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

It’s heavy

Paradoxically, low-fuel consumption engines are generally heavier. The lightest engines are two-stroke engines and they are also those that consume the most fuel. The most fuel-efficient engines are Diesel ones and they are the heaviest. If we look at the vehicle as a whole, we find the same paradox: while the lightening of vehicles undeniably leads to lower fuel consumption, a full hybrid vehicle designed to reduce fuel consumption will easily be loaded with 200 kg of additional equipment, which will nevertheless lead it to consume less.

full hybrid vehicle designed to reduce fuel
consumption will easily be loaded with
200 kg of additional equipment

The performance/weight ratio of the MCE‑5 VCRi
is comparable to that of most modern
gasoline or Diesel IC engines

Vibroacoustic perception from inside or outside
the MCE‑5 VCRi demo car is similar to that
of a conventional gasoline car

The weight of the MCE‑5 VCRi is under optimization:
the prototype engine block is being replaced by an
optimized aluminum one, which is 62% lighter

Of course, lightening remains a vital objective and justifies making substantial efforts on materials and on the optimization of all the elements making up the vehicle.

In the engine perimeter, we differentiate the weight on the scale that impacts the vehicle’s weight from the mass of the moving components and reciprocating parts.

Weight on the scale:

A heavy engine implies additional vehicle weight that will result in higher fuel consumption. This is particularly true during the urban driving cycle due to repeated accelerations and decelerations. In this case, the additional weight leads to an increase in the energy dissipated in the brakes.

An engine’s weight must be expressed in kg/Nm and kg/kW. Any other consideration is meaningless, otherwise we would be tempted to a compare motorcycle engine with that of a supertanker.

Engine weight must really take into account the weight of the whole powertrain, since the engine cannot run without its turbocharging, transmission, aftertreatment system and energy reservoir. The distribution of the masses within the drive system does not matter – what is important is the total weight of the “drive solution”.

From this standpoint, the MCE‑5 VCRi engine is in line with modern engine trends. It’s heavier if we consider its specific weight to cubic capacity (kg/cm3), but its weight /performance ratio (kg/Nm, kg/kW) positions it in within the average values of the most modern gasoline and Diesel engines. This position is due to the MCE‑5 VCRi engine’s exceptional specific performance (Nm/L et kW/L).

Mass of the reciprocating parts:

The mass of the engine’s reciprocating parts causes vibrations, friction losses and kinetic losses. Regardless of the engine, the vibrations induced by the reciprocating mass are lower than those generated by combustion and by crankshaft torque variations. An MCE‑5 VCRi 1.5L GDI engine delivering 180 kW produces free inertia forces comparable to those of a 2.0L Diesel engine whose most highly loaded two-stage turbocharged versions deliver 150 kW. Yet, the acyclisms of the MCE‑5 VCRi crankshaft are comparable to those of highly-loaded gasoline engines. When in the vehicle, it’s impossible to distinguish the MCE‑5 VCRi from a “normal” gasoline engine in terms of vibro-acoustics. MCE‑5 VCRi demo cars prove this fact and even show a significant decrease in the acoustic pressure measured and perceived by the driver.

In a conventional engine, the reciprocating mass also causes friction. This is less true for the MCE‑5 VCRi since the sliding between the piston and liner is mostly replaced by pure rolling, which is much less sensitive to the mass of the parts. This explains the reduced friction in the MCE‑5 VCRi despite a reciprocating mass comparable to that of a Diesel.

The kinetic losses due to the acceleration and deceleration of the moving parts must also be taken into account in the energy balance. These losses are similar to those generated by the acceleration and deceleration of the vehicle itself. From this standpoint, the MCE‑5 VCRi has several advantages: except for the piston, its parts move less quickly at same speed than those of a conventional engine (kinetic energy = 1/2.m.v2). Moreover, its crankshaft mass is near its center of rotation, which reduces its moment of inertia. This means that MCE‑5 VCRi “stores” a fairly low level of kinetic energy (j/rpm), compared with that stored by a naturally aspirated conventional engine with the same cubic capacity. In practice, the MCE‑5 VCRi’s exceptionally high torque reduces the mean engine speed, resulting in lower-amplitude engine speed variations and thus less kinetic energy dissipated. This low level of kinetic storage also gives the engine rapid spin-up (rpm/sec).

The overall assessment of the weight and mass of the MCE‑5 VCRi engine proves that it’s fully competitive with the best conventional gasoline or Diesel engines.

Comparison of the inertia and kinetic energy stored by the engine's moving parts
between a light 1.5 conventional NA engine and an MCE‑5 VCRi