Novel Testing of a Water-Breathing Naval Ramjet at Underwater Cruise Conditions

This paper presents, for the first time, firing tests and results measured during a hybrid-propellant marine water-breathing ramjet operation at underwater cruise conditions. The firing test demonstrated ignition under water, stable combustion, and a significant increase in chamber pressure due to the introduction of water by the ram effect. The exclusive test facility used to accommodate this unique experiment is described along with a detailed explanation of the motor design. In addition, a theoretical model to predict the performance of the motor is shown along with the numeric process used to solve the model. Measurements taken during the dynamic firing test reveal good compatibility with the theoretical model. The theoretical model was also used to evaluate values that could not be measured during the experiment. The results found during this work fit previous results attained by static firing tests, demonstrating significant improvement in specific impulse due to addition of water. An improvement of 50% in specific impulse was demonstrated when comparing the results of an underwater dynamic firing test of a marine ramjet to those of a parallel rocket test conducted under identical conditions in the water basin.