A two-step chemical scheme for auto-igniting and propagating kerosene flames at reheat conditions

Abstract

A methodology to build reduced schemes able to capture the main flame features and combustion mode in a sequential burner is proposed. This is here applied to derive a two-step scheme for kerosene flames at reheat conditions typical of aircraft engines for Large Eddy Simulations applications. It comprises 6 species (kerosene, O2, N2, CO2, CO, H2O) and two reactions where only two kinetic constants are adjusted: the pre-exponential constant of the reactions are changed as a function of the progress variable and equivalence ratio in order to match both auto-ignition times and premixed flame speeds in rich conditions. Vitiation levels are taken into account through the equivalence ratio ϕpf characterizing the oxidizer stream composition in the reheat combustor. The novel two-step scheme is validated against semi-detailed chemistry for 1D laminar kerosene/vitiated air flames with decreasing inlet velocity (thereby decreasing reactant residence time) changing from auto-igniting flames at high inlet velocities to propagating flames flashing back at low inlet velocities. The scheme is proved to capture auto-igniting as well as propagating flames found in afterburner conditions at very low computational cost and with a precision comparable to complex chemical schemes.