Effect of endothermic reactions on the global extinction strain rate of large hydrocarbon fuels

Abstract

When a hydrocarbon fuel is used as a coolant, the extreme environment can have a significant impact on the fuel composition. Heat exchange occurs through phase change, sensible heat extraction, and endothermic reactions experienced by the liquid fuel. From previous studies it has been demonstrated that the fuel composition changes significantly as well as the fuel properties as a result of the endothermic reactions. To investigate the effect of endothermic reactions on the fundamental flame behavior we have developed a counterflow flame burner that can measure the flame extinction strain rate of a thermally stressed fuel. The counterflow flame burner is coupled with a high-pressure reactor, capable of exposing the fuel to extreme conditions of 170 atm and 650 °C. Flame robustness is quantified by measuring the flame extinction strain rate. n-heptane is studied as a first attempt to understand the role of the endothermic reactions on the combustion and flame behavior of a liquid rocket propellant fuel. Modeling of the reactor and the counterflow flame is carried out using CHEMKIN. The flame extinction strain rate of the reacted n-heptane is compared with the unreacted n-heptane flame, thus allowing us to determine and extrapolate the role of endothermic reactions on the combustion behavior of jet and rocket fuels.