Experimental investigation of fuel cooled combustor

Hydrocarbon propelled scramjet engines are suitable for high-speed hypersonic flight. Yet, when flight velocities increase over Mach 5, vehicle thermal protection becomes very critical, as the incoming air cannot be used to cool down the engine. Consequently, scramjet engines cooling must be obtained by using the fuel as a coolant. In this sense, regenerative cooling is one of the most widely applied cooling technique; the fuel acts both as propellant and coolant, passing through cooling channels located between the inner and the outer wall of the engine, before being injected in the combustion chamber. In this context, a regeneratively cooled combustor allowing the experimental study of a regeneratively cooled scramjet has been designed. Tests are realized under both stationary and transient conditions using ethylene as fuel and air as oxidizer. The effect on combustor dynamics of two operating parameter, i.e. fuel mass flow rate (which is varied between 0.010 and 0.040 g.s-1) and equivalence ratio (which is varied between 1.0 and 1.5), has been investigated. It was observed that an increase in fuel mass flow rate between 16 and 20 % results in a raise of the heat flux density passing from the burned gases to the combustor wall between 2 and 28 %, due to a general increase in burned gases temperatures (about 5 to 20%). It was seen that, when equivalence ratio passes from 1.0 to 1.5, the average ratio between the heat flux density lost with the exhaust gases and the total heat flux density generated by fuel combustion passes from 0.24 to 0.15, depending on the operating conditions. The heat exchange efficiency of the cooling system has been evaluated. A hysteresis effect due to the heat transfer dynamics has been demonstrated. © 2016, American Institute of Aeronautics and Astronautics Inc, AIAA. All rights reserved.