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

It’s too bulky

Overall dimension is a relative notion. To estimate the overall dimensions of an engine, its power and torque are essential data and so is its energy efficiency. Energy efficiency usually has a tradeoff in excess weight but also in larger overall dimensions. At the same power, a Diesel engine is not only heavier, but its overall dimensions are also bigger than those of a gasoline engine. A full hybrid drive is so big that it’s only adapted to large vehicles, otherwise a specific vehicle would have to be built to house all of its equipment (batteries, transmission, generator, etc.).

It's only possible to equip a Renault Clio with a V6 engine
if it is mounted at the rear of the vehicle

Engine size and performance are linked to one
another: the compactness depends on kW/mm
and Nm/mm output in x, y and z axis

Energy efficiency and durability generally lead to a bulky size: a motorcycle engine with a high speed delivers high power at a reduced weight and size, however, it has high fuel consumption and a limited service life. Conversely, Diesel engines are bulky but have a low engine speed, low fuel consumption and a long service life.

In comparable conditions, more power also means bigger overall dimensions. The V8 engine of a Mercedes S-Class would not fit into a Renault Clio, but the power intended for the Clio is much lower than that required for the S-Class. It’s therefore useless to deplore the fact that the S-Class engine doesn’t fit into the Clio. The only solution to add power to the Clio would be to strongly supercharge its engine, to run it at higher speed or to house a bigger engine at the back of the vehicle.

An objective comparison must therefore be made at comparable torque and power. The engine’s dimensional performance density must be expressed in kW/mm and in Nm/mm, in the 3 directions x, y and z.

The architecture is also important. For example, it would be extremely difficult, if not impossible, to integrate into a vehicle an engine whose power output shaft is vertically positioned in its center. The connection to the transmission and the fitting of the engine into the engine compartment are also essential criteria.

The acceptable engine size limits differ depending on whether the vehicle is a minivan, a hatchback sedan, or a mid-sized sedan with a long or short hood, and on its engine compartment panel height. They also depend on whether the engine is mounted longitudinally or transversely. Regardless of the vehicle configuration, the overall dimensions of the engine and its movement boundaries (engine tilting under torque) have direct consequences on pedestrian protection and vehicle crash test performance.

The engine must of course be as compact as possible to leave more room to house other ancillaries. The compactness of an engine also reflects the ability to install it in the highest possible number of vehicles, which is crucial for obvious reasons of profitability. In the end, overall engine size must be assessed when equipped with its essential ancillaries (generator, water pump, transmission, aftertreatment) and/or its optional ancillaries (turbocharger, mechanical compressor).

It’s therefore essential to resituate the overall dimensions of an engine in its competitive arena, with the same torque and power performances and comparable energy efficiency.

The MCE‑5 VCRi engine is well positioned in this exercise. Only its height could potentially be a handicap for high capacities per cylinder (500cm3/cyl.). Such capacities per cylinder are not the focus of MCE‑5 VCRi and only concern extremely powerful vehicles. At a specific power of 110kW/L in MPFI and 130kW/L in GDI and at extreme torque values (respectively 280 and 320 Nm/L), the MCE‑5 VCRi is, in almost all cases, smaller than any Diesel engine and often smaller than conventional GDI turbo engines.

The height of the MCE‑5 VCRi is not a strong point, however, for 140 kW of output, its height from bearing
line to top deck is 215mm vs. 240 for a modern Diesel DI turbo, and from 215 to 225 mm for a 2L GDI turbo

The MCE‑5 VCRi in the demo car: there is no particular challenge for engine integration
despite 2 turbos and associated inter- and after-coolers