Study on the explosion dynamics of locally premixed NH3/H2 blended zero carbon fuel in semi-confined elongated space: Effects of equivalent ratio and blended ratio

NH3/H2 blended gas as a zero-carbon energy carrier holds significant potential in the energy transition, yet the explosion propagation risk of zero-carbon fuel in semi-confined elongated spaces remain unclear. This study investigates the explosion dynamics of NH3/H2 blended gas in semi-confined elongated spaces under different equivalent ratios (Φ) and hydrogen blended ratios (λ) through a combined approach of numerical simulation, experimental validation, and comparative analysis. The results demonstrate that the maximum explosion overpressure (Pmax) exponentially attenuates along the pipe's axial direction. Pmax progressively increased with λ, reached a peak value of 1.271 MPa at λ=0.75, which was a 33.9% increase compared to λ=0.25, while it initially increases and then decreases with Φ, attaining its maximum of 1.155 MPa at Φ=1.0.Flame temperature along the pipe axial direction first rises then decreases. The mid-pipe temperature peak initially increases and then decreases as Φ rises, increasing λ significantly raises flame temperature, peaking at 2249.9 K for Φ=1.0 and λ=0.75. Flame structure sequentially transforms from semi-circular to water droplet shaped, tulip shaped, and finger shaped. When λ=0.5, the shock wave velocity increases by 15.6% as Φ rises from 0.6 to 1.0 in the 0–1 m zone. When Φ=1.0, elevating λ from 0.25 to 0.75 results in a 9.7 % increase in shock wave propagation velocity within the 0–1.6 m zone. In the 0–1.4 m zone, flame propagation velocity decay first decreases then rises with Φ and rises with λ, all exceeding 50%. Transient temperature surges are observed in the 2.8–4.0 m zone, triggered by thermochemical instability.