Combustion Characteristics of a Coaxial Porous Injector

Abstract

A coaxial porous injector was proposed for gas–liquid combustion for improved mixing performance compared to a conventional shear coaxial injector. The coaxial porous injector discharged a gas jet in a direction normal to the center liquid core, and it was surmised that the momentum transfer from the radial gas jet to the axial liquid jet occurred more efficiently than with a traditional shear coaxial injector. To validate the effectiveness of this idea, the combustion performances of a coaxial porous injector and a shear coaxial injector were compared by conducting a hot-firing test using nitrous oxide-ethanol as propellant. The momentum flux ratio at the injector tip was selected as a spraying condition index, and the characteristic velocity efficiency was considered as a combustion performance parameter. The coaxial porous injector demonstrated higher combustion efficiency than the conventional shear coaxial injector, especially at lower-momentum flux ratio conditions. In addition, the comparison of spray images between the shear coaxial and coaxial porous injectors under ambient conditions supported the results of the hot-firing experiment.