3D CFD Analysis of Predicting Engine Blowby Considering Ring Dynamics

This paper reports on the development of a simulation model to predict engine blowby flow rates for a common rail DI diesel engine. The model is a transient, three-dimensional computational fluid dynamics (CFD) model. Managing blowby flow rates is beneficial for managing fuel economy and oil consumption. In doing so, an improved understanding of the blowby phenomenon is also possible. A mesh for the sub-micron level clearances (up to 0.5 microns) within the piston ring pack is created using a novel approach. Commercial CFD software is used to solve the pressure, velocity, and temperature distributions within the fluid domain. Ring motions within the piston grooves are predicted by a rigorous force balance. This model is the first of its kind for predicting engine blowby using a three-dimensional simulation model while solving the complete set of governing transport equations, without neglecting any terms in the equations. The predicted blowby flow rate has been validated with experimental results for two different engine geometries under different operating conditions and shows good agreement, with deviation of up to 10 L/min. The simulation approach has good mass conservation, up to 95.4%, even with sub-micron level clearances, thus proving the accuracy and robustness of the model in capturing fine-scale fluid dynamics and blowby phenomenon.