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The purpose of this study is to explore an effect of cooled-EGR on the diesel engine performance fueled with coconut-oil methyl ester (CME). The exhaust gas was cooled by the water at room temperature and was fed to the intake manifold, and the EGR rate was changed from 0 % to 30 % at every 10 %. The engine performances were measured at several EGR rates, fuel injection pressures and timings. Test fuels were CME and commercial diesel fuel. In the case of high EGR rate at which the compression ignition was deteriorated, the ignition timing of CME was always earlier than that of diesel fuel, therefore CME had good ignitability as compared with diesel fuel under EGR application. When the fuel injection pressure was increased at high EGR rate, the ignition delay was improved by the fuel atomization and air-fuel mixing effect.

The purpose of this study is to explore an effect of the coconut oil methyl ester (CME) and vegetable oil methyl ester (VME) on a low compression ratio diesel engine performance. CME and VME were produced from coconut oil and vegetable oil with methanol, respectively. Vegetable oil was assumed to contain 60 wt.% of soybean oil and 40 wt.% rapeseed oil. The engine performance was measured in the steady operating condition at 3600 rpm of engine speed. The ignition timings of CME and VME were advanced and the maximum cylinder pressures of CME and VME were higher as compared with the diesel fuel at low compression ratio, because CME and VME consisted of medium chain fatty acid methyl esters. The ignitability of CME was superior to VME, because CME consisted of saturated fatty acid. The brake thermal efficiency of diesel fuel was slightly higher than CME and VME at any compression ratios.

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.

Internal combustion engines today are required to achieve even higher efficiency and cleaner exhaust emissions. Currently, research interest is focused on premixed compression ignition (Homogeneous Charge Compression Ignition, HCCI) combustion. However, HCCI engines have no physical means of initiating ignition such as a spark plug or the fuel injection timing and quantity. Therefore, it is difficult to control the ignition timing. In addition, combustion occurs simultaneously at multiple sites in the combustion chamber. As a result, combustion takes place extremely rapidly especially in the high load region. That makes it difficult for the engine to operate stably at high loads. This study focused on the fuel composition as a possible means to solve these problems. The effect of using fuel blends on the HCCI operating region and combustion characteristics was investigated using a single-cylinder test engine.

Homogeneous Charge Compression Ignition (HCCI) has attracted a great deal of interest as a combustion system for internal combustion engines because it achieves high efficiency and clean exhaust emissions. However, HCCI combustion has several issues that remain to be solved. For example, it is difficult to control engine operation because there is no physical means of inducing ignition. Another issue is the rapid rate of heat release because ignition of the mixture occurs simultaneously at multiple places in the cylinder. The results of previous investigations have shown that the use of a blended fuel of DME and propane was observed that the overall combustion process was delayed, with that combustion became steep when injected propane much. This study focused on expanding the region of stable engine operation and improving thermal efficiency by using supercharging and blended fuels. The purpose of using supercharging were in order to moderated combustion.

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.

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).

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.

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.

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.

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.

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, 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.

There are strong demands today to further improve the thermal efficiency of internal combustion engines against a backdrop of various environmental issues, including rising carbon dioxide (CO2) emissions and global warming. One factor that impedes efforts to improve the thermal efficiency of spark ignition engines is the occurrence of knocking. The aim of this study was to elucidate the details of knocking based on spectroscopic measurements and visualization of phenomena in the combustion chamber of a test engine that was operated on three primary reference fuels with different octane ratings (0 RON, 30 RON, and 50 RON). The ignition timing was retarded in the experiments to delay the progress of flame propagation, making it easier to capture the behavior of low-temperature oxidation reactions at the time knocking occurred.

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 bio-fuel i.e. the cellulosic liquefaction fuel (CLF) was developed for diesel engines. CLF was made from woods by direct liquefaction process. When neat CLF was supplied to diesel engine, the compression ignition did not occur, so that blend of CLF and diesel fuel was used. The engine could be operated when the mixing ratio of CLF was up to 35 wt%. CO, HC and NOx emissions were almost the same as those of diesel fuel when the mixing ratio of CLF was less than 20 wt% whereas the thermal efficiency slightly decreases with increase in CLF mixing ratio.

In this study, light emission and absorption spectroscopic measurement techniques were used to investigate the Homogeneous Charge Compression Ignition (HCCI) combustion process in detail, about which there have been many unclear points heretofore. The results made clear the formation behavior and wavelength bands of the chemical species produced during low-temperature reactions. Specifically, with a low level of residual gas, a light emission band was observed from a cool flame in a wavelength range of 370–470 nm. That is attributed to the light emission of formaldehyde (HCHO) produced in the cool-flame reactions. Additionally, it was found that these light emission spectra were no longer observable when residual gas was applied. The light emission spectra of the combustion flame thus indicated that residual gas has the effect of moderating cool-flame reactions.

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.

In this study, it was shown that Homogeneous Charge Compression Ignition (HCCI) combustion in a 4-stroke engine, operating under the conditions of a high compression ratio, wide open throttle (WOT) and a lean mixture, could be simulated by raising the compression ratio of a 2-stroke engine. On that basis, a comparison was then made with the characteristics of Active Thermo-Atmosphere Combustion (ATAC), the HCCI process that is usually accomplished in 2-stroke engines under the conditions of a low compression ratio, partial throttle and a large quantity of residual gas. One major difference observed between HCCI combustion and ATAC was their different degrees of susceptibility to the occurrence of cool flames, which was attributed to differences in the residual gas state. It was revealed that the ignition characteristics of these two combustion processes differed greatly in relation to the fuel octane number.