MCE-5 VCRi: Pushing back the fuel consumption reduction limits

Its piston is naturally cold

The heat flow that crosses a piston is roughly proportional to the engine’s power. The piston’s temperature must be maintained below a certain threshold to guarantee sufficient mechanical strength. Hence, an engine with high specific power requires specific management of the piston temperature.

The MCE‑5 VCRi piston's pushrod-type shape
gives it excellent mechanical strength

Conventional pistons cool naturally through their rings, skirt and bottom of the crown. The top of the crown only participates in cooling during intake and the first half of the compression stroke. As of a certain specific power, it is necessary to use piston cooling oil jets. The oil jets require oversizing the oil pump, which has a direct impact on the engine’s friction (increase in FMEP - Friction Mean Effective Pressure). For engines with high specific power, the use of a variable capacity oil pump is preferable to limit any useless energy losses when the oil jets are not used. Ideally, this pump is associated with a solenoid valve allowing “intelligent” control of the oil jets.

The MCE‑5 VCRi piston naturally offers a larger exchange surface to release heat to the environment, thanks to its base structure made of fins that improve its cooling. Its push rod type shape gives it excellent mechanical strength.

The characteristics of the MCE‑5 VCRi piston thereby limit the flow from the cooling oil jets. Some studies even suggest that they can be eliminated. This benefit leads to a reduction in the friction losses from the oil pump and provides excellent mechanical strength to the engine at high powers.

Thermomechanical modeling correlated
with physical measurements made it possible
to optimize MCE‑5 VCRi piston geometry

Temperature telemetry via radio transmission
was a decisive tool for developing
the MCE‑5 VCRi piston