Effect of Engine Speed on Combustion Characteristics of a CNG-Fueled HCCI Engine at Ultra-Lean Equivalence Ratio

This study presents a detailed numerical investigation of the effect of engine speed on combustion characteristics of a Compressed Natural Gas (CNG)-fueled Homogeneous Charge Compression Ignition (HCCI) engine operating at an ultra-lean equivalence ratio of ۰.۲۵۹. A detailed chemical kinetic mechanism was implemented in CHEMKIN and coupled with a validated ۱۰-zone thermodynamic model to account for in-cylinder temperature stratification and its influence on auto-ignition behavior. Engine speed was varied from ۴۰۰ to ۱۱۰۰ rpm to examine its impact on in-cylinder pressure development, temperature evolution, combustion phasing (CA۱۰, CA۵۰, CA۹۰), and gross indicated work. The results indicate that decreasing engine speed enhances chemical residence time, leading to advanced auto-ignition, higher peak pressure, and stronger temperature rise. In contrast, increasing speed retards combustion phasing, lowers peak pressure and temperature, and weakens heat release intensity. At ۱۱۰۰ rpm, insufficient reaction time results in unstable combustion and misfire under ultra-lean conditions. Gross indicated work exhibits a non-monotonic trend, reaching a maximum at intermediate speeds where the balance between adequate reaction time and reduced heat losses is optimized. The findings highlight the strong coupling between chemical kinetics and engine timescale and provide valuable insights for optimizing CNG-fueled ultra-lean HCCI engine performance.

کلیدواژه ها:

HCCI engine ، CNG ، engine speed ، combustion phasing ، CHEMKIN