Engine fouling: causes, consequences and solution

The combustion

Fuel combustion occurs in the engine's combustion chamber, using an air-fuel mixture. This phenomenon is triggered by an energy input (compression for diesel engines, ignition for gasoline engines). Ideally, all the fuel molecules are completely burned during this combustion. But in reality, this is not what happens. In fact, some fuel molecules or impurities contained in it undergo incomplete combustion or are not burned. These residues composed of tar, soot, and carbon are then deposited on the valves and piston heads.

These residues can also be deposited in the back groove of the segments, causing an increase in friction between the segments and the cylinders.
This causes the degradation of the oil film and the sealing of the combustion chamber is no longer ensured.

The oil is then contaminated by the combustion gases and the engine consumes more fuel. With this loss of sealing, the oil rises into the combustion chamber and is partially burned.
The fumes from this combustion are rich in soot and tar of various types. They contribute to the fouling of exhaust gas post-treatment systems.

Once clogged, these devices no longer play their role of gas treatment and all polluting and harmful combustion gases/fumes are released as they are into the atmosphere.
Engine fouling is faster during short journeys because the engine's optimum operating temperature is not reached. Combustion therefore generates more deposits.

Injector diameters

The diameters of the injectors are increasingly smaller in order to vaporize the fuel in the form of extremely fine droplets. This allows the air-fuel mixture to be quickly homogeneous and to obtain good combustion.

Impurities contained in fuels can clog and even seize these injectors, fuel vaporization is no longer optimal, and combustion is of poorer quality, fuel consumption increases, as well as the formation of deposits.

Carbureted engines are not spared from fouling because the carbon deposits on the moving parts and the jets. In these cases, we also observe losses of engine power and a significant increase in fuel consumption. Additive fuels
Fuels are increasingly being added, particularly with biodiesels, which increases fouling.

Additive fuels

Fuels are increasingly being added with additives, particularly biodiesels, which increases fouling.

The composition of fuels is increasingly regulated and the authorities (the European Union) are imposing increasingly strict emission standards on manufacturers.

For diesel engines:
 

Standard	Euro 1	Euro 2	Euro 3	Euro 4	Euro 5	Euro 6
Nitrogen oxides (NOx)	-	-	500	250	180	80
Carbon monoxide (CO)	2 720	1 000	640	500	500	500
Hydrocarbons (HC)	-	-	-	-	-	-
HC + NOx	970	900	560	300	230	170
Particles (PM)	140	100	50	25	5	5

For petrol and LPG engines :
 

Standard	Euro 1	Euro 2	Euro 3	Euro 4	Euro 5	Euro 6
Nitrogen oxides (NOx)	-	-	150	80	60	60
Carbon monoxide (CO)	2 720	2 200	2 200	1 000	1 000	1 000
Hydrocarbons (HC)	-	-	200	100	100	100
HC + NOx	-	-	-	-	5	5
Particles (PM)	-	-	-	-	68	68

These standards require manufacturers to optimize their engines and use post-treatment technologies for pollution control. This also involves changing the composition of fuels (lead for gasoline and sulfur for Diesel).

Once clogged, these devices no longer play their role of gas treatment. The engine fails and the replacement of these pollution control systems becomes inevitable. Added to this are the risks of breakdowns linked, for example, to injector seizure and valve clogging.

They no longer play their role as a "trap" for the most polluting exhaust gases.

These gases are therefore released into the atmosphere.

Increased fuel consumption also contributes to the depletion of fossil resources.

Hence the need to regularly use additives to overcome these problems!

Fuel additives contain, among other things, molecules with detergent properties. The structure of these molecules gives them particular properties. The "head" is the polar part of the molecule and the "tail" is the non-polar part of the molecule. This structure makes it possible to:

Reduce surface tension which allows:

• Finer atomization of fuel at injection (increased number of finer fuel droplets)
• An increase in the exchange surface of fuel droplets with air
• More complete and efficient combustion, which implies a significant reduction in fuel consumption
• More hydrocarbons and burnt particles
• A concomitant reduction in greenhouse gas emissions (CO2 and NOx)

The formation of a monolayer on the surface of the fuel circuit allowing:

• Fuel flow optimization
• Improving the lubricity of fuels
• Protection against corrosion
• Reduced maintenance costs

The formation of micelles :

• Around debris and dirt particles (prevents them from being deposited and burned in the combustion chamber)
• Detergent action and cleaning of fuel circuits

Thanks to these properties, the regular use of additives to clean the entire fuel system of vehicles helps to maintain the original performance of the engine and, as a result, to limit pollutant emissions resulting from the natural fouling of thermal engines.