Effects of temperature perturbation on direct detonation initiation

Abstract

Direct detonation initiation is simulated considering detailed chemistry for H2/O2/Ar mixture. The objective is to examine and interpret the effects of local temperature perturbation on direct detonation initiation. Temperature perturbations with different amplitudes are introduced in the region where the blast wave decays quickly. For the case without temperature perturbation, the supercritical, critical and subcritical regimes for direct detonation initiation are identified by continuously decreasing the initiation energy. The quasi-steady period in the critical case is investigated in details. The thermal states of flow particles at different initial locations within the quasi-steady region are tracked and analyzed; and the mechanism for the development of an over-driven detonation after the quasi-steady period is discussed. When a cold spot with large amplitude of temperature perturbation is introduced, the direct detonation initiation is prohibited, which is expected since low temperature in a cold spot greatly reduce the chemical reaction rate. However, it is observed unexpectedly that a cold spot with small amplitude of temperature perturbation can promote direct detonation initiation. Similarly, a hot spot with small amplitude of temperature perturbation inhibits direct detonation initiation; and it promotes direct detonation initiation when its amplitude is large enough. Such unexpected observation is caused by the opposite effects of temperature perturbation: local low temperature reduces the chemical reaction rate while it also increases the local volumetric energy density.