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

It continuously controls the compression ratio

A VCR engine’s compression ratio control could be discrete, with for example two stages: a low compression ratio and a high compression ratio. VCR engines that apply this strategy have already been designed and they result in a limitation to the final energy performance.

2-stage VCR could be a temporary solution
before implementing "full VCR" if other
technological or economic advantages
compensate for the lack of controllability

If a VCR engine is only capable of providing two CR values, the best strategy would be to plan a very low compression ratio of roughly 7 or 6:1 to highly downsize the engine and a “standard” compression ratio of 10 or 11:1 to meet ordinary driving conditions. There are different problems resulting from this strategy. For example, it is impossible to increase the compression ratio at low loads to optimize efficiency. The CR is also too low at intermediate supercharging pressures, which reduces efficiency and makes it difficult to control the exhaust temperature. Compression ignition (Controlled Auto Ignition) becomes ineffective or even impossible and accessible fuel savings are drastically limited in this case.

For an engine with two compression ratios, another strategy could be to consider a minimum CR of 10 or 11:1 and a maximum CR of 13:1. In this case, the efficiency at low loads would be improved but the additional downsizing-downspeeding gains would be lost, making the VCR unprofitable when compared with conventional GDI turbo engines.

VCR strategy entails reaching for those last grams of fuel per kW and CO2 per km, which requires a continuously variable compression ratio. This function is part of the basic characteristics of MCE‑5 VCRi technology.

MCE‑5 VCRi's continuous and flexible compression ratio control serves the primary objective of VCR:
reaching the last grams of fuel per kW and CO2 per km