Over the last two decades, engine research has been mainly focused on reducing fuel consumption in view of compliance with stringent homologation targets and customer expectations. As it is well known, the objective of overall engine efficiency optimization can be achieved only through the improvement of each element of the efficiency chain, of which mechanical constitutes one of the two key pillars (together with thermodynamics).
In this framework, the friction reduction for each mechanical subsystems has been one of the most important topics of modern Diesel engine development. In particular, the present paper analyzes the lubrication circuit potential as contributor to the mechanical efficiency improvement, by investigating the synergistic impact of oil circuit design, oil viscosity characteristics (including new ultra-low formulations) and thermal management.
For this purpose, a combination of theoretical and experimental tools were used. The effects of oil pressure regulation, oil pump size and speed, oil temperature and viscosity have been thoroughly evaluated. Experiments were conducted both at component test rig for oil pump and at engine-vehicle test bench on a new common-rail light-duty Diesel engine family ranging from 3 to 6 cylinders.
The main results indicate that relatively small oil pumps rotating at high speeds are preferable, in combination to a low pressure target control and oil characterized by a viscosity in a certain range.