Downstream Ramjet-Mode Combustion in a Dual-Mode Scramjet Engine

Abstract

Downstream combustion ramjet-mode operation in a dual-mode engine combustor was studied experimentally with a Mach 2.5 wind tunnel. In this downstream combustion ramjet mode, subsonic combustion was attained in the downstream straight-duct section without a geometrical throat. The experimental results are presented. The total temperature and the total pressure in the vitiation air heater were 800 K and 1.0 MPa, respectively. Pitot pressure and gas sampling were measured on the exit plane of the combustion model. The combustion conditions of the downstream combustion ramjet mode were compared with those of the usual upstream combustion ramjet mode. Better thrust performance and combustion were observed in the upstream combustion ramjet mode. However, in the case of the downstream combustion ramjet mode, injection of a larger amount of fuel was possible and a large impulse function was attained. The downstream straight duct was required for sufficient reaction. The fuel did not go far upstream in the separation region in pseudo-shock. Nomenclature ER = equivalence ratio M = Mach number Pi = wall pressure at the entrance of the combustor Pp = pitot pressure Pw = wall pressure x = distance from backward-facing step y = vertical distance from the bottom z = transverse distance from side wall surface ηc = combustion efficiency φ = equivalence ratio