Direct Petrol Injection
       

Function

The designers pursue several development objectives with the petrol direct injection. If petrol is injected directly into the combustion chamber of the Otto engine, the condensation cooling effect of the fuel remains exclusive to the combustion chamber. You achieve a lower knocking proclivity, enabling a higher compression. With the same cubic capacity there is more torque and thus also a higher performance. The engine reacts quicker to the accelerator pedal, and for the part-load operation a measurable fuel consumption saving is aimed at.Historically, Daimler-Benz already in 1936 experimented with the petrol direct injection for aircraft engines in order to make the fuel supply independent of the flight conditions. In the second half of the 20-th century its triumphal implementation into passenger cars started. At first in combination with the two-stroke engine (Hanomag Gutbrod) which could be operated with pure air and without mixture lubrication. After its debut in the Mercedes 300 SL it remained quiet for a long time, until Mitsubishi took up the technology again in 1997.

How it works

After the throttle body injection and subsequently the multi-position injection, and now the direct injection, the preparation time for the fuel mixture has become ever shorter. Therefore, there are specific requirements for the pressure, meaning the kind of injection and the guidance of the airflow. Special research projects which observe the internal-motor processes with high-speed cameras are almost essential for the development of suitable combustion chambers, ignition systems and injection systems.

Future

If you want to alter the petrol direct injection from homogeneous working to stratified charge working obviously even more investigations of the flow conditions in the combustion chamber and the ray spreading of injectors are necessary. Also the control and the exhaust gas decontamination are substantially more difficult than with indirect injection. Therefore, many manufacturers walk on the easier way of sticking to the homogeneous working.Refinements are obviously implemented, e.g., precise controls of the aerial swirling in the inlet manifold, or specific changes of the suction ways. Switching is possible. In the lower speed range you might want to have an aerial roller, for the upper speed range a perfect flow through.

This will not stop the technological progression, becoming more and more similar to the common rail process and the Diesel engine, except of course for the ignition system. Hopefully soon also in terms of a favorable fuel consumption and the high torque also for the lower speed ranges. 08/09