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

It’s compact

Engine compactness is relative and as such we must only compare what is comparable. An engine’s size is expressed in torque per mm or power per mm (Nm/mm - kW/mm) as a function of the x, y and z axes (length, width and height). The perimeter taken into account is decisive: are we referring to the basic engine (excluding ancillaries) between the oil sump and the cylinder head cover? Or are we referring to the entire engine ready to start, including its after-treatment system? This can radically change the deal.

The MCE‑5 VCRi engine can power all vehicles,
from the smallest to the biggest

An MCE‑5 VCRi MPFI cylinder head beside
that of the EP6 PSA-BMW

We must also consider the energy efficiency of the solutions that we’re comparing; they generally add to the engine size. For example, a full hybrid powertrain is big but it's the price to pay to benefit from a substantial reduction in fuel consumption. Given the new regulatory and energy constraints, the “effective” compactness of a car engine is based on at least two fundamental ratios: performance/size and performance/fuelconsumption. This explains why one would never install an ultra-compact motorcycle engine into a car even if its power is in line with expectations: the resulting performance/fuel-consumption ratio would not be acceptable.

Compactness is sometimes sacrificed to improve driving pleasure: at equal performance, a V12 is longer than a V8 but gives much more pleasure and smoothness. Depending on the context, size is not the most important criteria: in a big American 4-wheel drive car, there is almost enough room to fit 2 compact European sedan engines. On the other hand, in a compact European sports car, the engine size compared to the vehicle size can sometimes reach the limits of what’s possible.

So how does the MCE‑5 VCRi behave in this multi-criteria space? Almost exactly like a conventional engine. Compared with a Diesel, at equal energy efficiency performance, an MCE5 gasoline engine is smaller in the x, y and z axes thanks to downsizing. What’s more, its after-treatment system is smaller and only requires a 3-way catalytic converter. It does however need 2 turbochargers, which is already true for some Diesel engines. With regard to a 3-cylinder MCE‑5 engine with an integrated MCE‑5 compressor, the unit is extremely compact since the engine is “auto-supercharged”.

At the same power, MCE‑5 VCRi is shorter than a conventional gasoline engine. In medium to low powers, it is also less high. However, in very high powers (high capacity per cylinder), it can be higher than a conventional gasoline engine, similarly to Diesel engines. In this last case, MCE‑5 VCRi compensates for this handicap – like Diesel – through a reduction in fuel consumption. In all cases, the impact of the size and integration of MCE‑5 VCRi into the vehicle is incomparably lower than any “full hybrid” solution with similar energy performance.

In the end, MCE‑5 VCRi offers an excellent compromise between performance/size and performance/fuel-consumption.

See also: «It’s too bulky»

At the same engine capacity, only the height
of the MCE‑5 VCRi from bearing line to top deck
is bigger than that of conventional gasoline engines

At the same engine capacity,
the MCE‑5 VCRi remains compact
Photo: 1st 1.5L MCE‑5 block in 2005 (V0)
beside that of a 1.5L Mitsubishi 4A91

The integration of the 160kW MCE‑5 VCRi in the democar
poses no problem despite a 2-stage turbocharging system