Hydrogen autoignition under varying methane blends: Experimental analysis and prediction model development

This study investigates the effects of methane volume fractions on hydrogen autoignition. Experiments are conducted on an autoignition platform with a cylindrical release tube, focusing on the impact of methane volume blending ratios (0 %, 10 %, 20 %, and 30 %) on critical autoignition pressure (P_cr), shock wave velocity, and flame morphology. Results show that methane significantly suppresses hydrogen autoignition. Under pure hydrogen conditions, the critical autoignition pressure (P_cr) is 4.44 MPa, and the average shock wave velocity is 1185.5 m/s. When 10 % methane is blended, the critical autoignition pressure (P_cr) markedly increases to 8.63 MPa (approximately twice that of pure hydrogen), while the shock wave velocity slightly increases to 1230.4 m/s. However, at 20 % and 30 % methane, autoignition is not observed even at pressures over 17 MPa. Theoretical model for shock-induced ignition is employed in combination with three commonly used reaction kinetics mechanisms: GRI 3.0, FFCM-1, and Aramco 2.0. The results indicate that the theoretical model exhibits significant deviations and is not well suited for predicting the autoignition behavior of methane-hydrogen mixtures. A GRNN model is developed by integrating experimental and literature data, achieving 72.55 % accuracy at low methane blending ratios, outperforming conventional models. This GRNN model provides a new approach for predicting autoignition criteria in methane-hydrogen mixtures, offering insights for safe discharge and storage tank design in industrial processes.