Interaction between a Fuel Droplet and Premixed Gas in Spontaneous Ignition Process

Abstract

Spontaneous ignition of an isolated fuel droplet in hot lean premixed gas was numerically simulated in order to study the interaction between a fuel droplet and premixed gas. Ambient pressure was 2.5 MPa, and ambient temperature was 753 K, so that they were within the operation range of practical reciprocal engines. Fuel was n-heptane both for the droplet and the premixed gas. Initial droplet diameter and equivalence ratio of premixed ambient gas were varied. Initial droplet diameter was set near ignitable limit of hot flame in the given ambient conditions, that is, 45 μm and below. Premixed ambient gas was set so lean that its hot-flame ignition delay was far longer compared to that of a droplet, that is, equivalence ratio was 0.2 and below. Even such lean fuel in the ambient gas lowered ignitable limit of hot flame in terms of initial droplet diameter and decreased cool-flame and hot-flame ignition delays of the droplet. Besides, the heat release from the droplet induced the burning of entire premixed gas, and the hot-flame ignition delay of premixed gas was drastically shortened.