Study on Coupling Relationships Among Target Parameters for Multi-Component Biodiesel Surrogate Fuels

Real biodiesel contains numerous components with complex molecular structures, and thus a representative surrogate fuel is required to develop tractable chemical kinetic mechanisms for biodiesel combustion. In this study, how physicochemical properties and molecular–structural descriptors interact when used as target parameters in biodiesel surrogate fuel formulation was clarified. Specifically, waste cooking oil biodiesel was selected as the target fuel, and methyl decanoate, methyl 3-hexenoate, n-hexadecane, and 1,4-hexadiene were selected as candidate components. A multi-objective genetic algorithm was employed to optimize component mass fractions under three target schemes, including physicochemical properties only, molecular–structural descriptors only, and a coupled scheme. Weight-perturbation calculations were then performed to quantify weight-dependent changes in target-matching errors and component fractions and to analyze the coupling mechanism among target parameters. The result shows that the coupled scheme provides the most balanced matching performance across physicochemical properties and molecular–structural descriptors while retaining all four components. Density, molar mass, the O/C ratio, viscosity, cetane number, and key molecular–structural descriptors exhibit the strongest coupling and dominate composition redistribution. The observed coupling among target parameters is realized through coordinated changes in component fractions, providing a basis for key-parameter screening in biodiesel surrogate fuel formulation.