The Physical and the Chemical Part of the Ignition Delay in Diesel Engines

The ignition delay in a diesel engine is generally seen as consisting of two different consecutive although overlapping phases: the physical and the chemical ignition delay. As is commonly accepted, the physical ignition delay corresponds to the mixture formation, and the chemical delay to the time necessary to get an exponential increase in the chemical reaction rate.

In this paper it is shown that if the assumption is made that the ignition of the spray is started by the ignition of a single droplet, the physical ignition delay is determined by the chemical ignition delay. If the results of the ignition delay measurements reported in the literature are interpreted with respect to this ignition model, better understanding of diesel ignition is obtained.