The measurement of pressure-volume diagram of a flat alpha-type Stirling engine based on laser triangulation and hybrid Harris corner methods

A pressure-volume diagram is often used to determine the indicated work of a Stirling engine. In this study, both the laser triangulation and hybrid Harris corner detection methods are proposed. The volume variations in the Stirling engines can be measured directly without complicated calculations. The variations in the pressure of the working fluid in the engine are measured by a piezoresistive pressure sensor. To confirm the proposed methods, a flat alpha-type Stirling engine was tested. In the laser triangulation method, a laser sensor is used to measure the variation in the crank angle of the shaft. In the hybrid Harris corner detection method, the crank angle of the shaft is obtained by analyzing the images of the mechanism recorded by a high-speed camera. The volume of the working spaces is obtained according to the geometry of the driving mechanism as well as the engine speed. In this study, the pressure-volume diagram of the proposed engine under different operating speeds is measured and compared. The results indicate that the difference in the engine speed and phase angle measured by both methods is 2.3 % and 2.9 %, respectively. The indicated powers of the engine measured by both methods with a heating temperature of 500 °C at 765 ± 5 rpm are 5.789 W and 6.904 W, respectively. The relative difference between the volume variations measured by both methods is lower than 0.5 %. The hybrid Harris corner detection method can obtain more precise results than the laser triangulation method.