CFD Results of Ignition Enhancement for Scramjet Combustion

Recent experimental evidence, obtained from the University of Queensland, has shown combustion occurring in a scramjet flow where the average conditions are too mild for self-ignition to occur. The conditions are also too mild for self ignition in a single reflected shock region. Paull et al1 postulate that the OH radicals required for ignition are generated and accumulated in a series of “hot pockets”. A hot pocket is the high temperature region behind a reflected shock in the scramjet. Each hot pocket is terminated by an expansion wave. The OH radicals are thought to be generated in the hot pocket and to remain chemically frozen during passage through the following expansion wave. The next hot pocket adds to their number. When OH concentration exceeds a threshold level, combustion proceeds with significant heat release. This process is known as a ‘radical farm’ effect. The results reported here are the observation and examination of radical farm behaviour in computed 2D scramjet combustion chamber flows of premixed hydrogen and air. Preliminary analysis is also reported of results of the corresponding 3D, non-premixed flow computation