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: Popen (venting structure opening), Pext (external explosion), and Phel (Helmholtz oscillations). Both Pext and Phel rise with increasing hydrogen content. At each blend level, Pext peaks at 1.87-6.42 kPa, while Phel ranges from 5.86 to 20.65 kPa. Pext plays a crucial role in peak overpressure during venting, particularly relevant for ventilation design considerations. To predict Pext, 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 methanehydrogen mixtures in the process industry.