Why injection ?

 

In a carburettor, the throttle lever controls a butterfly valve that allows more or less air to pass into the carburettor. The vacuum created by this passage of air in the narrowed portion of the carburettor causes aspiration of the fuel contained in the tank.

 

The ratio of fuel relative to the amount of air is managed by the tapered needle that more or less obstructs passage of the fuel. It is impossible to obtain a fuel-air ratio that is completely satisfactory for all ranges of use from idle to full power with constant variations due to external factors such as the temperature or pressure.

 

How does it work ?

 

An injector is mounted at the inlet of each cylinder head, just before the intake valve. At rest, the electromagnetic injector needle closes the orifice and opens when commanded to do so by the computer. It is the opening time (a few milliseconds) that determines the quantity of fuel injected.

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The injectors are fed by fuel rails under pressure of approximately 3 bars in order to ensure the fine vaporisation essential for good combustion.

 

What are the benefits?

 

All the cylinders receive exactly the same amount of fuel in the perfect quantity according to the engine’s needs. In addition, the mixing is done very close to the combustion chamber and is not degraded by passing through a relatively long duct.

 

How is this mixing done?

 

The quantity of fuel depends on the engine speed as well as the load, which is the power called for. At the same engine speed, you have to press the accelerator pedal of your car more to climb a hill than to cruise on a flat surface. The speed information is transmitted to the computer by the top dead centre sensor. A toothed wheel attached to the crankshaft triggers a pulse in the sensor with each revolution.

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Load information can come from a pressure sensor placed in the inlet pipe, or a position sensor on the throttle body controlled by the throttle lever. So, it is working by pressure or by position. We have decided on the first, which automatically compensates for a richer mixture with altitude.