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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.

Knocking is one phenomenon that can be cited as a factor impeding efforts to improve the efficiency of spark-ignition engines. With the aim of understanding knocking better, light emission spectroscopy was applied in this study to examine preflame reactions that can be observed prior to autoignition in the combustion reaction process of hydrocarbon fuels. Attention was focused on light emission behavior at wavelengths corresponding to those of formaldehyde (HCHO), Vaidya's hydrocarbon flame band (HCO) and the OH radical in a forced progression from normal combustion to a knocking state. Light emission behavior was measured simultaneously in the center and in the end zone of the combustion chamber when the engine was operated on two different test fuels. The test fuels used were n-heptane (0 RON) and a blended fuel (70 RON) consisting of n-heptane (0 RON) and iso-octane (100 RON).

The purpose of this study is to clarify ignition characteristics and engine performance of FAME for 4-stroke diesel engine in low compression ratios. Diesel fuel and coconut oil methyl ester (CME) were selected as test fuels, because CME consisted of saturate FAMEs which were good ignition characteristics. To reduce the compression ratio, thin copperplates were inserted between cylinder head and cylinder block and the compression ratio was reduced from 20.6 that was standard to 15. The engine starting test and an ordinary engine performance test were made at 3600 min.-₁. In engine starting test, the engine was soaked at room temperature and the ignition timing of diesel fuel was remarkably delayed compared with CME. When the compression ratio was 16, for diesel fuel, the misfiring cycles were included during engine warming up. In case of 15 of compression ratio, the engine could not be started by diesel fuel; however the engine could be run by CME.

This study examined the effects of fuel composition and intake pressure on two-stage high temperature heat release characteristics of a Homogeneous Charge Compression Ignition (HCCI) engine. Light emission and absorption spectroscopic measurement techniques were used to investigate the combustion behavior in detail. Chemical kinetic simulations were also conducted to analyze the reaction mechanisms in detail. Blended fuels of dimethyl ether (DME) and methane were used in the experiments. It was found that the use of such fuel blends together with a suitable intake air flow rate corresponding to the total injected heat value gave rise to two-stage heat release behavior of the hot flame, which had the effect of moderating combustion. The results of the spectroscopic measurements and the chemical kinetic simulations revealed that the main reaction of the first stage of the hot flame heat release was one that produced CO from HCHO.

Homogeneous Charge Compression Ignition (HCCI) combustion has attracted considerable interest in recent years as a new combustion concept for internal combustion engines. On the other hand, two combustion concepts proposed for two-cycle spark-ignition (SI) engines are Active Thermo-Atmosphere Combustion (ATAC) and Activated Radical (AR) combustion. The authors undertook this study to examine the similarities and differences between HCCI combustion and ATAC (AR) combustion. Differences in the low-temperature oxidation reaction behavior between these two combustion processes were made clear using one test engine.

The investigation regarding the plasma jet ignition was explored by using a combustion vessel. The first purpose is to elucidate the issuing duration and the penetration of hydrogen plasma jet. A temporal change of local electron temperature was measured along the central axis of plasma jet. A small characteristic length of igniter seems favorable with regard to the plasma jet penetration and the generation of high temperature, as compared with the case of the igniter that has the excessive cavity volume. The second purpose is to elucidate relationship between the characteristic length and the combustion enhancement effect, when the excessive volume of cavity and the excessive supplied electrical energy were used. The influence of the characteristic length on the plasma jet penetration and the combustion enhancement differs with the supplied energy. The combustion enhancement seems to be caused by the plasma jet in case of excessive supplied energy.

The investigation regarding performance of plasma jet igniters was explored by using a constant volume vessel. This study focused on investigating the relationship between the jet effect, the hot gas jet issued from the igniter, and combustion enhancement. The hot gas penetration was visualized by the schlieren system with CCD camera and image intensifier. In the cases of small energies, 0.63 and 0.90 J, the combustion enhancement effect is similar to that of combustion jet igniter. In cases of supplied energies, 2.45 and 5.00 J, the jet effect influences on the combustion enhancement effect for small characteristic length of the igniter.

Using absorption spectroscopy, simultaneous measurements were made of the behavior of the OH (characteristic spectrum of 306.4 nm), CH (431.5 nm) and C2(516.5 nm) radicals in the end-gas region and center of the combustion chamber of a spark-ignition engine during preflame reactions with four types of fuel having different octane numbers. The results of this research show that the behavior of the OH, CH and C2 radicals in preflame reactions differed significantly in both the center and end-gas region of the combustion chamber depending on the octane number of the fuel and also between normal and knocking combustion conditions.

Emission intensity was measured at a wavelength of 395 2 nm (corresponding to the characteristic spectrum of the HCHO radical) and absorbance was measured at 306 4 nm (corresponding to that of the OH radical). The emission intensity and absorbance waveforms recorded during engine operation on n-heptane show behavior indicative of the passage and degeneracy of cool flame in the preflame reaction interval. As the combustion chamber wall temperature approached an overheated state in the transition from normal combustion to knocking operation different preflame reaction behavior was observed which is thought to correspond to the presence of a negative temperature coefficient region related to the ignition delay time.

Homogenous Charge Compression Ignition (HCCI) combustion experiments were conducted in this study using a single-cylinder test engine fitted with a sapphire observation window to facilitate visualization of the entire cylinder bore area. In addition to in-cylinder visualization of combustion, spectroscopic measurements were made of light emission and absorption in the combustion chamber to investigate autoignition behavior in detail. Engine firing experiments were conducted to visualize HCCI combustion over a wide range of compression ratios from 12:1 to 22:1. The results showed that increasing the compression ratio advanced the ignition timing and increased the maximum pressure rise rate, making it necessary to moderate combustion. It was also found that autoignition can be induced even in a mixture lean enough to cause misfiring by raising the intake air temperature so as to advance the overall combustion process.

This study examined Homogeneous Charge Compression Ignition (HCCI) combustion characteristics in detail on the basis of in-cylinder combustion visualization, spectroscopic measurements of light emission and absorption and chemical kinetic simulations. Special attention was focused on investigating and comparing the effects of the fuel octane number and residual gas on combustion characteristics. The results made clear the relationship between the production/consumption of formaldehyde (HCHO) in the HCCI autoignition process and flame development behavior in the cylinder. Additionally, it was found that both the fuel octane number and residual gas have the effect of moderating low-temperature oxidation reactions. Furthermore, it was observed that residual gas has the effect of shifting the temperature for the occurrence of the hot flame to a higher temperature range.

The growing severity of global environmental issues in recent years, including air pollution and the depletion of fossil fuels, has made it necessary for internal combustion engines to achieve higher efficiency and lower exhaust emission levels. Calls for reducing atmospheric emissions of carbon dioxide (CO₂) necessitate thoroughgoing measures to lower the levels of CO₂ originating in the combustion process of internal combustion engines and to facilitate operation on diverse energy sources. Homogeneous Charge Compression Ignition (HCCI) combustion has attracted widespread interest because it achieves high efficiency and can reduce particulate matter (PM) and nitrogen oxide (NOx) emissions simultaneously. These characteristics are obtainable because HCCI combustion can take place at ultra-lean conditions exceeding the limits of flame propagation.

Controlled Autoignition (CAI) combustion processes can be broadly divided between a CAI process that is applied to four-stroke engines and a CAI process that is applied to two-stroke engines. The former process is generally referred to as Homogeneous Charge Compression Ignition (HCCI) combustion and the later process as Active Thermo-Atmosphere Combustion (ATAC). The region of stable engine operation differs greatly between these two processes, and it is thought that the elucidation of their differences and similarities could provide useful information for expanding the operation region of HCCI combustion. In this research, the same two-stroke engine was operated under both the ATAC and HCCI combustion processes to compare their respective combustion characteristics. The results indicated that the ignition timing was less likely to change in the ATAC process in relation to changes in the fuel octane number than it was in the HCCI combustion process.

In this research, an investigation was made of ion current and OH radical luminescence behavior in the progression from normal combustion to knocking operation. One pair each of an ion probe and a quartz observation window was fitted in the center and on the end of the combustion chamber. The peak values of the ion voltage drop and the OH radical emission intensity both increased as the cylinder head temperature and the cylinder pressure rose. It is possible to understand combustion conditions by analyzing measured waveformes of the ion voltage drop and the OH radical emission intensity.

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.

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 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.

In this research, the effect of high-temperature residual gas, resulting from the application of a certain level of EGR, on combustion was investigated using a two-stroke engine and alcohol fuels (ethanol and methanol) and gasoline as the test fuels. Measurements were made of the light emission intensity of the OH radical on the intake and exhaust port sides of the combustion chamber and of the combustion chamber wall temperature (spark plug washer temperature) and the exhaust gas temperature. Data were measured and analyzed in a progression from normal combustion to autoignited combustion to preignition and to knocking operation.

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 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.