Influence of ammonia content on ammonia-hydrogen-air premixed gas duct-vented explosions

Renewable energy is addressing some of the key challenges facing global society today, and zero-carbon energy systems are the fundamental way to achieve carbon neutrality. Therefore, hydrogen and ammonia have gained great attention as zero-carbon energy sources. To further study the combustion characteristics of ammonia-hydrogen-air premixed gas flame inside and outside the duct, the influence of ammonia doped amount (φ) on the flame morphology and the evolution of pressure inside and outside the duct under stoichiometric ratio was explored with the help of high-speed photography and pressure sensor in the 2000-mm-long stainless steel duct with a 400-mm-long and 70-mm-wide observation window. The results show that φ significantly affects the pressure inside and outside the duct, and the time to reach the reverse flow phenomenon caused by the secondary explosion also increases. The pressure measuring point PS1 is set at 400 mm away from the explosion vent in the duct to collect data. The pressure curves in the duct under each working condition are presented as a three-peak structure, named p1, p2, and p3. The three pressure peaks are caused by the rupture of the explosion vent film, the gas venting in the duct, and the gas reverse generated by the secondary explosion outside the duct. The size of p1 depends on the tensile strength of the explosion venting membrane, and its amplitude is almost independent of the φ. p2 and p3 both increase with the increase of φ, and the p3 increase rate is the largest when φ is in 50%–65%. p2 changes from a single peak to a fluctuating pressure platform in the pressure curve diagram, and the time of the platform extends with the increase of φ. The pressure measurement point PS2 is set at the horizontal central axis, 500mm away from the explosion vent outside the duct, to collect data. And the peak pressure of the secondary explosion outside the duct (pout) decreases with the increase of the φ, and the time to reach pout increases. This study provides a theoretical basis for the utilization of ammonia and hydrogen energy.