Investigation of Flame Acceleration Enhancement for a Pulse Detonation Engine Initiation System

Abstract

This paper reports on the investigation of a novel method for detonation initiation that can be used for a Pulse Detonation Engine (PDE). A common method used to initiate a detonation wave is via flame acceleration, this initiation mode is known as deflagration-to- detonation transition (DDT). Rapid flame acceleration in a tube is achieved by the use of repeated orifice plates to produce turbulence in the unburned gas flow ahead of the flame. Previous studies in fuel-air mixtures have shown that flame acceleration obtained in a classically configured orifice plate laden tube, i.e., uniformly spaced and sized orifice plates with one end igniter, results in a detonation run-up distance which 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, 15.2 cm inner-diameter tube equipped with a primary igniter mounted centrally on the tube endplate. Equally spaced orifice plates with blockage ratio of 0.43 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 six orifice plates. The firing time of each igniter bank is controlled by an electronic circuit. The concept is that each spark initiates a flame ball thereby augmenting the flame area, and hence the volumetric burning rate, relative to that obtained using one igniter located at the endplate. 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.