Design and Development of an Ultra-Low Friction and High Power-Density Diesel for the Indian Market

This paper explains the methodology to design a high power-density diesel engine capable of 180 bar peak firing pressure yet achieving the lowest level of mechanical friction. The base engine architecture consists of an 8 mm crank-offset which is an optimized value to have the lowest piston side forces. The honing specification is changed from a standard plateau honing to an improved torque plate slide honing with optimized surface finish values. The cumulative tangential force of the piston rings is reduced to an extreme value of 28.5 N. A rectangular special coated top ring and a low-friction architecture oil ring are used to reduce the friction without increasing the blow-by and oil consumption. A special low-friction coating is applied on the piston skirt in addition to the optimized skirt profile to have reduced contact pressure. The piston pin is coated with diamond-like carbon (DLC) coating to have the lowest friction. The main bearing and crankpin diameter and width are optimized to have the lowest friction yet meeting the bearing unit-load and oil film thickness requirements. A unique oil supply concept is introduced to reduce the oil flow through the main bearings by 24%. The oil pump is driven by a chain to reduce the operating speed and rotor diameter and inertia. Water pump efficiency is improved by adopting a closed-vane curved impeller and low-friction bearing. Chain guides are designed with polyamide 46 (PA46) material to reduce the friction; low friction coating on the chain links is used for further friction reduction. A low-friction single-plunger fuel injection pump (FIP) is used in place of a 3-plunger pump. Engine oil with special additives is used to reduce the cold-friction yet maintaining the required dynamic viscosity at high temperatures. Overall, the final measurement results confirm that the overall engine friction is measured to be about 0.806 bar at a motoring speed of 2000 rpm at 90 deg.C. coolant and oil temperature.

The authors give further insight into the future friction reduction potentials which include further reduction of oil ring tension (5N), belt system tension reduction by using an over-running alternator decoupler (OAD), the introduction of variable oil pump, switchable piston cooling jets and switchable water pump. With these measures, it is estimated that the engine friction can be further brought down to an ultra-low value of about 0.680 bar.