RANS investigation of the effect of pulsed fuel injection on scramjet HyShot II engine

Abstract

Effective and efficient fuel–air mixing plays a critical role in the successful operation of scramjet engines. To enhance the fuel–air mixing in supersonic combustion systems with a short flow residence time, the pulsed fuel injection strategy in a realistic scramjet combustor flow condition provided by the HyShot II is numerically studied in this work. For this, 2D and 3D simulations of the hydrogen fueled HyShot II scramjet with pulsed fuel injections are performed. Emphasis is placed on the cold flow field characteristics and fuel–air mixing performance in the combustor. Reynolds-Averaged Navier–Stokes equations are solved with the implementation of the two equation k–ω SST turbulence model via using the ANSYS FLUENT v17.1. The pulsed fuel injection is numerically achieved by implementing a time-dependent total pressure pulse with the shape of a square wave. The total pressure peak is maintained as same as the one that chokes the fuel injector in steady operations. The numerical model is validated first by comparing the results with the experimental data available in the literature. It is then used to study the effect of the pulse injection with different frequencies. It is found that complicated waves structures are formed inside the fuel injector in pulsed fuel injections due to the total pressure pulse. These waves propagate outside the fuel injector and lead to the fuel streams with wavy patterns and the unsteady shock structures in the combustion chamber. Fuel penetration depths are not found to be increased for pulsed injections in this study, but much high turbulent kinetic energy (TKE) levels are observed especially inside the fuel injector. With the help of increased TKE, mixing efficiency is found to be improved for all of the pulsed fuel injection by up to 30%. This mixing improvement also strongly depends on the frequency applied.