Flame acceleration and deflagration-to-detonation transition in a channel with continuous triangular obstacles: Effect of equivalence ratio

Aiming to gain sufficient data to develop methods capable of predicting and evaluating the danger of potential explosion or even detonation hazards associated with industrial process piping systems, this paper experimentally studied the effect of equivalence ratio on flame acceleration and deflagration-to-detonation transition (DDT) of hydrogen-oxygen mixture in a channel equipped with continuous triangular obstacles. This obstruction can simulate the effect of continuous blockage or rough walls in process pipelines. High-speed schlieren photography and OH* chemiluminescence recording were used for visualization. Results show that significant vortex motion accelerates the delayed combustion between obstacles and generates strong jet flow to promote flame acceleration. DDT occurs when the equivalence ratio (phi) is from 0.25 to 2.5. Minimum detonation initiation time and distance are obtained at phi = 1.0 and 1.1. The equivalence ratio significantly influences DDT by affecting deflagration speed and shock strength. DDT mechanism for equivalence ratios closer to 1.0 is the survival of local detonation generated by intricate flame-shock interactions. While for equivalence ratios far from 1.0, i.e., extremely lean or rich fuel (phi = 0.25, 2.0 and 2.5), DDT can be formed due to a combined effect of viscous heating at the boundary layer and preheat caused by shock compression.