Effects of carbon dioxide on the combustion characteristics of the laminar premixed n-heptane/air flames at elevated pressures

In this paper, the laminar combustion characteristics of n-heptane/carbon dioxide/air flames are numerically investigated by using the Chemkin/Premix Code and LLNL v3.1 mechanism. The equivalence ratios vary from 0.8 to 1.4 at the initial temperature of 298 K. The initial pressure is set as 1, 2, 5, 10, 20 atm. Laminar burning velocity (LBV), adiabatic flame temperature (AFT), net heat release rate (NHRR) and the mole fractions of H, O, OH, CO at stoichiometric ratio are studied with carbon dioxide (CO2) addition. Meanwhile, temperature sensitivity and rate of production (ROP) are analyzed. In addition, the physical and chemical effects of CO2 are investigated by introducing fictitious carbon dioxide (FCO2).The results show that with the increase of initial pressures, LBV decreases, AFT and NHRR increase, the peaks of intermediate products such as H, O, OH and CO decrease. The promoting effect of elementary reactions on temperature is greatly enhanced, while the inhibiting effect is slightly enhanced. With the increase of CO2 doping ratios, LBV, AFT and NHRR decrease, while the peaks of H, O, OH, CO increase first and then decrease. The promoting and inhibiting effects of elementary reactions on temperature are enhanced. Both physical and chemical effects of CO2 inhibit the combustion of n-heptane, where physical effect dominates. The total ROPs of H, O, OH change from consuming to producing, while the total ROP of CO is opposite.

Automated summary

This study investigated the laminar combustion characteristics of n-heptane flames with carbon dioxide addition. The results indicate that CO2 inhibits the combustion process primarily through effects on laminar burning velocity, adiabatic flame temperature, and intermediate product formation. Physical effects play a significant role in inhibiting heat release and promoting temperature.