Ignition of fuel sprays: Deterministic calculations for idealized droplet arrays

Abstract

One-dimensional unsteady calculations have been performed to study a spray ignition process. A monodisperse fuel-air spray in contact with a planar hot wall is considered. A hybrid Eulerian-Lagrangian numerical scheme has been used to solve the two-phase equations. The studied parameters are the droplet size, hot wall temperature, cold gas temperature, initial fuel vapor concentration, distance between the hot wall and the nearest droplets, equivalence ratio, and fuel type. The effect of different droplet heating models is discussed. It is shown that, at certain equivalence ratios, ignition delays and ignition energies can be less in heterogeneous situations than in the limitings premixed case. The critical dependence of ignition upon the distance of the heat source to the nearest droplet indicates that, in practice, ignition of heterogeneous mixtures is probabilistic. That is, ignition criterion are not precisely determined by fuel type, droplet size distribution, and equivalence ratiol a range of ignition delays or ignition energies is found.