Influence of upstream properties on detonation wave structure. Irreversible, unimolecular reaction with small rate parameter

Summary

Wood's analysis of detonation wave structure for an irreversible, unimolecular reaction with small rate parameter is used to study the influence of upstream properties on the coupling between pressure rise and reaction zones. The variation of a reduced distance Δζ due to adiabatic upstream burning, upstream heat addition, and variation of heat release per unit mass of reactant is considered. Δζ is the reduced distance between the point of minimum velocity (essentially the point of maximum pressure) and the point where the temperature is some chosen fraction of the final temperature, i.e., Δζ is a measure of the coupling between pressure rise and reaction zones.

The wave structure immediately downstream of the pressure rise zone is found to be most sensitive to adiabatic upstream burning but much less sensitive to upstream heat addition and variation of heat release per unit mass of reactant. The first two processes cause Δζ to decrease because the temperature and reaction rate at the pressure maximum are increased. The last process causes Δζ to increase slightly because in this case the temperature and reaction rate at the pressure maximum is decreased. The wave structure far downstream of the pressure rise zone is not altered by adiabatic upstream burning but is influenced by upstream heat addition and variation of heat release per unit mass of reactant. The latter two processes cause Δζ to decrease. It is also shown that the wave structure immediately downstream of the pressure rise zone, for detonation waves which initially consist of widely separated pressure rise and reaction zones, is very sharply altered by the three processes of upstream variation here considered. Upstream burning and upstream heat addition cause rapid reductions in |Δζ| while an increase in heat release per unit mass of reactant increases |Δζ| for the same reasons as noted in the case of more closely coupled waves.

Available experimental data are not directly applicable to the present results. However there is sufficient similarity between theory and experiment to support the qualitative trends predicted by this idealized analysis.