Cetane index

The cetane index (abbreviated: CI) describes - like the cetane number - the ignitability of diesel fuel and comparable substances (e.g. petroleum , gas oil components , marine diesel oil ). The index is a quantity calculated purely from density (kg / L) and boiling curve (EN ISO 3405: ​​2000). This international standard was originally developed to determine ignitability when a test engine was not available. This restriction no longer applies today; the cetane index - together with the cetane number - is still specified (DIN EN 590).

definition

The cetane index was originally calculated using the 2-parameter method (ASTM D976-06):

${\displaystyle CI=454{,}74-1641{,}416\cdot {\text{Dichte}}+774{,}74\cdot {\text{Dichte}}^{2}-0{,}554\cdot T_{50}+97{,}803\cdot \log(T_{50})^{2}}$

with T ₅₀ as the boiling point in ° C at which 50% of the product volume has evaporated. However, this method was too imprecise, so that DIN EN 590 (and DIN ISO 8217: 2005) is based on the so-called 4-parameter method (DIN EN ISO 4264: 2007), whereby:

• T10 (temperature in ° C at which 10% by volume of the product has evaporated) and
• T90 (temperature in ° C at which 90% by volume of the product has evaporated)

can be used as additional parameters.

The following also serves as an auxiliary variable:

${\displaystyle B=e^{-3{,}5\cdot ({\text{Dichte}}-0{,}850)}-1}$

Then we get for the cetane index:

${\displaystyle CI=45{,}2+0{,}0892\cdot (T_{10}-215)+(0{,}131+0{,}901B)\cdot (T_{50}-260)+(0{,}0523-0{,}42BB)\cdot (T_{90}-310)+0{,}00049((T_{10}-215)^{2}-(T_{90}-310)^{2})+107B+60B^{2}}$ (rounded to 0.1)

The cetane index is not applicable to pure hydrocarbons, cetane number improvers do not affect the index and coal-based distillates are also not displayed correctly. However , the method can be used for products made from tar sands and tight oil (“fracking oil”).

The areas recommended according to DIN EN ISO 4264 for using this method are:

Cetane number	32.5-56.5
density	0.805 to 0.895 kg / L
T 10	171 to 259 ° C
T 50	212 to 308 ° C
T 90	251 to 363 ° C

See also

• Marine diesel oil

literature

• Karl-Heinz Dietsche, Thomas Jäger, Robert Bosch GmbH: Automotive pocket book. 25th edition, Friedr. Vieweg & Sohn Verlag, Wiesbaden, 2003, ISBN 3-528-23876-3