Multi-dimensional computational combustion of highly dilute, premixed spark-ignited opposed-piston gasoline engine using direct chemistry with a new primary reference fuel mechanism

This work presents a modeling approach for multidimensional combustion simulations of a highly dilute opposed-piston spark-ignited gasoline engine. Detailed chemical kinetics is used to model combustion with no sub-grid correction for reaction rates based on the turbulent fluctuations of temperature and species mass fractions . Turbulence is modeled using RNG k-ϵ model and the RANS-length scales resolution is done efficiently by the use of automatic mesh refinement when and where the flow parameter curvature (2nd derivative) is large. The laminar flame is thickened by the RANS viscosity and a constant turbulent Schmidt (Sc) number and a refined mesh (sufficient to resolve the thickened turbulent flame) is used to get accurate predictions of turbulent flame speeds. An accurate chemical kinetics mechanism is required to model flame kinetics and fuel burn rates under the conditions of interest. For practical computational fluid dynamics applications, use of large detailed chemistry mechanisms with 1000s of species is both costly as well as memory intensive. For this reason, skeletal mechanisms with a lower number of species (typically ~100) reduced under specific operating conditions are often used. In this work, a new primary reference fuel chemical mechanism is developed to better correlate with the laminar flame speed data, relevant for highly dilute engine conditions. Simulations are carried out in a dilute gasoline engine with opposed piston architecture, and results are presented here across various dilution conditions.