The Effect of In Cylinder Turbulence on Lean, Premixed, Spark Ignited Engine Performance

Abstract

The intensity and structure of incylinder turbulence is known to have a significant effect on internal combustion engine performance. Changes in flow structure and turbulence intensity result in changes to the rate of heat release, cylinder wall heat rejection, and cycletocycle combustion variability. This paper seeks to quantify these engine performance consequences and identify fundamental similarities across a range of highspeed, mediumbore, leanburn, sparkignited reciprocating engines. Incylinder turbulence was manipulated by changing the extent of intake portinduced swirl as well as varying the level of pistongenerated turbulence. The relationship between incylinder turbulence and engine knock is also discussed. Increasing incylinder turbulence generally reduces combustion duration, but test results reveal that increasing swirl beyond a critical point can cause a lengthening of burn durations and greatly reduced engine performance. This critical swirl level is related to the extent of smallscale, pistongenerated turbulence present in the cylinder. Increasing incylinder turbulence generally leads to reduced cycletocycle variability and increased detonation margin (DM). The overall change in thermal efficiency was dependent on the balance of these factors and wall heat transfer, and varied depending on the operational constraints for a given engine and application. Single cylinder engine test data, supported with threedimensional computational fluid dynamics (CFD) results, are used to demonstrate and explain these basic combustion engine principles.