Cross-effect considered skeletal chemical mechanism construction for primary reference fuel/oxymethylene ethers blends using radical trace and sensitivity analysis

Oxymethylene ethers (OMEn, n = 1–6) are a class of synthetic liquid fuels that carry a great potential to reduce carbon dioxides (CO2) and particle matter emissions. However, the lower heating value of all OMEn is inferior to conventional diesel fuel, hindering their applications in compression-ignition engines. Instead, their utilizations as diesel additives have attracted considerable attention. Unfortunately, the blending chemistry of OMEn and alkanes has not been investigated thoroughly. This study proposes a practical skeletal oxidation mechanism for primary reference fuel (PRF)/OME1–6. First, the skeletal chemical mechanisms for OME3, iso-octane, and n-heptane are constructed utilizing reaction class-based global sensitivity analysis. Then, the interactions among the three fuels are identified through sensitivity analysis and OH radical trace. It is found that the cross effects of the three fuels mainly occur in low-temperature regimes, and H-atom abstraction reactions have a significant influence on the co-oxidation of blended fuels. Additionally, blending OME3 with n-heptane impedes the consumption of OME3 from undergoing certain pathways, including the formation of cyclic ether from QOOH and the second time oxygen addition. The reactivity of iso-octane/OME3 blends at low temperatures is majorly driven by OME3 because of the low reactivity of iso-octane. Based on reaction rate rules, the skeletal mechanisms for OME1–6 are derived on the basis of the OME3 mechanism constructed above. The experiments in jet-stirred reactors fueled with OME3/iso-octane and OME3/n-heptane respectively with various blending ratios are conducted to evaluate the performance of the present skeletal mechanism. In addition, the mechanism is comprehensively validated against the experimental data regarding neat fuels and their mixtures for PRF/OME1–6, including species concentrations in jet-stirred reactors and premixed flames, auto-ignitions in shock tubes and rapid compression machines, and laminar flame speeds under a wide range of operating conditions (p= 0.04–58 atm, φ=0.25–4.0, and T= 500–1800 K). Good consistencies between simulations and laboratory observations are achieved.