Preliminary analysis of scramjet engines based on engineering models

A mathematical model for analyzing two-dimensional scramjets was developed. The inlet was modeled with the oblique shockwave relationships. The combustor and nozzle were treated with quasi-one-dimensional flow assumption and finite rate chemistry was also considered for hydrogen-air combustion, with a separate mixing model. The viscous flow effects were taken into account estimating the skin friction coefficient and the heat flux through the walls. Experiments were used to validate the model, with overall good agreement. Next, numerical simulations were performed to study how selected flow properties vary as freestream velocity increases from 2.0 to 2.5 km/s, with a correspondent flight altitude of 30 km. Two baseline scramjet configurations were investigated, each one with a different combustor geometry. Firstly, fuel-air equivalence ratio effects were investigated. This study revealed that the equivalence ratio has a substantial influence on major combustor flow properties but only a moderate influence on ignition position. These effects were attenuated as freestream velocity increases. Following, comparisons were made between the two different scramjets considering the effects of the combustor geometry. Flow properties showed moderate changes between one configuration to another. The most pronounced difference was found in the maximum pressure position. Also, the differences found were attenuated as freestream velocity increases.