Energy deposition characteristics of a pulsed detonation igniter through geometric manipulation

Abstract

This study investigates the transient energy deposition mechanisms of a detonation wave undergoing diffraction through a geometric area expansion and contraction. A subcritical detonation diffracts across a sudden expansion. The two expansion ratios studied resulted in two different modes of re-initiation: transverse wall reflections for 2.5 times the incoming diameter (D1) and reflection from an aft wall for 5D1. Re-initiation forms a supercritical detonation generating amplified pressures up to 2.5 times the Chapman-Jouguet pressure (PCJ). For the 2.5D1 expansion, amplification occurs between 6 < x/D1 < 12, attenuates to 1.5PCJ between 12 < x/D1 < 28, and decreases back to PCJ at the exit contraction. For the 5D1 expansion, re-initiation occurs at the downstream wall and thus the pressure measured at the exit contraction is approximately 2PCJ. Placement of an exit contraction within 5D1 of the peak pressure enables an amplified detonation to be extracted at the exhaust. It is also shown that a supercritical detonation does not achieve further amplification because the cell count is greater than the critical threshold, preventing diffraction and re-initiation. Simultaneous high-speed CH* chemiluminescence and schlieren imaging illustrate the amplification mechanisms of the decoupling and re-initiation process. Simultaneous pressure and wave speed measurements coincide with the optical diagnostics in terms of the decoupling and re-initiation dynamics