Numerical study of test gas vitiation effects on hydrogen-fueled scramjet combustion

The effects of major vitiated species (H ₂O and CO ₂) and minor vitiated species (H, OH and O radicals) produced by combustion air preheater on ignition and combustion of hydrogen-fueled scramjet were numerically investigated. Firstly, kinetic analyses with CHEMKIN SENKIN code were conducted to evaluate the effects of contamination on the ignition delay times of hydrogen fuel over a range of temperature and pressure variations. Then numerical simulation of a three-dimensional reacting flow in hydrogen-fueled scramjet combustor was performed. The two-equation shear stress transport κ-ω turbulence model was used for modeling turbulence and 33 reactions finite-rate chemistry was used for modeling the H ₂/air kinetics. The results show that: free radical species such as H, O, and OH may significantly promote the ignition process of hydrogen-air at relatively low initial temperature and pressure. However, H ₂O and CO ₂ have inhibition effects on the ignition process. Under the same conditions, H ₂O has more effective inhibition effects than CO ₂. The temperature and pressure rise due to combustion are lower in the air vitiated with H ₂O and CO ₂ because of their higher heat capacities and more dissociation. Combustion efficiency and thrust calculated for vitiated air case are lower than clean air case. These results indicate the importance of accounting for vitiation effects when extrapolating performance data from ground test to flight demonstration.