Performance of a Dual-Mode Combustor with Multistaged Fuel Injection

Abstract

A scramjet combustor, which has a constant cross-sectional area combustor (designated as combustor 1), and a diverging combustor (designated as combustor 2), was examined with both single and two-stage fuel injection to determine whether it could be operated in the ramjet mode. The combustor was directly connected to a facility nozzle, the Mach number at the exit of the nozzle being 2.4. Total temperature and total pressure were 800 K and 1.0 MPa, respectively. Pitot pressure measurements and gas sampling for an equivalence (Φ) of 0.2 showed that there were both a separated region and a supersonic core region within combustor 1 with single-stage fuel injection. For Φ = 0.4, on the other hand, a uniform subsonic region without separation was formed. One-dimensional calculation showed that two-stage fuel injection, in which the second-stage fuel was injected into combustor 2, led to formation of a large subsonic region. The maximum (dF, [thrust with fuel]-[thrust without fuel]) was 37% higher than that with single-stage fuel injection, this increment being limited by occurrence of combustor-inletinteraction in both cases. Another type of two-stage fuel injection, in which both stages were within combustor 2, was conducted, and the maximum dF was found to be almost the same as that with two-stage fuel injection within both combustor 1 and combustor 2. It was also found that dF could be described as a linear function of an effective equivalence ratio ([total equivalence ratio] x [combustion efficiency at the combustor exit]) regardless of the fuel injection configuration. The effect on dF of the difference in total pressure loss due to the difference in fuel injection configuration was negligible because the scramjet combustor was operated in the ramjet mode. Ideal was estimated by one-dimensional calculation to evaluate the achievement factor for thrust ([thrust obtained by experiment]/[ideal obtained by one-dimensional calculation]), which was found to be 60% at most for the tested combustor under the tested conditions.