Explosion limit of hydrogen/oxygen mixture with water vapor addition

The explosion limits of H2/O2/H2O mixtures with different equivalence ratios are studied. It is shown that the explosion limit of the H2/O2/H2O mixture exhibits the similar Z-shape as that of the H2/O2 explosion limit. As the H2O mole fraction increases, both the first and second limits move towards higher temperatures. Temperature sensitivity analysis and reaction pathway analysis indicate that the third-body reaction related to H2O and the wall destruction of H/O are responsible for the first limit shift to higher temperatures. The second limit moves to higher temperatures due to the enhanced chain termination re-actions related to H and HO2, as well as the wall destruction of H, which simultaneously weakens the pathway for the production of O/OH. However, the third limit moves towards lower temperatures when the H2O mole fraction is 0.1-0.3, and then towards higher temperatures when it is greater than 0.3. The reaction path analysis indicate that the addition of H2O promotes the generation of OH. The physical and chemical effects caused by H2O are also studied. The results show that the inert H2O, which does not participate any reactions, causes the first and third limits towards higher temperatures, while the second limit move to lower temperatures. The physical effects and chemical effects caused by H2O result in the non-monotonic movement of the third limit. Compared with above stoichiometric conditions, the first and second limits of the lean mixtures are at lower temperature, whereas the third limit at higher temperatures. The rich mixtures exhibit opposite tendencies.(c) 2023 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.