Coupled Quantification of Physical and Chemical Inhibition Effects of N2 and CO2 on NH3/H2/air Explosions

This study investigates the explosion suppression of N2 and CO2 on NH3/H2/air mixtures (NH3:H2 = 4:6, φ = 0.6–1.5) in a 5 L constant volume chamber. Results show that CO2 exhibits superior efficacy compared to N2. At φ = 1.0, the addition of 25% CO2 reduces the maximum explosion overpressure and maximum pressure rise rate by 59.28% and 91.00%, respectively, whereas the corresponding reductions caused by 25% N2 are 29.28% and 83.85%. The laminar burning velocity decreases continuously with increasing inhibitor concentration under all investigated conditions, and the reduction caused by CO2 is markedly greater than that caused by N2. Kinetic analysis indicates that the stronger suppression effect of CO2 is mainly associated with its stronger dilution and heat-absorption effects, together with its stronger influence on radical evolution, as reflected by the more pronounced reduction in key radical concentrations. To compare the suppression behaviours of N2 and CO2 under different conditions, three indices—the experimental maximum explosion overpressure suppression efficiency (ST), the theoretical maximum explosion overpressure suppression efficiency (SE), and the operating-condition suppression efficiency (η)—were introduced as comparative parameters. These results provide useful insight into the different suppression behaviours of N2 and CO2 in NH3/H2/air explosions.