The Effect of Valve Lift on In-Cylinder Flow, Performance and Emissions in a Turbocharged DI Diesel Engine

A computational optimization was performed for a direct-injection diesel engine using three-dimensional modeling. Fully transient CFD analyses of different valve profile strategies for the intake and compression strokes are performed, to evaluate the effects on both engine performance and in-cylinder flow-field evolution. The turbulence model was used along with second order linear upwind scheme. Modifications are applied to intake valve for five different valve lift profiles. Organized flow structures (i.e., swirl) and turbulent flow patterns are investigated, in order to address the rules for ad-hoc strategies aiming at finding the best trade-off between the engine performance and pollutant emission. At first, results for the base case are validated against experiments at maximum power operation (2000 rpm); subsequently, four valve lift profiles, are performed. Relative valve profiles prove to influence the flow field within the combustion chamber, and therefore the subsequent spray evolution and fuel combustion, confirming the importance of an ad-hoc optimization.