Development of multiscale models for the performance of the gas and oil seals in rotary engines

Abstract

Rotary engines offer higher power density, fewer parts and lower vibrations than conventional reciprocating piston engines. However, rotary engines are more difficult to seal because of the rotor shape which leads to higher gas leakage and oil consumption resulting in lower efficiency and higher emissions. In order to address this problem, this thesis presents a set of multiscale models to assess rotary engine performances by estimating gas leakage, oil consumption, wear and friction. An oil seal multiscale model is developed to estimate internal oil consumption guided by oil transport visualization experiments carried using a laser-induced fluorescence technique. A finite element beam model is used to predict the clearance between the oil seals and the side housing for each crank angle in the cycle. From seal-housing clearance, oil transport through the oil seals is calculated using a control volume approach. The main mechanism leading to internal oil consumption is outward scraping of the oil seals due to a lack in conformability of the seals to the distorted side housing, especially next to the intake and exhaust ports. A set of multiscale models are developed for the performance of the apex and side seals. The models are formulated to couple gas flow to the dynamics and deformation of the seals while accurately describing the interfaces between the seals and their profile and groove. The models are used to predict apex and side seal behavior and understand the mechanisms leading to gas leakage. The main leakage mechanisms identified are leakage through (1) the corner seal clearance, (2) the spark plug holes, (3) the flanks of the seals at high speed, and (4) the side piece corner for the apex seals and at the ends of the side seals. The apex seal model shows good agreement with experiments, especially for the pressure in the apex seal groove. It is the first time such comprehensive models are developed for rotary engines and they will be valuable tools to help design more efficient and environment-friendly rotary engines.