Test Gas Vitiation Effects in a Dual-Mode Scramjet Combustor

Abstract

An experimental study was conducted to characterize the influence of combustion air preheater major vitiate species (H 2 O and CO 2 ) on scramjet combustion. These species were added to an initially clean airflow that was supplied by an electrically heated facility. With dry air, the scramjet combustor operated in the supersonic mode at an equivalence ratio in the range of 0.25-0.32 and transitioned to dual mode over an equivalence ratio range of 0.35-0.37. At an equivalence ratio of 0.27, the combustor operated in the supersonic mode for three cases: 1) dry air, 2) air vitiated with 5% H 2 O by mole, and 3) air vitiated with 5% H 2 O and 2.5% CO 2 by mole. In the second case, the combustor pressure distribution decreased 10% relative to dry air and, in the third case, another 2% decrease was measured. At an equivalence ratio of 0.35, the combustor operated in the dual mode with dry air, but in the supersonic mode with 7 % H 2 O. This is the first demonstration of mode transition solely caused by test gas vitiation. It is therefore important to account for such effects when extrapolating from vitiated ground testing to flight.