Numerical Simulation of Evaporation,Ignition and Combustion of Transient Sprays

Abstract

Numerical simulations of transient sprays were made based on an Eulerian gas and a Lagrangian drop formulation coupled with chemical reactions for the gas and for soot.Computed profiles of axial and radial velocity,species and soot concentration,gas temperature,local or total heat release rate are presented to understand the overall and the internal structure of the combusting spray.Some of the computed results are compared with experiments taken in a rapid compression machine.The results indicate the following. (1) The computations predict the ignition delay,the transient configuration of the spray flame and drop penetration distance reasonably well.(2) The drops evaporate in the early stage of the spray combustion and the drop penetration distance is predicted well by taking account of the secondary breakup of the drops in the evaporating sprays. The secondary breakup is liable to occur at high pressure and high temperature atmosphere.(3) Ignition occurs at a hot spot in the off-axis region and is followed by the rapid spread of the combustion and the fast release of heat. (4) A flame front is formed downstream from the nozzle exit. Near the flame front, the local heat release rate is very intense where premixed combustion occurs. Gaseous turbulent diffusion dominates combustion of the fuel in the core of spray.

Key words:

• Transient spray
• evaporation
• ignition
• spray combustion
• numerical simulation