Experimental and Numerical Investigations of Jet Impingement Cooling of Piston of Heavy-Duty Diesel Engine for Controlling the Non-Tail Pipe Emissions

The development of more efficient and powerful internal combustion engines requires the use of new and advanced engine technologies. These advanced engine technologies and emission requirements for meeting stringent global emission norms have increased the power densities of engine leading to downsizing. In all these engines, cylinder head and liner are normally cooled but the piston is not cooled, making it susceptible to disintegration/ thermal damage. Material constraints restrict the increase in thermal loading of piston. High piston temperature rise may lead to engine seizure because of piston warping. So pistons are additionally cooled by oil jet impingement from the underside of the piston in heavy duty diesel engines. 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 investigation presents and discusses the results of a simulation study with numerical and experimental investigation of the heat transfer between the constant heat flux applied to piston model and impinging jet. Using the numerical modeling, heat transfer coefficient (h) at the underside of the piston is predicted. 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 predict whether the selected grade of oil will contribute to mist generation. Using numerical simulation (finite element method) temperature profiles are evaluated for varying heat flux to demonstrate the effect of oil jet cooling. An experimental setup for the validation of computational results has been developed using production grade piston. Infrared camera (indirect contact temperature measurement technique) is used to investigate and validate the temperature profiles. High speed camera is used to investigate the oil jet breakup, localized pool boiling and mist generation due to impinging jet on the piston underside. Optimized conditions have been found for different parameters to avoid mist generation.