon fuel. The ability of hydrogen fuel to provide reliable performance while reducing environmental impact makes it crucial in the quest for net zero targets. This study compares gasoline and hydrogen combustion in a single-cylinder boosted direct injection (DI) spark ignition engine under various operating conditions. Initially, the engine was run over a wide range of lambda values to determine the optimal operating point for hydrogen and demonstrate lean hydrogen combustion’s benefits over gasoline combustion.</div> <div>Furthermore, a load sweep test was conducted at 2000 rpm, and the performance and emission results were compared between gasoline and optimized hydrogen combustion. An in-depth analysis was conducted by varying fuel injection time and pressure. This enabled us to explore the effects of these variables on the fuel’s performance and emissions, providing valuable insights for further optimization.</div> <div>The key findings of this study are significant. They note that hydrogen fuel allows the engine to operate under lean conditions with stable combustion up to 3.8 lambda. Lean combustion produces higher engine thermal efficiency, low cyclic variability, and near-zero NO<sub>x</sub> emissions. According to the study, hydrogen combustion produces zero emissions of hydrocarbons (HC), carbon monoxide (CO), and carbon dioxide (CO<sub>2</sub>) under a wide range of operating conditions, making it a clean and environmentally friendly fuel source. During low loading, exhaust hydrogen slip is less than 1000 ppm. This slip drops below 500 ppm as the load increases. Finally, the study proved that hydrogen is more stable than gasoline at a stoichiometric level. This suggests that hydrogen could replace gasoline in some applications, which has major implications for alternative energy.</div>

Parameter optimization for two-stroke direct-injection spark-ignition aviation kerosene engine

The type of two-stroke spark-ignition(SI) engine is still the main power sources of small and medium unmanned aerial vehicles. A transition from gasoline to aviation kerosene or light diesel fuel and from carburetor or port-injection equipment to direct-injection(DI) equipment is prevailing. However, the performance of two-stroke DI-SI engine fueled with aviation kerosene is not very good under medium and high loads. Therefore, using the two-stroke DI-SI kerosene engine modified from port-injection SI gasoline engine as the research subject, the effects of different parameters on engine combustion and performance were studied and parameter optimization was also carried out at high loads. Based on the optimal fuel injection parameters, the influences of ignition time, compression ratio, scavenging/exhaust port area and scavenging/exhaust phase on the operating characteristics of two-stroke engine were analyzed. It was indicated that ignition timing, compression ratio and scavenging/exhaust phase have obvious impacts on engine performance, while the scavenging port area shows little impact on engine performance. An optimization calculation with genetic algorithm was made by determining the optimal values of six parameters such as compression ratio, ignition time, scavenging port area, exhaust port area, scavenging phase and exhaust phase. After optimization, the power(P) of the engine was increased by 7.6 % and the thermal efficiency(η) was enhanced by 3.2 % without knock. The results will lay a foundation for further design and research of two-stroke aviation RP-3 SI-DI engine.

Effect of multi-injection strategy on characteristics of methanol-fueled direct injection spark ignition engine

Present paper numerically investigates the effect of injection strategy and start of injection (SOI) timing on in-cylinder flow, air–fuel mixing, fuel distribution near spark plug, engine performance, and exhaust emissions for highly stratified methanol-fueled, multi-injection, direct injection spark ignition engine having high compression ratio. SOI is kept constant at −23° crank angle (CA) after top dead center (ATDC) with a spark timing (ST) of −2° crank angle (CA) ATDC. Mass of fuel is divided into pilot and main injection ports having pilot to main fuel injection mass ratio of 1:1, 1:2, and 1:3 at 0° and 2° dwell times between main and pilot injections. As the quantity of fuel in main injection increases, pressure rise rate increases, which results in higher in-cylinder pressure and higher rate of burning that gives higher apparent heat release. Due to higher peak pressure rise rate and faster burning in the case of 2° crank angle (CA) dwell time, shorter combustion duration is achieved compared to 0° crank angle (CA) dwell time. In the case of multi-injection, faster burning rate enhanced in-cylinder temperature; therefore, nitrogen oxides (NOx) emissions are higher. Pilot to main fuel mass ratio of 1:3 has resulted highest indicated thermal efficiency, lowest specific fuel consumption, lowest soot, and carbon monoxide (CO) emissions.

Experimental Investigation of Gaseous Emissions and Hydrocarbon Speciation for MF and MTHF Gasoline Blends in DISI Engine

Article Experimental Investigation of Gaseous Emissions and Hydrocarbon Speciation for MF and MTHF Gasoline Blends in DISI Engine Rafiu K. Olalere 1,2, Gengxin Zhang 1, and Hongming Xu 1,3, * 1 Department of Mechanical Engineering, School of Engineering, University of Birmingham, Edgbaston, Birmingham B15 2TT, UK 2 Department Mechanical Engineering, Lagos State University of Science and Technology, Ikorodu 02341, Nigeria 3 State Key Laboratory of Automotive Safety and Energy, Tsinghua University, Beijing 100084, China * Correspondence: h.m.xu@bham.ac.uk Received: 8 November 2023 Accepted: 25 March 2024 Published: 28 March 2024 Abstract: With the increasing shortage of fossil energy, the development of engines urgently requires alternative fuels. Gaseous emissions of a gasoline direct injection spark ignition engine fueled with blends of 2-methylfuran (MF 20% vol. and gasoline 80% vol.) and 2-methyltetrahydrofuran (MTHF 20% vol. and gasoline 80% vol.) were experimentally investigated using Gasmeth FTIR. Experiments were conducted at air-fuel ratio (λ = 1) and at engine speed of 1500 rpm using the fuels optimised spark timing. Effects of fuel injection sweeps (180–280 °CA BTDC) on the emission characteristics of blends were investigated at the intermediate load of 5.5 bar IMEP. Hydrocarbon emission (HC) for gasoline is about 41% and 16% higher compared to MF20 and MTHF20 respectively. Carbon monoxide emission for the fuels increases as the injection timing is retarded but the Nitrogen oxide (NOx) emissions was observed to reduce with the retarded injection timing. Both MF20 and MTHF20 recorded high NOx emissions compared to gasoline. The results indicated ethylene (25–26%) as the major component of the HC speciation in the fuels investigated. The unburnt furan samples for blend fuels were determined to be less than 3% of HC emissions, which could be considered a safe level for exposure.

Effects of injection timing on mixture formation, combustion, and emission characteristics in a n-butanol direct injection spark ignition engine

The impact of injection timings on the in-cylinder flow field intensity, mixture formation process, combustion, and emission characteristics are analyzed. The range of injection timing is set between −320°CA and −260°CA. The research results indicate: Delaying the injection timing causes the spray plumes increasingly align with the tumble direction, consequently enhancing the in-cylinder tumble intensity and the turbulence near the spark timing. The mixture homogeneity is influenced by both the formation time and the in-cylinder flow field intensity. Moreover, combustion performance is linked to the homogeneity of the mixture and turbulence intensity near the spark timing. Despite the fact that postponed injection may augment both turbulence intensity and the equivalent ratio around the spark plug at the moment of spark, achieving higher explosion pressure, but the higher viscosity of n-butanol impedes droplet break-up, and its low volatility decelerates the evaporation rate, leading to poorer mixture homogeneity, reduced BMEP, and increased CO and soot emissions. However, at −300°CA start of injection, the extended mixing time optimizes the fuel-air mixture homogeneity, thus improving combustion quality and reducing CO, soot, and HC emissions, albeit leading to increased NOx emissions.

In-cylinder spray evolution in a motored central-injection gasoline engine: Imaging and simulating the effects of flash-boiling and intake crossflow

Accurate predictions of fuel spray behavior and mixture formation in simulations of direct-injection spark-ignition (DISI) engines are fundamental to ensure proper description of all subsequent processes including ignition, combustion, and emissions. In this work, the spray evolution in a single-cylinder optical DISI engine was studied experimentally and numerically with the goal of enabling predictive computational fluid dynamics (CFD) modeling of in-cylinder sprays. The authors explored a wide range of operating conditions characterized by several fuel injection temperatures and engine speeds, using a well-characterized nine-component gasoline surrogate known as PACE-20. The effect of flash boiling and intake crossflow on the spray is discussed, with a focus on evaluating the ability of the spray models to capture highly transient spray behavior. In the experiments, the fuel temperature was varied between 20°C and 80°C, allowing for non-flash- to flash-boiling transition to emerge with enhanced flashing intensity at the highest temperatures. Spray collapse resulted in vapor-rich regions, owing to the locally lower inertia of the fluid. Varying the engine speed from 650 to 1950 rpm promoted increasingly more turbulent in-cylinder crossflow which interacted with the spray during the injection event and resulted in enhanced spray dispersion. The CFD model was able to capture the spray morphology transition at different fuel temperatures and engine speeds adequately. It is shown that the spray breakup model could capture the transitional spray behavior induced by flash boiling atomization and intake flow via proper initialization of the spray cone angle and calibration of the spray models’ constants.

Effects of exhaust gas recirculation on nitrogen oxides, brake torque and efficiency in a hydrogen direct injection spark ignition engine

This study investigated the effects of exhaust gas recirculation (EGR) on emission and efficiency in a hydrogen direct injection spark ignition engine. EGR was supplied as the low-pressure (LP)-EGR system by controlling EGR valve from zero to 18.7% in terms of mass fraction. The result showed that EGR effect on nitrogen oxides (NOx) reduction became enlarged as higher engine speed due to increasing residual gas fraction. Also, under the same excessive air ratio (λ:2.2), EGR addition made NOx reduction from 89.9 to 98.7 % as varying engine speed. As NOx limit was low, the maximum brake torque was also reduced. However, by using appropriate EGR, NOx margin could be converted to increasing brake torque under the same NOx concentration level from 1.9% to 18.2% as varying engine speeds. From this result, to achieve the maximum output when reaching the turbocharger’s limit in a hydrogen engine and effectively reduce nitrogen oxide emissions, it is not only dependent on lean combustion but also effective to incorporate approximately 20% EGR into the operating strategy.

Effect of wall-impingement distance on fuel adhesion characteristics of split injection spray under cross-flow condition

In direct-injection spark ignition (DISI) engines, high-pressure fuel injectors introduce fuel into the cylinder, causing the spray to come into contact with and adhere to the cylinder wall; this is known as fuel adhesion. Over time, fuel adhesion contributes to carbon deposition on the cylinder wall, which affects its thermal conductivity and consequently diminishes engine combustion efficiency. This study investigates the influence of different impingement distances and cross-flow velocities on fuel adhesion under the triple injection strategy. The fuel adhesion propagation and side-view spray are measured using refractive index matching (RIM) and Mie scattering, respectively. The findings demonstrate that high cross-flow velocity promotes the fuel adhesion shape to be elongated strips. In the early stage, the growth rate of the fuel adhesion area increases with an increase in cross-flow velocity. In the later stage, the decrease rate in the fuel adhesion area initially increases with an increase in the cross-flow velocity; however, when the critical velocity threshold (20 m/s) is exceeded, the decrease rate in the fuel adhesion area tends to stabilize. The average fuel adhesion thickness then accordingly decreases with the increase in the cross-flow velocity and impingement distance in the later stage. In addition, the cross-flow promotes the volatilization of spray and fuel adhesion, thereby decreasing the fuel adhesion mass over time. In the context of carbon neutrality, this study underscores the importance of optimizing fuel injection conditions to reduce emissions and fuel consumption.

Influence of operating parameters on hydrogen DISI engine at injection pressure-drop by experimental investigation and Taguchi method

Hydrogen, as a low-density, zero-carbon energy source, often faces injection pressure drop when used as an alternative fuel for multi-parameter regulation in direct injection spark ignition (DISI) engines. In this paper, the effects of operating parameters including torque, excess air coefficient (λ), ignition timing, and injection timing on combustion, emissions, and energy distribution of a hydrogen DISI engine were first investigated at injection pressures of 100 bar and 30 bar, respectively, followed by Taguchi methodology and analysis of variance (ANOVA) to determine the optimal parameter combinations and their contribution to typical indicators of engine performance. The results showed that injection pressure-drop deteriorated the coefficient of variation (COVIMEP), nitrogen oxides (NOx) emissions, and brake specific fuel consumption (BSFC) in the set of cases. And the deteriorating BSFC is mainly due to the increase in heat loss power (PHL) or the exhaust power (PEx). Taguchi method and ANOVA showed that injection pressure drop changed COVIMEP and BSFC regarding optimal ignition timing selection and PEx regarding optimal injection timing selection and it also increased the torque contribution to COVIMEP by 26.54 %. PHL and PEx should be simultaneously considered because their choice of optimal operating parameters is a “Trade-off” relationship in most cases.

Study on the effect of injection strategy on the combustion and emission characteristics of direct injection spark ignition bio-butanol engine

Owing to its physicochemical similarities with gasoline and renewable nature, n-butanol (bio-butanol) has garnered significant researcher interest. However, the lower atomization and volatility of n-butanol pose challenges when implemented in direct-injection spark-ignition (DISI) engines, leading to inhomogeneous air-fuel mixtures which subsequently results in a deterioration of combustion performance and an uptick in pollutant emissions. This study uses numerical simulations to examine the effects of injection pressure and timing on mixture formation, combustion, and emission characteristics in n-butanol DISI engines. The results indicate that for n-butanol, characterized by its reduced volatility and atomization capabilities, enhancing injection pressure from 10 MPa to 20 MPa effectively improves combustion and emission performance. However, the benefits taper off with subsequent increases in pressure. At injection pressure of 20 MPa, optimizing injection timing offers better combustion and emission results than merely increasing injection pressure. An early injection, represented by −300°CA start of injection, provides extended evaporation and mixture diffusion, significantly improving mixture quality and resulting in better combustion and emission outcomes. At −260°CA start of injection, while peak in-cylinder pressures can be achieved more favorably, the resultant inhomogeneous in mixture distribution results in increased emissions of CO, soot, and HC.

Impacts of Injection Parameters on the Mixture Formation and Performance of Two-Stroke Spark-Ignition Direct-Injection Aviation Kerosene Engine

Abstract Two-stroke spark-ignition engines play a significant role in the field of power sources of small and medium unmanned aerial vehicles. There is a certain transition from burning gasoline to aviation kerosene (or heavy oil) and from carburetor or inlet injection system to direct-injection fuel system. However, the performance of two-stroke spark-ignition direct-injection engines fueled with aviation kerosene was not very ideal under heavy loads. Generally, the mixture formation is very important for engine combustion and performance, while injection parameters have great effects on mixture formation. Thus, various injection parameters of a two-stroke direct-injection kerosene engine were examined here. The results showed too early or too late injection timing (tinj) would deteriorate the mixture formation, resulting in lower brake power and brake thermal efficiency. Here the most suitable tinj was 150 deg CA BTDC. Too high or too low injection pressure (pinj) caused fuel short circuit loss and poor mixture quality, so the optimum pinj was 10 MPa. Too large injector installation angle (β) easily results in fuel spray impingement, and too small β causes fuel short circuit loss. Therefore, the best β was concluded to be 30 deg in this paper.

Selection of a Particulate Filter for a Gasoline-Powered Vehicle Engine in Static and Dynamic Conditions

Current challenges in terms of exhaust emission limits are related to the reduction of the particle numbers in spark ignition direct injection engines. The article concerns the analysis of the thermodynamic parameters of engine operation, allowing the selection of the particulate filter configuration and its technical parameters. The designed system consisting of an internal combustion engine and an exhaust system with an exhaust gas treatment system should be sufficient to meet ecological requirements in the form of reducing particulate matter emissions. The analysis of particulate matter emissions for the system without a filter and with a filter installed in the engine exhaust system was carried out for the mass, number and dimensional distribution of particulate matter. The result was an assessment of filtration efficiency for the entire spectrum of particulate diameters in the identified engine operating ranges. As a result, it was found that the particulate filter used in the engine exhaust system effectively reduces the particle number due to the greater filtration efficiency of large particles. The summary of the work related to the analysis of the ecological parameters of a spark ignition engine with direct fuel injection was a simulation of road tests of a vehicle with the proposed modified vehicle exhaust system equipped with a particulate filter. For this configuration, the analysis of particulate number emissions in the parameterized engine operating areas showed that it is possible to meet the particulate number emission limits, and the obtained road emission results are fully acceptable in terms of the obtained absolute values.

Study of single and split injection strategies on combustion and emissions of hydrogen DISI engine

Hydrogen energy shows excellent potential as an alternative fuel for internal combustion engines (ICE) in terms of cleanliness and efficiency. However, the specificity of hydrogen density and diffusion rate leads to further optimization of the working process of the hydrogen direct injection spark ignition (DISI) engines. In this study, the effects of single injection and split injection strategies on the combustion and emissions of a hydrogen DISI engine were investigated at medium/low load. The specific results showed that premature hydrogen injection could trigger pre-ignition events, and it was appropriate to set the earliest hydrogen injection timing to 180° CA BTDC after the intake valve closing. For the single injection strategy, the brake thermal efficiency (BTE) increased first and then decreased with the delay of the start of injection (SOI). When SOI = 100° CA BTDC, the optimal BTE (36.1 %) could be obtained, and nitrogen oxide (NOx) emissions could still be limited to less than 0.1 g/(kW·h). For the split injection strategy, Delaying the secondary end of injection (SEOI) beyond 30° CA BTDC rapidly worsened NOx emissions to over 1.5 g/(kW·h). Delaying SEOI achieved higher efficiency but slightly worse the coefficient of variation COVIMEP than the single injection strategy. In addition, increasing the secondary injection mass fraction (SIMF) to 30 % could achieve an 18 % higher peak heat release rate than a single injection and shorter combustion duration. However, over 20 % SIMF resulted in an increase of NOx emissions to over 4 g/(kW·h). The energy distribution indicated that adjusting the injection strategy to increase BTE was mainly achieved by reducing power of heat loss (PHL).

Comprehensive analysis on the effect of lube oil on particle emissions through gas exhaust measurement and chemical characterization of condensed exhaust from a DI SI engine fueled with hydrogen. Part 2: Effect of operating conditions

The need to cope with carbon dioxide abatement has prompted the development of innovative technologies for sustainable mobility. Meanwhile, these technologies consolidate, an important role will be played by internal combustion engines fed with non-fossil fuels such as hydrogen. Theoretically, the combustion of hydrogen should not produce carbon-based emissions. Nevertheless, particles can be found in the exhaust of hydrogen-fueled engines because of the lubricating oil. In this study, a thorough examination of the impact of the engine lubricant on the mechanisms leading to the formation of the particles and the high levels of hazardous pollutants was performed in this study. Experiments were carried out on a direct injection spark ignition engine fueled with hydrogen. The analysis was conducted at 2000 and 3000 rpm both low and full load. Number and size particle distribution were determined by means of on-line measurement on the diluted exhaust. Off-line chemical characterization through analytic techniques was realized on the condensed exhaust and on the particles collected on a filter. Experimental results pointed out that the extent of the particle size varies according to the engine speed and load, evidencing the different role of the oil ascribable to the environmental conditions. It was found that aromatic molecules and nanoparticles are present in the exhausts at all the investigated operating conditions, whereas soot aggregates are formed only at high engine speed.

Evaluation of engine performance and emissions in an optical DISI engine with various spark plug designs and gaps

This study aims to assess how spark-ignition engine performance and emissions are affected by both the design of the spark plug and the size of its electrode gap. Two distinct spark plug configurations (BUGAETS and NGK) with varying spark gap sizes of 1, 1.2, and 1.4 mm were used. Experiments were performed in an optical constant volume chamber as well as an optical direct injection spark ignition engine. At various equivalence ratios, the effects of both spark plugs on flame propagation, in-cylinder pressure, mass fraction burnt, and emissions for gasoline fuel were explored. For all spark plug gaps and equivalence ratios tested, the constant volume experimental results showed that the flame propagation area with the BUGAETS spark plug is faster than that with the NGK spark plug. According to the engine results, BUGAETS can produce an IMEP up to 2.4 % higher with a significant reduction in both cyclic variability and fuel consumption when compared to NGK. BUGAETS electrode consistently produces higher in-cylinder pressure and heat release rate than the NGK spark plug. When compared to NGK, the BUGAETS spark plug emits more NOx while emitting less hydrocarbon and particulate emissions. In terms of NGK electrode gaps, a comparison revealed that a gap size of 1.4 mm resulted in the most optimal engine performance and the lowest exhaust emissions. On the other hand, when it came to BUGAETS' spark plug, a gap size of 1.2 mm delivered the best engine performance and emissions out of all the tested gap sizes for the BUGAETS electrode.

Investigating the relationship between butanol molecular structure and combustion performance in an optical SIDI engine

Butanol has a high potential as a renewable substitution for gasoline in spark-ignition direct-injection (SIDI) engines. Different butanol isomers showed various flame characteristics that are strongly related to their molecular structure. However, there has been limited research on the implications of the butanol isomer's molecular structure on SIDI engine combustion, performance, and emissions. This study investigated butanol isomers as gasoline substitutes in SIDI range extender engines, with a focus on the effects of isomer molecular structures. This work employed a single-cylinder optical SIDI research engine and a high-speed camera to examine engine performance, flame kernel stability, flame propagation, and particle number (PN) emissions. The investigated blends comprised 70% toluene reference fuel (TRF) and 30% butanol isomers (1-butanol (n), 2-butanol (s), isobutanol (i), and tertbutanol (t)). Experimental tests are carried out at a 1000 rpm engine speed and a load of 5.7 bar IMEP, while the fuel condition is kept stoichiometric.The results elucidate that adding 1-butanol makes the flame kernel more stable and reduces COVimep compared to pure TRF. On the other hand, TRF-i, TRF-s, and TRF-t decrease flame initiation stability and increase COVimep. 1-butanol exhibited the highest apparent flame speed, IMEP, and peak in-cylinder pressure, followed by TRF, TRF-i, TRF-s, and TRF-t. Over half of the TRF-t cycles exhibited either no or a delayed flame kernel. Flame circularity improved with 1-butanol and diminished with the other blends. Diffusion flame intensity and PN emissions were higher for TRF, TRF-n, and TRF-t compared to TRF-s and TRF-i. In conclusion, linear chain butanol isomers with more internal C-H bonds and terminal C-OH bonds provide a more stable flame kernel and superior engine performance than branched isomers featuring internal C-OH bonds. The results from this study can be useful for expanding the practical applications of butanol isomers as a renewable fuel replacement in SIDI engines.

Improving the lean burn performance of a high compression ratio methanol engine by multiple-injection

Methanol is a promising fuel for achieving carbon neutrality in sectors requiring internal combustion engines. The multiple-injection approach is effective in reducing cycle-to-cycle variations and improving the performance of methanol engines under lean burn conditions. This study proposes a concept for transforming diesel engines into methanol engines with flexible injection and lean burning capabilities. This study fills the research gap in the study of lean methanol combustion in swirl combustion chambers. The effects of 22 different multiple-injection strategies on combustion characteristics, emission performance, and combustion stability are experimentally assessed in a direct-injection spark ignition engine with an excess air ratio (λ) of 1.35. Each multiple-injection strategy is comprehensively evaluated using a merit function and compared with the baseline case that uses single injection. The results show that the double- and triple-injection strategies substantially shorten the durations of combustion and flame development. Therefore, a higher effective expansion ratio is obtained. Meanwhile, the cycle-to-cycle variation in the IMEP decreases from 4.2% of the baseline to 1.49% at T8. CO and HC emissions deteriorate; however, NOx and CO2 emissions under triple injection are lower than those under the baseline. The T7 case with triple injection achieves the highest thermal efficiency, which is 6.8% higher than that for the baseline case. Overall, triple injection achieves higher merit function values, which indicates a better capability to improve lean-burn performance than double injection.

직접분사식 암모니아 엔진에서 연료 분사 시기 및 점화 에너지 변경에 따른 연소 및 배기, 효율 특성 비교

직접분사식 암모니아 엔진에서 연료 분사 시기 및 점화 에너지 변경에 따른 연소 및 배기, 효율 특성 비교

Impact of fuel surrogate formulation on the prediction of knock statistics in a single cylinder GDI engine

The statistical tendency of an optically accessible single-cylinder direct-injection spark-ignition engine to undergo borderline/medium knocking combustion is investigated using 3D-CFD. Focus is made on the role of fuel surrogate formulation for the characterization of anti-knock quality and flame speed of the actual fuel. An in-house methodology is used to design surrogates able to emulate laminar flame speed and autoignition delay times of the injected fuel. Two different surrogates, characterized by increasing level of complexity, are compared. The most complex one (six components) improves the representation of the real fuel, highlighting the crucial role of accurate fuel kinetics to predict flame propagation and unburnt mixture reactivity. A devoted chemical mechanism including the oxidation pathways for all the species in the surrogate is also purposely developed for the current analysis. Knock is investigated using a proprietary statistical knock model (GruMo-UNIMORE Statistical Knock Model, GK-PDF), which can infer the probability of knocking events within a RANS formalism. Predicted statistical distributions are compared to measured counterparts. The proposed numerical/experimental comparison demonstrates the possibility to efficiently integrate complex-chemistry driven information in 3D-CFD combustion simulations without online solving chemical reactions: a combination of laminar flame speed correlations, ignition delay look-up tables, and a statistics-based knock model is adopted to estimate the percentage of knocking cycles in a GDI engine while limiting the computational cost of the simulations.

A 3D computational study of the formation, growth and oxidation of soot particles in an optically accessible direct-injection spark-ignition engine using quadrature-based methods of moments

The accurate prediction and assessment of soot emissions in internal combustion engines play a central role in the development of modern, sustainable powertrains. The modeling of soot requires high-fidelity models capturing both the gaseous soot precursors with suitable mechanisms and an accurate description of all physico-chemical processes related to the solid particulate. Semi-empirical models based on acetylene are frequently used but are limited in covering complex fuel compositions.For this reason, we present the coupling of a detailed quadrature-based method of moments (QMOM) soot model to a state-of-the-art flow solver for the simulation of gasoline engines. A close coupling with the underlying gas phase and the additional consideration of polycyclic aromatic hydrocarbons (PAHs) as precursors allow an accurate description of the entire cause-and-effect chain. The fully coupled model is then applied in a 3D-CFD simulation of an optically accessible research engine to investigate the formation, growth and oxidation of soot particles. Experimental high-speed measurements of soot- luminescence and extinction were used for validation purposes. Together with all preceding models along the engine cycle, the newly implemented model is used to identify the root cause of the observed soot formation hotspots. Particular emphasis is placed on the effects of soot oxidation.