Flamelet and distributed combustion in premixed turbulent flames

Abstract

Calculations are reported that compare the properties of idealized premixed flames in which either flamelet or distributed combustion occurs. The calculations are based on the Monte Carlo solution of a modelled transport equation for the joint probability density function (pdf) of the velocities and the reaction progress variable. In the joint pdf equation, it is the molecular diffusion term that is fundamentally different for the two types of combustion, and consequently different models for the term are employed. For flamelet combustion, at moderate at high Damkohler numbers, the progress variable pdf is a double-delta-function distribution, and the turbulent flame speed is more than twice the turbulence intensity (independent of the Damkohler number). For distributed combustion, on the other hand, even at high Damkohler number, the progress variable pdf shows significant probability of partially reacted fluid. The flame speed is less than in flamelet combustion and incraases with Damkohler number.