A study of upward oil jet impingement on flat and concave heated surfaces and the application to IC engine piston cooling

This thesis presents research on upward pointing oil jets that provide cooling of downward facing heated surfaces. The specific purpose of this research is to improve understanding of the oil jet cooling of internal combustion engine pistons. In this research, the cooling of heated blocks with flat and concave surfaces was investigated. Temperature measurements were obtained using an array of thermocouples embedded inside the heated blocks. A flash illumination and high resolution CCD camera system was used to observe the liquid jet impingement. Observations identified a 'bell-sheet' flow pattern, jet interference, jet splatter and jet breakup which provided insights into the liquid jet impingement processes normally encountered on downwardfacing surfaces. Bespoke contracting-type nozzles were used to produce the jet flow structure. The data from these nozzles were used to generate new empirical correlations for oil jet cooling of downward-facing flat surfaces and for predicting the size 6f impingement. The results obtained from these tests were also used for comparison with cooling jets from production automotive piston cooling nozzles. The research has demonstrated that the effectiveness of oil jet cooling can be affected by preheating the oil and varying the injector size to alter the targeted cooling efficiency, and liquid loss due to jet breakup and splatter. Local heat transfer coefficients were observed to increase when the jet Reynolds number increased. Piston undercrown cooling was studied using a range of oil jet configurations. The cooling rates improved with optimised targeted jets. The results also indicated that the undercrown geometry designs such as crosshatched surfaces, undercrown-skirt and gudgeon-pin boss, were significant for enhancing the local rate of forced convective heat transfer. New empirical correlations were developed from the experimental results that enabled prediction of the heat transfer coefficient and jet impingement size for high Prandtl number liquid jets impinging onto downward-facing surfaces. The heat transfer correlations were developed for normal (θ = 90°) and inclined (θ = 75°, 60° and 45°) jet impingements.