Thrust generation by pulse combustion of gas in a submerged chamber

Abstract

This paper presents the results of experimental and theoretical studies of the hydrodynamic processes occurring during gas combustion in a vertical cylindrical chamber submerged in water. It is shown that combustion of a single portion of a stoichiometric propane–oxygen mixture leads to cyclic generation of force impulses on the thrust wall: the first impulse is generated due to the combustion of gas, and the subsequent impulses are generated due to hydrodynamic oscillations of the gas cavity. A total specific impulse of 104–105s (105–106m/s) was experimentally obtained.Expressions for the adiabatic oscillation period of the gas cavity and the maximum impulse of the force acting on the thrust wall during expansion of the cavity were obtained by approximate calculations. It is shown that the period is proportional to the length of the chamber to a power of 0.65, and the maximal force impulse is proportional to the square root of the length of the chamber. The oscillation periods calculated from the maximum size of the cavity are in good agreement with experimentally measured period of the first pulsation. Calculated force impulses are larger than experimental ones, which is attributed to thermal and hydrodynamic losses.The results of the study are applicable to water propellers, devices for regenerating filters, generating acoustic waves, and cleaning underwater bodies.