Hydrogen detonation onset behind two obstructions with unequal blockage ratio and opening geometry

Abstract

Experiments on detonation onset behind two solid obstructions with uneven blockage ratio (BR) and opening shape were carried out in premixed, stoichiometric, hydrogen-oxygen mixtures at 20 kPa. Three geometric features of the second obstruction (OB2) were investigated: the opening shape, BR, and minimum opening vertical dimension (d/λ). Obstructions with blockage ratio increase across the obstacle pair (40%–80% and 40%–60%) presented shorter detonation onset time than obstacle pairs with unvaried BR (40%–40%). Modifications in the second obstacle geometry for pairs with 40%–40% and 40%–80% blockage had minimal effect on DDT time and obstacle-induced shock strength. Conversely, obstacle pairs with 40%–60% blockage experienced significant variation depending on the geometry employed. Critical conditions of detonation initiation immediately behind the second obstacle were found to correlate with BR and effective opening dimension (deff/λ); For OB2 with 60% and 80% BR, DDT limits correlate well with the upper and lower limits constrained by D−deff2λ≥1 and deffλ≥1, respectively. The Taguchi analysis showed that the second obstacle blockage is the factor that most influenced early detonation onset, both the shape and opening dimension had minor effects. This finding confirms the importance of BR pattern for overpressure estimation during gaseous explosions.