Proof-of-Principle Experiment of a Shock-Induced Combustion Ramjet

Abstract

By injecting and mixing the fuel upstream of the combustor and initiating the combustion of the fuel-air mixture by a shock wave in the combustor, shock-induced combustion ramjets offer the potential to drastically reduce the length and mass of scramjet propulsion systems. Based on extensive numerical gas dynamic and thermo-mechanical analysis, an axi-symmetric dual cone test object was designed and manufactured to demonstrate that it is possible to inject hydrogen into a high enthalpy supersonic air flow without causing premature ignition and subsequently induce combustion of this mixture by a strong oblique shock wave. The test object was instrumented with 16 thermocouples and a shadowgraph technique was used to visualize density changes in the flow field. A test series was executed in the TNO Free Jet Test Facility using the Mach 3.25 free jet nozzle in which the air flow stagnation temperature and the injected hydrogen mass flow rate was varied. Due to thermal expansion of the strut holding the test object, a small angle-of-attack was induced and resulted in different types of combustion occurring at the top and bottom sides of the test object. At the bottom, hydrogen was captured and subsequently burned in the boundary layer separation zone resulting in very high local heat loads. At the top side of the test object, shock-induced combustion occurred in the inviscid flow field only at a higher level of stagnation temperature with a peak heat load clearly downstream of the boundary layer separation zone. This experimental result is an important step in demonstrating the feasibility of a shock-induced combustion ramjet as a future hypersonic propulsion system.