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In this study, a one-equation LES sub-grid model from Menon, et al. [5] is used in simulating the diesel combustion process. In addition, based on the one-equation methodology of Menon et al., a new one-equation LES scalar transport model is formulated. These models allow for the turbulent transfer coefficients for both momentum and scalar flux to be determined independent of each other. The turbulent viscosity, μt, is determined as a function of the sub-grid kinetic energy, which is in turn determined from the one-equation model. The formulation for the scalar transfer coefficient, μs, is similar to that of the turbulent viscosity, yet is made to be consistent with scalar transport. Results for the LES momentum transfer are compared to experimental data of a backward facing step. This model, in conjunction with the LES scalar flux model, is verified by comparing with experimental data for a non-reacting turbulent jet.

In this study, a new combustion model for simulating the diesel combustion process is introduced. This model was verified by comparing numerical simulations to experimental data for a six-mode test cycle using a Caterpillar 3400 series engine. Additional comparisons are made for baseline cases for both a Caterpillar 3500 series engine and a Sandia optical access engine. In the combustion model, reactions limited by diffusion are modeled using a probability density function (PDF) model. For kinetically limited (premixed) combustion, an Arrhenius rate is used. To include effects of temperature fluctuations, this reaction rate is weighted by a temperature probability density function. A transport equation for premixed fuel was implemented to transition between the premixed and diffusion burning modes. The ratio of fuel in a computational cell that is premixed is used to determine the combustion mode.