Numerical Investigation of the Influence of Fuel Concentration Gradient on Propane/Oxygen Detonation Propagation

In this paper, one- and two-dimensional numerical simulations are carried out to study the effects of fuel concentration gradients (such as steep, intermediate and shallow) on the detonation wave behavior. The equivalent ratio range of detonation propagation, the quenching mechanism and the change of cell size are discussed in detail. The simulation results show, as the fuel concentration gradient increases, the detonation wavefront decays faster and decouples into a leading shock and a following flame at equivalence ratios of 0.68, 0.64 and 0.62, respectively. Moreover, there are two modes of the quenching mechanism. One occurs in the steep gradient that the detonation wave fails rapidly. The O2 in front of the detonation wave passes through the detonation wave and forms some unburned O2 pockets. The unburned pockets are affected by the marginal walls and reduce the heat release. The other occurs in the intermediate and shallow gradients that more triple points will survive in the flow field, which leads to a difference in the propagation speed of the detonation wavefront. This makes the detonation wavefront bent and deformed. The unburned O2 pockets are affected by the strong instability near the triple points and show different distribution characteristics compared with the steep gradient, which may be helpful to the detonation propagation. In addition, as the fuel concentration gradient increases, the triple points moving toward the wall gradually disappear while the triple points that move toward the center can continue to survive, which leads to the gradual increase in cell size and irregularity of the cell structure.