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This study focused on a non-equilibrium plasma discharge as a means of assisting HCCI combustion.Experiments were conducted with a four-stroke single-cylinder engine fitted with a spark electrode in the top of the combustion chamber for continuously generating non-equilibrium plasma from the intake stroke to the exhaust stroke. The results showed that applying non-equilibrium plasma to the HCCI test engine advanced the main combustion period that otherwise tended to be delayed as the engine speed was increased. In addition, it was found that the combined use of exhaust gas recirculation and non-equilibrium plasma prevented a transition to partial combustion while suppressing cylinder pressure oscillations at high loads.

It is difficult to control the ignition timing of Homogeneous Charge Compression Ignition (HCCI) engines because they lack a physical means of igniting the mixture. Another issue of HCCI engines is their narrow operating range owing to the occurrence of misfiring at low loads and abnormal combustion at high loads. As a possible solution to these issues, this study focused on the generation of a streamer discharge using nonequilibrium plasma as a means of assisting HCCI combustion. A two-stroke engine that allowed visualization of the entire bore area was used in this study. A primary reference fuel blend (50 RON) was used as the test fuel. The streamer discharge was continuously generated in the end-gas region during a 360 deg. interval from the scavenging stroke to the exhaust stroke using a spark plug from which the ground electrode had been removed. Experiments were conducted in which the applied voltage of the streamer discharge was varied to investigate its effect on combustion.

This study investigated the effect of streamer discharge on autoignition and combustion in a Homogeneous Charge Compression Ignition (HCCI) engine. A continuous streamer discharge was generated in the center of the combustion chamber of a 2-stroke optically accessible engine that allowed visualization of the entire bore area. The experimental results showed that the flame was initiated and grew from the vicinity of the electrode under the application of a streamer discharge. Subsequently, rapid autoignition (HCCI combustion) occurred in the unburned mixture in the end zone, thus indicating that HCCI combustion was accomplished assisted by the streamer discharge. In other word, ignition timing of HCCI combustion was advanced after the streamer discharging process, and the initiation behavior of the combustion flame was made clear under that condition.

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.

Recently, urgent needs have arisen for improving the fuel economy of passenger cars. To improve the fuel comsumption, it is necessary to develop a technology that can improve fuel efficiency and weight-saving. This paper describes the development of a soundproof package to balance weight-saving with performance of acoustic isolation used to reduce engine noise. First, we developed a hybrid statistical energy analysis (HSEA) model to evaluate the performance. Second, by using the HSEA model, we (1) analyzed the power flow and dominant path from noise source to interior cavity, (2) extracted efficient sections such as dash, dash penetration parts, and floor so as to improve the performance. Using the above process, we developed a soundproof package that improves the performance without increasing the weight. As a result, we balanced weight-saving with performance of acoustic isolation using the HSEA model.

Attention has recently been focused on homogeneous charge compression ignition combustion (HCCI) as an effective combustion process for resolving the essential nature of combustion. Meanwhile, dimethylether (DME) has attracted interest as a potential alternative fuel for compression ignition engines. Authors measured the combustion process of DME HCCI by using a spectroscopic method. A diesel engine was used as the test engine. The results of these analyses showed that changes in the compression ratio, intake air temperature and equivalence ratio influenced the ignition timing in the HCCI combustion process. This paper discusses these effects in reference to the experimental and calculated results.

Attention has recently been focused on homogeneous charge compression ignition (HCCI) as an effective combustion process for resolving issues inherent to the nature of combustion. Dimethyl ether (DME; CH3OCH3) has attracted interest as a potential alternative fuel for compression ignition engines. We measured the HCCI process of DME in a test diesel engine by using a spectroscopic method. Simultaneous measurements were also done on exhaust emissions of hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). Based on the experimental data, this paper discusses the relationship between the equivalence ratio and the observed tendencies.

This study attempted to elucidate combustion conditions in a progression from normal combustion to knocking by analyzing the ion current and light emission intensity that occurred during this transition. With the aim of understanding the combustion states involved, the ion current was measured at two positions in the combustion chamber. Light emission spectroscopy was applied to examine preflame reactions that are observed prior to autoignition in the combustion process of hydrocarbon fuels. The results obtained by analyzing the experimental data made clear the relationship between the ion current and light emission during the transition from normal combustion to knocking operation.

A hybrid SEA modeling scheme has been developed and applied to obtain an accurate SEA model for a passenger car. In this study, using the SEA model as a reference, uniqueness of the SEA model will be discussed. The SEA model uniqueness will be measured in terms of how accurately dominant power flows are described in comparison with the reference SEA model. An innovative scheme to quantify the differences of the dominant power flow between the test SEA model and the reference SEA model will be developed. Using the scheme, it will be shown that the test SEA model approaches to the reference SEA model as the energy ratios are being matched. Here, the energy ratios, between input power subsystem and a subsystem responding to an excitation given to the input power subsystem, are measured. They have been used to develop the reference SEA model.

A hybrid SEA modeling scheme has been developed and applied to obtain an accurate SEA model for a passenger car. In this study, the detailed workflow associated with the hybrid SEA modeling scheme will be described. Each step in the workflow will be discussed in terms of the obtained data, the corresponding analysis and results. In those steps, several innovative methods for developing the hybrid SEA model will be presented. Finally, a road noise analysis will be performed using the hybrid SEA model to validate the SEA model for the passenger car. In order to demonstrate the accuracy of the model, the analysis results such as the sound pressure level of car interior will be compared with the measurements.

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. Light emission intensity was measured at wavelengths of 306.4 nm (characteristic spectrum of OH), 329.8 nm (HCO), 395.2 nm (HCHO). A four-cycle, air-cooled, single-cylinder gasoline engine with a side valve arrangement was used as the test engine. Light emission behavior was simultaneously observed at two positions (the end zone and the center zone) in the combustion chamber. The test fuel used was n-heptane (0 RON). The test engine was operated at three speed levels (1400, 1800 and 2200 rpm). As a result, preflame reactions were observed. It was also observed that the tendencies seen for the preflame reaction interval varied depending on the engine speed.

In this study, the heated fuels were provided to the diesel engine in order to activate the fuel before the injection. Two test fuels: the normal diesel fuel and cetane, which have different boiling points were used. For both normal diesel fuel and cetane, crank angles at ignition and maximum pressure are delayed and the maximum combustion pressure is decreased as the fuel temperature rises. In cases of large and middle mass flow rate of fuel injection, the brake thermal efficiency and brake mean effective pressure are decreased when the fuel temperature is higher than 570 [K]. However, in the case of small mass flow rate of fuel injection, the brake thermal efficiency is almost independent of fuel temperature. HC and CO concentrations in the exhaust gas emission show constant values regardless of fuel temperature. However, NOx concentration is gradually decreased as the fuel temperature rises.

A new concept of combustion which is using the characteristic of plasma jet ignition, that is the plasma jet diffusive combustion is proposed. The constant volume vessel is used for the experiment, and methanol is charged in the cavity of plasma jet injector and the air at room temperature and atmospheric pressure is charged in the combustion chamber. The combustion characteristic is analyzed by measuring the combustion pressure and visualization of the combustion process. The plasma jet injector configuration and the ratio of methanol volume to cavity volume influence not only the plasma jet diffusive combustion process but also the maximum combustion pressure. In cases of small orifice diameter, the plasma jet diffusive combustion is not recognized, and the maximum combustion pressure increases as the orifice area becomes large.

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).

The uniform lean methanol-air mixture was provided to the diesel engine and was ignited by direct diesel fuel injection. In this study, the internal EGR is added to this ignition method in order to activate the fuel in the mixture and to increase the temperature of the mixture before the ignition. It is confirmed that the lean methanol-air mixture of air-fuel ratio between 130 and 18 could be ignited and burned when the back pressure of 80 [kPa] is added. The ignition and combustion characteristics can be improved by the internal EGR, however the engine performance and NOx emission deteriorated.

The uniform lean methanol-air mixture was provided to the diesel engine and was ignited by the direct diesel fuel injection. The internal EGR is added to this ignition method in order to activate the fuel in the mixture and to increase the mixture temperature. The test engine was a 4-stroke, single- cylinder direct-injection diesel engine. The cooling system was forced-air cooling and displacement volume was about 211 (cm3). The compression ratio was about 19.9:1. The experiment was made under constant engine speed of 3000 (r/min). The boost pressure was maintained at 101.3 (kPa). Five values of mass flow rate of diesel fuel injection were selected from 0.060 (g/s) to 0.167 (g/s) and five levels of back pressure: 0), 26.7, 53.3, 80.0 and 106.6 (kPa) were selected for the experiment. The effect of internal EGR is varied by the back pressure level.

There is an urgent need today to improve the thermal efficiency of spark- ignition (SI) engines in order to reduce carbon dioxide emission and conserve energy in an effort to prevent global warming. However, a major obstacle to improving thermal efficiency by raising the compression ratio of SI engine is the easily occurrence of engine knocking. The result of studies done by numerous researchers have shown that knocking is an abnormal combustion in which the unburned gas in the end zone of the combustion chamber autoignites. However, the combustion reaction mechanism from autoignition to the occurrence of knocking is still not fully understood. The study deals with the light absorption and emission behavior in the preflame reaction interval before hot flame reactions.

In plasma jet ignition, combustion enhancement effects occur toward the plasma jet issuing direction. Therefore, when the igniter is attached at the center of cylindrically shaped combustion chamber, plasma jet should issue toward the round combustion chamber wall. The plasma jet igniter that had an annular circular orifice has been developed. The purpose of this study is to elucidate the relationship between the newly developed plasma jet igniter configuration and the combustion enhancement effects. In this newly developed plasma jet igniter, the fine scale turbulence appears on the flame front and flame propagates very rapidly. Plasma jet influences on the flame propagation for long period when the plasma jet igniter has issuing angle 90 [deg.] and large cavity volume. However, in the early stage of combustion, flame front area of issuing angle 45 [deg.] is larger than that of 90 [deg.], because the initial flame kernel is formed by the plasma jet.

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.

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.