- Diesel fuel
- Cetane number
- cloud point
Diesel fuel comes from petroleum. Diesel is somewhat heavier than petrol and contains more combustion heat. Unlike petrol, diesel is highly ignitable, because it must ignite spontaneously as quickly as possible. There are 2 types of diesel fuel; summer diesel and winter diesel. More about this under Cetane number in the next section.
Diesel fuel must be able to easily self-ignite. The time that elapses between the injection of the fuel and the start of combustion should be as short as possible. The readiness of the fuel to self-ignite is expressed by the cetane number. The higher the cetane number, the easier the fuel ignites. If the diesel engine has to run at high revs, the fuel must have a higher cetane number (indirect injection engines 56, for direct injection engines 70). The time that the fuel can ignite is short at high speeds.
The natural color of diesel is light yellow. Coloring agents have been added for various reasons.
If the outside temperature drops, the fluidity of the diesel fuel decreases. The cloud point is the temperature at which the paraffin crystals in the fuel begin to separate. The petroleum industry supplies summer and winter fuel. With the summer fuel, solidification phenomena as a result of the paraffin secretion can occur at -8 degrees. Winter fuel gives no problems down to -15 degrees. The engine can only be restarted when the clogged parts are warmed up.
For the proper functioning of a diesel engine, it is very important that the fuel has the right viscosity. If the viscosity is too low, the fuel has a poor lubricity and it is easier to leak at the injection pump. If the viscosity is too high, the injection system is subjected to additional load. Both too low and too high a viscosity influence the droplet size of the injected fuel and thus also the course of the combustion.