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An investigation was made into two approaches to air-fuel mixture formation in direct injection SI engines in which charge stratification is controlled by swirl or tumble gas motions, respectively. Particle image velocimetry (PIV), laser-induced fluorescence (LIF) and air-fuel ratio measurement by infrared absorption were used to analyze fuel transport from the fuel injector to the spark plug and the fuel vaporization process. The results obtained were then compared with measured data as to combustion stability. As a result, the reason why the effects of injection timing on combustion stability were different between the two approaches was made clear from the standpoint of the mixture formation process.

It is well known that ultra-lean combustion can result in higher thermal efficiency, better fuel economy, and greatly reduced NOx emissions. Accomplishing ultra-lean combustion is very difficult with a conventional spark plug, and ignition instability can be cited as one of the factors. Therefore, it is thought that ignition system innovation is important for the achievement of ultra-lean combustion in gasoline engines. This study investigated high-speed plasma ignition as a new ignition system for internal combustion engines. High-speed plasma refers to the transient (non-equilibrated) phase of plasma before formation of an arc discharge; it is obtained by applying high voltage with an ultra-short pulse between coaxial cylindrical electrodes. High-speed plasma can inherently form a multi-channel discharge, with the electrical discharge spreading over a much larger volume than a spark discharge does.

A new combustion concept, called spark-ignited compression ignition (SI-CI) combustion, is proposed for expanding the operation range of homogeneous charge compression ignition (HCCI) combustion. The authors previously showed that raising the mixture temperature before compression so as to induce auto-ignition near top dead center reduces the quantity of trapped gas, resulting in a lower maximum indicated mean effective pressure (IMEP). With the newly proposed combustion concept, auto-ignition of a homogeneous lean mixture is accomplished by the additional compression resulting from SI combustion of a small quantity of stratified mixture instead of raising the intake air temperature. This SI-CI combustion process reduced the necessary increase in intake air temperature compared with conventional HCCI combustion. A higher maximum IMEP was achieved with SI-CI combustion than with conventional HCCI combustion, as was planned.

Since the stable operating region of a gasoline-fueled HCCI engine is limited to the part load condition, a mode change between SI and HCCI combustion is required, which poses an issue due to the difference in combustion characteristics. This report focuses on the combustion characteristics in the transitional range. The combustion mode in the transitional range is investigated by varying the internal EGR rate, intake air pressure, and spark advance timing in steady-state experiments. In this parametric study, stable SI-CI combustion is observed. This indicates that the combustion mode transition is possible without misfiring or knocking, regardless of the speed of variable valve mechanism which includes VVA, VVEL, VTEC, VVL and so on, though the response of intake air pressure still remains as a subject to be examined in the actual application.

The authors have previously proposed a plume ignition and combustion concept (i.e., PCC combustion), in which a hydrogen fuel is directly injected to the combustion chamber in the latter half of compression stroke and forms a richer mixture plume. By combusting the plume, both cooling losses and NOx formation are reduced. In this study, thermal efficiency was substantially improved and NOx formation was reduced with PCC combustion by optimizing such characteristics as direction and diameter of the jets in combination with combustion of lean mixture. Output power declined due to the lean mixture, however, was recovered by supercharging while keeping NOx emissions at the same level. Thermal efficiency was further improved by slightly re-optimizing the jet conditions.

It is known that the regular gasoline and primary reference fuel (PRF), that have the same research octane number, show the different HCCI engine performance, because of the different phasing and heating value of low temperature heat release. This means that the research octane number is not an “all-round” auto-ignition index, and another index must be developed to evaluate the HCCI combustion characteristics. In this paper, eleven pure hydrocarbon components were blended into twenty three different kinds of model fuels (surrogate fuels), labeled BASE, MC01-MC11 and K01-K11, and the HCCI engine tests were performed under five different intake air temperature conditions to change the auto-ignition characteristic of each hydrocarbon component. As HCCI combustion can be described as a lean and slow gasoline knocking phenomenon, an analysis of HCCI combustion data gives us much more important knowledge of gasoline knocking phenomenon.

Emissions remain a critical issue affecting engine design and operation, while energy conservation is becoming increasingly important. One approach to favorably address these issues is to achieve homogeneous charge combustion and stratified charge combustion at lower peak temperatures with a variable compression ratio, a variable intake temperature and a trapped rate of the EGR using NVO (negative valve overlap). This experiment was attempted to investigate the origins of these lower temperature auto-ignition phenomena with SCCI and CAI using gasoline fuel. In case of SCCI, the combustion and emission characteristics of gasoline-fueled stratified-charge compression ignition (SCCI) engine according to intake temperature and compression ratio was examined. We investigated the effects of relative air/fuel ratio, residual EGR rate and injection timing on the CAI combustion area.

This paper presents a study of mixture formation in the combustion chamber of a direct-injection SI engine. In-cylinder flow measurement was conducted using laser Doppler velocimetry (LDV) and particle image velocimetry (PIV), and visualization of fuel vapor behavior was done using laser-induced fluorescence (LIF). Further, fast response flame ionization detector (FID) was used to measure the hydrocarbon (HC) concentrations in the vicinity of the spark plug. Thereby mixture concentrations in the vicinity of the spark plug, within the mixture distribution observed using LIF, were quantified. Results revealed that an upward flow forms near the center of the cylinder in the latter half of the compression stroke and goes from the piston crown toward the cylinder head. This upward flow is caused by the synergistic effect of the swirl motion generated in the cylinder and the cylindrical bowl provided in the piston crown eccentrically to the central axis of the cylinder.

A chemical kinetics and computational fluid-dynamics (CFD) analysis was performed to evaluate the combustion of syngas derived from biomass and coke-oven solid feedstock in a micro-pilot ignited supercharged dual-fuel engine under lean conditions. For this analysis, a reduced syngas chemical kinetics mechanism was constructed and validated by comparing the ignition delay and laminar flame speed data with those obtained from experiments and other detail chemical kinetics mechanisms available in the literature. The reaction sensitivity analysis was conducted for ignition delay at elevated pressures in order to identify important chemical reactions that govern the combustion process. We have confirmed the statements of other authors that HO2+OH=H2O+O2, H2O2+M=OH+OH+M and H2O2+H=H2+HO2 reactions showed very high sensitivity during high-pressure ignition delay times and had considerable uncertainty.

The objective of this study is to investigate the initial flame propagation characteristics of turbulent flame in an engine cylinder through time-series analysis of radical emissions. A spark plug with optical fiber was developed in this study. The plug sensor is M12 type that makes it possible to mount in practical engine. The spark plug sensor can detect radical emissions in time-resolved spectra through time-series spectroscopic measurement. In this spectra, some kinds of radical emissions such as OH*(306nm), CH*(431nm) and C2*(517nm) based on principle of chemiluminescence are observed. In this study, the spark plug sensor was applied to both compression-expansion machine (CEM) and practical engine. As a result of CEM with bottom viewed high-speed camera, three kinds of spectra could be detected.

It is important to develop the technique for measuring the cycle-to-cycle variation of combustion in order to reduce the fuel consumption of the commercial spark ignition engine. In previous study, we had proposed using the spark plug as an ion probe to measure the appearance time of maximum pressure under the lean mixture conditions of the research engine. In this paper the combustion diagnostics for the commercial engine was performed using the spark plug as an ion probe. Under idling conditions the ion current often appeared during the exhaust process. This ion current is dominated by the flame contact area and the flame velocity. In this case there is good correlation between the characteristic value of the ion current and the indicated mean effective pressure (IMEP). Finally using the spark plug as an ion probe can detect the combustion quality under conditions with large cyclic variation.

A new technique for combustion diagnostics of a spark ignition engine was developed. In this method the ion sensor with the circular configuration was installed into the cylinder head gasket. This sensor is expected to be applied for production engine. The signal measured by the ion sensor was similar with that of cylinder pressure. The peak timing of ion current was consistent with the peak timing of pressure. There was a strong correlation between IMEP and the peak timing of ion current. This sensor is available to detect combustion quality in a spark ignition engine.

Low temperature heat release (LTHR) in HCCI combustion changes according to fuel chemical composition and engine test conditions. In this study 11 pure hydrocarbon components were blended into 12 different model fuels to evaluate the effects of fuel composition on LTHR heating value, LTHR CA50 (crank angle at 50% completion of LTHR), high temperature heat release (HTHR), and engine performance. From the heat release analysis of the test data from a supercharged 4-cylinder engine, it was determined that the HTHR CA50 (crank angle at 50% completion of HTHR) was strongly indicative of combustion stability and maximum rate of pressure rise. Moreover, the functional dependence of HTHR CA50 on LTHR heating value and LTHR CA50 was quantified. Test fuels denoted MD05, Base, MC05 and MX05 were prepared by adding 5.2vol%, 9.3vol%, 15.0vol%, and 18.2vol% of n-hexane, respectively, to a blend of 10 pure hydrocarbons.

In order to reduce the exhaust emission and the fuel consumption in a spark ignition engine, the combustion diagnostics had been developed. However, there are few sensors which can detect the combustion quality for the individual cycle and cylinder in production engines. In previous study, the new technique using a gasket ion sensor for measuring the combustion quality has been proposed. In present study, the flame propagation pattern in a spark ignition engine was detected by using a gasket ion sensor with a circular electrode. The waveforms of ion current obtained from a circular ion sensor were compared with the flame propagation pattern obtained from multiple ion sensors. When the mixture was ignited in offset center of the cylinder, the flame propagation pattern was distorted from the spherical pattern. Then the waveforms of ion current from the circular ion sensor were varied from the waveform for a center ignition.

It is well known that the wavelet transform is a useful time-frequency analysis method for an unsteady signal and major attention has been focused on the selection of the mother wavelet (MW) because the MW plays an important role in the wavelet transform. In this study, we analyze the pressure signal in a spark-ignition engine and the vibration of the engine block measured by a knock sensor under the knocking conditions when knocking is caused. We then propose a new method of the knocking detection that utilizes the knocking signal measured with a knock sensor as a MW. We call this method the Instantaneous Correlation Method (ICM). The degree of similarity between the MW and the vibration of the engine block was judged and only the knocking signal from the vibration of the engine block was extracted. The results obtained here show that the method proposed in this study is useful for knocking detection even if the engine speed is very high of 6000rpm.

To allow the HCCI vehicles to enter the market in the future, it is important to investigate the combustion deviations and operational range differences between the same research octane number fuels. In this paper, eighteen kinds of two hydrocarbon blended fuels, which were composed of n-heptane and another hydrocarbon, such as iso-octane, diisobutylene, 4-methyl-1-pentene, toluene or cyclopentane, were evaluated. Those fuels were blended to have the same research octane numbers of 75, 80, 85 and 90 by changing the blending volume ratio of n-heptane and counterpart hydrocarbon. Intake air was supercharged to 155 kPa abs and its temperature was kept at 58 °C. The HCCI engine was operated at 1000 rpm. Neither hot EGR, nor any other combustion stratification system was utilized in order to investigate the purely hydrocarbon effects on HCCI combustion.

Bio-gas as an internal combustion (I.C.) engine fuel has many advantages such as cheaper fuel cost, low emission levels and especially the neutral recirculation loop of carbon dioxide, which is one of the principal factors in global warming. In this study, positive potentialities of bio-gas were investigated using a micro co-generation engine. The mixing ratio of methane (CH4) and carbon dioxide (CO2) was changed to simulate various types of bio-gases. Intake air and fuel flow rates were controlled to change the equivalence ratio. The engine load condition could be changed with the electric output power used. Base on the result, the higher CO2 content rate slowed down the engine speed in the same load condition and the combustion speed generally decreased under the same load condition with maintaining the engine speed. However thermal efficiency increased with lean burn conditions and NOX emission decreased with higher CO2 mixing rates.

The combustion and exhaust emissions characteristics of a supercharged dual-fuel natural gas engine with a single cylinder were analyzed. We focused on EGR (Exhaust Gas Recirculation) to achieve higher thermal efficiency and lower exhaust emissions. The combustion of diesel fuel (gas oil) as ignition sources was visualized using a high-speed video camera from the bottom of a quartz piston. The luminous intensity and flame decreased as the EGR rate increased. Furthermore, the ignition delay became longer due to the EGR. Characteristics of the combustion and exhaust emissions were investigated with changing EGR rates under supercharged conditions. The indicated mean effective pressure and thermal efficiency decreased with increasing EGR rate. In addition, NOx emissions decreased due to the EGR. In this study two-stage combustion was observed.

This study investigated the effect of some pilot fuel injection parameters, like injection timing, injection pressure and injection quantity on engine performance and exhaust emissions of a supercharged producer gas-diesel dual fuel engine. The engine has been tested to be used as a co-generation engine and its power output is an important matter. Experiments have been done to optimize the injection timing, injection pressure and injection quantity for the maximization of engine power. At constant injection pressures, there is an optimum amount of pilot injection quantity for that maximum engine power is developed without knocking and within the limit of maximum cylinder pressure. Above or below of that amount engine power is decreased. Higher injection pressures generally show better results than lower ones. However, good results can also be obtained with lower injection pressure, if maximum power timings can be selected.

A single cylinder, supercharged dual fuel gas engine with micro-pilot fuel injection is operated using methane only and methane-hydrogen mixtures. Methane only experiments were performed at various equivalence ratios and equivalence ratio of 0.56 is decided as the optimum operating condition based on engine performance, exhaust emissions and operation stability. Methane-hydrogen experiments were performed at equivalence ratio of 0.56 and 2.6 kJ/cycle energy supply rate. Results show that indicated mean effective pressure is maintained regardless of hydrogen content of the gaseous fuel while thermal efficiency is improved and presence of hydrogen reduces cyclic variations. Increasing the fraction of hydrogen in the fuel mixture replaces hydrocarbon fuels and reduces carbon monoxide and hydrocarbon emissions.