Interference Between Cnstituents in Spontaneous Ignition and Flame Propagation of Hydrocarbons

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The purpose of this study is to clarify fuel effects on spray ignition and ignition of premixture with attention to interference between constituents in fuels. First the change of fuel during its ignition process was investigated in chemical aspects using a gas sampling technique in a rapid compression machine and a flow reactor. The results show that the fuel breaks down to small hydrocarbons before rapid and large amount heat release begins due to temperature increase by heat supplied from adjacent initially oxidized mixture. The production rate of intermediate chemical species including the small hydrocarbons affects the ignition delay of a fuel spray.Secondly the relation between fuel-air mixing and fuel effect was discussed based on the results obtained by using a newly constructed constant volume vessel equipped with a high-pressure fuel injection system. Ignition delays and courses of pressure during ignition process were measured and examined at the injection pressure of 80-160MPa and with the nozzle hole diameter of 0.14-0.22mm. The results reveal that the fuel effect on ignition delay diminishes at the high-pressure injection case with small nozzle holes. The effect was observed only in the case of low ambient pressure in which the fuel oxidation speed is slower. It is supposed that fast temperature increase in local mixtures shortens the time necessary for accumulating small hydrocarbons due to rapid fuel-air mixing. In a certain rage of ambient temperature, straight chain saturated hydrocarbons are dominant sources to generate intermediate species, while aromatic hydrocarbons in fuels act as inactive species before ignition. This is the reason why the ignition is delayed when aromatics are added into fuels. Dependency of nominal activation energy on temperature is influenced not only by fuel composition but also by fuel-air mixing rate.