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Combustion experiments were conducted with an optically accessible engine that allowed the entire bore area to be visualized for the purpose of making clear the characteristics that induce extremely rapid HCCI combustion and knocking accompanied by cylinder pressure oscillations. The HCCI combustion regime was investigated in detail by high-speed in-cylinder visualization of autoignition and combustion and emission spectroscopic measurements. The results revealed that increasing the equivalence ratio and advancing the ignition timing caused the maximum pressure rise rate and knocking intensity to increase. In moderate HCCI combustion, the autoignited flame was initially dispersed temporally and spatially in the cylinder and then gradually spread throughout the entire cylinder.

This study clarified the influence of hot gas jet on combustion enhancement effect for lean mixture in the plasma jet ignition. The hot gas jet was generated by the high temperature plasma and was ejected from igniter after plasma jet finished issuing. In combustion tests, propane-air mixture at equivalence ratio of 0.6 was used and the mixture was filled in the combustion chamber at atmosphere pressure and room temperature. For generation of the hot gas jet, the standard air was filled in chamber at same conditions and the hot gas jet was visualized by schlieren method in the absence of combustion. The combustion development processes were also visualized and the combustion pressure was measured. The discharge voltage, discharge current and the plasma luminescence were also measured. The plasma luminescence disappeared within 0.05 ms for any experimental conditions. When cavity depth was deep and orifice diameter was small, the maximum plasma luminescence height was short.

The purpose of this study is to elucidate the development process of hot kernel generated by the laser induced breakdown and to clarify the relationship between corona discharge application and flame propagation. The mixture can be ignited by the laser induced breakdown. Nd:YAG laser is used for the ignition and laser light is optically focused on the central part of combustion chamber by a plano convex lens. The hot kernel is observed in the absence of combustion and is rapidly developed into the laser incidence side. The homogeneous propane-air mixture is used and six equivalence ratios between 0.7 and 1.5 are tested. For generating the positive corona discharge in the combustion chamber, a non-uniform electric field is applied by the needle to plane gap. In a lean mixture, the whole flame front shifts to downward from the breakdown point and, in the rich mixture region, the combustion is strongly enhanced.

The new fuel injection method which is using the high-voltage electrical discharge has been proposed. The plasma jet ignition technology is applied to this injection system, and the component parts of fuel injector are similar to the plasma jet igniter. The purpose of this study is to elucidate the spray characteristics and the fuel injection development processes of this injection method. To obtain the influence of injector configuration and supplied electrical discharge energy on the fuel spray, the fuel is ejected into the open atmosphere and fuel injection development process is visualized by the schlieren method. The penetration depth, maximum width and projected area of fuel spay increase with increasing in the electrical discharge energy and an orifice diameter. In the case at which the large electrical discharge energy is provided, the fuel injection is finished within a short duration and the mean fuel spray velocity becomes fast.

The flame propagation behavior of homogeneous hydrogen-air mixture under application of high-voltage uniform or non-uniform electric field was explored by using combustion vessel. When a uniform electric field was applied, two plate electrodes were attached to ceiling and bottom of combustion chamber and, to apply a non-uniform electric field, an electrode in ceiling was needle-shaped and an electrode in bottom was plate-shaped. The positive or negative polarity DC high voltage was applied for an electrode in ceiling. When a positive polarity non-uniform electric field was applied to the mixture at any equivalence ratios and the input voltage was higher than 12 kV, the flame propagation was enhanced in the downward direction. This is because the corona wind was generated from the tip of needle-shaped electrode to grounded electrode by the brush corona.

The flame propagation behavior of hydrogen-air and propane-air mixtures under application of high-voltage non-uniform electric field was explored by using combustion vessel. Both mixtures were ignited by laser-induced breakdown of Nd:YAG laser. In a case of propane-air mixture, top of flame front was drawn to the electrode and bottom of flame front was expanded. In a case of hydrogen-air mixture, the wrinkle caused by the preferential diffusion was enhanced by corona discharge, however the entire flame front was merely moved toward downward by corona wind. Therefore, the non-uniform electric field strongly influences charged particles originated in hydrocarbon of propane-air mixture.

A new diffusion combustion method characterized by plasma jet ignition is proposed. In this new diffusion combustion, the fuel is injected and ignited by the high-voltage electrical discharge, so this combustion method can be applied for various fuels which have different ignitability. Tests were carried out with seven fuels by using a combustion bomb. When a small orifice was used, fuels which had branched chain molecular structure were hardly ignited. In case of large orifice, all test fuels were surely ignited, and the maximum combustion pressures of branched chain structure molecular fuels were higher than those of straight chain structure molecular fuel.

The purpose of this study is to elucidate flame propagation behavior of homogeneous propane-air mixture under application of non-uniform electric field. A needle-shaped electrode was attached to the ceiling and a plate electrode was set at bottom of combustion chamber, so that the electric field was applied in the direction of the chamber's vertical axis. A homogeneous propane-air mixture was supplied at equivalence ratio of 1.0 and was ignited by leaser induced breakdown under atmospheric pressure and room temperature. It was found that the flame front and plate electrode were repelled each other and a thin air layer was formed between the flame and plate electrode when a relatively low positive DC non-uniform electric field was applied to the needle-shaped electrode. It might be thought that the induced current was generated in the flame front, so that the flame front and plate electrode repelled each other.

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.

The purpose of this research was to obtain a better understanding of engine knocking phenomena. Measurements were made of the behavior of formaldehyde (HCHO), an important intermediate product of cool flame reactions, and of the HCO radical, characterized by distinctive light emission during blue flame reactions. The test engine was operated on a blended fuel (50 RON) of n-heptane and iso-octane. Simultaneous measurements were made of the behavior of HCHO and the OH radical using absorption spectroscopy and of the behavior of HCO and OH radicals using emission spectroscopy. Absorbance spectroscopic measurements revealed behavior thought to correspond to the passage of a cool flame and emission spectroscopic measurements showed behavior thought to correspond to the passage of a blue flame.

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.

An air motor with regenerating system for propulsion of a bicycle was newly developed. An air motor was driven by the compressed air and the bicycle was propelled. When the bicycle was decelerating, the air motor was acted as a compressor and the kinetic energy of bicycle was regenerated as compressed air. The purpose of this study is to elucidate the performance of air motor and driving characteristic of bicycle. The air motor in this study was the reciprocating piston type like an internal combustion engine, and cylinder arrangement was in-line two-cylinder. The output power increased with an increase of supply air pressure although the maximum cylinder pressure was less than the supply air pressure. The output power decreased as the revolution increased due to friction loss. The maximum cylinder pressure reduced as the rotational frequency increased because the inlet valve opening duration was decreased.

In this study, optical measurements were made of the combustion chamber gas during operation of a Homogeneous Charge Compression Ignition (HCCI) engine in order to obtain a better understanding of the ignition and combustion characteristics. The principal issues of HCCI engines are to control the ignition timing and to optimize the combustion state following ignition. Autoignition in HCCI engines is strongly influenced by the complex low-temperature oxidation reaction process, alternatively referred to as the cool flame reaction or negative temperature coefficient (NTC) region. Accordingly, a good understanding of this low-temperature oxidation reaction process is indispensable to ignition timing control. In the experiments, spectroscopic measurement methods were applied to investigate the reaction behavior in the process leading to autoignition.

In this study, a spectroscopic method was used to measure the combustion characteristics of a test diesel engine when operated on dimethyl ether (DME) under a homogenous charge compression ignition (HCCI) combustion process. A numerical analysis was made of the elementary reactions using Chemkin 4.0 to perform the calculations. The results of the analysis showed that compression ratio changes and the methane additive influenced the autoignition timing in the DME-HCCI combustion process. In the experiments, reducing the compression ratio delayed the time of the peak cylinder pressure until after top dead center, thereby increasing the crankshaft output and thermal efficiency. The addition of methane enabled the DME-HCCI engine to provide crankshaft output equivalent to that seen for diesel engine operation at a low equivalence ratio. This paper discusses these effects in reference to the experimental and calculated results.

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.

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. However, because HCCI engines lack a physical means of initiating ignition, it is difficult to control the ignition timing. Another issue of HCCI engines is that the combustion process causes the cylinder pressure to rise rapidly. The time scale is also important in HCCI combustion because ignition depends on the chemical reactions of the mixture. Therefore, we investigated the influence of the engine speed on autoignition and combustion characteristics in an HCCI engine. A four-stroke single-cylinder engine equipped with a mechanically driven supercharger was used in this study to examine HCCI combustion characteristics under different engine speeds and boost pressures.

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.

This study was conducted to investigate the influence of cooled recirculated exhaust gas (EGR) on abnormal combustion in a Homogenous Charge Compression Ignition (HCCI) engine. The condition of abnormal HCCI combustion accompanied by cylinder pressure oscillations was photographed with a high-speed camera using a 2-stroke optically accessible engine that enabled visualization of the entire bore area. Exhaust gas was cooled with a water-cooled intercooler for introducing cooled EGR. Experiments were conducted in which the quantity of cooled EGR introduced was varied and a comparison was made of the autoignition behavior obtained under each condition in order to investigate the influence of cooled EGR on abnormal HCCI combustion. The results revealed that cylinder pressure oscillations were reduced when cooled EGR was introduced. That reduction was found to be mainly ascribable to the effect of cooled EGR on changing the ignition timing.

One issue of downsized and supercharged engines is low-speed pre-ignition (LSPI) that occurs in the low-speed and high-load operating region. One proposed cause of LSPI is the influence of the engine oil and its additives. However, the effect of engine oil additives on pre-ignition and the mechanism involved are still not fully understood. This study investigated the influence of engine oil additives on abnormal combustion in a spark-ignition engine. A four-stroke air-cooled single-cylinder engine with a side valve arrangement was used in conducting combustion experiments. The research methods used were in-cylinder pressure analysis, in-cylinder visualization and absorption spectroscopic analysis. Engine oil additives were mixed individually at a fixed concentration into a primary reference fuel with an octane number of 50 and their effect on knocking was investigated.

The purpose of this study is to elucidate the flame propagation behavior under the electric field application by using the constant volume vessel. The laser induced breakdown applies the ignition and Nd:YAG laser is used. A homogeneous propane-air mixture is used and three equivalence ratios, 0.7, 1.0 and 1.5 are tested. In the uniform electric field, the premixed flame rapidly propagates toward both upward and downward directions and the flame front becomes a cylindrical shape. The maximum combustion pressure decreases with an increase of input voltage because of an increase of heat loss to the electrode, however the combustion duration is hardly affected by the input voltage. In the non-uniform electric field, the flame propagation velocity of downward direction increases. The combustion enhancement effect is remarkably when the input voltage is larger than 12 kV because the brush corona occurs and intense turbulence is generated on the flame front.