NUMERICAL STUDY OF IGNITION WITHIN HYDROGEN-AIR SUPERSONIC BOUNDARY-LAYERS

Development of scramjet engines requires a better knowledge of the cou pling between supersonic flow and combustion chemical kinetics. In thi s paper we consider a stationary uniform, laminar supersonic flow of a hydrogen-air mixture on a flat plate. Conditions of the flow at the o uter edge of the boundary layer are chosen such that the chemical time is ''infinitely'' large when compared to the transit time over the co mputational domain. Ignition is triggered inside the boundary layer by viscous dissipation effects and/or wall temperature. This problem is solved numerically by a finite difference technique coupled with a che mical kinetics special solver and using classical boundary-layer assum ptions, with two different types of boundary conditions: 1) adiabatic wall, and 2) constant temperature wall. Ignition of the reactive mixtu re within the boundary layer is observed as soon as either the freestr eam Mach number or the wall temperature are large enough. The combusti on zone can be described as made up of three different regions, each o f which depending on a particular coupling between chemical kinetics a nd fluid dynamics. The structure of this combustion zone is calculated for various freestream Mach numbers, different chemical kinetic mecha nisms, reactive mixture equivalence ratios, and freestream and wall te mperatures.