Evolution perspectives

Carmakers references for VCR Fuel Consumption reduction

There is a fundamental difference between FCR and VCR engines: all that is possible on a FCR engine is possible on a VCR engine, but not the contrary. This could rapidly lead to significant differences between the two approaches in terms of Fuel Consumption and pollutants emissions reduction.

VCR strategy will not only allow engines to conform to short term objectives of automotive industry, it will also offer a wide technical room for maneuver and remarkable evolution perspectives:

1)
As Compression Ratio control permits to avoid knocking whatever the supercharging pressure, VCR engines allow extreme specific power and torque (extreme downsizing) with no consequences on the average Compression Ratio under normal driving conditions.
2)

VCR engines operate under high compression ratio at part loads (up to 16:1 or 17:1). This provides a better indicated efficiency than that of FCR engines and allows for a significant idle speed reduction (reduced misfiring and cyclic irregularities).
3)
VCR permits to reduce exhaust gases temperature under extreme supercharging pressure by always retaining the best combination between Compression Ratio and ignition advance. This permits decreasing the engine thermal stress and avoiding charge enrichment at high power (better efficiency, low pollutants emissions).
4)

VCR improves charge scavenging efficiency to increase torque and power. As a reminder, charge scavenging permits replacing all burnt gases in the combustion chamber by new air-fuel mixture. Residual exhaust gases removal is done thanks to an appropriate intake-exhaust overlap combined to supercharging.
As the combustion chamber volume of VCR engines is widely increased under high supercharging (low compression ratio), the effective engine capacity is increased (when burnt gases are entirely removed, cylinder capacity + combustion chamber volume = effective engine capacity).
  5)
VCR will allow implementing the adaptive Atkinson cycle (the only load control strategy that allows for high pumping losses reduction while remaining under stoichiometric combustion on the entire load-speed range).
  6)
VCR will permit increasing load-speed range of effectiveness of lean-mixtures strategies such as lean-burn and stratified charge or Compression Ignition (pressure and temperature control permits to push back the bounds of combustion under ultra-lean mixtures and to precisely set Auto Ignition timing).
  7)
VCR will permit implementing specific cold starting procedures to accelerate 3-way catalyst raise to temperature while controlling NOx generation (a low Compression Ratio permits increasing exhaust gases temperature while reducing NOx generation).
  8)
VCR ensures an efficient transition between gasoline and natural gas: bi-fuel vehicles can automatically adapt their compression ratio to the current fuel octane number and natural gas quality.

Conclusion

VCR engines present a high evolution potential compared to that of FCR engines.

In the short-term, VCR features will permit to widely reduce SI engines Fuel Consumption and pollutants emissions. As VCR is a generic approach to improve all existing engine strategies, VCR is a major profitability source for automotive industry.

 
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