Picard, M., Tian, T., and Nishino, T., "Modeling of the Rotary Engine Apex Seal Lubrication," SAE Technical Paper 2015-01-2035, 2015, doi:10.4271/2015-01-2035.
The Wankel rotary engine is more compact than conventional piston engines, but its oil and fuel consumption must be reduced to satisfy emission standards and customer expectations. A key step toward this goal is to develop a better understanding of the apex seal lubrication to reduce oil injection while reducing friction and maintaining adequate wear. This paper presents an apex seal dynamics model capable of estimating relative wear and predicting friction, by modeling the gas and oil flows at the seal interfaces with the rotor housing and groove flanks. Model predictions show that a thin oil film can reduce wear and friction, but to a limited extent as the apex seal running face profile is sharp due to the engine kinematics. The seal-housing interface remains between the boundary and mixed lubrication regimes, which leads to large asperity contact pressure and therefore significant wear of the running face, and an effective friction coefficient that varies between 0.03 to 0.11 depending on speed and load.