Theory of spherically symmetrical droplet combustion with gas-phase fuel pyrolysis

Simplified analyses of spherically symmetrical combustion of an isolated fuel droplet are developed to account for fuel pyrolysis. Fuel pyrolysis is modeled as a high activation-energy process that occurs within a thin zone between the droplet and the flame. Accounting for fuel pyrolysis changes classical expressions for the transfer number because the flame must supply energy for fuel pyrolysis, which requires the flame to be located closer to the droplet. Sample calculations for combustion of heptane droplets in air at one atm indicate that transfer numbers, burning rates, and quasi-steady flame standoff ratios can be appreciably reduced when fuel pyrolysis effects are included in the analyses.