Numerical investigation on the performance of internal flow and atomization in the recessed gas-centered swirl coaxial injectors

Abstract

Recessed gas-centered swirl coaxial (GCSC) injector has been widely applied in the liquid rocket engine (LRE), and its internal flow and atomization have a significant impact on the combustion downstream. The oxygen (gas)-kerosene (liquid) two-phase flow in the recessed chamber of GCSC injectors under the conditions of back pressure of 17 MPa is numerically simulated by the volume-of-fluid (VOF) method. The liquid film, atomization and gas-liquid two-phase flow fields are obtained for liquid flow with or without swirling. The atomization of liquid kerosene does not have typical atomization characteristic of a swirling injector but accomplishes in the recessed chamber by action of pneumatic force. The swirling flow in the outer injector is helpful to achieve higher gas-to-liquid axial momentum ratio for good atomization performance and smaller injector size as well as lower gas-to-liquid momentum ratio for longer liquid-film length and more steady mass flowrate. The droplet sizes of the spray, the length of liquid film and the sizes of GCSC injectors decrease with increase of the gas-to-liquid (axial) momentum ratio, while the liquid mass flowrate in the outer injector becomes much unstable due to a recirculation flow adjacent to the exit of outer injector. Therefore, it is found that increasing the gas-to-liquid (axial) momentum ratio has two contradictory effects on improving atomization performance and promoting combustion instability. To balance these contradiction influences, the corresponding limits of the gas-to-liquid (axial) momentum ratio for well-working GCSC injectors are defined in this paper. The lower and upper limits of the gas-to-liquid momentum ratio are 7.6 and 14, and the gas-to-liquid axial momentum ratio corresponds to 17.6 and 31. In actual engineering project, the gas-to-liquid (axial) momentum ratios of the GCSC injector investigated in this paper is 9 (20). It indicates that the limits proposed in this paper are reasonable.