Numerical Study on Heat Release Rate Markers with Nonunity Exponents for Ammonia–Methane Premixed Flames

• Published in: Energy & fuels 2023-10, Vol.37 (19), p.15043-15053
• Main Authors: Xue, Qingqing, Xing, Jiangkuan, Tang, Xinzhou, Luo, Kun, Wang, Haiou, Fan, Jianren
• Format: Article
• Language: English
• Subjects: Combustion
• ISSN: 0887-0624; 1520-5029
• DOI: 10.1021/acs.energyfuels.3c02013

As one of the carbon-free fuels, ammonia has great application potential in energy systems. However, its relatively low reactivity makes it usually required to be cofired with small-molecule reactive fuels, such as methane and hydrogen, to achieve stable combustion. Heat release rate, as an important property of the flame behavior, could not be directly measured through the experimental method and is closely dependent on the equivalence ratio and fuel composition. Although many previous works have been reported for hydrogen/hydrocarbon fuels, the heat release rate markers (HRRMs) for ammonia–methane cofiring flames have not been comprehensively explored yet. Therefore, the present work aims to identify the accurate and general HRRMs for premixed ammonia–methane flames under wide ranges of equivalence ratios and blending ratios. Specifically, series of one-dimensional freely-propagating premixed flames were calculated and used to construct a database for the identification of the optimal HRRMs. Subsequently, the optimal HRRMs were identified from the flame database using a grid-searching method for the exponential pairs of the interested species. Finally, the identified HRRMs were further validated on two-dimensional turbulent premixed flames in a posterior manner. The results showed that the heat release rate of ammonia–methane cofiring flames can be accurately approximated using [ OH ] 0.86 [ C H 2 O ] 0.78 , when considering only species that can be measured by laser-induced fluorescence. Another excellent reconstruction marker would be [ NO ] 1.23 [ N H 2 ] 0.80 , for cases where the ammonia content is high.