Coefficient Of Variation Of Indicated Mean Effective Pressure Research Articles

Investigating the influence of varying split injection profiles on stability of diesel engine operated under partially premixed mode with methanol

The present study explores the prospects of operational stability of dual fuel operation comprehensively, considering that; methanol and diesel are of two different kinds which exhibit different combustion processes. To this effect, investigating the stability of engine operation under such condition becomes important. In this investigation, the harshness of the operation and the non-repeatability of the combustion cycles are examined, which have been identified as the major stability indicator in many studies. Such stability indices are characterized in this study through a comprehensive set of parameters, including of maximum pressure rise rate (ROPRmax) and coefficient of variation of indicated mean effective pressure (COVIMEP); and of peak pressure (COVPP) and crank angle of 50% mass fraction burn (COVCA50). The experimental investigation is carried out under a split injection strategy by varying injection timings as well as injection mass percentages at predefined methanol injection durations. It is shown that the partially premixed mode under the split injection strategy exhibits significant potential in reducing the harshness of operation indicated by lower peak pressure rise and increasing the repeatability of the combustion cycles implied by the substantially lower scores of the considered parameters for mapping stability.

A comprehensive experimental study to analyze the cyclic variation of a hydrogen-blended ammonia engine with the Miller cycle

The effects of multiple operating parameters (including speed, valve timing, λ, manifold absolute pressure, spark timing, and hydrogen injection timing) on the coefficient of variation of indicated mean effective pressure (CoVIMEP) of a hydrogen-blended ammonia engine have not been adequately evaluated, which motivates this study. Specifically, CoVIMEP is decreased from exceeding 2.4 % to approximately 0.7 % when the speed increases from 1300 rpm to 2000 rpm. Optimizing valve timing keeps CoVIMEP below 0.8 % by improving the airflow exchange process, and the engine tends to realize lower CoVIMEP at close stoichiometric ratio conditions and low pumping loss. Furthermore, adjusting spark timing affects CoVIMEP by varying the ignition process's stability, with a combustion center of gravity around 9°CA ATDC being suggested. The hydrogen direct-injection timing influences the combustion process's instability by varying the mixture concentration gradient, and the late injection strategy allows the engine to achieve a CoVIMEP of less than 0.9 %.

Cyclic Combustion Variability of Dimethyl-Ether-Fueled Agricultural Tractor Engine

Abstract Combustion in dimethyl-ether (DME)-fueled engines needs to be assessed carefully for its widespread acceptability from a drivability viewpoint. Since the test engine used in an off-highway segment, it was tested in a steady-state cycle for engine performance, combustion, emissions, and their cyclic variations, which were the only parameters to assess the drivability. This study investigated and analyzed the cyclic variations of a 100% DME-fueled engine equipped with modified mechanical fuel injection equipment. It was compared with baseline diesel to understand its positive and negative aspects. Experiments were conducted at different engine speeds (1200,1600, and 2000 rpm) and loads (No Load, 1.29, 2.59, 3.88, 5.18, and 6.47 bar brake mean effective pressure (BMEP)) . In-cylinder pressure was recorded for 250 consecutive engine cycles, and many combustion parameters were comparatively analyzed for diesel and DME fuelings. The coefficient of variation (COV) of maximum in-cylinder pressure (Pmax) was lower for DME than diesel at 1600 rpm and comparable at the other remaining engine speeds (1200 and 2000 rpm). Variations in COV of Pmax were higher at low loads and negligible at high loads for both test fuels. At 2000 rpm, the crank angle positions at which Pmax occurred were distributed in a narrow range for DME, representing higher combustion stability than baseline diesel. Variations in the maximum rate of pressure rise (RoPRmax) were lower for DME at 3.88 and 6.47 bar BMEP, while these were higher at 1.29 bar BMEP than baseline diesel. COV of indicated mean effective pressure (COVIMEP) decreased from lower to higher loads for diesel and DME fueling at 1600 and 2000 rpm engine speeds. The differences in COVIMEP between diesel and DME were negligible at higher loads, representing engine stability similar to baseline diesel. Combustion parameters assessed indicated that DME fueling led to lower cyclic variations than baseline diesel as the engine operated from lower to higher loads. At lower loads, DME fueling showed higher cyclic variations than baseline diesel.

Experimental investigation on combustion and emission characteristics of diesel methanol dual fuel (DMDF) engine at various altitudes

In order to reveal the effects of diesel and diesel methanol dual fuel (DMDF) on engine performance at different altitudes, especially on combustion stability. In this study, a comparison of experimental research on characteristics of combustion, economy, and emissions for a turbocharged DMDF at various simulated altitudes (10m, 700m, 1670m, and 2400m) and three working conditions (1200rpm-72 Nm, 1800rpm-158 Nm, and 2200rpm-153 Nm) were conducted and analyzed combustion characteristics, economy and emissions. At 1800rpm and 2200rpm, with the increment of altitude, the peak value of the cylinder pressure, the pressure rise rate, and the brake thermal efficiency (BTE) for DMDF mode were higher than diesel mode, while combustion center (CA50) and combustion duration of diesel mode higher than DMDF mode. At 1200rpm and 1800 rpm, the maximum heat release rate (HRR) of DMDF mode was higher than diesel mode. When the altitude rose from 10m to 2400m, the coefficient of variation of peak pressure (COVPP) of DMDF mode increased while the coefficient of variation of indicated mean effective pressure (COVIMEP) of DMDF mode decreased, which means the combustion of dual-fuel is relatively stable. The exhaust temperature of DMDF mode was lower than that of diesel mode at various altitudes. Compared with diesel mode, NOX and Soot emissions in DMDF model significantly decreased at different altitudes and working conditions.

Research on combustion and emission characteristics of a hydrous ethanol/hydrogen combined injection spark ignition engine under lean-burn conditions

Ethanol, as one of the carbon-neutral fuels for spark ignition (SI) engine, has been widely used. Dehydration and purification of ethanol during production process will lead to high energy consumption. If hydrous ethanol can be directly applied to the engine, the cost of use will be greatly reduced. Due to the high latent heat of vaporization of ethanol and water, it is necessary to consider the performance of atomization, evaporation and combustion stability when hydrous ethanol is used in engine. As a zero-carbon fuel, hydrogen has excellent characteristics such as low ignition energy, fast flame propagation speed and wide combustion limit. The combination of hydrous ethanol and hydrogen can reduce the use cost and ensure better combustion performance. Therefore, this study explores the performance of hydrous ethanol/hydrogen in SI combined injection engine. The hydrous ethanol is injected into the intake port and the hydrogen is directly injected into the cylinder during the compression stroke. In this study, we firstly analyze the optimal water blending ratio (ω) of hydrous ethanol, which including 0, 3%, 6%, 9% and 12%. The experimental results show that the hydrous ethanol with 9% water ratio has the best performance without hydrogen addition. Based on the 9% water ratio, the effects of hydrogen blending ratio (0, 5%, 10%, 15% and 20%) on the combustion and emission under different excess air ratio (λ) (1, 1.1, 1.2, 1.3, 1.4). Hydrogen addition can increase the degree of constant volume combustion, so that the maximum cylinder pressure and temperature increase with the increase of the hydrogen blending ratio (HBR). When λ = 1.3 and HBR = 20%, the maximum in-cylinder pressure can be increased by 108.64% compared to pure hydrous ethanol. Hydrogen effectively increases the indicated mean effective pressure (IMEP) and reduces the coefficient of variation of IMEP (COVIMEP). Adding hydrogen can reduce CO and HC emissions, while NOx emissions will increase. When λ = 1.2 and HBR increasing from 0 to 20%, the NOx emissions increase by 106.75%, but it is still less than the NOx emissions of pure hydrous ethanol at λ = 1. On the whole, hydrogen direct injection can improve the combustion performance of hydrous ethanol and achieve stable combustion under lean-burn conditions.

Analysis of Combustion and Cycle to Cycle Variations of an Ethanol (E100) Fueled Spark-Ignition Engine

Ethanol, produced from biomass, is a renewable fuel that can be an attractive alternative fuel to gasoline for the increasing concerns of energy security and the environment. In the present work, combustion characteristics of ethanol (E100) fueled spark-ignition engine are compared with base gasoline fuel, and consecutively evaluated the cycle-to-cycle variations (CCV) of the engine parameters using statistical analysis. These investigations were performed on a 250cc air-cooled four-stroke single-cylinder port-fuel injection spark-ignition fueled with ethanol and gasoline fuels. The engine was operated at 3500 rpm and 4000 rpm of engine speed while maintaining the same loads for ethanol and gasoline. It was found from the results that the peak in-cylinder pressure (Ppeak) is lower with ethanol than gasoline at a given load. The Ppeak decreased from 27.5 to 25.5 bar when ethanol was used in the engine at 9.8:1 compression ratio, 3500 rpm, and 5 Nm load. Moreover, the mass fraction burned of the air-fuel mixture was faster for ethanol as compared to gasoline. The CCV with Ppeak, location of Ppeak, engine speed, and indicated mean effective pressure (IMEP) were evaluated. The result showed that CCV of Ppeak and its location were lowered for ethanol related to gasoline. A decrement in the coefficient of variation (COV) of Ppeak and its location from 11.6% to 8.3% and 12.6% to 11.7%, respectively, were observed when ethanol was utilized in the engine instead of gasoline at 3500 rpm and 5 Nm load. This resulted in a decrease in the COV of IMEP and engine speed by 2.8% and 0.25%, respectively, for ethanol as compared to gasoline at 3500 rpm and 5 Nm. This study results indicate the combustion stability of spark ignition engine with ethanol (E100) is better than gasoline fuel.

Retracted: “Characterization of the stability indices of a methanol induced partially premixed diesel dual fuel operation under varying split injection profiles: An experimental endeavour”

Abstract The present investigation attempts to explore the prospects of the engine operational stability of a methanol induced partially premixed dual fuel operation under split injection strategy operating on a conventional single cylinder diesel engine coupled with a dedicated CRDI. The operation of such LTC regimes often deals with the stability concerns which are primarily characterized as the harshness of the operations and the non-repeatability of the combustion cycles. These two markers of operational stability have been mapped in this study through a comprehensive set of metrics of maximum pressure rise rate (ROPRmax) and Coefficient of Variation of Indicated Mean Effective Pressure (COVIMEP), Peak Pressure (COVPP) and Crank Angle of 50% mass fraction burn (COVCA50). The parametric investigation has been carried out at three different injection timings and pilot mass percentages at predefined methanol injection durations. The results have shown tremendous reductions in the non-repeatability of the combustion cycles and the harshness of the engine operation under split injection strategy, indicated by the lower scores of the stability indicators in comparison to the baseline single injection operation. Subsequently, the lowest scores of the maximum pressure rise rate and the Coefficient of Variation of indicated mean effective pressure, peak pressure and CA50 for the entire scope of investigation were registered as 0.62bar/CA, 0.75%, 0.48% and 1%, which were apparently observed as 65.5%, 86.36%, 94% and 53% lower than the corresponding scores registered in the baseline single injection operation.

Assessing the cyclic-variability of spark-ignition engine running on methane-hydrogen blends with high hydrogen contents of up to 50%

The cyclic variability in a spark-ignition (SI) engine is examined fueled with methane/hydrogen blends with the use of an in-house computational fluid dynamics (CFD) code. A recent methodology is followed, which has been developed with the main aim at providing accurate predictions of the coefficient of variation (COV) of the indicated mean effective pressure (IMEP) in a fraction of time. Instead of simulating several tens of engine cycles, the methodology is based on the numerical results obtained from just 5 cycles, which are then processed for developing suitable fitted correlations of the main parameters as a function of a normalized distance. The latter expresses the distance of the spheres of the initial flame within the computational cell at the spark-plug region with the local turbulent eddy, and provides a smooth transition from the laminar burning regime to the fully turbulent one. This sub-model is included in the ignition numerical approach and is applied here in a SI engine with 3 different hydrogen contents, 10%, 30% and 50%, and three equivalence ratios, 1, 0.8 and 0.7, showing that the COV of IMEP is well predicted compared to the available measured data. Other parameters of engine cycle variations are also examined, such as the distribution of the IMEP. The variability of NO (nitric oxide) emissions is also examined, showing that for the stoichiometric cases it follows a distribution similar to a normal (Gaussian) one, while for lower ratios it is positively skewed. Overall, the methodology seems to provide reliable results for the whole range of the operating conditions examined, while the next steps of this activity will focus on similar cases for engine with variable speed and load, with the final goal to include additional mechanisms that contribute to the engine cycle variations.

Implementation of Common Rail Direct Injection System and Optimization of Fuel Injector Parameters in an Experimental Single-Cylinder Diesel Engine

The diesel engine is one of the solutions to slow down fossil fuel depletion due to its high efficiency. However, its high pollutant emission limits its usage in many fields. To improve its efficiency and emissions, a conventional mechanical fuel injection system (MFI) was be replaced with common rail direct injection (CRDI) system for the purpose of this study. In this way, injection parameters such as injection timing, injection pressure and multiple injection schemes can be tuned to enhance the engine performance. The rail pressure and engine speed response of the modified diesel engine was tested. It was found that by advancing the start of injection timing (SOI) timing or increasing the rail pressure, the brake torque generated can be increased. Multiple injection schemes can be implemented to reduce the peak heat release rate (HRR). Post injection was observed to increase the late combustion HRR. The maximum pressure rise rate (PRR) can be reduced by applying pilot injection. Further research was conducted on optimizing fuel injector parameters to improve the indicated mean effective pressure (IMEP) consistency and reduce injector power consumption. The consistency of IMEP was indicated by coefficient of variation (CoV) of IMEP. The injector parameters included open time, low time and duty cycle of injector signals. These parameters were optimized by carrying out response surface methodology. The optimized parameters were observed to be 230 µs for open time, 53µs for low time and 27.5% for duty cycle. The percentage of error of CoV of IMEP and injector power were found to be lower than 5% when the predicted results are compared with experimental results.

An experimental investigation on combustion and performance characteristics of supercharged HCCI operation in low compression ratio engine setting

This study investigates the effects of boost pressure on combustion and performance of an early direct injection homogenous charge compression ignition (HCCI) engine at a low compression ratio (CR). A 2.0 L, four-cylinder, four-stroke, gasoline direct injection engine was converted to operate in early direct injection HCCI mode. In addition, a supercharger unit was developed for engine boosting. The experiments were performed at different intake manifold absolute pressures (MAP) from 1.0 to 1.6 bar at different engine loads using n-heptane fuel. The effects of boost pressure were investigated on HCCI combustion and engine performance characteristics using volumetric efficiency, in-cylinder pressure, heat release rate (HRR), maximum in-cylinder pressure and gas temperature, CA50 (crank angle by which 50% of the fuel is burnt), combustion duration, apparent combustion efficiency, indicated mean effective pressure (IMEP), brake mean effective pressure (BMEP), friction mean effective pressure (FMEP), indicated thermal efficiency (ITE), brake thermal efficiency (BTE), heat loss, exergy of heat loss, coefficient of variation of IMEP (COVIMEP), maximum pressure rise rate (MPRR) and ringing intensity (RI). The experimental results showed that high-efficiency HCCI operation is feasible at an engine compression ratio as low as 9.2 once the engine variables are properly optimized and an appropriate level of supercharging is utilized. An increase in indicated thermal efficiency was seen as boost pressure increased. In addition, combustion phasing advanced by increasing boost pressure or increasing air–fuel equivalence ratio values. Combustion events with CA50 2–3 °CA aTDC show the highest thermal efficiency especially at low boost pressure conditions. In addition, the pressure rise rate and ringing intensity increased by increasing air–fuel equivalence ratio and MAP. The test results also showed that HCCI operating range can be extended with the increase of intake manifold pressure especially at high load limits.

Influence of water port injection on cycle-to-cycle variations in heavy-duty natural gas engine under low load

Water injection is regarded as an effective approach to decrease thermal load and suppress knock onset in heavy-duty natural gas engines. However, the cycle-to-cycle variations in heavy-duty natural gas engines via water injection has rarely been investigated. In this study, the effects of water port injection on cycle-to-cycle variations in a natural gas engine were analyzed experimentally. The engine speed was fixed at 1600 r/min, and engine load was set at a low load with a brake mean effective pressure of 0.387 MPa. Three excess air-fuel ratios (λ = 1.0, 1.2, and 1.4) were defined; and four water to natural gas mass ratios (WNMRs) were set. The results demonstrated that the variations of multicycle cylinder pressure traces consistently increased with the increase in WNMR. The interdependence between the peak in-cylinder pressure (Pmax) and its corresponding crank angle became more dispersed, and the frequency distribution of Pmax covered a wider range with increasing WNMR. The obvious fluctuations and wide range of distribution of indicated mean effective pressure (IMEP) were determined by water addition. The higher the λ, the larger the fluctuations and wider the range of distribution of IMEP. The coefficient of variation of IMEP (COVIMEP) increased with the increase in WNMR and λ. However, the maximum COVIMEP among the three λs and four WNMRs did not exceed 3%. Thus, it can be concluded that no drivability problem is associated with water injection under low load.

Emissions and performance with diesel and waste lubricating oil: A fundamental study into cold start operation with a special focus on particle number size distribution

This study investigates the effect of engine temperature during cold start and hot start engine operation on particulate matter emissions and engine performance parameters. In addition to a fundamental study on cold start operation and the effect of lubricating oil during combustion, this research introduces important knowledge about regulated particulate number emissions and particulate size distribution during cold start, which is an emerging area in the literature. A further aspect of this work is to introduce waste lubricating oil as a fuel. By using diesel and two blends of diesel with 1 and 5% waste lubricating oil in a 6-cylinder turbocharged engine on a cold start custom test, this investigation studied particle number (PN), friction losses and combustion instability with diesel and waste lubricating oil fuel blends. In order to understand and explain the results the following were also studied: particle size distribution and median diameter, engine oil, coolant and exhaust gas temperatures, start of injection, friction mean effective pressure (FMEP), mechanical efficiency, coefficient of variation (CoV) of engine speed, CoV of indicated mean effective pressure (IMEP) and maximum rate of pressure rise were also studied. The results showed that during cold start the increase in engine temperature was associated with an increase in PN and size of particles, and a decrease in FMEP and maximum rate of pressure rise. Compared to a warmed up engine, during cold start, PN, start of injection and mechanical efficiency were lower; while FMEP, CoV of IMEP and maximum rate of pressure rise were higher. Adding 5% waste lubricating oil to the fuel was associated with a decrease in PN (during cold start), decreased particle size, maximum rate of pressure rise and CoV of IMEP and was associated with an increase in PN and nucleation mode particles (during hot start) and FMEP.

Experimental Study of Spark Plasma Stretching and Combustion Variations Analysis Using Flame Luminosity Images From an Optically Accessible Internal Combustion Engine

Abstract Understanding the behavior of spark plasma and flame initiation in internal combustion engines leads to improvement in fuel economy and exhaust emissions. This paper experimentally investigated spark plasma stretching and cycle-to-cycle variations under various engine speed, load, and air–fuel mixtures using natural luminosity images. Natural luminosity images of combustion in an IC engine provide information about the flame speed, rate of energy release, and combustion stability. Binarization of the intensity images has been a desirable method for detecting flame front and studying flame propagation in combustors. However, binarization can cause a loss of information in the images. To study spark plasma stretching, the location of maximum intensity was tracked and compared to the trajectory of the flame centroid in binarized images as a representative for bulk flow motion. Analysis showed comparable trends between the trajectories of the flame centroid and spark stretching. From three air–fuel mixtures, the spark plasma for the lean mixture appeared to be more sensitive to the stretching. In addition, this research investigated combustion variations using two-dimensional (2D) intensity images and compared the results to coefficient of variation (COV) of indicated mean effective pressure (IMEP) computed from in-cylinder pressure data. The results revealed a good correlation between the variations of the luminosity field during the main phase of combustion and the COV of IMEP. However, during the ignition and very early flame kernel formation, utilizing the luminosity field was more powerful than in-cylinder pressure-related parameters to capture combustion variations.

Performance and combustion characteristics of an SI engine fueled with fusel oil-gasoline at different water content

The main objective of the current study is to investigate the impacts of fusel oil-gasoline blends with different water content on performance and combustion characteristics of an SI engine. The water content of fusel oil is reduced by employing rotary extractor method. The parameters examined in the current study are the effects of test fuels upon engine performance criteria, fuel combustion, location of CA50 and coefficient of variation of indicated mean effective pressure (COVIMEP). The experiments are conducted in a SI engine with two blending ratio of gasoline-fusel oil (FBWE10 and FAWE10) in addition to pure gasoline as a standard fuel under different engine speeds and constant 45% of WOT engine load. The study results reveal that engine power, torque, and brake thermal efficiency have slightly improved with fusel oil-gasoline blends that were obvious clearly after reduction of water content. On the other hand, though the brake specific fuel consumption of FAWE10 slightly improve compared to FBWE10 but still higher than gasoline. Furthermore, the peak in-cylinder pressure, rate of heat release, and rate of pressure rise enhanced with fusel oil-gasoline blends. The (CA 0–10) and (CA 10–90) duration could be simultaneously decreased by reducing the water content of fusel oil, all of that are helpful to improve the stability of combustion and thought to be reasons for the reduction in COVIMEP. As a conclusion, the reduction of fusel oil water content has played positively to enhance the combustion and performance characteristics of the fuel blend and result in more stable engine operation.

Improvement of emission characteristics and thermal efficiency in diesel engines by fueling gasoline/diesel/PODEn blends

PODEn (polyoxymethylene dimethyl ethers) stand for the mixtures of ethers with the chemical formula CH3O(CH2O)nCH3, which have high cetane number and nearly 50% oxygen content. Gasoline/Diesel (GD) blends reduce the soot emissions of diesel engines with the penalty of combustion efficiency. In order to reduce emissions and improve thermal efficiency of diesel engines, blends of GDP (gasoline/diesel/PODEn) were proposed and studied in this work. Experiments were carried out in a diesel engine fueled with pure diesel, GD blends, and GDP blends. The results show that both GD blends and GDP blends have single-stage premixed heat release. GDP blends have shorter ignition delay, lower max pressure rise rate and COVIMEP (coefficient of variation of indicated mean effective pressure) than GD blends. GD blends have lower soot emissions than diesel fuel, while GDP blends have lowest soot emissions and exhibit best NOx-soot trade-off. GDP blends also have higher combustion efficiency and thermal efficiency than GD blends, even slightly higher than diesel fuel.

Experimental Study on the Cycle-to-Cycle Combustion Variations in a Spark Ignition Engine

A cyclic variability has long been recognized as limiting the range of operating conditions of spark ignition engines, in particular, under idling conditions. The coefficient of variation (COV) in indicated mean effective pressure (IMEP) defines the cyclic variability in indicated work per cycle, and it has been found that vehicle drivability problems usually result. For analysis of the cyclic variations in spark ignition engines at idling, the results show that cyclic variability by the COV, COV of IMEP, the lowest normalized value (LNV), and burn angles can help to design the spark ignition engine.

Improving low load combustion, stability, and emissions in pilot-ignited natural gas engines

Stringent environmental policies and the ever-increasing demand for energy have triggered interest in novel combustion technologies that use alternative fuels as energy sources. Of these, pilot-ignited natural gas engines that employ small diesel pilots (∼1-5 per cent on an energy basis) to compression ignite a premixed natural gas-air mixture have received considerable attention. This paper discusses the effect of intake charge temperature and pilot injected quantity on the onset of ignition (ΔIGN) and combustion (ΔCOM) in a pilot-ignited natural gas engine with specific focus on early diesel pilot injection [begining of injection (BOI) at about 60° before top dead centre (BTDC)] for low-load operation. Both ΔIGN and ΔCOM had a strong influence on performance and emissions at 60° BTDC. At advanced BOI for both half and quarter-load operation, the best performance and hydrocarbon (HC) emissions could be obtained by optimally advancing ΔIGN relative to TDC and minimizing the cyclic variability in the ΔIGN. Furthermore, a clear dependence of ΔCOM on ΔIGN was observed with the optimally advanced and the least-variable ΔIGN producing the least ΔCOM variations. Engine performance, stability, and emissions were more sensitive to intake charge temperatures in comparison with pilot injected quantities. The best improvement in performance and emissions was obtained with increasing intake temperature at half load, where fuel conversion efficiency (FCE) increased from approximately 31 per cent to 38 per cent, coefficient of variation of indicated mean effective pressure (COVIMEP) decreased from about 11 per cent to 4 per cent, and HC emissions decreased from 72 to 23 g/kW h, while oxides of nitrogen (NOx) emissions increased from 16 to 142 mg/kW h. Performance and emissions trends at quarter load were similar to those observed at half load.

An experimental study on engine performance with high ignition energy

The objective of this research is to investigate the improvement of engine performance with high ignition energy. In order to study this objective, two different spark ignition engines are employed and four different ignition systems are adopted. The ignition energy, combustion pressure, exhaust gases and fuel consumption are measured to evaluate engine performances. In addition, the heat release rate, mass fraction burned and coefficient of variation (COV) of indicated mean effective pressure (IMEP) are calculated with the measured pressures. The results reveal that high ignition energy shortens the combustion duration, improves the engine stability and reduces fuel consumption. When a higher ignition energy is applied to a lean mixture, the emission of hydrocarbons (HC) is reduced while an engine with the conventional ignition energy produces higher HO emission. A faster heat release rate and a higher mass fraction burned also result. When the same amount of ignition energy is applied to a lean mixture, the burning velocity is slow as the discharge duration becomes longer, but the COV of IMEP is improved.