AUTOIGNITION-DELAY MEASUREMENT OVER LEAN TO RICH MIXTURES OF N-BUTANE AIR UNDER SWIRL CONDITIONS

The autoignition delays over lean to rich mixtures of n-butane/air under various speeds of swirl flow were measured in a rapid compression experiment, together with photographic observation at 3000 frames per second. A lot of interesting features of the autoignition delay and the autoignition process were observed. Especially, it has been found that the swirl preferentially lengthens the autoignition delays of richer mixtures while lean mixtures with equivalence ratios less than about 0.6 are affected only little. With the results of computer simulation, it is concluded that this preferential effect indicates that the adiabatic core, in which the autoignition chemistry proceeds adiabatically, breaks more easily in richer mixtures at higher swirl speeds. Although the detailed mechanism of this preferential breakdown could not be clarified, this and other features of the autoignition under the swirl were fully discussed and interpreted.