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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.

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.

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.

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.

Improving the thermal efficiency of internal combustion engines requires operation under a lean combustion regime and a higher compression ratio, which means that the causes of autoignition and pressure oscillations in this operating region must be made clear. However, there is limited knowledge of autoignition behavior under lean combustion conditions. Therefore, in this study, experiments were conducted in which the ignition timing and intake air temperature (scavenging temperature) of a 2-stroke optically accessible test engine were varied to induce autoignition under a variety of conditions. The test fuel used was a primary reference fuel with an octane rating of 90. The results revealed that advancing the ignition timing under lean combustion conditions also advanced the autoignition timing, though strong pressure oscillations on the other hand tended not to occur.

Technologies for further improving vehicle fuel economy have attracted widespread attention in recent years. However, one problem with some approaches is the occurrence of abnormal combustion such as low-speed pre-ignition (LSPI) that occurs under low-speed, high-load operating conditions. One proposed cause of LSPI is that oil droplets diluted by the fuel enter the combustion chamber and become a source of ignition. Another proposed cause is that deposits peel off and become a source of ignition. A four-stroke air-cooled single-cylinder engine was used in this study to investigate the influence of Ca-based additives having different properties on abnormal combustion by means of in-cylinder visualization and absorption spectroscopic measurements. The results obtained for neutral and basic Ca-based additives revealed that the former had an effect on advancing the time of autoignition.

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 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.

Homogeneous Charge Compression Ignition (HCCI) engines have attracted much attention and are being widely researched as engines characterized by low emissions and high efficiency. However, one issue of HCCI engines is their limited operating range because of the occurrence of rapid combustion at high loads and misfiring at low loads. It is known that knocking accompanied by in-cylinder pressure oscillations also occurs in HCCI engines at high loads, similar to knocking seen in spark-ignition engines. In this study, HCCI combustion accompanied by in-cylinder pressure oscillations was visualized by taking high-speed photographs of the entire bore area. In addition, the influence of internal exhaust gas circulation (EGR) on HCCI knocking was also investigated. The visualized combustion images revealed that rapid autoignition occurred in the end-gas region during the latter half of the HCCI combustion process when accompanied by in-cylinder pressure oscillations.

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.

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.

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.

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.

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.

Engine downsizing with a turbocharger / supercharger has attracted attention as a way of improving the fuel economy of automotive gasoline engines, but this approach can be frustrated by the occurrence of abnormal combustion. In this study, the factors causing abnormal combustion were investigated using a supercharged, downsized engine that was built by adding a mechanical supercharger. Combustion experiments were conducted in which the fuel octane number and supercharging pressure were varied while keeping the engine speed, equivalence ratio and intake air temperature constant. In the experiments, a visualization technique was applied to photograph combustion in the combustion chamber, absorption spectroscopy was used to investigate the intermediate products of combustion, and the cylinder pressure was measured. The experimental data obtained simultaneously were then analyzed to examine the effects on combustion.

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.

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.

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.