Reduction and optimization of ammonia-hydrogen combustion reaction kinetic model for HCCI engines

Abstract

To obtain a smaller-scale ammonia-hydrogen hybrid mechanism with better predictive performance suitable for HCCI engine combustion, the stagni mechanism, which is closer to the combustion temperature, pressure and equivalence ratio conditions of HCCI engine, is selected as the original mechanism based on six ammonia-hydrogen detailed mechanisms, and the new detailed mechanism is obtained by adjusting the reaction rate constants related to HCCI combustion. Using three reduced methods, Directed Relation Graph with Error Propagation (DRGEP), Directed Relation Graph with Path Flux Analysis (DRGPFA) and Full Species Sensitivity Analysis (FSSA). Based on the allowable residual of 5%, the detailed mechanism of ammonia-hydrogen combustion is reduced. Based on sensitivity analysis to select key primitive responses, the pre-exponential factors of the reduced mechanism were designed by response surface method, and a series of optimization parameters were obtained. The optimization parameters are used to optimize the pre-exponential factor and verify the optimization mechanism. The results show that under the combination of R45=3.2×1011, R46=2.53862×1019, R103=338; R6=5.12×1022, R28=249 and R79=1.2×1012, the response value of predicting ignition delay time and laminar flame speed is the largest, and the error between the optimization mechanism and the detailed mechanism is the smallest, which proves the accuracy of the optimization parameters. The optimized mechanism has good prediction performance under HCCI conditions and can be used as an ammonia-hydrogen mixing mechanism suitable for HCCI engines.

Keywords

• ammonia
• hydrogen
• combustion reaction kinetic model
• homogeneous charge compression ignition
• mechanism reduction
• mechanism optimization
• response surface analysis