Spontaneous ignition of fuel droplets in lean premixtures of fuel vapor and air

Experiments were carried out on the spontaneous ignition of single fuel droplets in lean premixtures of fuel vapor and air. The n-dodecane droplet was rapidly inserted into high temperature environments and the ignition delay time was obtained from the measurement of OH emissions. Methane and propane were employed as the fuel of premixtures. The waiting time between the introduction of premixture into the hot furnace and the start of experiment of droplet ignition is defined as the residence time. The calculation of chemical reaction of fuel vapor-air mixtures in high temperature during the residence time was also conducted in order to explore the time history of chemical species concentration. In the case of short residence time where the reaction of premixtures does not proceed so much, the ignition delay time is almost the same as that in the air environment, which indicates that the existence of fuel vapor in ambient environments has little effect on the spontaneous ignition behavior. The ignition delay time becomes larger than that in air in the long time residence time, which is due to the decrease in the oxygen concentration in premixtures.