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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.

Knocking combustion experiments were conducted in this study using a test engine that allowed the entire bore area to be visualized. The purpose was to make clear the detailed characteristics of knocking combustion that occurs accompanied by cylinder pressure oscillations when a Homogeneous Charge Compression Ignition (HCCI) engine is operated at high loads. Knocking combustion was intentionally induced by varying the main combustion period and engine speed. Under such conditions, knocking in HCCI combustion was investigated in detail on the basis of cylinder pressure analysis, high-speed photography of the combustion flame and spectroscopic measurement of flame light emissions. The results revealed that locally occurring autoignition took place rapidly at multiple locations in the cylinder when knocking combustion occurred. In that process, the unburned end gas subsequently underwent even more rapid autoignition, giving rise to cylinder pressure oscillations.

This study investigated the origin of knocking combustion accompanied by pressure wave and strong pressure oscillations in a Homogeneous Charge Compression Ignition (HCCI) engine. Experiments were conducted with a two-stroke single cylinder optically accessible engine that allowed the entire bore area to be visualized. The test fuel used was n-heptane. The equivalence ratio and intake temperature were varied to induce a transition from moderate HCCI combustion to extremely rapid HCCI combustion accompanied by in-cylinder pressure oscillations. Local autoignition and pressure wave behavior under each set of operating conditions were investigated in detail on the basis of high-speed in-cylinder visualization and in-cylinder pressure analysis. As a result, under conditions where strong knocking occurs, a brilliant flame originates from the burned gas side in the process where the locally occurring autoignition gradually spreads to multiple locations.

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).

This study focused on the use of a two-component fuel blend and supercharging as possible means of overcoming these issues of HCCI combustion. Low-carbon gaseous fuels with clean emissions were used as the test fuels. The specific fuels used were dimethyl ether (DME, cetane number of 55 or higher) that autoignites easily And exhibits pronounced low-temperature oxidation reactions, methane (cetane number of 0) that does not autoignite readily and is the main component of natural gas which is regarded as petroleum substitute, and propane (cetane number of 5) that is a principal component of liquefied petroleum gas. The results of previous investigations have shown that the use of a blended fuel of DME and methane produces a two-stage main combustion process under certain operating conditions, with the result that combustion is moderated.

In-cylinder visualization of the entire bore area at an identical frame rate was used to investigate knocking conditions under spark ignition (SI) combustion and under Homogeneous Charge Compression Ignition (HCCI) combustion in the same test engine. A frequency analysis was also conducted on the measured pressure signals. The results revealed that a combustion regime accompanied by strong pressure oscillations occurred in both the SI and HCCI modes, which was presumably caused by rapid autoignition with attendant brilliant light emission that took place near the cylinder wall. It was found that the knocking timing was the dominant factor of this combustion regime accompanied by cylinder pressure oscillations in both the SI and HCCI combustion modes.

Issues that must be addressed to make Homogeneous Charge Compression Ignition (HCCI) engines a practical reality include the difficulty of controlling the ignition timing and suppression of rapid combustion under high load conditions. Overcoming these issues to make HCCI engines viable for practical application is indispensable to the further advancement of internal combustion engines. Previous studies have reported that the operating region of HCCI combustion can be expanded by using DME and Methane blended fuels.(1), (2), (3), (4), (5) The reason is that the reaction characteristics of these two low-carbon fuels, which have different ignition properties, have the effect of inducing heat release in two stages during main combustion, thus avoiding excessively rapid combustion. However, further moderation of rapid combustion in high-load region is needed to expand the operation region. This study focused on supercharging and use of blended fuels.

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.

In this study, the effect of autoignition behavior in the unburned end-gas region on pressure wave formation and knock intensity was investigated. A single-cylinder gasoline engine capable of high-speed observation of the end gas was used in the experiments. Visualization in the combustion chamber and spectroscopic measurement of light absorption by the end gas were carried out to analyze autoignition behavior in the unburned end-gas portion and the reaction history before autoignition. The process of autoignition and pressure wave growth was investigated by analyzing multipoint pressure histories. As a result, it was found that knocking intensity increases through interaction between autoignition and pressure waves.

In this study, a detailed analysis was made of supercharged HCCI combustion using a two-component fuel blend of dimethyl ether (DME), which has attracted interest as a potential alternative fuel, and methane. The quantity of fuel injected and boost pressure were varied to investigate the equivalence ratio and operating region conducive to optimal HCCI combustion. The results revealed that varying the boost pressure according to the engine load and applying a suitable equivalence ratio induced two-stage main combustion over a wide load range, making it possible to avoid excessively rapid combustion.

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.

The Homogeneous Charge Compression Ignition (HCCI) engine has attracted much interest in recent years because it can simultaneously achieve high efficiency and low emissions. However, it is difficult to control the ignition timing with this type of engine because it has no physical ignition mechanism. Varying the amount of fuel supplied changes the operating load and the ignition timing also changes simultaneously. The HCCI combustion process also has the problem that combustion proceeds too rapidly. This study examined the possibility of separating ignition timing control and load control using an HCCI engine that was operated on blended test fuels of dimethyl ether (DME) and methane, which have vastly different ignition characteristics. The influence of the mixing ratios of these two test fuels on the rapidity of combustion was also investigated.

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.

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.

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.

This study investigated the effects of recirculated exhaust gas (EGR) and its principal components of N2, CO2 and H2O on moderating Homogeneous Charge Compression Ignition (HCCI) combustion. Experiments were conducted using two types of gaseous fuel blends of DME/propane and DME/methane as the test fuels. The addition rates of EGR, N2, CO2 and H2O were varied and the effects of each condition on HCCI combustion of propane and methane were investigated. The results revealed that the addition of CO2 and H2O had the effect of substantially delaying and moderating rapid combustion. The addition of N2 showed only a slight delaying and moderating effect. The addition of EGR had the effect of optimally delaying the combustion timing, while either maintaining or increasing the indicated mean effective pressure and indicated thermal efficiency ηi.

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.