Numerical decoupling of CO2 effects on laminar combustion characteristics of Ethanol/Iso-octane/Air mixtures at engine-like temperatures

• Dilution, thermal, direct chemical and third-body effects were assessed by virtual gases. • Third-body effect enhanced while direct chemical effect inhibited laminar flame speed. • Chemical effect of CO 2 dominated laminar flame speed suppression at high temperatures. • Laminar flame speed was linearly correlated with (H + OH + O) max at different temperatures. Understanding the influences of CO 2 on pre-mixed flames under engine-relevant temperatures facilitates more precise modulation of exhaust gas recirculation (EGR). Therefore, this study adopted a decoupling method to investigate the effects of CO 2 on laminar flame characteristics of ethanol/ iso -octane fuel at 500–1000 K under dilution ratios of 0–50 %. The dilution, thermal, direct reaction and third-body effects were isolated by introducing virtual gases of V-N 2 , V-CO 2 , and T-CO 2 . The results showed that the chemical effects (including direct reaction and third-body effects) had the largest influence (40–46 %) on the laminar flame speed (LFS), followed by dilution (32–36 %) and thermal (22–24 %) effects. The thermal effect of CO 2 on LFS was studied by flame thickness and thermal diffusivity. The results showed that the introduction of CO 2 reduced LFS, and this effect gradually increased with the increases of temperature and dilution ratio. A larger LFS reduced the flame thickness and flow stability. Increasing the initial temperature greatly increased the thermal diffusivity by over 127 %. With the increase of the dilution gas, the thermal diffusivity decreased quickly and the thermal effect was strengthened. The chemical effect of CO 2 on LFS was studied by analyzing the sensitivity, mole fraction and rate of production. CO 2 participated in the main reaction R67 (CO + OH ↔ CO 2 + H), resulting in a significant decrease in the concentration of H radicals. LFS was directly related to H, O, and OH radicals. Furthermore, the LFS at different temperatures was linearly fitted with the (H + OH + O) max . This study provided a theoretical basis for the evaluation of key combustion parameters for precise control of EGR in gasoline engines.