Coherent Flamelet Mlodeling of Diesel Engine Combustion

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Abstract
A turbulent combustion model based on the coherent flamelet model was developed in this study and applied to diesei engines. The important physics involved in each phase of diesei engine combustion were defined and modeled as directly as possible. The combustion event was broken into three phases: low temperature ignition kinetics, high temperature premixed burn kinetics, and diffusion burn. Two transition steps were developed to model the progression of combustion between each of these phases. The ignition phase was accomplished using the Shell ignition model. The transition to the high temperature premixed burn kinetics was accomplished using a criteria based on heat release rate and temperature. The high temperature premixed burn kinetics were modeled using a global Arrhenius equation for the rate of reaction. The transition to the diffusion burn was based on a critical Damkohler number. Finally, the coherent flamelet model was used as a foundation for the diffusion burn portion of the model. The model was implemented into the multidimensional computational computer code KIVA-II. The sensitivity of the combustion events to several of the model parameters was examined and the results were used to pick the optimum settings for the model. Previous experiments on a Caterpillar model E 300, # 1 Y0540 engine, a Tacom LABECO research engine, and a single cylinder version of a Cummins N14 production engine were used to validate the cylinder averaged predictions of the model. The characteristics of the modeling approach were also addressed by examining the spatial resolution of the model results inside the engine cylinder. The location and magnitude of model heat releases, flame areas, and equivalence ratios were examined. The results of this approach to the modeling of diesei engine combustion could be used to enhance to modeling of engine emissions.

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