Experimental and Numerical Investigations into the Effects of Vent Area on the Explosion Propagation Characteristics and Flow Field Evolution of Premixed NH3/H2/Air

To mitigate the potential explosion hazards associated with ammonia/hydrogen blended fuels, experiments and numerical simulations were conducted to investigate the effect of ventilation area on explosion propagation. A three-dimensional numerical model incorporating an external air domain was developed to characterize the evolution of exhaust and fuel diffusion process. The results show that “tulip” flames formed under all tested vent coefficients ( K v ), but their formation locations are strongly dependent on K v . As K v increases from 4.64 to 29.01, the complete reaction time is prolonged from 0.019 s to 0.032 s, accompanied by intensified oscillations in flame speed. Meanwhile, the maximum vented overpressure increases with K v , causing the dominant pressure peak to shift sequentially from P 1 to P 2 and finally to P 3 . The simulations reveal that restricted vent areas reduce the volumetric discharge rate of unburned gas while markedly increasing its discharge velocity. A smaller vent area decreases the fuel mass within the external reaction limit. However, the higher discharge speed promotes intense dilution and dispersion, which could lead to a larger external flammable cloud volume. This study provides new insights into the evolution of external flow fields during vented explosions and into the mechanisms governing external explosions.