Optimization of the Bearing Oil Supply Concept of a High Power- Density Diesel Engine to Minimize Oil Pump Friction 2020-28-0338
Reducing the mechanical friction of an internal combustion engine plays a major role in improving the brake specific fuel consumption (BSFC) at the engine level. Hence, it is important to reduce the friction at every component and sub-system level. In the present work, the oil pump friction of a 1.5 litre 4-cylinder diesel engine is optimised by reducing the oil pump displacement volume by 20%. This could be achieved by adapting an optimised oil supply concept which could reduce the oil leakage through main bearings and connecting rod bearings.
A 1-dimensional oil flow simulation was carried out to predict the oil flow distribution across the engine at difference speeds. The results indicate that the oil leakage through main bearings and connecting rod bearings contribute to ~25% of the total oil flow requirement of the engine. In a conventional oil supply concept, the big-end bearing of each connecting rod is connected to the adjacent main bearing through an internal oil hole. Though this is a standard and robust concept, the oil leakage through the bearings is relatively higher that demands a bigger oil pump. Hence, several design options were investigated to reduce the overall oil leakage through the bearings. A 3-dimensional elasto hydrodynamic (3D EHD) simulation was carried out to assess the oil leakage rates of different concepts. Moreover, the robustness of the bearings was also checked by comparing the minimum oil film thickness, total contact pressure, asperity contact pressure and adiabatic temperature rise. Based on the results, the oil feed concept was optimized in such a way that the big-end bearings of two connecting rods are connected to one main bearing. Moreover, the main bearing shells were optimized in line with the new oil supply concept to overcome the challenges of operating under the peak cylinder pressure of 180 bar.
Overall, with this optimized oil supply concept, the oil pump size could be reduced from a theoretical displacement volume of 24 cc / revolution to 19.5 cc / revolution. Thus, the optimization of the oil supply concept of the engine bearings helped to reduce the oil pump size and corresponding power consumption significantly.
Vikraman Vellandi, Prasad NAMANI, S. Suresh Bagavathy, Madhu Chalumuru