Interference Between Cnstituents in Spontaneous Ignition and Flame Propagation of Hydrocarbons

本研究的目的是澄清燃料对喷雾点火和预混料点火的影响，并注意燃料成分之间的干扰。首先，利用快速压缩机和流动反应器中的气体取样技术，从化学角度研究了燃料在点火过程中的变化。结果表明，由于相邻初氧化混合物提供的热量使温度升高，燃料先分解为小碳氢化合物，然后开始快速大量放热。包括小碳氢化合物在内的中间化学物质的生成速度影响燃油喷雾的点火延迟。其次，根据新建造的装有高压燃油喷射系统的定容容器的实验结果，讨论了燃料-空气混合与燃油效果的关系。在喷射压力为80 ~ 160mpa，喷嘴孔径为0.14 ~ 0.22mm的条件下，对点火延迟和点火过程中的压力变化过程进行了测量和研究。结果表明，在小喷孔高压喷射工况下，燃油对点火延迟的影响减小。该效应仅在低环境压力下观察到，其中燃料氧化速度较慢。据推测，由于燃料-空气的快速混合，局部混合物温度的快速升高缩短了小碳氢化合物积聚所需的时间。在一定的环境温度范围内，直链饱和烃是产生中间物质的主要来源，而燃料中的芳烃在着火前是不活跃的物质。这就是为什么在燃料中加入芳烃时点火延迟的原因。标称活化能随温度的变化不仅受燃料成分的影响，还受燃料-空气混合率的影响。

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.