CH₂O 链长对正庚烷/PODE_2-3 混合燃料自着火特性的影响

To investigate the influence of increasing the CH₂ O chain length in PODE on the promotion of n-heptane autoignition,a relative synergy factor(R_SF ) was introduced to quantitatively assess the influences of PODE₂ and PODE₃ on n-heptane autoignition at various initial conditions of temperature, pressure and equivalence ratio. The underlying mechanisms driving these effects were examined via rate of production(ROP) analysis of key radicals and the evolution of key species' mole fraction. The results indicate that the temperature has the most significant influence on R_SF, demonstrating that synergistic promotion of n-heptane autoignition by PODE is most sensitive to temperature variations. The strongest promotion occurs in the medium-to-high temperature range (800− 1 200 K). Increasing the PODE blending ratio initially enhances n-heptane autoignition and subsequently weakens, reaching a peak effect at 60%. The maximum R_SF of the n-heptane/PODE₃ blend is 0.79, which is significantly higher than that of the n-heptane/PODE₂ blend(0.57), indicating that the promoting effect on n-heptane autoignition is enhanced with the increase of the CH₂ O chain length in PODE. In OH and HO₂ mixtures, the dominant OH formation pathway follows HO₂ →H₂ O₂ →2OH. Additionally, each of the two mixed fuels has an important pathway, namely CH₄ →CH₃ →CH₃ O+OH for n-heptane/PODE₂ and CH₃ O₂ →CH₃ O₂ H→CH₃ O+OH for n-heptane/PODE₃ blends. The difference in the OH radical yield between n-heptane/PODE₃ and n-heptane/PODE₂ is 0.28, indicating that the n-heptane/PODE₃ blend exhibits a higher OH production rate, faster OH formation, and greater overall reaction activity. Compared to PODE₂, PODE₃ increases of H₂ O₂ accumulation and OH generation during ignition, contribute to a richer radical pool.Consequently, blending n-heptane with PODE₃ results in a more reactive radical pool.These findings confirm that as the CH₂ O chain length in PODE increases, its promotion of n-heptane autoignition is enhanced.