Laminar burning characteristics of ammonia/ methanol mixtures and reaction kinetics analysis at high pressures

The growing emphasis on sustainable and low-carbon energy alternatives has underscored the importance of ammonia and methanol as potential substitute fuels. Investigating their laminar combustion characteristics under high pressure is crucial for developing advanced combustion technologies. This study applied a Constant Volume Combustion Bomb (CVCB) to capture shadow images of spherical flames of ammonia/methanol mixtures using up to 1.0 MPa initial ambient pressure, and investigate laminar burning velocities across various ambient temperatures (423–523 K), methanol energy fractions (20%–50 %), and oxygen concentrations (21%–29 %). The results revealed that higher temperature, methanol energy fraction, and oxygen concentration all significantly increased the laminar burning velocity of ammonia/methanol mixture, and the peak velocity was observed at Φ = 1.05, shifting towards Φ = 1.0 with increased methanol energy fraction and oxygen concentration conditions. It suggests that an appropriate methanol energy fraction can enhance the laminar burning characteristics under high-pressure lean combustion conditions, which may provide insights into optimizing related combustion performance. Furthermore, an optimized reaction mechanism with 62 species and 404 reactions, which was suitable for high-pressure combustion conditions, was developed based on the experimental result. Kinetics analyses revealed that the reaction of O2 + H = O + OH critically influences laminar burning velocity. Variations in methanol energy fraction and oxygen concentration lead to changes in the concentration ratio of O2 to H, influencing the laminar burning velocity indirectly. Additionally, increasing methanol energy fraction or oxygen concentration led to higher OH concentrations, thereby enhancing hydrodynamic instability. The underlying mechanisms driving these changes differ: higher oxygen concentration promoted chain branching reactions, generating large amounts of OH, while an increased methanol energy fraction facilitated the production of HO2, which not only assisted in the initial fuel decomposition but also further generated OH.