Experimental Study on Combustion Modes in a Scramjet Engine

Abstract

Effects of experimental parameters on combustion modes were investigated experimentally in a directly connected wind tunnel facility that supplied vitiated airflow with total pressure of 1.0 MPa, total temperature of 1500 to 2400 K, and Mach number of 2.5. A supersonic combustor with constant cross-sectional area was used. No backward-facing steps and diverging section were attached. Fuel hydrogen was injected at an angle of 30 degrees to the airflow. The combustion modes were categorized into four: non-ignition, weak combustion, supersonic combustion, and dual-mode combustion. These combustion modes were organized in terms of total temperature, combustor length, and equivalence ratio. The effect of reaction in recirculation region formed upstream the injection holes became considerable with increasing the equivalence ratio. Under the same condition of combustor length, total temperature, and equivalence ratio, the combustion mode transited in a shorter combustor length in case of normal injection than in case of oblique injection. In case of normal injection, the size of the recirculation region probably had a greater effect on combustion modes than the combustor length. A simple model to predict the condition of the transition to the supersonic or dual-mode combustion was suggested, and agreed relatively well with experimental results in case of low equivalence ratio.