Fuel Reactivity Controlled Autoignition and Combustion Characteristics in a Supersonic Combustor With Different Turbulence Models

Abstract

The choice of turbulence model significantly impacts the prediction of the supersonic combustion flow field. In this study, the transient autoignition process and steady supersonic combustion performance of methane fuel with adjustable reactivity in a scramjet combustor were numerically investigated, employing different turbulence models including standard k -ε, renormalization group (RNG) k -ε, and realizable k -ε. Within the flight Mach number range of 3.5–7.0 and activation energy coefficient range of 0.5–1.0, five distinct autoignition modes are observed: misfire, blowoff, diverging section combustion, flashback, and constant-area section combustion. For a given combustor inlet Mach number, equivalence ratio, and fuel temperature, each turbulence model corresponds to a distinct autoignition boundary. This discrepancy reflects the variations in the interaction between supersonic flow and chemical reaction. Moreover, the disparities are also evident in the characteristics of the steady supersonic combustion flow field. Specifically, at a flight Mach number of 7.0 and an activation energy coefficient of 1.0, both the standard k -ε and realizable k -ε models exhibit similar trends in the streamwise distribution of static temperature, as well as static pressure, Mach number, and combustion efficiency. When using the RNG k -ε model, autoignition occurs closer to the fuel injector, thereby attenuating flow disturbance caused by combustion heat. Consequently, mixing between the main flow and fuel is not significantly enhanced, resulting in a lower combustion efficiency at the combustor outlet. With the activation energy coefficient reduced to 0.5, reactions occur more readily under the Ma0=7.0 condition. All three k -ε turbulence models predict a constant-area section combustion mode, while they display notable differences in the reacting flow fields. These findings are valuable for analyzing how different turbulence models influence the autoignition process and for performance evaluation in supersonic combustion.