Numerical investigation on different effects of recirculated species on UHC and CO formation during lean homogeneous combustion

Although numerous studies have investigated the effect of EGR on engine combustion, no study has investigated the effect of each recirculated species separately on the engine emissions and combustion. This study investigated the effects of different components of the recirculated exhaust gas on the emission formation during lean homogeneous combustion. Due to lean combustion, O₂, N₂, CO₂, and H₂O are the main components of the exhaust gases. In addition, CO is also produced by the lean homogeneous combustion, which caused the chamber temperature to be low. The combustion chamber is simulated using a thermodynamic model and a quasi-developed chemical kinetic mechanism. The amount of added EGR is 0-40% by volume, and its various effects are investigated using the artificial inert species method. The basic results are validated against experimental data for different initial conditions. According to the results, N₂ due to its higher mass fraction and H₂O due to its higher heat capacity have the highest thermal effect. H₂O has the maximum thermal effect, and N₂ has the maximum dilution effect on thermal efficiency. The thermal effect of O₂ differs from those of the other species. All three effects of EGR reduce UHC. However, there is no regular trend for CO. H₂O and CO have increasing chemical effects, and O₂ and other free radicals have reducing chemical effects on CO. H₂O has the most thermal effect, O₂ has the most chemical effect, and N₂ has the most dilution effect on reducing UHC.