Inhibition Mechanism of CH₄ Addition on the Pressurized Hydrogen Spontaneous Ignition

Abstract

It is well known that the high spontaneous ignition risk of pressurized hydrogen poses a serious threat to hydrogen storage safety. Aiming to reveal the inhibition mechanism of the fuel-blending strategy on autoignition, the spontaneous ignition of the H 2 /CH 4 mixture suddenly released into a one-dimensional (1D) tube at high pressure is studied numerically with highresolution difference schemes and a detailed kinetics model. First, the basic spontaneous ignition features are obtained. It is observed that under the shock wave compression effect, the air in front of the high-pressure hydrogen jet is heated up to 1200 K when the bursting pressure is 90 atm. Thus, the onset of autoignition always occurs under a quite fuel-lean, high-pressure, and hightemperature condition. Moreover, after autoignition, multiflame regions are found in the mixing layer, which are two short-lived premixed flames and a diffusion flame. The 1D result suggests that the occurrence of the spontaneous ignition is not dependent on the wall boundary layer and the shock wave interactions. Subsequently, autoignition under different blending levels is examined. The comparison shows that a minor amount of CH 4 addition (3% by mole) results in a sixfold increase in the ignition delay. Through the simulations of the fuel with artificial property, reaction sensitivity analysis, and Damkoḧler number evaluation, it was found that the addition decreases the shocked air temperature, reduces the H radical accumulation rate, and increases the relative loss of free radicals on the reaction front. Our work demonstrates that the key to the fuel-blending strategy for diffusion autoignition inhibition is increasing the fuel molecular weight.