Session: 06-01 SI Engine Modeling

Track: Track 6: Modeling and Simulation

Paper Number: 90213

90213 - Evaluation of Spray and Combustion Models for Simulating Dilute Combustion in a Direct-Injection Spark-Ignition Engine_x000B_ 

Dilute combustion in spark-ignition engines has the potential to improve thermal efficiency by mitigating knock and by reducing throttling and wall heat losses. However, ignition and combustion processes can become unstable for dilute operation due to a lowered laminar flame speed, resulting in excessive cycle-to-cycle variability (CCV) of the combustion process. To compensate for the slower combustion in less reactive mixtures, a modified intake port geometry can be employed to generate a strong tumble flow in the cylinder and elevate turbulence levels around the spark plug, thereby promoting a faster transition to turbulent deflagration. Consequently, the optimization of combustion-chamber geometry and operating strategy is crucial to maximizing the benefits of using dilute combustion with enhanced in-cylinder turbulence across a wide range of operating conditions. Computational fluid dynamics (CFD) simulations can be utilized for virtual engine optimization tasks, but this would require the models to be truly predictive regarding the impact of changes to the engine design and operational parameters.

In this study, multi-cycle large-eddy simulations (LES) are performed for a direct-injection spark-ignition engine to investigate the model performance in predicting engine combustion characteristics with respect to changes in the intake configuration and mixture diluents. A tumble plate that blocks the lower part of the intake port inlet is used to vary the tumble strength, while two diluents (nitrogen or excess air) are used to dilute the mixture. A set of CFD models that have been recently developed under the PACE (Partnership for Advanced Combustion Engine) program are employed to improve the simulation accuracy. The developed models take into account the drag of non-spherical droplets, flash-boiling behavior of liquid sprays, spray-wall interaction, surrogate formulation of a research-grade E10 gasoline, and fast chemical kinetic solvers. Simulation results are compared to experimental engine data in terms of cylinder pressure, apparent heat release, mass fraction burned timing, and CCV. It is found that LES employing the state-of-the-art CFD models are capable of accurately reproducing the trends observed from the engine tests that incorporated both intake-port design changes and different types of diluents.

Presenting Author: Joohan Kim Argonne National Laboratory