THE SENSITIVITY OF CHEMICAL KINETICS WITH TWO CHARACTERISTIC LENGTHS OF DETONATION DYNAMICS IN HOMOGENEOUS GASES

摘要

This work discusses the sensitivity of chemical kinetics with two characteristic lengths of detonation dynamics calculated with a steady, weakly diverging, reaction-zone model. These are the chemical lengths defined as the distance from the detonation leading shock to the inflection point of the temperature profile and the minimum radius for the existence of a self-sustained, spherically diverging detonation. Two detailed chemical kinetic mechanisms are implemented in the model to estimate the characteristic lengths for H_2/O_2 and H_2/air mixtures at different equivalence ratios and initial pressures. A high sensitivity to the chemical kinetic scheme is obtained, with discrepancies ranging from 20% to 80%. Calculated and measured critical radii are found to be of the same order, which supports the premise of this work to assess sensitivity from a hydrodynamic model rather than from unsteady 3D simulations. Nevertheless, the differences are very important, especially at higher initial pressures. Importantly, these large differences from one scheme to the other are of the same order as between experimental data themselves. The same high sensitivity should thus be expected from numerical simulations and, therefore, chemical kinetics requires proper calibration in a large range of initial pressures to reproduce experimentally observed detonation dynamics. The predictive ability of simulations should be considered with caution, especially if detailed chemical kinetic schemes are implemented. Detonation studies should remain driven by experiments and sound dimensional analysis. More fundamental work aimed at improving high-pressure, high-temperature chemical kinetics is necessary before simulation can be used as an effective design tool for detonation-based propulsive devices such as pulsed or rotating detonation engines.