Modeling laminar burning velocity of gasoline using an energy fraction-based mixing rule approach

Abstract

To determine an optimum combustion chamber design and engine operating strategies, computational fluid dynamics simulations of direct-injection spark-ignition engines have become an indispensable step in the powertrain development process. The laminar burning velocity of gasoline is known as an essential input parameter for combustion simulations. In this study, a new methodology for modeling the laminar burning velocity of gasoline for direct-injection spark-ignition engine simulations is proposed. Considering the gasoline as a complex mixture of hydrocarbon fuel, three hydrocarbons, iso-octane, n-heptane, and toluene were incorporated as surrogate fuel components to represent gasoline with distinct aromatic laminar flame characteristics compared to alkane. A mixing rule, based on energy fractions, was adopted to consider the compositional variation of gasoline. The laminar burning velocities of iso-octane, n-heptane, and toluene were calculated under wide thermo-chemical conditions in conjunction with detailed chemical reaction kinetics in the premixed flame simulation. Finally, a set of laminar burning velocity model equations was derived by curve-fitting the flame simulation results of each hydrocarbon component in consideration of the effect of temperature, pressure, and diluent. The laminar burning velocity model was validated against the measurement data of gasoline’s laminar burning velocity found in the literature, and was applied to the computational fluid dynamics simulation of a direct-injection spark-ignition engine under the various operating conditions to explore the prediction capability.