An analysis of the ignition of slot-injected gaseous hydrogen in a supersonic air stream

The effects of an initial air-side boundary layer on the ignition of slot-injected gaseous hydrogen by a hot supersonic air stream are treated analytically. Essentially, the treatment is based on the assumption of unit turbulent Prandtl and Lewis numbers, a mass flow difference model for the eddy viscosity and a linearization of the boundary layer equations performed in the Howarth-Dorodnitzin plane. Once the flow field is determined, an isotherm and streamline pattern is constructed. These patterns can be examined to see if regions exist with both T > T ig and fuel concentration above the lean ignition limit. If not, ignition is not possible. If these conditions are met in a region, then the streamline through this area can be followed downstream to see if sufficient time for ignition is available before passing into a colder or leaner region. Previously determined ignition delay correlations are used to estimate an ignition delay time which is then compared to the residence time of a fluid particle in the ‘hot spot’ in order to assess the likelihood of ignition. The results of parametric numerical examples are presented and discussed to display the influence of the various parameters.