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Petrol Injection

Inlet manifold injection and direct injection to improve emissions and fuel consumption

Since the eighties, the emissions of petrol engines in all operational modes must be controlled. This led to a widespread introduction of the fuel injection. Before, from about 1951, it was reserved for few vehicles, often especially sporty models. At first there is the indirect injection into the inlet manifold, from 1997 also electronically and directly into the combustion chamber. Mechanical direct injection is as old as the fuel injection itself.

Intermittent and sprayed

Only systems with limited time openings of the injectors (intermittent) survived. The inlet valve opening period ranges in the area of milliseconds, however, may outlast with high revs the length of a stroke. The ray is always sprayed, in contrast to the modern diesel injection. With indirect injection the ray hits the throttle valve (throttle body injection) or the intake valve (multi-position injection.) With direct injection it is added to the air in different swirling degrees.

Main influencing variables: air mass and engine rotational speed

Ignition + injection = Motronic

Meanwhile, all control devices for the mixture formation are combined with those of the ignition, reducing the number of sensors and improving the engine management. The number of sensors is relatively evenly spread between the inlet side and exhaust gas side. In addition, there are the usual transducers for the revs and temperature. Throttle plate control motor and bypasses are outdated, because the control device regulates the accelerator pedal. The accelerator pedal is only linked to a potentiometer. Sporadically, even the throttle valve has become obsolete.

Lower fuel consumption for the future

The emissions of the petrol engine are clean, only the CO2-emission is still too high. The engines are becoming stronger and stronger. Taking their power into account, the fuel consumption is not so high after all, but in comparison to a diesel and in view of the future still intolerable. The fuel injection cannot master all the requirements by itself, however, will have to contribute with higher injection pressures, and changes of the ray angle. 06/07