Commercially available fuels vaporise at different temperatures. The vaporisation process is simulated as distillation with the gas chromatograph. The distillation process is recorded in a boiling profile. The data obtained is compared with the standardised characteristic values of the individual fuel types.
This shows whether fossil diesel or biodiesel meet the requirements of the standard. Incorrect refuelling or impurities, such as petrol with diesel, diesel with biodiesel, can also be clearly detected. Even a mixture of conventional fuels with vegetable oil is visible. However, such contamination is usually detected by other test methods, such as FT-IR spectroscopy or viscosity change.
For diesel fuel, the cetane index, a measure of ignitability in accordance with EN 590, can also be determined with the help of the “simulated distillation” and the density. The cetane index provides information on the speed of self-ignition of the diesel fuel after injection. The higher the cetane index, the better the diesel grade because the time between injection and combustion decreases and the ignitability increases.
Fossil diesel fuel, which must contain 7 % biodiesel according to the standard, must have a cetane index of at least 46. Diesel fuels with a higher biodiesel content of 10, 30 or even 100 % have a lower cetane index. If a borderline value or even lower value is determined in the analysis performed in the OELCHECK laboratory, this indicates a diesel whose biodiesel content is higher than in EN 590 and whose use can cause a reduction in engine performance or ignition problems.