Kraftstoffe

Zusammenfassung

Downsizing in combination with turbocharging currently represents the main technology trend for meeting CO₂ emissions with gasoline engines. Besides the well-known advantages of downsizing the compression ratio has to be reduced in order to mitigate knock at higher engine loads along with increased turbocharging demand to compensate for the reduction in power. Another disadvantage occurs at part load with increasing boost pressure levels causing the part load efficiencies to deteriorate. The application of a variable compression ratio (VCR) system can help to mitigate these disadvantages.

The 2-stage VCR system with variable kinetic lengths entails variable powertrain components which can be used instead of the conventional components and thus only require minor modifications for existing engine architectures. The presented variable length connecting rod system has been continuously developed over the past years. The working principle and the system properties based on the current state of development will be shown in detail.

Various compression ratio ranges and considerations for actuation speed are being discussed in detail. A comparison of 2-stage versus fully variable compression ratio systems will be discussed and an outlook will be provided of how the presented 2-stage system and a fully VCR system can be utilized in current state-of the- art turbocharged direct-injected gasoline engines with the potential for significant CO₂ reduction.

Various fuel qualities in different markets worldwide, demand different layout of the compression ratio due to the changing knock behavior of the fuels. A VCR system has the potential to decrease fuel consumption and emissions dependent on the fuel quality. Advantages of VCR with multi fuel applications will be discussed.