Abstract
For modern, light-duty engine applications, the development of improved operating strategies to expedite catalyst heating during cold-start operation is essential for further reduction of emissions and meeting of future regulations. The development of such strategies would benefit from numerical modeling tools capable of accurate prediction of charge preparation, combustion, and emissions formation at cold-start conditions. Traditional development of simulation tools has primarily focused on standard engine operating conditions, and, as a result, these tools have difficulty accurately capturing extreme behavior during cold-start operation such as extensive wall wetting due to fuel-spray impingement on cold cylinder surfaces, late combustion phasing to increase exhaust enthalpy, and continued oxidation of reactants in the exhaust system. A major objective of the multi-national-laboratory Partnership to Advance Combustion Engines (PACE) consortium is the development and evaluation of new modeling approaches for cold-start operation. In this paper, we present recent progress in simulating charge preparation in a light-duty, multi-cylinder, gasoline engine during cold-start relevant conditions as defined by the U.S. DRIVE Advanced Combustion and Emission Control (ACEC) Tech Team cold-start protocols for catalyst heating. We focus study on fuel spray and spray-wall interactions resulting in extensive film formation due to cold cylinder walls. Simulation results are evaluated at steady-state, cold-start relevant operating conditions. Predictions for film formation and composition with conventional (baseline) models are compared to results with new simulation tools and approaches developed under PACE including the Corrective Distortion Spray Model developed by Sandia National Laboratories, which accounts for non-spherical droplet shapes, and a new spray-wall interaction model developed by Argonne National Laboratory, which accounts for multi-droplet, non-uniform impingement. The current study expands on past studies validating these new submodels with spray-chamber experimental measurements to examine the impact they have on full engine CFD simulations.
