CFD Modeling of Spark Ignited Gasoline Engines- Part 1: Modeling the Engine under Motored and Premixed-Charge Combustion Mode

One of the best tools to explore complicated in-cylinder physics is computational fluid dynamics (CFD). In order to assess the accuracy and reliability of the CFD simulations, it is critical to perform validation studies over different engine operating conditions. Simulation-based design of SI engines requires predictive capabilities, where results do not need to be tuned for each operating condition. This requires the models adopted to simulate their respective engine physics to be reliable under a broad range of conditions. A detailed set of experimental data was obtained to validate the CFD predictions of SI engine combustion. Experiments were performed at the Engine Research Center of the University of Wisconsin-Madison under three modes of engine operation: motored engine operation, premixed-charge spark-ignition engine operation, and direct-injection spark-ignition engine operation over different engine conditions. 3D CFD simulations of the experimental conditions were performed using ANSYS Forte CFD, with automatic mesh generation and selective mesh refinement at boundaries and critical flow regions. Combustion was modeled using a validated, detailed reaction mechanism, along with a flame-propagation model. In the results reported here, CFD simulations of an engine operated under both motored and premixed-charge conditions were performed. Motored operation allows for validation of the gas exchange process along with compression and expansion of the gas with wall heat transfer. The premixed-charge spark-ignition engine operation considers premixing and pre-vaporization of the fuel in the intake system and was used to assess the performance of the fuel-combustion model in predicting turbulent combustion due to gas-phase chemical reactions and flame-front propagation through the premixed fuel-air mixture. In these Part 1 results, CFD predictions under motored and premixed-charge conditions were validated against experimental data and were found to be in good agreement over a range of engine conditions with the same CFD model and sub-model setup for all conditions. In the companion Part 2 paper, the same setup was used for direct-injection gasoline SI engine operation, adding fuel-injection modeling and spray validation.