Lubricant thermo-viscosity effects on turbocharger performance at low engine load

This work presents the performance and efficiency of a needle bearing type turbocharger under low load condition as affected by lubrication oil temperature and viscosity. The turbocharger on a test bench was propelled by known component exhaust gases with controllable mass flow and temperature at the turbine side. Two API SN multi-grade lubrication oils 0W-20 and 10W-40 were tested. The lubricant flow rates were kept constant by external supply at different inlet temperatures. The turbocharger efficiencies were determined by the measured inlet and outlet temperatures, pressures and flow rates for both turbine and compressor sides as well as the shaft rotational speeds. The experimental results were revealed that the higher inlet temperatures related to the thinner lubricant resulted in higher turbocharger efficiency. It suggests that the lubricant thermal manipulation is required for turbocharger under low load condition to operate within the design performance window.