Effects of radicals on initiations of detonations in a pulse detonation engine

Initiations of detonations are studied. Through numerical experiments it is shown that the initiation is facilitated if hot products from a previous cycle is mixed with the fresh fuel-air mixture. Among other things the hot products consist of free radicals, and the elevated temperature increases the reaction rate of the fuel-air they are mixed with. The effect of adding these hot products are studied through numerical experiments. Simulations of initiations of detonations - both direct and through transitions from deflagrations - show that the likelihood for a detonation to evolve is greatly enhanced if hot products are initially mixed with the cold fuel-air mixture. By initially removing the radicals from this mixture it is demonstrated that it is the radicals - and not the elevated temperature - that is responsible for this effect. The importance of the radicals is also verified through simulations of constant volume explosions. Furthermore it is shown that the state of the hot products and the quantities of radicals, which remains in the engine after the detonation has left the pulse detonation engine and the pressure has decreased to ambient (i.e., the engine is ready for the next cycle), are more than enough to provoke these dramatic changes.