Experimental Study of the Lubricating Oil Impact on the Unsteady Performance of an Automotive Turbocharger

Turbocharging technique is a key technology for the development of hydrogen engines, allowing high lambda values to reach low NOx emissions. In ultra-lean mixture conditions, the thermal management of the lubricating oil and its cold condition becomes a crucial aspect that cannot be neglected. Accordingly, the impact of different lubricating oils and different lubricant thermal conditions is highlighted referring to the performance of a turbocharging system for automotive application. To this aim, an experimental campaign is conducted at the test bench for components of propulsion systems of the University of Genoa. Tests are performed on a turbocharger equipped with a variable geometry turbine under both steady and unsteady flow conditions, considering different positions of the turbine regulating device. A 4-cylinder engine head was coupled to the turbocharger in order to reproduce the pulsating flow related to the opening and closing of the engine valves. The influence of the lubricants on the assessment of turbine thermo-mechanical efficiency is analyzed under steady flow conditions considering different lubricating oils. The study reports the effects of the oil temperature on instantaneous turbine power and turbocharger efficiency under unsteady flow conditions. This analysis aims to provide a comprehensive understanding of turbocharger performance during the engine warm-up phase. The effects of heat transfer between turbocharger components are taken into account, along with the impact of different oil temperatures on friction losses and their effects on the instantaneous rotational speed of the turbocharger. The aim of this work is to provide valuable information on the actual performance of the turbocharger under unsteady flow condition with reference to the impact of the lubricating oil characteristic on the boost pressure provided to the engine.