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The Homogenous Charge Compression Ignition (HCCI) engine is positioned as a next-generation internal combustion engine and has been the focus of extensive research in recent years to develop a practical system. One reason is that this new combustion system achieves lower fuel consumption and simultaneous reductions of nitrogen oxide (NOx) and particulate matter (PM) emissions, which are major issues of internal combustion engines today. However, the characteristics of HCCI combustion can prevent suitable engine operation owing to the rapid combustion process that occurs accompanied by a steep pressure rise when the amount of fuel injected is increased to obtain higher power output. A major issue of HCCI is to control this rapid combustion so that the quantity of fuel injected can be increased for greater power. Controlling the ignition timing is also an issue because it is substantially influenced by the chemical reactions of the fuel.

In this study, experiments were conducted using a blend of two types of fuel with different ignition characteristics. One was dimethyl ether (DME) that has a high cetane number, autoignites easily and displays low-temperature oxidation reaction mechanisms; the other was methane that has a cetane number of zero and does not autoignite easily. A mechanically driven supercharger was provided in the intake pipe to adjust the intake air pressure. Moreover, flame light in the combustion chamber was extracted using a system for observing light emission that occurred in the space between the cylinder head and the cylinder and in the bore direction of the piston crown. The results of previous studies conducted with a supercharged HCCI engine and a blended fuel of DME and methane have shown that heat release of the hot flame is divided into two stages and that combustion can be moderated by reducing the peak heat release rate (HRR).

Engine downsizing with a turbocharger / supercharger has attracted attention as a way of improving the fuel economy of automotive gasoline engines, but this approach can be frustrated by the occurrence of abnormal combustion. In this study, the factors causing abnormal combustion were investigated using a supercharged, downsized engine that was built by adding a mechanical supercharger. Combustion experiments were conducted in which the fuel octane number and supercharging pressure were varied while keeping the engine speed, equivalence ratio and intake air temperature constant. In the experiments, a visualization technique was applied to photograph combustion in the combustion chamber, absorption spectroscopy was used to investigate the intermediate products of combustion, and the cylinder pressure was measured. The experimental data obtained simultaneously were then analyzed to examine the effects on combustion.

The ignitability and engine performance of FAMEs at the cold condition were experimentally investigated by using two FAMEs, i.e. coconut oil methyl ester (CME) and soybean oil methyl ester (SME). The cold start test and forced over cooling test were conducted. In the forced over cooling test, engine was forced cooled by the injecting water mist to engine cooling fin. In the cold start test, the cylinder pressure of CME rose earliest because CME has a superior ignitability. The crank angle at ignitions of diesel fuel and CME were not so affected by the forced over cooling, however ignition timing of SME was remarkably delayed. In cases of forced over cooling, COV of maximum combustion pressure of CME was lower than that of normal air cooling condition. The forced over cooling has a potential to reduce NOx emission, however HC, CO and smoke concentrations were increased in a high load due to incomplete combustion.

There are few investigations to change wood biomasses to the industrially available energy, so that a new conversion technology of biomass to liquid fuel has been established by the direct liquefaction process. However, cellulosic liquefaction fuel (for short CLF) cold not mixed with diesel fuel. In this study, the plastic was mixed with wood to improve the solubility of CLF to diesel fuel. CLF made by the direct co-liquefaction process could be stably and completely mixed with diesel fuel in any mixing ratio and CLF included 2 wt.% of oxygen. The test engine was an air-cooled, four-stroke, single cylinder, direct fuel injection diesel engine. In the engine starting condition test, the ignition timing of 5 wt.% CLF mixed diesel fuel was slightly delayed at immediately after the engine started, however the ignition timing was almost the same as diesel fuel after the engine was warmed-up.

A new bio-fuel i.e. the cellulosic liquefaction fuel (CLF) was developed for diesel engines. The cellulosic liquefaction fuel (CLF) was made from woods by the direct liquefaction process. CLF could not be completely mixed with diesel fuel, however CLF could be mixed with Fatty Acid Methyl Ester (FAME) and a diesel engine could be operated by CLF and FAME blends. In this study, CLF was divided into three fractions: 473 to 523 K (CLF1), 523 to 573 K (CLF2) and 573 K or more (CLF3) by fractional distillation in order to find CLF fraction which was suitable for diesel engine, and coconuts oil methyl ester (CME) was used as FAME. In the fuel droplet combustion tests, the combustion durations of CLFs were longer than those of diesel fuel and CME, and the combustion duration increased as the distillation temperature range rose, because CLF contained a lot of flame-resisting components like aromatic compounds.

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.

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 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.

In order to investigate the effects of a DC electric field and its polarity on the knock intensity in a spark-ignition engine, an experimental study was carried out with a rapid compression machine. To get a good understanding of the effect of an electric field on knocking combustion, the high-speed direct photographs were taken. The ionization current measurements were also carried out using the electrode as an ionization probe The major findings of present investigation of the effects of DC electric fields on the knocking combustion process in a spark-ignition engine could be summarized as follows: It was clearly indicated that the knock intensity decreases with the increase of the electric field regardless its polarity. The knock intensity was strongly dependent upon the burned mass fraction at the onset of the end-gas autoignition, and decreased as the burned mass fraction increased.

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.

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.

To get a simple and low cost Stirling engine that would be manufactured and used in any district of the world, a unique atmospheric Stirling engine named NAS-1 is under study at NIHON University. NAS-1 was originally planned to be used for the solar field, so the cylinder head was designed to have a glass head at its top with the concentrated solar beam penetrating the glass. NAS-1 uses a rubber diaphragm for the power piston, and it has proved to be very reliable and successful. It has James Watt's approximate linear motion link mechanisms (Watt link) for the main crank shaft, instead of the usual crossed head to eliminate liquid oil lubrication. This kind of engine has been thought to furnish very simple, low cost and efficient power for future clean energy fields. This engine design is simple, low in cost, and doses not involve problems of high pressure, and does not produce any pollutants whatsoever such as carbonic acid gas, NOx and others' pollution.

The application of emulsified fuel for diesel engines is expected to reduce NOx and soot simultaneously. The purpose of this study is to clarify the influence of water content in emulsified fuel and fuel injection timing on diesel engine performance. The engine performance of emulsified fuel was compared with the water injection method. In the water injection test, water was injected to intake manifold and diesel fuel was directly injected into combustion chamber. Two emulsified fuels of which mixing ratio of water and emulsifier to diesel fuel were 15 and 30 vol.% were tested. Engine performance and exhaust gas emission of water injection method were almost similar to those of diesel fuel, so that water presented in combustion chamber had almost no influence on engine performance. Therefore, it can be considered that the micro explosion of fuel droplet enhanced the fuel atomization and mixing of fuel and air.