Effects of fluctuations in concentration on detonation propagation

Abstract

The authors examine the effects of inhomogeneity in the equivalence ratio on detonation propagation by using a set of two-dimensional numerical simulations of the detailed reaction chemistry of an H2/air mixture. A random field of fluctuations but with statistical characteristics is introduced, and several combinations of the root mean square (RMS) and characteristic length scales of the fluctuations are considered to investigate the evolutions of the cellular structure, speed of detonation, and shock pressure under these setups. The results indicate that an increase in the RMS enlarged the cell formed by the original triple points as well as the characteristic length scale to promote the transition from a single cellular pattern to a double cellular pattern. The large cell of the double cellular pattern was formed by triple points generated from local explosion, and the decoupling or curvature of the detonation wave within an extremely lean region was important for this process. Moreover, sustainable detonation propagation under these configurations benefited from the strong transverse detonation generated by the local explosion as well as the propagation of these original triple points along the stoichiometric region, where their collisions reinitiated detonation in the extremely lean region. The instantaneous and average speeds of detonation were calculated. The former followed the trend of evolution of the normalized potential instantaneous energy release, whereas the latter decreased with an increase in ∅′. However, the value of l∅ had a non-monotonic influence that can be attributed to two factors.