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We have investigated combustion characteristics of lean gasoline-air pre-mixture ignited by gas-oil injection using a high compression D.I. diesel engine. Gasoline was supplied as an uniform lean mixture by using carburetors, and gas-oil was directly injected into the cylinder. Two different types of combustion chamber were attempted. It was confirmed that the lean mixture of air-fuel ratio between 150 and 35 could be ignited and burned by this ignition method. An engine with the re-entrant type combustion chamber had an advantage for combustion and ignition. The brake mean effective pressure increased when relatively rich mixture was provided with a small amount of the gas-oil injection. As the gas-oil injection increased, HC concentration decreased, and NO and CO concentration increased. The exhaust gas emission of pollutants could be reduced when lean mixture was ignited by an optimum gas-oil injection.

With the aim of elucidating the mechanism causing abnormal combustion, a study was made of light emission and absorption characteristics at wavelengths corresponding to the spectra of the OH (characteristic spectrum of 306.4 nm), CH (431.5 nm), C2 (516.5 nm) radicals. Spectral properties were measured in the end-gas region of the cylinder for various types of fuel having different octane numbers. During combustion in an actual engine, the behavior of the CH and C2 radicals prior to the occurrence of abnormal combustion characterized by knock is indicative of behavior in the negative temperature coefficient (NTC) region. The experimental results revealed that the behavior of the OH, CH, C2 radicals differs between normal and abnormal combustion.

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.

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.

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.

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.

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.

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.

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 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.

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.

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.

This research focused on the light emission behavior of the OH radical (characteristic spectrum of 306.4 [nm]) that plays a key role in combustion reactions, in order to investigate the influence of the residual gas on autoignition. Authors also analyzed on the heat release and thermodynamic mean temperature due to research activity state of unburned gas. The test engine used was a 2-stroke, air-cooled engine fitted with an exhaust pressure control valve in the exhaust manifold. Raising the exhaust pressure forcibly recirculated more exhaust gas internally. When a certain level of internal EGR is forcibly applied, the temperature of the unburned end gas is raised on account of heat transfer from the hot residual gas and also due to compression by piston motion. As a result, the unburned end gas becomes active and autoignition tends to occur.

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.

Knocking is one phenomenon that can be cited as a factor impeding efforts to improve the efficiency of spark-ignition engines. With the aim of understanding knocking better, light emission spectroscopy was applied in this study to examine preflame reactions that can be observed prior to autoignition in the combustion reaction process of hydrocarbon fuels. Attention was focused on light emission behavior at wavelengths corresponding to those of formaldehyde (HCHO), Vaidya's hydrocarbon flame band (HCO) and the OH radical in a forced progression from normal combustion to a knocking state. Light emission behavior was measured simultaneously in the center and in the end zone of the combustion chamber when the engine was operated on two different test fuels. The test fuels used were n-heptane (0 RON) and a blended fuel (70 RON) consisting of n-heptane (0 RON) and iso-octane (100 RON).

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.

Although metallic compounds are widely known to affect combustion in internal combustion engines, the potential of metallic additives in engine oils to initiate abnormal combustion has been unclear. In this study, we investigated the influence of combustion chamber deposits derived from engine oil additives on combustion in a spark-ignited engine. We used a single-cylinder four-stroke engine, and measured several combustion characteristics (e.g., cylinder pressure, in-cylinder ultraviolet absorbance in the end-gas region, and visualized flame propagation) to evaluate combustion anomalies. To clarify the effects of individual additive components, we formed combustion products of individual additives in a combustion chamber prior to measuring combustion characteristics. We tested three types of metallic additives: a calcium-based detergent, a zinc-based antiwear agent, and a molybdenum-based friction modifier.

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-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.

Supercharged direct-injection engines are known to have a tendency toward abnormal combustion such as spontaneous low-speed pre-ignition and strong knock because they operate under low-speed, high-load conditions conducive to the occurrence of irregular combustion. It has been hypothesized that one cause of such abnormal combustion is the intrusion of engine oil droplets into the combustion chamber where they become a source of ignition. It has also been reported that varying the composition of engine oil additives can change susceptibility to abnormal combustion. However, the mechanisms involved are not well understood, and it is not clear how the individual components of engine oil additives affect autoignition. In this study, abnormal combustion experiments were conducted to investigate the effect on autoignition of a calcium-based additive that is typically mixed into engine oil to act as a detergent.