Detailed chemical reaction models of hydrogen-air mixture in stratosphere

The present paper is a part of our study concerning the jet nozzle emissions of a hydrogen-fueled future HSCT engine, whereupon environmental compatibility needs to be strictly watched to prevent our globe from destruction due to NOx/HOx contamination and Ozone depletion. An emphasis is upon the thermo-chemical process to produce pollutants, namely, NOx at such a propulsion system that inevitably operates in the stratospheric atmosphere. Calculations were first performed for H2 combustion with high temperature air, whence the resultant composition of H-N-O chemically active reactants was input to the vehicle external nozzle entrance. This preparation is necessary to simulate the core exhaust gas chemistry without carrying out the engine through-flow analysis. Non-equilibrium chemical kinetic models were then applied for identifying the chemical reaction process between the hot core exhaust jet and the ambient stratospheric air of low temperature. Computational improvements concerning the numerical stiffness due to multi-species reactions were also achieved under a newly developed scheme to increase the time step by a factor of 100 with numerical stability which is promising to be coupled with the fluid dynamic equations to reveal the details of reactive supersonic shear flow. The latter aspect will be treated in a companion paper shortly to follow elsewhere.