EXPERIMENTAL AND NUMERICAL ANALYSIS OF THE PISTON COOLING JET'S PERFORMANCE

Recently, with development in the output power and material cost efficiency, the value of thermal and mechanical stress on many engine parts such as piston is increased. On the other hands, the strength of aluminum alloys used for piston manufacturing decreases with temperature. So, for lightweight pistons, the strength reduction should be minimized to maintain the mechanical integrity of the part. This drives piston designers to use strong and lightweight materials that can sustain a harsh thermal environment through improved oil cooling. In addition to modify the power output, piston cooling reduces the carbonization and pre-ignition caused by hot spots on sharp edges of the piston crown. In this study, in order to evaluate the piston cooling functionality and validate the numerical simulation, a test rig is designed and manufactured and it is equipped with glassy piston and cylinder to show the oil contact surface. Using this test rig, flow rate is measured in different oil pressures and temperatures. In addition, heat transfer coefficient for various engine speeds is determined. Also a numerical model has been developed using CFD approach for analysis of piston cooling oil jet and validated with existing experimental results at axisymmetric condition. Finally, oil contact area and heat transfer coefficient are predicted at the bottom of piston for real piston cooling jet conditions.