Diesel Fuel:
Diesel fuel is derived from crude oil. Diesel is heavier than gasoline and contains more combustion heat. Unlike gasoline, diesel is very prone to ignite as it needs to auto-ignite as quickly as possible. There are two types of diesel fuel: summer diesel and winter diesel. More on this under Cetane Number in the next paragraph.
Cetane Number:
Diesel fuel needs to easily undergo auto-ignition. The time elapsed between fuel injection and the start of combustion should be as short as possible. The readiness of the fuel for auto-ignition is expressed by the cetane number. The higher the cetane number, the easier the fuel ignites. If the diesel engine must run at high speeds, the fuel needs to have a higher cetane number (indirect injection engines 56, for direct injection engines 70). At high speeds, the time for the fuel to ignite is short.
Color:
The natural color of diesel is light yellow. For various reasons, dyes are added.
Cloud Point:
As the outside temperature drops, the fluidity of diesel fuel decreases. The cloud point is the temperature at which paraffin crystals in the fuel begin to separate. The petroleum industry provides summer and winter fuel. With summer fuel, solidification due to paraffin separation can occur at -8 degrees. Winter fuel poses no problems down to -15 degrees. Only warming of the clogged parts can restart the engine.
Viscosity:
For the proper functioning of a diesel engine, it is very important that the fuel has the correct viscosity. With too low a viscosity, the fuel provides poor lubrication and leaks can occur more easily at the injection pump. Too high a viscosity places additional stress on the injection system. Both too low and too high viscosity affect the droplet size of the injected fuel and, consequently, the combustion process.