Experimental Investigations on the Ignition Delay Time of Freely Falling Liquid Fuel Droplets

The ignition delays of freely falling liquid fuel droplets in a high-temperature environment were determined experimentally as a function of the surrounding parameters and droplet composition. Two different groups of fuels have been categorized based on the viscosity and volatility of each fuel. In the first group, for diesel and kerosene, the ignition delay time decreases with increasing system temperature due to low viscosity and thereby high volatile nature of fuels. Whereas, in the second group, C-heavy oil and blended renewable fuel shows an increase in the ignition delay time with increasing the system temperature and thereby shows the negative temperature coefficient (NTC) behavior due to high viscosity and low volatile characteristics of those fuels. In the case of low viscosity carbon residue fuels with low ignition temperature, they may vaporize early and decrease in the ignition delay time. But for high viscosity carbon residue fuels and with high ignition temperature, it may prolong the vaporization time and thereby physical delay. Evidently, the physical parameters and therefore the physical delay are the predominant factors in the NTC behavior of such high hydrocarbon liquid fuel droplets.