TURBULENT COMBUSTION OF PREMIXED FLAMES IN CLOSED VESSELS

An extensive series of experiments on spark-ignited explosions of prop ane-air mixtures in both turbulent and quiescent conditions in a cubic dosed vessel is described. Turbulence was produced by a moving grid, and the development with time of pressure and of flame area (from ligh t emission) recorded. The effects of grid-hole diameter, grid velocity , spark timing after passage of the grid, equivalence ratio, and initi tial pressure were investigated. Estimates of the rate of strain in th e unburnt gases were derived from hot-wire anemometry. Results indicat ed that rate of strain was a major factor governing the rate of combus tion. Theoretical simulations of explosions with a simple model were m ade, in which turbulence was characterized solely by the rate of strai n, and in which the decay of turbulence during explosions and the effe ct of changes in pressure on both burning velocity and flow field were taken into account. The simulations were compared with experimental r esults, and reinforced the idea that turbulence has the dual effect of causing wrinkling of flames and, especially for weaker mixtures, redu cing the burning velocity. An empirical relationship was found in whic h the logarithmic rate of wrinkling was proportional to the square roo t of the rate of strain. Some simple conclusions are drawn regarding p ractical application of the results.