Hydrogen influence on confined explosion characteristics of hydrocarbon-air mixtures at sub-atmospheric pressures

The peak explosion pressure and maximum rate of pressure rise of explosions in confined spaces are key safety parameters to evaluate the hazard of processes running in closed vessels and to design enclosures able to withstand explosions or of their vents used as relief devices. These properties are examined in the present paper, for hydrogen-hydrocarbon-air mixtures at sub-atmospheric pressures, using propane and n-butane as test fuels and variable hydrogen ratios between 0 and 0.3. The experimental study was carried out in a sphere and a cylindrical chamber at room temperature and sub-atmospheric pressures (between 0.3 and 1.0 bar). On the basis of pressure recordings, the characteristic explosion indices, i.e., the maximum explosion pressure (pmax), maximum rate of pressure rise ((dp/dt)max), deflagration index (KG), and time to peak pressure (θmax) were derived. Numerical simulations were used to determine the adiabatic explosion pressures and adiabatic flame temperatures of isochoric combustion.The effects of initial pressure (p0), hydrogen concentration, and shape and size of the explosion vessel on explosion indices are discussed. For each hydrogen concentration of the blended fuels, linear correlations pmax = f(p0) and (dp/dt)max = f(p0) were found. In addition, the heat loss to the walls during explosion propagation was estimated on the basis of the difference between the adiabatic and experimental explosion pressures. The amount of heat lost increases with the increase of hydrogen blending ratio and vessel asymmetry.