Model Predictions for Tumble and Turbulence in SI Engine Combustion Chambers

Tumble, as an organized rotary charge motion in an axial plane is known to bring improvements in combustion of spark ignition engines through the production of a well-timed turbulence. Though, this motion was first observed in a pancake chamber, its real benefits are realised in four valve pentroof engines with suitably designed intake ports. The present work elucidates the application of an improved quasi-dimensional model in assessing the effect of changes in chamber geometry in terms of a non-dimensional tumble parameter. Beside physical understanding of the tumble motion, the engine turbulence is also synthesized to gain insight into the turbulent behaviour. The prediction of mean flow and turbulence characteristics in the pentroof and pancake chamber are in conformity with earlier experimental studies reported in literature. The chamber geometry is found to have a significant influence on bulk motion and turbulence levels at ignition.