On the Mechanism of Rapid Flame Propagation in a Rotating Flow

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The rapid flame propagation in a rotating flow is explained on the vortex bursting mechanism, in which it is considered that the hot burned gas of low density is forcibly involved into the unburned gas mixture of high density. In the first year, the relation between the flame speed and the rotating gas speed was examined and it was pointed out that quantitatively the theory could not explain the results.In the next year, the pressure distribution across the flame front was exaimed to substantiate the theory in which the pressure ahead of the flame is assumed to be lower than that behind the flame, because the centrifugal force is weak in the hot burned gas of low density, and hence, the pressure on the axis of rotation cannot be decreased much as compared with the ambient pressure, whereas the centrifugal force is strong in the unburned gas of high density, and hence, the pressure on the axis of rotation becomes much lower than the ambient pressure. Resultingly, the pressure behind the flame becomes higher than the pressure ahead of the flame.Using a high-response, micro-diffential manometer and a transient memory, the pressure distribution was measured for the flame propagating in a rotating mixture. For comparison, the pressure distribution was also measured for the flames propagating in a quiescent combustible mixture and in a non-rotating mixture stream. The results show that, as the theory predicts, the predicts, the pressure ahead of the flame is lower than the pressure behind the flame. However, it is shown that the flame apeed is only one half or one third the predicted speed. This is confirmed by the additonal experiments this year. The results obtained in the first year have been published in Progress in Astronautics and Aeronautics, and those in the last year will appear in Combustion Science and Technolgy.