Exploring the chemical kinetic effects on the direct detonation initiation in H2-O2-Ar mixtures

Abstract

Chemical kinetics plays an important role in the direct detonation initiation (DDI) of various combustible mixtures. However, its impact on detonation dynamics has rarely been studied with detailed mechanisms. This study introduces the active subspace method to systematically explore the chemical kinetics impact on the unsteady detonation dynamics in DDI of H2-O2-Ar mixture, with a 13-species detailed mechanism. The kinetic effects on the ZND structure with sub-CJ shock speed (sub-CJ ZND structure) is first investigated, where three important reactions to the sub-CJ minimum shock speed, H + O2 = O + OH, H + O + M = OH + M and H2O + H2O = H + OH + H2O are identified. Then the active subspace method is further employed to analyze the kinetics impact on the critical initiation energy ( E cr ) predicted with the critical decay rate (CDR) model and critical decay time (CDT) model. Results show that the CDT model, which utilises the sub-CJ ZND model to compute the critical parameters, can properly capture the one-dimensional detonation dynamics. All the important reactions identified with the CDT model agree well with those of one-dimensional simulations. In contrast, the CDR model shares a similar active subspace with the constant volume auto-ignition process and fails to identify the less important reactions. The consistency in the key reactions between one-dimensional simulations and the CDT model implies that it is viable to employ the CDT model as an efficient surrogate for quantifying the kinetic effects in unsteady detonation dynamics.