Low- to intermediate-temperature oxidation characteristics of a seven-component NG-diesel surrogate fuel: An experimental and modeling study

Natural gas (NG)-diesel dual-fuel combustion improves efficiency and reduces emissions in compression-ignition engines, yet the coupled oxidation chemistry at low-to-intermediate temperatures remains insufficiently understood. In this work, the oxidation characteristics of a seven-component NG-diesel surrogate (methane, ethane, propane, n -tetradecane, isocetane, decalin, and 1-methylnaphthalene) were investigated in an atmospheric jet-stirred reactor over 500–1050 K at equivalence ratios of 0.5 and 1.0 with 0–40% diesel blending. A detailed kinetic mechanism was developed to interpret fuel interactions and captures the major species mole fraction profiles. Results show that diesel nonlinearly promotes NG oxidation, with small additions lowering the oxidation onset temperature, whereas increases beyond 25% yield limited benefit. Reaction pathway analysis reveals that cross-fuel interactions are initially weak, mediated primarily by shared small-molecule aldehydes and olefins. Sensitivity analysis identifies OH and methyl radicals as key species controlling the oxidation process. Ethane and propane show an apparent NTC-like behavior only in the NG-diesel blends, consistent with non-monotonic OH/HO 2 evolution and weakened radical-initiated H-abstraction from these light alkanes. Methyl radicals promote diesel consumption and contribute to methane regeneration, establishing a radical-facilitated linkage between NG and diesel oxidation. These findings offer fundamental insights supporting the optimization of NG-diesel dual-fuel engines. Graphical abstract • A detailed chemical kinetic mechanism for a seven-component NG-diesel surrogate is developed. • Diesel addition enhances NG oxidation and plateaus beyond 25% diesel. • Diesel-derived chain-branching chemistry initiates NG low-temperature oxidation. • Methyl radicals mediate the kinetic coupling between NG and diesel oxidation.