Influence of the hydrogen transverse injection mode in a scramjet combustor performance

Abstract

This paper focuses on the numerical investigation of the transverse hydrogen injection technique in the supersonic airflow on the combustor performance of a scramjet technological demonstrator developed at Universidade Federal do Rio Grande do Norte (UFRN). The UFRN's scramjet vehicle was designed to be fully operational at a hypersonic velocity of 2050 m/s (Mach number 6.8), at 30 km of altitude, which provided a temperature of 1156.95 K and supersonic velocity of 1414.39 m/s (Mach number 2.1), at the combustion chamber entrance. Hydrogen was transversally injected into supersonic airflow at a sonic speed of 1318.46 m/s. A set of 2D-RANS simulations of the reactive flow was performed in combination with a simplified chemical kinetics approach based on the finite-rate chemistry model, defined by a one-step global reaction based on Arrhenius expression to combustion modeling. The turbulence was modeled by the k-kl-ω transition model. Different transverse fuel injections with different dimensions and positioning of injectors were evaluated keeping the same inlet conditions: single-injection versus dual-injection modes. A detailed visualization of several flow phenomena, such as the formation of shock waves, and the performance combustion parameters on the combustor surface were discussed. The analyses indicated hydrogen combustion with a predominantly supersonic flow regime. The transversal injection caused the detachment of the boundary layer as indicated by the recirculation flow structures in the neighboring region next to the injectors. Flow analyses indicate that the purely oblique shock trains were established tending to redirect the airflow over the mixing layer and accelerate the hydrogen burning. Nevertheless, the results showed that this was a local effect since the downstream both mixing and combustion efficiency increased. The dual-injection mode proved to be a promising injection method due to the higher global fuel penetration, elevated from 27,9% to 33,8%, and higher combustion efficiency, increased from 10,33% to 21,99%, with reduced addition of total pressure loss, concerning the single-injection case. Additionally, the growth behavior of performance curves showed that an extension of the combustor downstream length can be indicated to maximize combustor performance.