Injectors, valves: be careful to avoid fouling the injection system

Fouling of the injection system can occur in fuel-powered engines, such as diesel engines, leading to increased fuel consumption and reduced engine life.

The fuel injector: a sensitive mechanism

Having replaced carburetors in the 1980s, fuel injection has considerably improved engine performance and reduced fuel consumption. Now controlled in real time by the vehicle’s computer control unit, the injection system continuously adapts to weather conditions, temperature, engine speed and the amount of pressure on the accelerator pedal, in order to deliver the right amount of fuel to the engine.

In lightweight vehicles, the injector, a component the size of a pen, sprays fuel at high pressure (up to more than 2000 bars in diesel engines) through holes with diameters ranging from 80 to 200 microns, just slightly larger than the diameter of a strand of hair. The fuel is sprayed out in the form of microscopic droplets.

The injector then releases the precise amount of fuel, either in the intake pipe (before the valve) in vehicles which use indirect injection (gasoline) or directly into the combustion chamber in vehicles which use direct injection (diesel or gasoline).

In indirect injection, the vaporized fuel and air are propelled together by the intake valve into the cylinder, where combustion is then triggered by the spark plug. However, this type of intake is losing ground to direct injection. Formerly used only in diesel engines, direct injection is becoming more common in gasoline engines.

Causes of fouling

Fouling is the accumulation in the injection system of deposits resulting from incomplete combustion and greasy soot (also called scale). It is also caused by chemicals in the fuel, which as they deteriorate, lead to the formation of varnish, or lacquers. Fouling especially affects the intake valves used for indirect injection and the injectors used for direct injection.

Although manufacturers are now looking to use materials which are more resistant to fouling, new engines are more vulnerable. This is due to higher temperatures and pressures, as well as tighter clearances between mechanical parts in these engines.

That’s because, by lodging in the injector’s micro-holes, deposits can eventually reduce the pressure of the fuel jet, thus interfering with the homogeneity of the air-fuel mixture, which in turn alters engine performance. This can set a vicious circle in motion as fouling leads to more fouling. Fuel consumption increases, performance decreases, the engine wears out prematurely and your vehicle releases more carbon dioxide and pollutants into the atmosphere.

Detergents for fouled injectors and valves

The emission of black smoke, difficulties when starting the engine, jerky deceleration, reduced engine performance or over-consumption of fuel are all signs that should alert you.

The best solution for preventing fouled injectors or intake valves is to use high-quality fuels which contain additives, such as TOTAL EXCELLIUM. Thanks to the detergents contained in these fuels, they effectively clean and remove fouling from the injection system on a daily basis.