The conflicting requirements of better fuel economy, higher performance and lower emissions from an automobile engine have brought many new challenges that require development teams to look beyond conventional test and seek answers from simulations. One of the relatively unexplored areas of development where frictional losses haven't been completely understood is the flow in the crankcase. Here computational engineering can play a significant role in analyzing flow field in a hidden and complex region where otherwise testing has serious limitations.
Flow simulation in the crankcase poses significant complexity and provides an opportunity to enhance the understanding of underlying physics by using multi-physics analyses tools available commercially. In this study, air space under the piston and above the oil level in oil pan is simulated. It is known that bay-to-bay breathing and windage holes account for considerable amount of power losses in the crankcase. Therefore, this study is intended to (but not limited to) the estimation of pumping losses (i.e., power required for piston to overcome the resistance offered by air in the crankcase) in addition to gaining insight into flow field to improve breathing between bays. The simulation is carried out with air as fluid and oil is kept stationary to maintain a constant level in the oil pan. Various meshing and mesh moving techniques were employed. This includes, arbitrary sliding interface (ASI) of counter weights and mesh morphing to replicate piston motion. Time dependent momentum and energy equations were solved for air as compressible media.
The study found that one of the major components that can have significant effect in reducing pumping losses and oil aeration is the design of windage tray. The windage tray design can be used for effective oil drainage along with reducing the splashing and sloshing of oil in the crankcase. The openings in the windage tray can be optimized for location and size so as to reduce pumping losses as well as oil aeration. This will have positive impact on engine power as well as fuel efficiency. Windage hole size, number and location also helps in determining the flow through drainbacks, and consequently affect the tuning of PCV and makeup air valves.