Flame acceleration enhancement by distributed ignition points

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Journal of Propulsion and Power
This paper reports on the investigation of a novel method for promoting flame acceleration leading to detonation initiation in a tube. A common method used to initiate a detonation wave is via flame acceleration in an obstacle laden tube. Previous studies with fuel-air mixtures have shown that the measured detonation run-up distance, and corresponding run-up time, is too long for a PDE application. The objective of the present investigation is to enhance the flame acceleration process that leads to DDT by using multi-point ignition. Experiments were performed in a 3.05 m long, 14 cm inner-diameter tube equipped with a primary igniter mounted centrally on the tube endplate. Equally spaced orifice plates were placed in the first 2 m of the tube. A bank of four circumferentially equally spaced automotive spark plugs are located after each of the first three orifice plates. The firing time of each igniter bank is variable. The results indicate that flame acceleration is augmented early in the tube and maintained to the end. The reduction in the distance required for the flame to accelerate to a velocity on the order of the speed of sound in the combustion products is modest, on the order of 10%. However, the reduction in the time required to reach this velocity is much more pronounced which has an impact on the PDE cycle frequency. Flame acceleration was further enhanced by replacing the first few orifice plates with perforated plates with the same total flow area, e.g., the flame run-up distance was shortened by 30%. However, detonation initiation was not observed over the 3 m length of the tube in stoichiometric propane-air mixtures.