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Direct Petrol Injection


In the developement of petrol-direct injection the constructors followed several objectives. When petrol is injected directly into the combustion chamber of an Otto- engine, through condensation of the fuel, the cooling effects exclusively the combustion chamber. This causes a lower knocking tendency and a higher compression is possible. With the same cubic capacity a higher torque is achieved, thus, also a higher performance. The engine reacts better to changes of the gas-pedal position. In the partial-load operation, the aim is to achieve a measurable amount of fuel saving.

Historically seen, the petrol direct injection was first introduced in the two-stroke engine (Gutbrod), only afterwards was it installed in the Mercedes 300 SL. The reason for this provides a further argument in favour of this type of mixture preparation. The two-stroke suffers particularly from scavenging losses and here, the direct injection can be a big help. This is also an advantage for the four-stroke engine with valve-overlap. The relatively short-term injection - before the combustion - cannot be lost through the exhaust valve. This is different in external mixture preparation. The Mitsubishi company by the way, were in 1997, the first ones to take up the subject again, under the description, Gasoline Direct Injection.


After the central injection the mixture forming times for the indirect multi-point injection and now also the direct injection, have become shorter and shorter. Thereby, special demands are made of the pressure or the type of injection and the guidance of the air-flow. Special research including the observation of the internal engine processes through high-speed cameras, has become almost essential for the development of suitable combustion chambers, ignition- and injection systems.

The future

Apparently, the change-over from homogeneous operation to stratified-charge operation in the direct-petrol injection, requires even more researching in the field of flow-ratios in the combustion chamber and the jet-dispersion from the injection valves. The regulation and the exhaust-gas decontamination are also much more difficult, which is why a great many manufacturers have opted for the more simple solution of homogeneous operation.
In this field, there are still possibilities for refinement, e.g., the precise control of the air-swirling in the inlet manifold, apart from the specific alteration of the inlet paths. Changeover points are a possibility which would create an air-cylinder in the lower RPM range and in the upper range, a perfect flooding would be achieved.
This will not stop the assertion of this technology, and together with the Common-Rail-system of the Diesel engine, apart from the ignition system, from becoming more and more similar. Hopefully, as soon as possible also in the advantages of lower fuel consumption and high torque in the lower RPM range. 04/12