Reduced Fuel Consumption Engine for a CO2 < 125 g/km Vehicle, Through Friction Losses Reduction and Combustion Optimization

Abstract

Friction reduction is a very challenging theme in research and development on reciprocating engines, and in particular on engines for passenger cars. The points for improvement are several: valve train and timing command, piston package, liners, crankshaft, ancillaries and related command, lubrication, cooling, and involve optimization of couplings, components design, materials, manufacturing technology, etc. This paper presents a comprehensive activity of engine development, which starts from considerations about the single contribution of each functional group of the engine on total friction, selects the fields of research where the most effective results can be expected, and concludes with results obtained on a Demonstration Vehicle. The fuel consumption reduction obtained is about 11% with respect to (w.r.t.) the reference vehicle in the NEDC, with better performance. No modifications in terms of drag force, weight and gearbox/tyre configuration have been made to the vehicle itself. The main themes of development have been: a new lightened valve train, also featuring “shimless” mechanical tappets; and a new piston package, which includes a piston with only two segments, a newly designed con-rod and a lightened piston pin . The range of FMEP reduction obtained is about 10–26% w.r.t. base engine over the whole engine speed and load map, with the strongest effect in the low speed and load range. Additionally, a new thermodynamic package has been developed, including a new intake manifold and combustion chamber, to improve engine performance at full load and to have a further reduction in BSFC at part load. Furthermore, combustion optimization allows for a synergic effect together with friction reduction at low engine speed and load, which reflects in real-life vehicle urban driving. In fact, lower friction reduces the indicated torque needed for a given mechanical torque. At low engine speed load, lower IMEP gives lower thermodynamic efficiency and higher combustion instability. A parallel improvement in combustion efficiency reduces this negative effect, giving a higher engine efficiency. Combustion optimization also led to a reduction in the engine speed at idle, due to the improved combustion stability. This gives an additional reduction of vehicle fuel consumption. Finally, functionality and durability of the new components have been tested and validated. In particular, the new two-segments pistons have been optimized for blow-by and oil consumption, obtaining results equal to or lower than the standard package. Both the piston package and the new lightened valve-train have been tested for durability with procedures usually required for production validation.