Experimental and numerical investigations of jet impingement cooling of flat plate for controlling the non-tail pipe emissions from heavy duty diesel engines

The continuous increase in power density has led to higher thermal loading of pistons of heavy duty diesel engines. Material constraints restrict the maximum operating temperature of a piston. High piston temperature rise may lead to engine seizure because of piston warping. To avoid this, pistons are usually cooled by oil jet impingement from the underside of the piston in heavy duty diesel engines. Impingement heat transfer has been used extensively because of the high rates of cooling it provides. The associated high heat transfer rate is due to the oil jet that impacts hot impingement surface at high speed. However, if the temperature at the underside of the piston, where the oil jet strikes the piston, is above the boiling point of the oil, it may contribute to the mist generation. This mist significantly contributes to non tail-pipe emission (non-point source) in the form of unburnt hydrocarbons (UBHC's). This paper presents and discusses the results of a numerical and experimental investigation of the heat transfer between a constant heat flux flat plate and an impinging oil jet. Piston boundary conditions are applied to the flat plate. Using the numerical modeling, heat transfer coefficient (h) at the underside of the piston is calculated. This predicted value of heat transfer coefficient significantly helps in selecting right oil grade, oil jet velocity, nozzle diameter and distance of the nozzle from the underside of the piston. It also helps to predict whether the selected grade of oil will contribute to mist generation. Using numerical simulation (finite element method) temperature profiles are evaluated by varying heat flux. Infrared camera is used to investigate and validate the temperature profile of the flat plate. High speed camera is used to capture the mist generation and oil jet breakup due to impinging jet.