Single Cylinder Spark Ignition Engine Research Articles

Impacts of low-temperature heat release on unstretched laminar burning velocity in advanced flex-fuel gasoline-ethanol engines

Improving brake thermal efficiency (BTE) of flex-fuel engines can contribute to decarbonizing conventional and hybridized vehicles running on spark-ignited (SI) engines. High compression ratio (CR) and burning velocity under exhaust gas recirculation (EGR) conditions can improve the engine BTE. Ethanol fuel, which has been attracting increasing attention recently, can improve brake thermal efficiency due to its high-octane number and fast laminar burning velocity (LBV). With higher CRs, low-temperature heat release (LTHR) occurs in the unburned mixture, which affects the compositions, oxidation, and in-cylinder temperature. Such thermodynamic changes on unstretched LBV have not been thoroughly investigated, especially in production-intent next-generation flex-fuel engines. This study aims to clarify the LTHR impacts on LBV under EGR conditions using ethanol-blended gasoline surrogate fuels. The testbed used a single-cylinder SI engine fueled by E0 (gasoline surrogate), E20 (20 % ethanol + 80 % E0 by volume), E40, E60, E85, and E100. Detailed chemical reaction calculations were conducted using the boundary conditions obtained from production-intent, strong-tumble flow, and flex-fuel engine experiments. This work predicted LTHR in an unburned mixture using a zero-dimensional detailed chemical reaction calculation. LBV is predicted by a 1D kinetic laminar flame code. As a result, LTHR proceeds before the main combustion. The results show that the temperature increase associated with LTHR increases the burning velocity, while the partial oxidants decrease the burning velocity. Moreover, this work examined higher CRs using detailed chemical reaction calculations, and the results show that fuels with higher ethanol blending ratios can increase LBV in the late combustion phase.

Evaluation of the Possible Effects of Varying the Volumetric Ratio of Lpg on the Spark Ignition Engine's Performance, Emissions, and Combustion

This study investigated the performance, emission reactions, and combustion of liquefied petroleum gas (LPG) at various volumetric ratios with gasoline. The experiments were carried out on a single cylinder spark ignition (SI) engine at different engine loads (500 to 3000 W). In general, the use of LPG has a negative effect on performance and combustion, while making a positive contribution to emissions. The brake thermal efficiency (BTE) and brake specific fuel consumption (BSFC) values closest to 100% gasoline were obtained with 25% LPG and were lower by 0.36% and 4.55%, respectively. Conversely, using LPG resulted in lower emissions of carbon dioxide (CO2), hydrocarbons (HC), and carbon monoxide (CO). The lowest emissions were obtained with the use of 100% LPG as 0.5%, 65 ppm and 9.5%, respectively. Compared to 100% gasoline, 20.63%, 27.78% and 5.19% improvements were achieved. Finally, the cylinder gas pressure value was negatively affected using LPG. Compared to 100% gasoline, the gas pressure value obtained with 75% LPG content fuel was 7.81% lower. It has been concluded that LPG is an environmentally friendly alternative fuel in terms of emissions, and considering the decrease in performance values, 25% LPG can be used successfully in SI engines instead of 100% LPG.

Numerical Analysis of the Effect of Ethanol-Gasoline Blends on a Single-Cylinder Spark-Ignition Engine Performance and Emissions

— With the rapid increase in the number of vehicles fueled by gasoline plying on the roads, there has been a rising need in the search for alternative fuels, which are more environmental friendly in order to reduce the amount of vehicular exhaust emissions. This can be achieved by using blended mixtures of gasoline with alcoholic fuels among which, ethanol is found to be most suitable due to its easy availability, low costs, safety and low impact on the engine performance. This study aims to investigate the performance of a single-cylinder, four-stroke spark-ignition engine using different ethanol-gasoline blends, namely E0, E10, E20 and E30. The engine's torque, brake power, brake thermal efficiency, brake-specific fuel consumption, and exhaust emissions were analysed using numerical simulation. Results revealed that raising the proportion of ethanol in the fuel mixture resulted in reduced brake power and torque upto 16% as a result of decrease in calorific value of the mixture. The engine's brake thermal efficiency decreased by upto 3% while the brake-specific fuel consumption increased upto 12% with increase in ethanol concentration. Exhaust emissions, including NOx and HC, were found to be influenced by engine speed, with NOx emissions increasing and HC emissions decreasing as speed increased. The study also revealed that increasing ethanol concentration in the fuel resulted in reduced engine exhaust emissions by upto 47% and 10% for NOX and HC emissions respectively. The study concluded that among all the blends used, optimum performance was obtained for E30 blend with reduction in exhaust emissions but at the expense of slight reduction in engine performance.

Effect of Fuel Injection Parameters on Engine Performance in A Conventional Single Cylinder Spark Ignition Engine

In this study, a 1D model was created using the Ricardo-Wave program for a single-cylinder, spark ignition, four-stroke, direct injection engine with a stroke volume of 398 cc. Air-fuel ratio (AFR), mixture temperature (MT), and start of injection (SOI) were used as fuel injection parameters. Using these parameters, 343 different cases were created. Brake power, thermal efficiency, and fuel consumption were used as engine performance parameters. By holding one injection parameter constant, a contour plot was created to examine the effect of the other two parameters on the engine performance parameter. According to the results, the effect of MT and SOI on brake power is 1%, the effect of AFR on brake power is 9.6%, the effect of MT and SOI on thermal efficiency is 1%, and the effect of AFR on thermal efficiency is 12.8%. The effect of MT and SOI on fuel consumption is 0.04%, the effect of AFR on fuel consumption is 22.9%, and the effect of AFR on brake specific fuel consumption is 22.9%. These results indicate that the most significant effect is provided by AFR, while MT and SOI also have a slight impact on engine performance.

Effects of dual injection operations on combustion performances and particulate matter emissions in a spark ignition engine fuelled with second-generation biogasoline

The automotive industry must mitigate climate change by reducing vehicle carbon emissions and promoting sustainable transportation through technical solutions and innovations. Biofuels are seen as a solution to reduce CO2 emissions, but they may affect fuel performance and emissions. Second-generation biogasoline mixed with ethanol has proven that it can be introduced as a drop-in fuel with the same performance and tailpipe emissions at the same level as fossil fuels. However, particulate matter (PM) emissions are significantly higher than fossil fuels. This study aims to experimentally investigate the effect of port and direct fuel injections on the PM emissions in a boosted spark ignition (SI) engine fuelled by Euro 6 standard biofuel with a 99 octane number blended with 20% ethanol compared to a fossil fuel baseline. The single-cylinder SI engine was equipped with two fuel injectors, a direct injector and a port fuel injector, and operated with externally boosted air. The split injection ratio was adjusted from 100% direct injection (DI) to 100% port fuel injection (PFI) to investigate the combustion characteristics and particulate emissions (PM) at different engine loads and speeds. The results indicate that by changing 100% DI to 80% PFI, PM emissions numbers between particle sizes of 23 and 1000 nm were dropped by 96.56% at a low load operation of 4.6 bar IMEP for the 99 RON E20 biogasoline and by 84% for the 95 RON E10 fossil fuel while maintaining the same indicated thermal efficiency and a similar level of other emissions. However, at a higher load above 10 bar IMEP, it was found that full DI operation reduced particulate numbers (PN) by 64% and 38% for 99 RON E20 biogasoline and 95 RON E10 fossil fuel at 20 bar IMEP, respectively, and enabled more stable operation at 3000 rpm with higher load operation regions.

Experimental investigation for enhancing the performance of hydrogen direct injection compared to gasoline in spark ignition engine through valve timings and overlap optimization

Recent advances in hydrogen internal combustion technologies highlight its potential for high efficiency and zero carbon emissions, offering a promising alternative to fossil fuels. This paper investigates the effects of valve timings and overlaps on engine performance, combustion characteristics, and emissions in a boosted direct-injection single-cylinder spark ignition engine using both gasoline and hydrogen. Optimized direct hydrogen injection effectively eliminates backfires and hydrogen slip during positive cam overlaps, significantly reducing the pumping mean effective pressure. The study’s primary finding demonstrates the potential of hydrogen to operate as a direct substitute for a gasoline engine without necessitating changes to the cam profiles at the high load operation. Furthermore, the study demonstrates that hydrogen leads to much higher thermal efficiencies across a wider range of engine loads when operated at a lean, air-to-fuel ratio of 2.75. The engine operating with such a lean-burn hydrogen mixture keeps the engine-out NOx emission at ultra-low levels. Compared to gasoline, hydrogen exhibits greater stability and a reduced reliance on camshaft timing during engine operation.

Effects of exhaust gas recirculation and ethanol-gasoline blends on combustion and emission characteristics of spark ignition engine

The combined influences of exhaust gas recirculation (EGR) and ethanol-gasoline blends on the combustion process and emissions of a single-cylinder spark ignition engine were numerically examined. Four different EGR values were employed, i.e. 0%, 2.5%, 5%, and 10%, to reveal the effect of EGR on engine performance. The engine was operated at a load of 100% and a speed of 3000 rpm. The peak values of in-cylinder pressure and temperature gradually decreased as increasing the EGR ratios. These peaks move towards the TDC as increasing the ethanol fraction in blends due to high oxygen in the mixture and burning flame speed in the cylinder. Ethanol fractions ranging from 5% to 15% can effectively improve the negative effects of EGR ratios. When increasing the ethanol fraction, the CO2 rapidly increased and concentrated around the TDC. The NOx emissions are significantly increased with increasing ethanol fraction. In the case of pure gasoline, the NOx emissions are substantially suppressed and exhibit a remarkably low value as increasing the EGR ratios. The best combination for diluting NOx emissions to a very low level is ethanol fraction ranging from E5 to E10, while the EGR rates range from 5% to 10%.

Elucidating Optimal Exhaust Manifold Divergence and Temperature Distribution in Improving Low-End Engine Speed Performance

The exhaust manifold plays a crucial role in optimizing the performance of Spark-Ignition (SI) engines by effectively expelling combustion products. This study focuses on the optimization of the exhaust manifold design and temperature distribution in a 115-cc single-cylinder SI engine. The objective is to investigate the association between the design characteristics of the exhaust manifold, particularly its divergence, and the engine's performance in terms of brake power. Using computer-aided design (CAD), a three-dimensional model of the exhaust manifold with reduced diameter was developed. The optimized design aimed to enhance the engine's overall performance by achieving lower temperatures, particularly at low-end speeds. Subsequently, a 1D engine study was conducted to evaluate the performance of the engine with the optimized exhaust manifold design and validate the improved temperature distribution. The results demonstrate that the optimized exhaust manifold design leads to higher brake power while maintaining lower temperatures, especially at low-end speeds. This highlights the importance of exhaust manifold optimization and temperature distribution in maximizing the efficiency of the selected SI engine. To further enhance the engine's performance, future research should focus on identifying the most appropriate value for the exhaust manifold's divergence. This will contribute to the ongoing development of more efficient and high-performance SI engines. The findings of this study provide valuable insights into the optimization of exhaust manifold design and temperature distribution for improved engine performance in the context of the tested engine.

Experimental Investigation of the Effects of Gasoline-Methyl Ethyl Ketone Fuel Blends on Engine Performance and Exhaust Emissions

Gasoline engines have been widely used because of operating with stoichiometric ratio and lower exhaust emissions compared to compression ignition engines. However, thermal efficiency is less than diesel engines due to lower compression ratio. In the present study, the influences of methyl ethyl addition were researched on engine performance, CO, CO2 and HC emissions in a single cylinder spark ignition engine. For this purpose, the test engine was run at wide-open throttle, engine speeds of 2400, 2800, 3200, 3600, 4000 rpm and the variations of engine torque, effective power, specific fuel consumption (SFC), thermal efficiency, CO, CO2 and HC emissions were investigated. It has been observed that engine power and torque increase and SFC decreases as methyl ethyl ketone is added to gasoline. It was observed that the thermal efficiency at 2800 rpm increased by 6.47%, 13.81% and 19.51%, respectively, with MEK20, MEK30 and MEK40 test fuels compared to gasoline. As the methyl ethyl ketone ratio in the blended fuels increased, HC and CO emissions reduced compared to gasoline. As a result, it was seen that methyl ethyl ketone additive can be utilized easily in a spark ignition engine without making any modification.

A CFD ignition model to predict average-cycle combustion in SI engines with extreme EGR levels

Control of the combustion process in Spark-Ignition (SI) engines operated with extreme dilution from exhaust gas re-circulation (EGR) represents one of the major limitations in the industrial design of such technology. Numerical approaches able to describe in detail the formation of the early flame kernel become essential to face such an ambitious task. This work presents a RANS-based multi-dimensional model of the combustion process, including an advanced description of the ignition stage to consider its stochastic re-ignitions within the average cycle prediction. The spark-channel is described as a column of Lagrangian parcels that represent early flame kernels, whose growth is controlled by the laminar flame speed and energy input from the electrical circuit. The spatial evolution of each parcel is computed according to a scaled value of the average-flow speed, to mimic the smooth but short elongation of the mean-cycle channel produced by stochastic restrikes affecting the single-cycle arcs. To clarify this phenomenon and assess the proposed CFD method, a series of experiments are performed in a single cylinder SI engine with optical access, running at a low-load cruise-speed operating condition. Increasing EGR levels are tested up to the onset of misfire, with measurements of the secondary-circuit features and of the flame evolution through high-speed imaging. Satisfactory results are achieved in terms of numerical-experimental comparison of the cycle-averaged in-cylinder pressure, discharge parameters, and spatial flame distribution, demonstrating the reliability of the proposed numerical approach.

Experimental evaluation of spark behavior under diluted conditions in an optically accessible engine

An optically accessible single-cylinder spark-ignition engine operated under homogeneous, part-load conditions is experimentally investigated using optical and spark diagnostics to evaluate the relationship between the spark, flow, and flame with increasing dilution using several levels of exhaust gas recirculation (EGR). Voltage and current measurements of the secondary spark circuit are compared with simultaneous high-speed spark plasma imaging, particle image velocimetry measurements of the flow field, and burned gas images. Specifically, characteristic restrike cycles and normal cycles are examined under the 0 % EGR and 12.9 % EGR conditions to reveal a relationship between the magnitude and direction of the velocity near the spark plug and the spark’s behavior coupled with that of the subsequent flame propagation. Through the use of conditional statistics and correlation analysis of data sets of all non-restrike and all restrike cycles, the horizontal velocity across the spark gap was identified as a critical quantity in facilitating more stable and faster combustion under diluted mixture conditions.

Cyclic Variability Analysis of an Engine Fueled With Gasoline/Natural Gas Using Return Maps and Symbol Sequences

Abstract The present work investigates the cyclic variability of a single-cylinder spark ignition engine fueled with gasoline/natural gas. Return maps and symbol sequence analysis are used to analyze the cycle dynamics at different engine loads and mixture strength. Cycle dynamics is found to be stochastic in nature at high engine loads with low cyclic variability. The frequency of deterministic patterns with close coupling between consecutive cycles is found to be high at low loads with high cyclic variability. In comparison to gasoline, the deterministic effects are found to be more predominant for natural gas fueled engine. The paper also demonstrates that the identification of deterministic patterns and omitting them through an efficient engine management system brings the engine to a stable state from unstable state. The research provides an estimate of how much better engine performance could be achieved with the knowledge of determinism in the system and the subsequent application of this knowledge for efficient engine control.

AI-driven optimization of ethanol-powered internal combustion engines in alignment with multiple SDGs: A sustainable energy transition

With the escalating requirement for global sustainable energy solutions and the complexities linked with the complete transition to new technologies, internal combustion engines (ICEs) powered with biofuels like ethanol are gaining significance over time. However, problems linked to the performance and emissions of such ICEs necessitate accurate prediction and optimization. The study employed the integration of artificial neural networks (ANN) and multi-level historical design of response surface methodology (RSM) to address these challenges in alignment with the Sustainable Development Goals (SDGs). A single-cylinder spark ignition (SI) engine powered with ethanol-gasoline blends at different loads and speeds was used to gather data. Among six initially trained ANN models, the most efficient model with a regression coefficient (R2) of 0.9952 (training), 0.98579 (validation), 0.98847 (testing), and 0.99307 (overall) was employed to predict outputs such as brake power, brake specific fuel consumption (BSFC), brake thermal energy (BTE), concentration of carbon dioxide (CO2), carbon monoxide (CO), hydrocarbons (HC), and oxides of nitrogen NOx. Predicted outputs were optimized by incorporating RSM. On implementing optimized conditions, it was observed that BP and BTE increased by 19.9%, and 29.8%, respectively. Additionally, CO, and HC emissions experienced substantial reductions of 28.1%, and 40.6%, respectively. This research can help engine producers and researchers make refined decisions and achieve improved performance and emissions. The study directly supports SDG 7, SDG 9, SDG 12, SDG 13, and SGD 17, which call for achieving affordable, clean energy, sustainable industrialization, responsible consumption, and production, taking action on climate change, and partnership to advance the SDGs as a whole respectively.

Grid Integration of Livestock Biogas Using Self-Excited Induction Generator and Spark-Ignition Engine

This study developed a grid-connected biogas power generation system for a rural community using a 3-phase 2.2 kW squirrel-cage induction machine as the self-excited induction generator. The generator was driven by a 196 cc single-cylinder spark-ignition engine fueled by biogas. We developed a back-to-back converter that consists of a 3-phase PWM rectifier as the generator-side converter and a single-phase LCL-filtered grid-connected inverter. The generator-side converter transferred the active power to the grid-side converter and supplied the reactive power control back to the generator. The notch filter-based bus voltage control on the generator side mitigated the inter-harmonics in the generator current. The injected grid current complied with the IEEE 1547 standard because of the multi-frequency unbalanced synchronous reference frame control. The proposed system was validated with biogas produced from pig manure at a pig farm in central Thailand, which found a maximum output of 1.2 kW with a thermal system efficiency of 10.7%. The proposed system was scheduled to operate at 1.2 kW for 8 h per day with a levelized cost of 0.07 US$/kWh, 42% cheaper than the retail electricity price, and a payback period of 2.76 years. The proposed system is suitable for a farm with a minimum of 34 pigs.

Hydrogen production in ammonia-fueled spark ignition engines

Anhydrous ammonia (NH3) is a promising carbon-free fuel for internal combustion engines (ICEs) that can be generated from renewable energy sources and stored at high energy density. Ammonia is typically mixed with a small fraction of hydrogen (H2), which serves as combustion promoter to achieve stable combustion over a large range of engine operation. To overcome the difficulties of storing hydrogen, ammonia can be converted to hydrogen onboard by means of a catalytic reactor fed by waste thermal energy from the engine exhaust or by partial oxidation. This work explores an alternative method of producing hydrogen by partial oxidation of fuel-rich ammonia–air mixtures to hydrogen in an engine cylinder while generating useful work. Such an approach eliminates the need for costly catalyst materials and poses the possibility of a dedicated reforming cylinder to provide hydrogen for other cylinders in a multi-cylinder engine. Experiments were conducted in a single-cylinder spark-ignition (SI) engine with parametric sweeps of intake temperature, intake pressure, equivalence ratio, and spark timing. Experimental results show that 6% exhaust gas hydrogen concentration is attainable and 40% of the unburned fuel energy can take the form of hydrogen. Rich equivalence ratios produced higher concentrations of hydrogen and elevated intake temperatures extended the rich stable-operation limit of the engine. Low order chemical modeling yields insights into hydrogen production throughout the engine cycle, revealing that initial consumption of ammonia is advanced of hydrogen production and that competing elementary reactions for the formation and destruction of hydrogen drive its net quantity in the exhaust.

Effect of passive pre-chamber orifice diameter on the methane combustion process in an optically accessible SI engine

Due to its potential to extend the lean limit or overcome knock-limited conditions on spark-ignited (SI) engines, the pre-chamber spark-ignition (PCSI) concept has gained attention as an efficient alternative to the conventional ignition architecture. Nevertheless, especially in engine-like conditions, the effect of the main geometrical parameters on combustion development is still not fully understood and might be a hindrance to the use of this technology. In this sense, the current study aims to evaluate the effect of the orifice diameter on the jet characteristics and main chamber combustion of a novel passive pre-chamber in an optically accessible single-cylinder SI engine, as well as to compare the PCSI with the typical SI ignition method. High-speed broadband chemiluminescence imaging was used to track the jet penetration and flame front propagation of three mixture compositions at various spark timings (ST). Additionally, based on the in-cylinder pressure, a heat-released analysis was performed to assess the overall combustion process. When compared with the typical SI, the pre-chamber concept presented a higher equivalent flame front velocity, which is also corroborated by the higher in-cylinder pressure rise rate and rate of heat released. For all mixtures tested, the 1.2 mm orifice diameter PC presented the shortest flame development angle (crank angle interval between ST and 10 % of mass fraction burned in the MC), followed by 1.5 and lastly 1.0 mm. When comparing different STs, the shortest flame development angle occurred at MBT condition. Despite the highest flame development angle, the PC 1.0 mm case presented the lowest main chamber combustion duration (CA10-90), which increases as the orifice diameter is increased.

Experimental Investigation of the Effect of Nitromethane Addition to Gasoline Fuel on A Single-Cylinder Spark-Ignition Engine Performance and Emissions

In this study, the effect of nitromethane addition to gasoline fuel on engine perfor-mance and emissions in a single-cylinder spark-ignition engine was experimentally inves-tigated. By adding 5% and 10% nitromethane to gasoline, experiments were carried out at full load at six different cycles. Engine load, fuel consumption, exhaust gas tempera-ture, and emissions were measured during the experiments. According to the measured experimental data, engine power, torque, specific fuel consumption, exhaust gas tem-perature, average effective pressure, thermal efficiency, CO, CO2, HC, and NOx values were compared with each other. According to these results, nitromethane's addition im-proved engine power, torque, specific fuel consumption, and thermal efficiency. It is un-derstood that the addition of nitromethane to gasoline improves combustion efficiency and increases thermal efficiency. With the addition of nitromethane, an increase in CO2 emission, which is a product of complete combustion, and a decrease in CO emission occurred. This supports the increase in combustion efficiency. HC emissions have de-creased. There has been an increase in NOx emissionsIn addition, since the addition of more than 10% nitromethane causes engine instability, it has created difficulties in using it without modification in the engine.

EXPERIMENTAL INVESTIGATION OF THE PERFORMANCE AND EMISSION CHARACTERISTICS OF METHANOL-ETHANOLGASOLINE BLENDING WITH ISO-BUTANOL ADDITIVE ON THE SPARK-IGNITION ENGINE

Nowadays, alternative fuels for internal combustion engines (IC) have gained traction due to environmental concerns and the necessity to reduce reliance on fossil fuels. Iso-butanol is an alternative fuel with low emissions that can be used in IC engines. The performance and emissions of a single-cylinder spark-ignition (SI) engine running on pure gasoline and iso-butanol additives (iB) at various engine load and blending ratios of EM10, EM10iB3, EM10iB5, and EM10iB10 were investigated experimentally in existing dual ethanol-methanol-gasoline blended fuel (EM10). The calorific value of the fuel sample containing iso-butanol additive is 6.3% higher than that of the EM10 blended fuel. As per engine performance and emissions, iso-butanol additive blended fuel had a better brake power than the EM10 blended fuel, with a mean increase of 3.1%, 1.2%, and 3.8% for the EM10iB3, EM10iB5, and EM10iB10, respectively. The EM10iB5 significantly increased brake thermal efficiency (BTE) by 5.4% higher than EM10 blended fuel. The CO and HC emissions from iso-butanol additive blends were reduced by 1.8% and 7.1%, respectively, compared to EM10 blended fuel. When combined with existing lower ratios of EM10 blended fuel, the iso-butanol additive is found to be a viable alternative fuel for SI engines.Keywords: Dual-alcohol blend, engine performance, emission characteristics, iso-butanol additive, heat of evaporation

Experimental study of gasoline engine with EGR dilution based on reactivity controlled turbulent jet ignition (RCTJI)

The exhaust gas recirculation (EGR) method can suppress knock and improve the thermal efficiency of engines, but it also deteriorates the combustion stability and engine power. Turbulent jet ignition (TJI) is a reliable ignition way for improving ignition stability and burning rate. However, the EGR in the pre-chamber will worsen the reactivity of the fuel-air mixture in the pre-chamber and subsequently lower the intensity of the TJI. To this end, the reactivity controlled turbulent jet ignition (RCTJI) based on a newly air-assisted pre-chamber turbulent jet ignition with a scavenging function has been proposed to improve the reactivity in the pre-chamber for the first time. The combustion characteristics, pressure oscillation, and combustion stability of a single-cylinder spark-ignition engine under four ignition modes of spark ignition (SI), passive TJI, active TJI, and scavenged TJI have been investigated. The results show that three TJI modes can obviously shorten the combustion duration due to the fast jet flame. Compared to the SI mode, the spark timing of TJI is not sensitive to the change in EGR rate. In particular, the scavenged TJI could effectively promote the chemical reactivity in the pre-chamber, and subsequently improves the intensity of the turbulent jet flame and shortens the ignition delay and combustion duration. As a result, using the scavenged TJI can effectively reduce cycle variation and achieve the lowest indicated specific fuel consumption (ISFC) at high EGR rates. However, with the increase in EGR rate, the SI combustion gradually becomes unstable. In contrast, the scavenged TJI can effectively extend the EGR tolerance. In addition, the present work further has confirmed the three main combustion stages of jet ignition in terms of the heat release rate.

The Influence of Flow on Cycle-to-Cycle Variations in a Spark-Ignition Engine: A Parametric Investigation of Increasing Exhaust Gas Recirculation Levels

Cyclic variability is investigated in an optically accessible single-cylinder spark-ignition research engine by introducing artificial exhaust gas in controlled amounts to the homogenous air–fuel mixture before ignition. A skip-fire scheme ensures the absence of internal exhaust gas recirculation (EGR) and allows the engine to be fired continuously for acquisition of large statistics. Four operating conditions ranging from a stable 0% EGR case up to a highly unstable extreme EGR case are analyzed to examine the increasing effects of homogeneous EGR on the cycle performance. To that end, high-speed measurements of the velocity field via particle image velocimetry and flame imaging in the tumble plane allow the determination of phenomena leading to various flame positions and sizes as well as faster and slower combustion cycles. Through extensive conditional statistical and multivariate correlation techniques, flames are found to be heavily influenced by large-scale velocity motion, especially with the presence of greater EGR which leads to lower flame speeds. The greater sensitivity of slower flames to variations in the velocity field manifests itself in an exponential increase in cyclic variability of the maximum in-cylinder pressure and causes misfire cycles where the flame is blown off or quenched at the cylinder roof. In the most extreme cycles at the highest EGR level, the state of the large-scale velocity structures at the time of ignition determines whether the flame propagates towards the center of the cylinder (and is blown off or quenched) or if the flame sustains growth by propagating within the lingering tumble vortex.