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This study clarified the influence of hot gas jet on combustion enhancement effect for lean mixture in the plasma jet ignition. The hot gas jet was generated by the high temperature plasma and was ejected from igniter after plasma jet finished issuing. In combustion tests, propane-air mixture at equivalence ratio of 0.6 was used and the mixture was filled in the combustion chamber at atmosphere pressure and room temperature. For generation of the hot gas jet, the standard air was filled in chamber at same conditions and the hot gas jet was visualized by schlieren method in the absence of combustion. The combustion development processes were also visualized and the combustion pressure was measured. The discharge voltage, discharge current and the plasma luminescence were also measured. The plasma luminescence disappeared within 0.05 ms for any experimental conditions. When cavity depth was deep and orifice diameter was small, the maximum plasma luminescence height was short.

The purpose of this study is to elucidate the development process of hot kernel generated by the laser induced breakdown and to clarify the relationship between corona discharge application and flame propagation. The mixture can be ignited by the laser induced breakdown. Nd:YAG laser is used for the ignition and laser light is optically focused on the central part of combustion chamber by a plano convex lens. The hot kernel is observed in the absence of combustion and is rapidly developed into the laser incidence side. The homogeneous propane-air mixture is used and six equivalence ratios between 0.7 and 1.5 are tested. For generating the positive corona discharge in the combustion chamber, a non-uniform electric field is applied by the needle to plane gap. In a lean mixture, the whole flame front shifts to downward from the breakdown point and, in the rich mixture region, the combustion is strongly enhanced.

The aim of this research was to investigate the mechanism causing autoignition and the effect of exhaust gas recirculation (EGR) on combustion by detecting the behavior of the OH radical and other excited molecules present in the flame in a spark ignition engine. The test equipment used was a 2-cycle engine equipped with a Schnürle scavenging system. Using emission spectroscopy, the behavior of the OH radical was measured at four locations in the end zone of the combustion chamber. The OH radical plays an important role in the elemental reactions of hydrocarbon fuels. When a certain level of EGR was applied according to the engine operating conditions, the unburned gas became active owing to heat transfer from residual gas near the measurement positions on the exhaust port side and the influence of excited species in the residual gas, and autoignition tended to occur.

The study deals with the light absorption and emission behavior in the preflame reaction interval before hot flame reactions.(1-3) Absorption spectroscopy was used to measure the behavior of HCHO and OH radicals during a progression from normal combustion to knocking operation. Emission spectroscopic measurements were obtained in the same way that radical added HCO. Radical behavior in preflame reactions was thus examined on the basis of simultaneous measurements, which combined each absorption wavelength with three emission wavelength by using a monochromator and a newly developed polychromator.(4-5) When n-heptane (0 RON) and blended fuel (50 RON) were used as test fuel, it was observed that radical behavior differed between normal combustion and knocking operation and a duration of the preflame reaction was shorter during the progression from normal combustion to a condition of knocking.

In plasma jet ignition, combustion enhancement effects are caused toward the plasma jet issuing direction. Therefore, when the igniter is attached at the center of cylindrically shaped combustion chamber, the plasma jet should issues toward the round combustion chamber wall. The plasma jet igniter that had a concentric circular orifice has been developed. It is expected that the plasma jet is issued and is diffused from concentric circular orifice toward the combustion chamber wall. Relationship between plasma jet and igniter configuration was experimentally clarified. Plasma jet can issue from the entire concentric circular orifice for some igniter. Plasma jet is extended with increasing concentric circular orifice area. Plasma jet penetration increases with increasing concentric circular orifice width.

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.

In this study, a spectroscopic method was used to measure the combustion characteristics of a test diesel engine when operated on dimethyl ether (DME) under a homogenous charge compression ignition (HCCI) combustion process. A numerical analysis was made of the elementary reactions using Chemkin 4.0 to perform the calculations. The results of the analysis showed that compression ratio changes and the methane additive influenced the autoignition timing in the DME-HCCI combustion process. In the experiments, reducing the compression ratio delayed the time of the peak cylinder pressure until after top dead center, thereby increasing the crankshaft output and thermal efficiency. The addition of methane enabled the DME-HCCI engine to provide crankshaft output equivalent to that seen for diesel engine operation at a low equivalence ratio. This paper discusses these effects in reference to the experimental and calculated results.

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. However, because HCCI engines lack a physical means of initiating ignition, it is difficult to control the ignition timing. Another issue of HCCI engines is that the combustion process causes the cylinder pressure to rise rapidly. The time scale is also important in HCCI combustion because ignition depends on the chemical reactions of the mixture. Therefore, we investigated the influence of the engine speed on autoignition and combustion characteristics in an HCCI engine. A four-stroke single-cylinder engine equipped with a mechanically driven supercharger was used in this study to examine HCCI combustion characteristics under different engine speeds and boost pressures.

This study was conducted to investigate the influence of cooled recirculated exhaust gas (EGR) on abnormal combustion in a Homogenous Charge Compression Ignition (HCCI) engine. The condition of abnormal HCCI combustion accompanied by cylinder pressure oscillations was photographed with a high-speed camera using a 2-stroke optically accessible engine that enabled visualization of the entire bore area. Exhaust gas was cooled with a water-cooled intercooler for introducing cooled EGR. Experiments were conducted in which the quantity of cooled EGR introduced was varied and a comparison was made of the autoignition behavior obtained under each condition in order to investigate the influence of cooled EGR on abnormal HCCI combustion. The results revealed that cylinder pressure oscillations were reduced when cooled EGR was introduced. That reduction was found to be mainly ascribable to the effect of cooled EGR on changing the ignition timing.

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.

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.

Homogeneous Charge Compression Ignition (HCCI) combustion has attracted widespread interest in recent years as a clean, high-efficiency combustion system. However, it is difficult to control the ignition timing in HCCI engines because they lack a physical means of inducing ignition. Another issue of HCCI engines is their narrow operating range because of misfiring that occurs at low loads and abnormal combustion at high loads. As a possible solution to these issues, this study focused on the application of a streamer discharge in the form of non-equilibrium plasma as a technique for assisting HCCI combustion. Experiments were conducted with a four-stroke single-cylinder engine fitted with an ignition electrode in the combustion chamber. A streamer discharge was continuously generated in the cylinder during a 720-degree interval from the intake stroke to the exhaust stroke.

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.

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.

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.

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.

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.

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 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.

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).