A new kinetic model for the closed-cycle diesel engine ignition and combustion characteristics

To investigate closed-cycle diesel engine (CCDE) ignition and combustion characteristics, a new kinetic model (Carbon-dioxide Oxygen Environment, COE) is presented, which considered the CO 2 chemical effect based on diesel surrogate fuel (n-heptane, C 7 H 16 ). Firstly, the COE model is established by simplifying the LLNL mechanism, adding the new reaction pathways using quantum chemistry and modifying the kinetic parameters. Secondly, a visualization constant volume combustion chamber experimental system is constructed to record the non-premixed ignition and combustion process of C 7 H 16 under different CO 2 /O 2 environments (35% CO 2 /65% O 2 , 40% CO 2 /60% O 2 , 50% CO 2 /50% O 2 , 60% CO 2 /40% O 2 ). Finally, ignition characteristics, combustion characteristics, sensitivity analysis, and chemical effect of CO 2 under different CO 2 /O 2 environments are discussed between simulation and experiment. The results show that the COE model is suitable for studying the closed-cycle diesel engine ignition and combustion characteristics, whose maximum errors of ignition delay time and ignition location are 6.1% and 6.7%, respectively. The phenomenon of combustion decay appears before the end of combustion at 35% CO 2 and 40% CO 2 . The average flame length decreases significantly by 47.8% due to flame lift-off at 60% CO 2 . The cumulative flame intensity decreases by 34.4% at 60% CO 2 compared to 50% CO 2 . The sensitivity coefficient of H 2 O 2 + M → 2OH + M to temperature increases by 6.2% as CO 2 increases from 40% to 60%. The ratio of the chemical to physical effects of CO 2 rises from 7.6% to 17.3% as the CO 2 volume fraction increases. The third-body effect promoting OH formation more significantly than the inhibitory effect of the direct chemical effect.