Performance Evaluation of Ramjet Model in a Pulse Facility at Mach 4.5

Experimental tests on a small-scale gas-fuelled ramjet model were conducted in a pulse facility at Mach 4.5. The purpose was the generation of positive thrust and the optimization of the fuel injection system in order to maximize the combustion efficiency and, consequently, engine propulsion parameters such as specific thrust and specific impulse. Two independent fuel injection systems were used. A primary system was designed to operate as a combustion starter in the early phase of each test and as a cold fuel injector for the rest of the test time, while a secondary system injected cold fuel at all times. Hydrogen was generally used in both injectors, but in a few tests methane was also used as secondary fuel. The analysis of the test data allowed the evaluation of the main engine propulsion parameters and in particular the characterization of the engine performance in terms of thrust increment, uninstalled thrust, and specific impulse. Four different configurations of the secondary injection system were tested for a wide equivalence ratio range. Two of them gave the best results, with a maximum thrust coefficient of 0.63 and a specific impulse of the order of 10 km/s over a wide range of fuelling conditions.