A Simple Model of Off-Stoichiometric Premixed Fuel Rich Spray Flames with Droplet Evaporation and Pyrolysis

Abstract

Fuel droplets that manage to traverse the main reaction zone of a one-dimensional offstoichiometeric fuel-rich laminar spray flame enter a hot, oxygen-free environment under which conditions their pyrolysis occurs. Under such circumstances the droplets release pyrolysis products which may diffuse back towards the flame front thereby effectively supplying a second (pool of) fuel different to the (first) fuel that was released due to pre-flame droplet evaporation.A new simple mathematical model of the propagation of a spray flame that includes this phenomenon is presented in this work for the first time and a formula is given for the burning velocity. It is shown that under certain operating conditions flame velocity enhancement may occur as a result of the additional fuel supply. Although the effect is limited to a few percent it is pointed out that it may be significant in cases of borderline flame stability and/or ignition/extinction.