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Swirl injector spray at high fuel temperature has features of rapid atomization and evaporation, compared to those at normal fuel temperature. These have a possibility to improve fuel consumption and emissions under cold start condition. The purpose of this study was to reveal the feasibility of improving cold start emissions of a DI engine by using high temperature fuel spray, to make a simulation procedure which can reproduce the spray formation process at high gasoline temperature and to incorporate it with a 3-D in-cylinder calculation of the mixture of in-cylinder gas and the spray. Results show that heating fuel was an affect to reduce the mass of wall-film. Thus using high temperature fuel has the possibility to improve fuel consumption and exhaust emissions under cold start condition.

In this experimental study, measurements were made on the characteristics of evaporating steady-state fuel spray injected into a high pressure and temperature cylindrical vessel by means of an electronically controlled common rail injection system. A fuel consisting of two components, n-octane and n-hexane, having different boiling points was used to investigate the characteristics of evaporation and mixing with the surrounding gas. Fluorescence characteristics of dopants excited by the YAG laser were calibrated by means of a spectroscope having an optical fiber. From the measurement of fluorescence wavelength, we decided that fluorobenzene and diethy-methyl-amine (DEMA) in a solution of fuel. Then, two-dimensional images were analyzed for each fuel component at liquid and gas phases, simultaneously. The results show that the density and temperature of the surrounding gas are two dominant factors influencing the penetration and evaporation of the spray.

A numerical model has been developed for predicting exhaust gas emissions including NOx HCHO, CH3OH and other chemical species in a direct injection diesel engine fueled with methanol. In this model, 39 species with related 157 elementary reactions are taken into account. The effects of air excess ratios and load conditions on the exhaust gas emission characteristics were investigated based on this kinetic model. The model can predicts the formation and destruction of chemical species in the combustion process and the formation of formaldehyde and NO2 during the expansion stroke.

An experimental study was carried out to make a quantitative analysis of fuel droplet diameter at a high pressure and temperature occurring in combustion systems. A fueling system was developed to atomize fuel into droplets having a single small diameter. By using this system, fueling was made into a visualized device where high pressure and temperature nitrogen flew under steady-state conditions. The laser induced fluorescence method was utilized to determine the n-dodecane fuel and iso-octane fuel droplet behavior and the phase doppler particle analyzer to measure the diameter and velocity of the droplets. As a result, quantitative analysis of a fuel droplet got possible. The results indicate that due to its lower boiling point, iso-octane droplets tend to evaporate much faster then dodecane droplerts.

In this study, the effect of town gas composition on gas engine rating is evaluated. Engine test work was carried out using a range of gases to characterize the tendency for knocking combustion to occur under stoichiometric and lean conditions. A matrix of 133 gases at a stoichiometric mixture ratio and that of 100 gases under a lean condition were used to allow in the statistical analysis of test results. Analyzing the test results, it is identified that efficacy on gas engine rating is n-C4H10, i-C4 H10, C3H8, C2H6 and H2 in a descending order. It is also clarified that the hydrocarbons have almost the same effect on gas engine rating under stoichiometric and lean conditions, whereas hydrogen greatly affects the rating under the lean condition.

An experimental study has been carried out to investigate the effects of supercharging on diesel spray dynamics and combustion characteristics. A rapid compression and expansion machine has been developed to reproduce diesel sprays and combustion. A copper vapor laser is used as a light source to visualize the spray. By synchronizing the laser output to a high speed 16 mm camera, instantaneous photographs of the spray can be taken. It is shown that supercharging can increase air entrainment in the spray and its evaporation. As a result, ignition lag can be reduced while the early part of diffusion combustion is increased.

A numerical simulation model has been developed to predict the direct-injection stratified charge combustion in a constant-volume vessel. Important factors such as local fuel concentrations, their fluctuations and turbulent flow characteristics were measured throughout the vessel as functions of time. These data were utilized to estimate the burning rate composed of the turbulent fuel-air mixing rate and chemical reaction rate. The model can predict the combustion pressures and heat release rates measured for different ignition timings and spark locations.

Two conventional combustion chamber types and a re-entrant type of direct-injection diesel engine were compared in order to investigate the effects of heat transfer and in-cyliner flow associated with the combustion chamber geometry on combustion itself, engine performance and exhaust gas emissions. Heat transfer calculation and heat release analysis have shown that the re-entrant chamber tends to reduce ignition lag due to the higher chamber wall temperatures. In-cylinder flow measurements using hot wire anemometry have indicated that the re-entrant chamber generates a higher turbulence level, particularly around the top dead center, causing an increase in the rate of heat release. Thus, the re-entrant chamber can favorably improve both fuel economy and smoke, even though fuel injection timing is retarded to reduce NOx emission.

An experimental study has been made on stratified charge combustion which may possibly realize lean combustion in a speak ignition engine. In order to simulate charge stratification, methane was injected into a constant volume vessel, and its temporal and spatial concentrations were measured using a hot wire probe. Thus, fuel distribution maps were drawn throughout the vessel for successive timings after fuel injection. Then, ignitability was determined for various spark plug locations and related to the measured stratified charge. The results have shown that a local mixture exceeding its flammable limit for mean fuel-air ratio can be ignited with a proper turbulence of fuel concentration and that for fast burning of the whole charge, spark ignition should be made at a downstream point of the fuel jet.

本研究では、予燃焼室ディーゼル機関を対象とし、主・副両室内の燃焼ガスを高速電磁弁によって採取・分析し、燃焼過程におけるNOx生成の時間的変化を追跡した。その結果、NOxは予燃焼室内での生成は比較的少なく、噴孔を通過した後の主燃料室内での燃焼により、多く発生することが確認された。また、各種の運転条件や予燃焼室の設計因子がNOxの生成過程に及ぼす影響についても明確にされた。