In Low-Speed Pre-Ignition (LSPI) in petrol engines with direct injection the fuel-air mixture ignites without being triggered by the spark plug. This unscheduled combustion causes extreme pressures in the engine and – depending on the design – can cause serious damage or even completely destroy the engine the first time it occurs. Essentially, low-speed pre-ignition has two causes:
As a result of fuel being injected into the cylinder, the cylinder wall, which is lubricated with oil, is covered with fuel. This creates a mixture of oil and fuel from which drops can be released during the compression phase. This fuel-oil mixture has a higher combustibility than pure petrol.
At higher pressures and increasing temperatures these drops can self ignite, which, ultimately, can trigger low-speed pre-ignition of the entire fuel-air mixture in the combustion chamber.
In addition to the gaseous fuel-air mixture, the combustion chamber can also contain particles or deposits of solid substances. These can loosen as a result of vibrations or fuel injection. The freely moving particles absorb heat in the combustion chamber and cannot dissipate this heat via the walls or components.
If the temperature is sufficiently high, these red-hot particles can also cause premature injection.
In modern petrol engines, deposits or particles in the combustion chamber are almost impossible to prevent.
The reasons for this include very different driving profiles by the drivers and very inconsistent compositions of fuels and engine oils.
As a result, these influencing factors can lead to sooty combustion or oil contamination in the combustion chamber. The resulting soot or oil particles accumulate on the walls or components, such as pistons or injectors. Vibrations or fuel injection can loosen these particles and cause them to become red hot.
If the particles are large enough that they do no extinguish in good time, they can cause premature ignition of the fuel-air mixture – with the described consequences.
All of these factors increase the risk of damage to petrol engines in modern vehicle generations. This risk can be reduced considerably by using microflex® 978 Combustion Chamber Cleaner.
Drivers can simply put the additive into the vehicle tank. The following filling intervals should be complied with: