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Internal combustion engines have been required to achieve even higher efficiency in recent years in order to address environmental concerns. However, knock induced by abnormal combustion in spark-ignition engines has impeded efforts to attain higher efficiency. Knock characteristics during abnormal combustion were investigated in this study by in-cylinder visualization and spectroscopic measurements using a four-stroke air-cooled single-cylinder engine. The results revealed that knock intensity and the manner in which the autoignited flame propagated in the end gas differed depending on the engine speed.

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.

DME is alternate fuel for diesel engines, however DME has defects such as small lower calorific value, inferior lubricity and weak fuel penetration. To compensate disadvantages, In-direct injection 2-stroke diesel engine with low pressure fuel injection system was proposed. The fuel injection timing near TDC gave good performance because the heat loss of low temperature oxidation reaction reduced. The brake torque and brake thermal efficiency of 2-stroke IDI diesel engine were lower than those of 4-stroke engine. However, the exhaust gas emissions were very low level because the intake air leaked through the exhaust port and the exhaust gas was diluted.

Lean-burn technology is regarded as one effective way to increase the efficiency of internal combustion engines. However, stable ignition is difficult to ensure with a lean mixture. It is expected that this issue can be resolved by improving ignition performance as a result of increasing the amount of energy discharged into the gaseous mixture at the time of ignition. There are limits, however, to how high ignition energy can be increased from the standpoints of spark plug durability, energy consumption and other considerations. Therefore, the authors have focused on a multistage pulse discharge (MSPD) ignition system that performs low-energy ignition multiple times. In this study, a comparison was made of ignition performance between MSPD ignition and conventional spark ignition (SI). A high-speed camera was used to obtain visualized images of ignition in the cylinder and a pressure sensor was used to measure pressure histories in the combustion chamber.

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.

In recent years, it has been expected the conversion of wasted biomass to industry available energy. In this study, 80 wt.% of wood and 20 wt.% of polypropylene were liquefied by the mineral oil used as solvent. The liquefied material was distilled, and distillation fraction of temperature from 493 to 573 K was recognized as light oil fraction CLF (Cellulose Liquefaction Fuel) and that from 378 to 493 K was recognized as naphtha fraction CLF. CLFs were blended with light oil and, in engine performance test, mixing ratio of light oil fraction CLF was 5 wt.%, and in vehicle running test, weight mixing ratios were 5 or 10 wt.%. In engine performance test, indicator diagrams and rate of heat releases of light oil fraction CLF 5 wt.% mixed light oil were almost equivalent to those of light oil in all load conditions, and engine performance and exhaust gas emissions were also almost equivalent to light oil.

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 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.

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.

Engine knock is the one of the main issues to be addressed in developing high-efficiency spark-ignition (SI) engines. In order to improve the thermal efficiency of SI engines, it is necessary to develop effective means of suppressing knock. For that purpose, it is necessary to clarify the mechanism generating pressure waves in the end-gas region. This study examined the mechanism producing pressure waves in the end-gas autoignition process during SI engine knock by using an optically accessible engine. Occurrence of local autoignition and its development process to the generation of pressures waves were analyzed under several levels of knock intensity. The results made the following points clear. It was observed that end-gas autoignition seemingly progressed in a manner resembling propagation due to the temperature distribution that naturally formed in the combustion chamber. Stronger knock tended to occur as the apparent propagation speed of autoignition increased.

The use of a higher compression ratio is desirable for improving the thermal efficiency and specific power of spark-ignition engines, but it gives rise to a problem of engine knock. In the present research, an investigation was made of the role of the preflame reaction region of a spark-ignition engine in the occurrence of autoignition. Emission spectroscopy was used to measure the behavior of formaldehyde (HCHO) in a cool flame. In addition, measure the behavior of the faint light attributed to the HCO radical in a blue flame with the concurrent measurement of the OH radical. The emission waveforms measurements obtained for HCHO when n-heptane (ORON) was used as the fuel, It is thought that these tendencies correspond to the passage and degeneracy of a cool flame. Further, the emission waveforms measured for the HCO radical when blended fuels (6ORON, 8ORON) were correspond to that of a blue flame.

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.

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.

Homogeneous Charge Compression Ignition (HCCI) combustion has attracted much interest as a combustion system that can achieve both low emissions and high efficiency. But the operating region of HCCI combustion is narrow, and it is difficult to control the auto-ignition timing. This study focused on the use of a two-component fuel blend and supercharging. The blended fuel consisted of dimethyl ether (DME), which has attracted interest as alternative fuel for compression-ignition engines, and methane, the main component of natural gas. A spectroscopic technique was used to measure the light emission of the combustion flame in the combustion chamber in order to ascertain the combustion characteristics. HCCI combustion characteristics were analyzed in detail in the present study by measuring this light emission spectrum.

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.

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.

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.

Effects of measurement method, coolant temperature and fuel composition on soot emissions were examined by engine experiments. By reducing the pressure fluctuation in the sampling line, the measured soot emissions with better stability and reproducibility could be obtained. With lower coolant temperatures, larger soot emissions were yielded at much advanced fuel injection timings. Compared to gasoline, soot emissions with a blend fuel of normal heptane, isooctane and toluene were significantly decreased, suggesting the amounts of aromatic components (toluene or others) should be increased to obtain a representative fuel for the predictive model of particulate matter in SIDI engines.

Hydrogen has attracted attention as one of the key fuels for making internal combustion engines carbon neutral. However, the combustion characteristics of hydrogen differ greatly from those of conventionally used hydrocarbons. Therefore, in order to develop next-generation internal combustion engines that operate on hydrogen, it is first necessary to have a thorough understanding of the combustion characteristics of hydrogen. Engines that can take maximum advantage of those characteristics should be developed on the basis of that knowledge. Toward that end, the purpose of this study was to investigate the fundamental combustion characteristics of hydrogen in a test engine. This paper presents the results of an investigation of the effects on low-temperature oxidation reactions and autoignition when hydrogen was blended into dimethyl ether (DME) [1, 2], a gaseous hydrocarbon fuel.

This paper deals with the steering system with conventional round steering-wheel from the view point of Steer-by-Wire system design. Steering gear ratio and control force characteristics are selected as interface variables of the steering system. The concept of ideal steering gear ratio which is derived on the basis of mapping of steering wheel angle and vehicle path angle is proposed to determine steering gear ratio. Simulator experiments are conducted to investigate the effects of interface variables on system and driver’s control performance. Validity of proposed ideal steering gear ratio would be confirmed. Candidates for objective task performance measure to define desirable control force characteristics would be determined from the test results.