Abstract: Water/fuel ratio is an important working parameter of water ramjet engines. A high water/fuel ratio tends to result in a low temperature flow in the water ramjets. When the temperature drops severely, condensation of water steam may occur and the reaction of steam and metal may stop, which will reduce the engine performance as a result. Taking the effects of these two factors into account, a method to select the overall and primary water/fuel ratios is investigated to obtain a high engine performance. For the configuration of the discussed water ramjet, two water intakes are positioned along the combustion chamber. The selection is based on a theoretical optimum water/fuel ratio from thermodynamic calculation, which is then modified in consideration of heat loss in real experiments. Ground direct-connect experiments are conducted under different water/fuel ratios. The results show that optimal overall and primary water/fuel ratios exist, and the method to predict them is also verified.

Key words: water ramjet engine, water/fuel ratio, combustion, thermodynamics, test