Numerical investigations of supersonic combustion characteristics of thermally cracked fuels at typical pyrolysis temperatures

Abstract

Insight into supersonic combustion characteristics of thermally cracked fuels in a scramjet combustor is crucial for the development of next-generation supersonic flight vehicles. In the present study, four typical thermally cracked fuels at pyrolysis temperatures of 450, 550, 600, and 650 ℃ (denoted as ckori, ck550, ck600, and ck650) were selected. Improved delayed detached eddy simulation (IDDES) modeling with a compact skeletal mechanism and a transported multi-regime flamelet model was carried out to simulate the supersonic combustion of the target fuels in a full-scale scramjet combustor. Supersonic flow, mixing, and combustion characteristics of these fuels were quantitatively compared. Discrepancies in the combustion process are mainly at the cavity region, where the mixing efficiencies and combustion intensities of the first three fuels increase monotonically with the increasing pyrolysis temperature, while that of ck650 locates between ck550 and ck600. The increase in pyrolysis gas content will enhance the mixing process, while the increase in injection pressure will suppress the heat/mass transport between fuel and incoming air. The mixing process dominates the distributions of intermediate radicals and main products. The first three fuels tend to combust under fuel-rich condition, while ck650 tends to combust under the stoichiometric condition, which explains the distributions of OH, CO, and CO2 concentrations. The premixed and non-premixed combustion modes coexist in the model scramjet combustor, and the non-premixed combustion mode dominates the combustion process of thermally cracked fuel.