Evaluation of Reduced n-Heptane Mechanisms in Dual-Fuel Combustion

Numerical simulations are carried out to evaluate the performance of different reduced n-heptane mechanisms in dual-fuel combustion. Three reduced nheptane mechanisms with a size <70 species are tested in the present study. The ignition characteristics of methane and n-heptane for these mechanisms are first evaluated by performing zero-dimensional (0-D) homogeneous reactor (HR) calculations for a pressure range of 36 – 48 atm and equivalence ratio of 0.4. Results from all three mechanisms show good agreement with measurements. Next, computational fluid dynamic simulations of a n-heptane spray in a premixed methane/air mixture are carried out using the three mechanisms, in which the ambient temperature and density are set to 900 K and 14.8 kg/m³, respectively.  Dual-fuel is considered by varying the equivalence ratio of methane (휙CH₄) in the ambient gas from 0 to 0.5. The ignition delay time of the pure n-heptane spray is predicted to be within 21% as compared to measured data. It is shown that despite having reasonable performance in 0-D HR calculations, the ignition process in dual-fuel spray combustion varies for different mechanisms which may affect the conclusion of a study. Therefore, an extensive model evaluation is required prior to actual application.