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Effect of the ambient O2 concentration and pressure on the spray combustion characteristics of diesel fuel was experimentally examined using a high-temperature, high-pressure combustion vessel. The sequential images were captured by using a high-speed color video camera and were analyzed using the two color method to quantify the temporal variation of the soot temperature and KL factor. Based on a series of systematic experiments, it is confirmed that O2 concentration is the dominant factor affecting both the ignition delay and combustion period. The volumetric fraction of O2 in ambient air has great effect on flame temperature and NOx emission, however ambient pressure has little effect on both values. On the contrary both of the volumetric fraction of O2 in ambient air and the ambient pressure have large effect on soot production.

The objective of this study is to understand the fundamental spray combustion characteristics of FAME mixed with diesel oil. To examine the phenomena in detail, diesel spray flame formed in a constant volume high pressure vessel was visualized and the flame temperature and the KL factor were analyzed by two color method of luminous flame. The FAMEs examined in this study are PME, RME and CME, and compared with the combustion characteristics of diesel oil. From the systematic experiments, it is confirmed that the ignition delay and combustion period of bio diesel fuels are almost equivalent with those of diesel oil. The flame temperature decreased slightly with the bio fuel. Furthermore the total KL factor, a measure of the amount of soot in flame, decreased drastically by using the bio diesel fuel in the order of the mass fraction of oxygen in the molecule.

The effects of CO2 and N2 mixing and the effect of O2 concentration on intermittent spray combustion were examined experimentally under the same condition of ambient temperature and pressure, and the same injection pressure. Through the systematic experiments, it was confirmed that the O2 concentration is the dominant factor affecting ignition delay and combustion duration. The flame temperature becomes lower with the decrease of O2 concentration mainly due to the dilution effect. The decrease of flame temperature due to the dilution effect and that due to the thermal/chemical effect of CO2 was quantified. Concerning the soot production, with the decrease of O2 concentration, it is suppressed during the early stage of combustion, however it becomes higher in the middle to later stage of combustion.

In order to study the effects of EGR on diesel combustion fundamentally, the effects of CO2 and N2 mixing into ambient air on intermittent spray combustion were examined experimentally. Under the same condition of ambient temperature and pressure, and the same injection pressure, the rates of CO2 or N2 mixing were changed from 0 to 15% and the combustion characteristics of diesel spray were examined. Through the systematic experiments, it was explored that the ignition delay and the combustion period became longer with the increase of CO2 and N2 mixing, and the effect was larger in the case of CO2 mixing. The flame temperature became lower with the N2 mixing mainly due to the dilution effect. In the case of CO2 mixing, the flame temperature decreased notably, and the flame region with higher temperature became very small. The reason of this tendency was attributed to the dilution effect, the higher heat capacity of CO2 and the chemical effect of CO2.

The effects of aromatic components in fuel on ignition and combustion of intermittent spray were examined experimentally. Four types of fuel with different aromatic components, and with similar cetane number and calorific value were used in this study. Fuels were injected into the high-temperature and high-pressure vessel with the injection pressures of 100 MPa and 60 MPa using an electronically controlled fuel injection system developed by the authors. Injection rate shaping applied to the experiments was rectangular, which is a typical injection rate shaping of a common rail type injection system. Images of spray flames were captured using an ICCD camera under ambient conditions corresponding to a turbo-charged diesel engine, 6.1 MPa and 1030 K. A two-color pyrometry technique was applied to the images of spray flame to quantify two-dimensional distributions of flame temperature and soot in flame.

The effects of fuel injection rate shaping and injection pressure on flame temperature and soot production in intermittent spray combustion were investigated. Two-color technique was applied to the luminous image of free spray flame captured by an ICCD camera to evaluate the 2-D temperature and soot distributions in flame. In addition to the experiments, CFD calculations using KIVA-3V code were carried out and compared with the experimental data. The experimental and computational results showed that fuel injection rate shaping affected the temporal change of flame temperature and the emission of NOx. The optimal mode of injection rate shaping, in terms of NOx reduction, varied according to injection pressure. Concerning the soot production, fuel injection rate shaping affected the regions of soot production and the injection pressure affected soot oxidation especially in the latter stage of combustion.

The effects of fuel injection rate shaping and injection pressure on diesel combustion were investigated using an electronically controlled fuel injection system. An analysis of non-evaporating spray reveals that the rate of injection rate increase affects temporal spray evolution, and also that higher injection pressures enhance spray development, particularly in terms of spray width, for all modes of injection rate shaping. From photographs of spray flame and luminous flame radiation data, it is clarified that the enhancement of spray development significantly influences the growth of the spray flame in the initial stages of combustion and affects main combustion. The optimum mode of injection rate shaping, in terms of shortening the main combustion period, varies according to injection pressure.