Experimental and theoretical investigations into overpressure during confined space explosions of methane-hydrogen mixture

This study aimed to deeply explore combustion and explosion behaviors within confined spaces fueled by methane-hydrogen blends. By experimenting in a 55 m³ chamber, it examined how different hydrogen mixing ratios (5%, 10%, 15%, and 30%) affect flame spread and overpressure buildup at an equivalence ratio of 1.1. Results showed that two main flame patterns emerge during venting: mushroom clouds and jet flames. Higher hydrogen percentages cause mushroom clouds to form earlier and grow larger; notably, a 30% blend produces a cloud 12% quicker than a 10% blend, reaching a maximum radius of about 2.7 m. Three types of overpressure were identified: P_open (venting structure opening), P_ext (external explosion), and P_hel (Helmholtz oscillations). Both P_ext and P_hel rise with increasing hydrogen content. At each blend level, P_ext peaks at 1.87–6.42 kPa, while P_hel ranges from 5.86 to 20.65 kPa. P_ext plays a crucial role in peak overpressure during venting, particularly relevant for ventilation design considerations. To predict P_ext, the study tested three engineering models and found that Taylor's spherical piston theory provided the closest match to experimental data, with a maximum error under 30% compared to other models. In summary, this research offers essential theoretical knowledge and practical evidence for designing safer ventilation and explosion relief systems for facilities handling methane-hydrogen mixtures in the process industry.