Comparison of two enhancement strategies of preheating and hydrogen addition for premixed NH3/H2/air flame: From the perspective of flame instability and heat release

• Published in: Fuel (Guildford) 2025-03, Vol.384, p.134075, Article 134075
• Main Authors: Ma, Pengcheng, Deng, Haoxin, Wen, Xiaoping, Song, Jun, Wang, Fahui, Chen, Guoyan
• Format: Article
• Language: English
• Subjects: Ammonia/hydrogen/air; Elevated temperature; Flame instability; Laminar burning velocity
• ISSN: 0016-2361
• DOI: 10.1016/j.fuel.2024.134075

•The laminar burning velocity of NH3/H2/air mixture under two strategies was obtained.•The flame instability of NH3/H2/ air mixtures was studied by linear stability theory.•The thermal and chemical effects of NH3/H2/air mixtures were separated by virtual nitrogen.•The CE of NH3/H2/air mixture under two strategies was compared by the mixture heating value. Preheating and hydrogen addition are two effective strategies for enhancing ammonia premixed flames. This study aims to compare these strategies across multiple dimensions, with a particular focus on flame instability. The comparison is anchored on consistent laminar burning velocities (LBVs), obtained from measurements in a constant-volume combustion chamber. Effective Lewis number (Leeff) and other parameters are compared through numerical simulation, while flame instability is compared using linear stability theory. The results show that the effect of the preheating strategy and the hydrogen addition strategy is the same in terms of Leeff change. In terms of flame thickness and thermal expansion ratio, the thermal expansion ratio of the NH3/H2/air mixture is smaller under the preheating strategy. And the flame thickness of the mixture under the hydrogen addition strategy is thinner. From the perspective of flame propagation image, NH3/H2/air flame is more stable under preheating strategy. Viewed through the perspective of hydrodynamic instability, the NH3/H2/air flame is more significant under the hydrogen addition strategy. With consideration for the heating value of mixture, the mixture heating value of NH3/H2/air is higher under the hydrogen addition strategy. Considering multiple dimensions, it can be concluded that, under the premise that the combustion effect of the two enhancement strategies is consistent, the preheating strategy outperformed the hydrogen addition strategy due to its ability to maintain a more stable flame structure.