Regarding concepts for naturally aspirated engines, the high potential for fuel economy of Gasoline Direct Injection can only partially be utilized within the constraints of current or future emission legislation like EURO III / IV or LEV/ULEV. Instead of an expected improvement of 20 - 25 % currently only 10 - 15% can be obtained by the engine alone without vehicle optimizations considering all limitations of high volume production. A detailed analysis reveals concrete measures for further improvement.
The application of DI gasoline technology clearly favors the combination with other fuel efficient technologies like downsizing by turbocharging and the application of a variable effective compression ratio by intake valve timing variation.
Using the flexibility of direct gasoline injection some deficiencies of these technologies can be eliminated. In view of an advanced DI gasoline engine concept, the following aspects were investigated:
It was analyzed, if stratified part load operation will be improved by turbocharging. The main subject her was the possible extension of the stratified operational range.
Regarding the driveability of downsizing concepts, transient effects were investigated regarding load response of the engine.
The concept of variable effective compression by intake valve timing retard was analyzed by thermodynamic cycle simulation and multicylinder engine verification in order to improve the engine efficiency further in a broad load range. For an integrated concept combining turbocharging and variable effective compression, a predicted fuel economy potential of up to 28% can be expected from engine technology with further advantages in transient response and driveability to be experienced in real customers use.