Measurement of underseal pressure of a rotary engine apex seal and consideration of the pressure with modified rotor housing

To quantify the underseal pressure characteristics of an evolved 2 mm thick apex seal, the pressures under the apex seal and in the leading and trailing working chambers were measured using a cantilevered eccentric shaft single rotor engine equipped with a multichannel slip ring. A theoretical model that treats the vicinity of the apex seal as a labyrinth passage was applied to calculate the underseal pressure from the measured leading and trailing working chamber pressures and the flow coefficients for flow into and out of the underseal volume were adjusted so that the underseal pressure matched the measured value. These flow coefficients were used to study the effects of rotational speed, underseal volume, and apex seal clearance on the underseal pressure. In addition, since the combustion pressure rise near top dead center acts on one flank of the rotor and deflects the eccentric shaft to move the flank away from the inner surface of the rotor housing at high load, causing the leading and trailing apex seals to move outward in the seal slots. It has been proposed to improve sealing in these regions by making the rotor housing inner surface partially convex inward or outward from its basic shape to control the radial movement of the apex seal. A new underseal model with isothermally varying volume was introduced to the previous model, which showed that the modified rotor housing is effective in increasing the underseal pressure.