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The uniform lean gasoline-air mixture was provided to diesel engine and was ignited by direct diesel fuel injection. The mixing region that is formed by diesel fuel penetration and entrainment of ambient mixture is regarded as combustible turbulent jet. The ignition occurs in this region and the ambient lean mixture is burned by flame propagation. The lean mixture of air-fuel ratio between 150 and 35 could be ignited and burned by this ignition method. An increase of diesel fuel injection is effective to ensure combustion and ignition. As diesel fuel injection increases, HC concentration decreases, and NOx and CO concentration increases.

One issue of Homogeneous Charge Compression Ignition (HCCI) engines that should be addressed is to suppress rapid combustion in the high-load region. Supercharging the intake air so as to form a leaner mixture is one way of moderating HCCI combustion. However, the specific effect of supercharging on moderating HCCI combustion and the mechanism involved are not fully understood yet. Therefore, experiments were conducted in this study that were designed to moderate rapid combustion in a test HCCI engine by supercharging the air inducted into the cylinder. The engine was operated under high-load levels in a supercharged state in order to make clear the effect of supercharging on expanding the stable operating region in the high-load range. HCCI combustion was investigated under these conditions by making in-cylinder spectroscopic measurements and by analyzing the exhaust gas using Fourier transform infrared (FT-IR) spectroscopy.

There is an urgent need today to improve the thermal efficiency of spark- ignition (SI) engines in order to reduce carbon dioxide emission and conserve energy in an effort to prevent global warming. However, a major obstacle to improving thermal efficiency by raising the compression ratio of SI engine is the easily occurrence of engine knocking. The result of studies done by numerous researchers have shown that knocking is an abnormal combustion in which the unburned gas in the end zone of the combustion chamber autoignites. However, the combustion reaction mechanism from autoignition to the occurrence of knocking is still not fully understood. The study deals with the light absorption and emission behavior in the preflame reaction interval before hot flame reactions.

The study deals with the light absorption and emission behavior in the preflame reaction interval before hot flame reactions.(1-3) Absorption spectroscopy was used to measure the behavior of HCHO and OH radicals during a progression from normal combustion to knocking operation. Emission spectroscopic measurements were obtained in the same way that radical added HCO. Radical behavior in preflame reactions was thus examined on the basis of simultaneous measurements, which combined each absorption wavelength with three emission wavelength by using a monochromator and a newly developed polychromator.(4-5) When n-heptane (0 RON) and blended fuel (50 RON) were used as test fuel, it was observed that radical behavior differed between normal combustion and knocking operation and a duration of the preflame reaction was shorter during the progression from normal combustion to a condition of knocking.

The purpose of this paper is to find a universal law to predict a turbulent burning velocity under various operating conditions and engine specifications. This paper presents the relationship between turbulent burning velocity and Karlovitz number. The turbulent burning velocity was measured using a single-cylinder gasoline engine, which has an external Exhaust Gas Recirculation (EGR) system. In the experiment, various engine operating parameters, e.g. engine speed and EGR rates, and various engine specifications, i.e. different types of intake ports were tested. Karlovitz number was calculated with Three Dimensional Computational Fluid Dynamics (3D-CFD) and detailed chemical reaction calculation, which condition was based on the experiment. The experimental and calculation results show that turbulent burning velocity is predicted by using Karlovitz number in the engine conditions, which varies depending on engine speed, EGR rates and the designs of intake ports.

In plasma jet ignition, combustion enhancement effects are caused toward the plasma jet issuing direction. Therefore, when the igniter is attached at the center of cylindrically shaped combustion chamber, the plasma jet should issues toward the round combustion chamber wall. The plasma jet igniter that had a concentric circular orifice has been developed. It is expected that the plasma jet is issued and is diffused from concentric circular orifice toward the combustion chamber wall. Relationship between plasma jet and igniter configuration was experimentally clarified. Plasma jet can issue from the entire concentric circular orifice for some igniter. Plasma jet is extended with increasing concentric circular orifice area. Plasma jet penetration increases with increasing concentric circular orifice width.

In plasma jet ignition, combustion enhancement effects occur toward the plasma jet issuing direction. Therefore, when the igniter is attached at the center of cylindrically shaped combustion chamber, plasma jet should issue toward the round combustion chamber wall. The plasma jet igniter that had an annular circular orifice has been developed. The purpose of this study is to elucidate the relationship between the newly developed plasma jet igniter configuration and the combustion enhancement effects. In this newly developed plasma jet igniter, the fine scale turbulence appears on the flame front and flame propagates very rapidly. Plasma jet influences on the flame propagation for long period when the plasma jet igniter has issuing angle 90 [deg.] and large cavity volume. However, in the early stage of combustion, flame front area of issuing angle 45 [deg.] is larger than that of 90 [deg.], because the initial flame kernel is formed by the plasma jet.

The investigation regarding the performance of newly developed plasma jet igniter is explored by using vessel. In plasma jet ignition, combustion enhancement effects occur toward the plasma jet issuing direction. Therefore, when the igniter is attached at the center of cylindrically shaped combustion chamber, plasma jet should issue toward the round combustion chamber wall. The plasma jet igniter that had a concentric circular orifice has been developed. The maximum combustion pressure increases and the burning period decreases with increasing the cavity volume. This feature is similar to that of the ordinary plasma jet igniter. However, the combustion enhancement effect is almost independent of the orifice area.

The uniform lean methanol-air mixture was provided to the diesel engine and was ignited by the direct diesel fuel injection. The internal EGR is added to this ignition method in order to activate the fuel in the mixture and to increase the mixture temperature. The test engine was a 4-stroke, single- cylinder direct-injection diesel engine. The cooling system was forced-air cooling and displacement volume was about 211 (cm3). The compression ratio was about 19.9:1. The experiment was made under constant engine speed of 3000 (r/min). The boost pressure was maintained at 101.3 (kPa). Five values of mass flow rate of diesel fuel injection were selected from 0.060 (g/s) to 0.167 (g/s) and five levels of back pressure: 0), 26.7, 53.3, 80.0 and 106.6 (kPa) were selected for the experiment. The effect of internal EGR is varied by the back pressure level.

Unresolved issues of Homogeneous Charge Compression Ignition (HCCI) combustion include an extremely rapid pressure rise on the high load side and resultant knocking. Studies conducted to date have examined ways of expanding the region of stable HCCI combustion on the high load side such as by applying supercharging or recirculating exhaust gas (EGR). However, the effect of applying EGR gas to supercharged HCCI combustion and the mechanisms involved are not fully understood. In this study, the effect of EGR gas components on HCCI combustion was investigated by conducting experiments in which external EGR gas was applied to supercharged HCCI combustion and also experiments in which nitrogen (N2) and carbon dioxide (CO2) were individually injected into the intake air pipe to simulate EGR gas components. In addition, HCCI combustion reactions were analyzed by conducting chemical kinetic simulations under the same conditions as those of the experiments.

The uniform lean methanol-air mixture was provided to the diesel engine and was ignited by direct diesel fuel injection. In this study, the internal EGR is added to this ignition method in order to activate the fuel in the mixture and to increase the temperature of the mixture before the ignition. It is confirmed that the lean methanol-air mixture of air-fuel ratio between 130 and 18 could be ignited and burned when the back pressure of 80 [kPa] is added. The ignition and combustion characteristics can be improved by the internal EGR, however the engine performance and NOx emission deteriorated.

The uniform lean gasoline-air mixture was provided to the diesel engine and was ignited by the direct diesel fuel injection. In this study, the internal EGR is add to this ignition method in order to activate the fuel in the mixture before the ignition. It is confirmed that the lean mixture of air-fuel ratio between 150 and 40 could be ignited and burned by this ignition method when the back pressure of 80 [kPa] is added, and the burning period is shorted by internal EGR. However, as the back pressure increases, NOx concentration is increased by the high temperature residual gas.

This research focused on the light emission behavior of the OH radical (characteristic spectrum of 306.4 [nm]) that plays a key role in combustion reactions, in order to investigate the influence of the residual gas on autoignition. Authors also analyzed on the heat release and thermodynamic mean temperature due to research activity state of unburned gas. The test engine used was a 2-stroke, air-cooled engine fitted with an exhaust pressure control valve in the exhaust manifold. Raising the exhaust pressure forcibly recirculated more exhaust gas internally. When a certain level of internal EGR is forcibly applied, the temperature of the unburned end gas is raised on account of heat transfer from the hot residual gas and also due to compression by piston motion. As a result, the unburned end gas becomes active and autoignition tends to occur.

A great deal of interest is focused on Homogeneous Charge Compression Ignition (HCCI) combustion today as a combustion system enabling internal combustion engines to attain higher efficiency and cleaner exhaust emissions. Because the air-fuel mixture is compression-ignited in an HCCI engine, control of the ignition timing is a key issue. Additionally, because the mixture ignites simultaneously at multiple locations in the combustion chamber, it is necessary to control the resultant rapid combustion, especially in the high-load region. Supercharging can be cited as one approach that is effective in facilitating high-load operation of HCCI engines. Supercharging increases the intake air quantity to increase the heat capacity of the working gas, thereby lowering the combustion temperature for injection of the same quantity of fuel. In this study, experiments were conducted to investigate the effects of supercharging on combustion characteristics in an HCCI engine.

Homogeneous Charge Compression Ignition (HCCI) combustion offers the advantages of high efficiency and low emissions of pollutants. However, ignition timing control and expansion of the stable operation region are issues remaining to be addressed in this combustion process. Detailed analyses of ignition and combustion characteristics are needed to resolve these issues. HCCI combustion of a low octane number fuel is characterized by two-stage heat release attributed to a cool flame and a hot flame, respectively. In this study, spectroscopic techniques were used to investigate the effect of exhaust gas recirculation (EGR) on ignition and combustion characteristics using a low octane number fuel, which is apt to give rise to a cool flame. The reaction mechanism of a cool flame produces formaldehyde (HCHO). Measurements were made of spontaneous light emission and absorption at wavelengths corresponding to the light emitted at the time HCHO was produced.

A new concept of combustion which is using the characteristic of plasma jet ignition, that is the plasma jet diffusive combustion is proposed. The constant volume vessel is used for the experiment, and methanol is charged in the cavity of plasma jet injector and the air at room temperature and atmospheric pressure is charged in the combustion chamber. The combustion characteristic is analyzed by measuring the combustion pressure and visualization of the combustion process. The plasma jet injector configuration and the ratio of methanol volume to cavity volume influence not only the plasma jet diffusive combustion process but also the maximum combustion pressure. In cases of small orifice diameter, the plasma jet diffusive combustion is not recognized, and the maximum combustion pressure increases as the orifice area becomes large.

In this study, the heated fuels were provided to the diesel engine in order to activate the fuel before the injection. Two test fuels: the normal diesel fuel and cetane, which have different boiling points were used. For both normal diesel fuel and cetane, crank angles at ignition and maximum pressure are delayed and the maximum combustion pressure is decreased as the fuel temperature rises. In cases of large and middle mass flow rate of fuel injection, the brake thermal efficiency and brake mean effective pressure are decreased when the fuel temperature is higher than 570 [K]. However, in the case of small mass flow rate of fuel injection, the brake thermal efficiency is almost independent of fuel temperature. HC and CO concentrations in the exhaust gas emission show constant values regardless of fuel temperature. However, NOx concentration is gradually decreased as the fuel temperature rises.