The role of turbulence in the characteristic velocity and length of rocket combustors

Abstract

High-fidelity direct numerical simulations are conducted to investigate combustion performance in high-pressure methane-oxygen diffusion flames with different inlet turbulence. The results are post-processed to investigate the influence of turbulence on characteristic velocity and length. It is found that despite the eminent fuel-rich non-premixed configuration of the flame, a substantial amount of heat release takes place in premixed lean conditions. It is found that the occurrence of this phenomenon increases with the turbulent kinetic energy due to the mixing enhancement driven by the greater strain rate. The greater prevalence of lean combustion is beneficial for combustion performance near injection but detrimental for the completion of chemical reactions at downstream positions. It is found that excessive upstream oxygen consumption is responsible for this result. With more prevalence of lean combustion, oxygen is depleted sooner, and alternative reaction paths through carbon dioxide reduction are necessary to finalize the burning process. Moreover, it is observed that lower entry turbulence is beneficial for the downstream mixing intensity since it enhances the generation of radial velocity shear and flame-generated turbulence. The opposing effects of turbulence upstream and downstream determine the existence of optimal turbulence characteristics providing minimum characteristic length while achieving complete burnout. The combustion chamber volume savings associated with this optimal configuration are in the order of 50%.