Modeling and Analysis of Different Aspects of Finite-rate Chemical Kinetics in Hypersonic Combustors

Abstract

Hypersonic air-breathing propulsion systems offer more efficient access to space compared to traditional rocket based propulsion systems due to their higher specific impulse and reusability. However, actual implementation of hypersonic air-breathing engine is hampered by a number of technical challenges. First, a vehicle operating at high speeds (Mach 5 and above) will experience extremely high temperatures especially at the combustor walls. One proposed concept is to use the on board fuel itself for active cooling of the hot surfaces which results in significant reduction of the weight of the vehicle by eliminating the need for carrying cooling fluids and heat exchanger.When hydrocarbon fuels are exposed to high temperatures in cooling channels, they not only absorb heat physically (sensible heat), but also crack to smaller hydrocarbons and absorb chemical heat. This process is called endothermic pyrolysis which has two main benefits. First, it increases the cooling capacity of the fluid beyond its sensible heat by nearly a factor of two. Second, the cracked fuel components produced from the pyrolysis reduce the induction time of the fuel-air mixture in the combustor, which is an important parameter in hypersonic flights with short flow residence times. The fundamental analysis performed to understand various rate controlling reactions contributing to fuel pyrolysis in cooling channels and ignition phenomena in turbulent flame holding regimes are expected to advance design of future hypersonic vehicles.iii