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

Key results

The results were measured on the different MCE‑5 VCRi prototypes:
single-cylinder engines, multi-cylinder engines and a demo car

One of the automobile industry’s main priorities is to reduce engine cubic capacity (downsizing) and mean operating speed (downspeeding) in order to reduce vehicle fuel consumption levels. This is also the primary objective of MCE‑5 VCRi technology. To do this, it is necessary to reach the highest possible specific torque and power with the shortest possible turbo-lag, and the lowest possible specific consumption at high loads.

With exceptional specific torque and power of 320 Nm/L and 120 kW/L, MCE‑5 VCRi surpasses all the existing fixed compression ratio engines, and with 60 to 70% more torque than will have future fixed compression ratio turbo GDI engines planned for the next decade (40 bar of BMEP vs. 25).

The 120 kW/L of specific power delivered by the twin turbo MCE‑5 VCRi GDI is 20% higher than that of the best existing turbo GDI engines.

These excellent specific performances are reached thanks to MCE‑5 VCRi’s wide range, reduced friction and high load capacity MCE‑5 transmission mechanism.

These performances reflect the exceptional ability of MCE‑5 VCRi to downsize and downspeed car engines, resulting in a significant decrease in fuel consumption and associated CO2 emissions.

The 1.5L MCE‑5 VCRi prototypes deliver the torque of
a naturally-aspirated 4.8L engine and the power of a 3.2L V6 engine

There is no hard downsizing without high supercharging. MCE‑5 VCRi’s supercharging with two turbocompressors contributes to its efficiency, with both excellent isentropic efficiency and excellent responsiveness to reach 80% of torque in under 2 seconds at 1500 rpm. Supercharging efficiency is one of the keys to the success of this type of engine, with good exhaust temperature control, high efficiency at high loads and supercharging pressures in the order of 4 bar of absolute pressure.

Particular attention was paid to the development of the two-stage supercharging of the MCE‑5 VCRi.
It comprises a low-pressure stage, a high-pressure stage and two air-water coolers
positioned after each compressor (intercooler, aftercooler)

MCE‑5 VCRi makes it possible to optimize the compression ratio according to speed and load, resulting in increased thermodynamic efficiency and significantly improved combustion stability. On the compression ratio map, we can distinguish high-load points for which the main objective is maximum torque and the most used, low-load points, for which the aim is to maximize efficiency.

The compression ratio always serves the best compromise between
efficiency, performance, pollutant emissions, stability and safety

In the driving cycle (example: NEDC), MCE‑5 VCRi reduces vehicle fuel consumption by combining the gains provided by downsizingdownspeeding with those provided by compression ratio optimization.

MCE‑5 VCRi’s limited friction losses also contribute to the results obtained. Note that the fuel consumption reduction is higher for powerful cars than for small ones.

The forecasted fuel consumption
reductions refer to the NEDC

VCR redefines the energy
balance of engines

The gains made by MCE‑5 VCRi are more due to the repositioning of the engine’s
operating points than to the improvement of the BSFC map

On a Peugeot 407 type vehicle, the most basic MCE‑5 VCRi MPFI reduces fuel consumption by 31%.
The most sophisticated version of the MCE‑5 VCRi planned for the near future could this
reduction down to 45% while providing 16% more power and 62% more torque


MCE‑5 VCRi also procures many other advantages that result in even greater fuel efficiency, more comfort and driving pleasure and reduced vehicle costs:

Remarkable combustion stability:
MCE‑5 VCRi combustion stability is exceptionally high. Its coefficient of variation always remains under 3% (combustion speed dispersion), which makes it possible to reduce its idle speed to 550 rpm.

With a high compression ratio and a limited FMEP (Friction Mean Effective Pressure) of roughly 0.55 bar, the hourly fuel consumption of an idling MCE‑5 VCRi is lower than 300g of fuel. This opens up many possibilities and, in particular, that of not having to use Stop & Start, which avoids stopping the heating or air conditioning in the passenger compartment and also avoids cooling the catalyst.

At high torque, MCE‑5 VCRi’s combustion stability leads to improved vehicle NVH behavior, with increased driving pleasure.

During the catalyst light-off phases (strategies to rapidly increase catalyst temperature), it’s possible to obtain more exhaust enthalpy from the MCE‑5 VCRi at the same level of stability.

It is therefore possible to either reduce the quantity of pollutants emitted in the certification driving cycle or to reduce the cost of the catalyst.

More effective after-treatment strategies:
During the catalyst’s temperature increase phase (light-off), it’s possible to obtain more exhaust enthalpy with the same level of combustion stability.

This higher exhaust gas temperature can be obtained while producing less HC and CO. It is thereby possible to reduce the quantity of pollutants emitted in the certification driving cycle, and possibly to reduce the cost of the catalyst.

With regard to pollutant emissions during the engine’s most highly loaded phases (full torque), it’s possible to benefit from better-positioned ignition advance by setting the compression ratio at the correct value. This leads to improved thermodynamic efficiency and cooler exhaust gases. It’s then possible to limit or even eliminate the enrichment of the air-fuel mixture and to avoid high pollutant emissions and high fuel consumption at full power.

VCR is also an interesting strategy to increase the external cooled EGR rate, since combustion stability is the main factor that limits the use of external EGR. By increasing the accessible level of EGR, it’s possible to substantially decrease fuel consumption at high powers (20% and more for loaded cycle).

VCR + GDI + two-stage turbocharging with air-water cooling + cooled EGR should lead to “always lambda 1” engines throughout the whole range of use.

For Gasoline Direct Injection, VCR adjusts the distance between the injector and the piston. At high loads, it’s therefore possible to avoid wetting the piston, while at low loads, the piston bowl near the injector better confines the fuel spray and avoids wetting the cylinder walls. Particulate and soot emissions are thereby reduced by a factor of 4 to 5.