Turbocharging Concepts for Downsized DI Gasoline Engines

Reducing engine swept volume (so-called ‘downsizing’) offers the potential to meet future tighter CAFÉ standards and reduced CO₂ vehicle emissions in Europe. In downsizing the gasoline engine, a key challenge is controlling octane requirement without sacrificing fuel economy.

The authors have investigated five alternative approaches on a turbocharged DI gasoline engine:

• Conventional stoichiometric operation, with reduced compression ratio (CR)
• Lean Boost DI (LBDI) with lean operation at full-load to control octane requirement while maintaining a high CR
• EGR Boost with cooled EGR dilution rather than excess air to control octane requirement
• Miller cycle concept, where valve-timing strategies are employed to reduce the effective compression ratio at high load
• Dual injection strategies to control octane requirement

Each approach has been investigated using engine performance and vehicle simulation codes. Experimental investigations have been carried out using a 1.125L I3 multi-cylinder engine. The most promising concept, LBDI, has been further developed using the multi-cylinder engine installed in a Ford Focus C-class vehicle.