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Between Petrol and Diesel Engine

The internal combustion engine still capable of development.

Although many thousands of engineers have dealt with the internal combustion engines and have undoubtedly realized countless improvements, there remains a large and promising area for further improvements. They drag their basic disadvantages with them from the early beginning.
First of all there is the petrol engine; the more expensive is the fuel, the higher its antiknock rating and consequently the less prone is the fuel to ignite. Its combustion must wait under all circumstances for the electric spark. For it engineers sometimes accept large efficiency losses.
Then the diesel engine: it puts the fuel under very high pressure (using a lot of energy, too), injecting it in sharp, very fine rays in such a way that it is difficult for the air to mix with the fuel before or during the combustion. As a result undesirable particles are being formed.

No necessity for an electric ignition.

A new engine should unite the advantages of both worlds, ruling out the above sketched disadvantages. The first presumption is an engine without electric ignition, similar to the diesel engine. The fuel this vehicle is going to consume is, if you listen to Mercedes engeneers, normal sold 95-octane petrol. Maybe Sunfuel is the fuel of the closer future.

What about high pressure injection?

So it is in the end just another improvement of the Diesel engine? No, because presumably the injection system will rather resemble that of the petrol direct fuel injection with clearly lower pressures. High pressures are not necessary as the injection takes place before or at the latest at the beginning of the compression stroke. And the injection will probably not take place with a sharp ray, but well distributed for a better mixture of the air - fuel mixture.

Such a complicated and fast regulation is only possible today.

It is obvious; this future engine should be self-igniting, receiving its fuel, in principle, together with the air. To manage the self-ignition exactly at the right time, a lot of control units are necessary. The following systems can help to control the temperature and therewith the self-ignition point:

- Pressure of the external compressors,
- Variable compression,
- Exhaust gas recirculation,
- Knock control system,
- Lambda control,
- Variable camshaft adjustment,
- Variable valve lift.

Excess air is the ultimate goal

So far, so there's at least one gasoline engine which requires no spark plugs to an average speed. Its self-ignition is caused consciously, however, in a way controlled that the mechanism is not damaged. This technique currently works only with turbocharger but it could also well be used in a naturally aspirated engine with variable compression. Whether it all works well with the more economical stratified charge is still written in the stars ... 06/08

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