Influence of chemical kinetics on spontaneous waves and detonation initiation in highly reactive and low reactive mixtures

TL;DR

This study compares simplified one-step chemical models with detailed chemical models in simulating detonation initiation, revealing significant differences especially in methane-air mixtures, and highlights the limitations of simplified models for accurate explosion mechanism analysis.

Contribution

The paper demonstrates that one-step models inadequately capture the chemical kinetics influencing detonation initiation, especially in methane-air mixtures, emphasizing the need for detailed chemical modeling.

Findings

One-step models underestimate hot spot sizes needed for detonation.

Detonation initiation thresholds differ significantly between models.

Detailed models show higher sensitivity to temperature gradients.

Abstract

Understanding the mechanisms of explosions is important for minimizing devastating hazards. Due to the complexity of real chemistry, a single-step reaction mechanism is usually used for theoretical and numerical studies. The purpose of this study is to look more deeply into the influence of chemistry on detonation initiated by a spontaneous wave. Results of high resolution simulations performed for one-step models are compared with simulations for detailed chemical models for highly reactive and low reactive mixtures. The calculated induction times for H2/air and for CH4/air are validated against experimental measurements for a wide range of temperatures and pressures. It is found that the requirements in terms of temperature and size of the hot spots, which produce a spontaneous wave capable to initiate detonation, are quantitatively and qualitatively different for one-step models compared to the detailed chemical models. The impact of detailed chemical model is particularly pronounced for the methane-air mixture. In this case, not only the hot spot size is much greater than that predicted by a one-step model, but even at elevated pressure the initiation of detonation by a temperature gradient is possible only if the temperature outside the gradient is so high, that can ignite thermal explosion. The obtained results suggest that the one-step models do not reproduce correctly the transient and ignition processes, so that interpretation of the simulations performed using a one-step model for understanding mechanisms of flame acceleration, DDT and the origin of explosions must be considered with great caution.