Scarcelli, R., Matthias, N., and Wallner, T., "Numerical Investigation of Combustion in a Lean Burn Gasoline Engine," SAE Technical Paper 2013-24-0029, 2013, doi:10.4271/2013-24-0029.
This research effort focuses on lean-burn combustion in gasoline internal combustion engines. Gasoline is largely known to be characterized by narrow flammability range, which makes the use of ultra-lean mixtures very challenging. In order to fully explore the gasoline lean burn potential, a promising strategy should combine advanced intake geometries, injection strategies, and ignition technologies.In this paper, a CFD methodology is developed in order to provide proper insight into lean-burn gasoline combustion. A baseline homogenous/lean case is analyzed and numerical results are validated against engine data.Two critical issues are addressed. First, a relatively large detailed mechanism is validated against the experimental data for extreme operating conditions (low pressure values, lean mixtures). The large cycle-to-cycle variation characterizing lean combustion is shown experimentally. An advanced numerical approach is proposed that delivers oscillation in the CFD results as an effect of the reduced numerical diffusion. The results indicate that the CFD methodology presented in this paper has a potential in describing the average behavior of the engine while future work will address cycle-to-cycle variation and combustion stability.Secondly, the effect of the intake geometry on the in-cylinder flow and flame propagation is shown. Numerical simulations are able to highlight combustion features that are of primary importance for future engine optimization.