Compression Ratio and Piston Recess

Compression Ratio and Piston Recess

The reduction in the temperature level in DFI engines due to internal mixture formation also reduces knock sensitivity and therefore additionally allows the compression ratio to be increased. The higher compression ratio improves the engine efficiency and reduces fuel consumption as well as exhaust emissions.

The mixture formation and combustion processes for direct fuel injection (DFI) require a new piston crown shape. The piston crown forms a relatively large part of the combustion chamber and has a major influence on efficient combustion. Its shape also affects mixture formation and mixture stabilization in the spark plug area, particularly during injection processes in the compression phase. The piston crown shape in the new 911 Turbo was also adapted to increase the compression ratio from 9.0:1 to 9.8:1 and therefore to improve the efficiency of the engine.

The new 911 Turbo features high-pressure stratified charge injection as well as secondary-air injection. Here, fuel is injected once into the specially moulded piston recess in a targeted manner. This creates a stratified charge around the spark plug, which in turn produces a mixture with optimum ignition properties.

Increase in compression ratio to 9.8:1 (predecessor 9.0:1) possible through a reduction in the temperature level in DFI engines - resulting in lower knock sensitivity. This improves efficiency and reduces fuel consumption thereby lowering engine exhaust emissions.







With high-pressure stratified charge injection, fuel is injected once into the specially shaped (arrow) piston recess in a targeted manner. The result is an optimum starting mixture with the lowest possible enrichment.