Technique of Measuring Piston Secondary Motion Using Laser Displacement Sensors

An experimental technique for measuring the distinct modes of piston secondary motion is described in this study. The measurement system consists of three laser displacement sensors with the laser spots aimed at the piston crown, where the target area is machined with flat slot and a 45° slope profile to provide the necessary reflective angle in order to obtain the rotational and lateral motion of the piston head. The Pearson’s correlation coefficient revealed a strong relationship between the rotational motion and the lateral motion of the piston at a low engine speed of 100 rpm, and this correlation is weakened as the speed increases up to 500 rpm. The lateral motion results captured by the laser displacement sensor are verified by comparing the frequency components of the lateral motion with the frequency components of the lateral acceleration measured using a triaxial accelerometer. The measurements of the distinct modes of the piston secondary motion are shown to be valid and reasonable.