IP 498: Determination of ignition delay and derived cetane number (DCN) of middle distillate fuels by combustion in a constant volume chamber

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  • Method adopted/last revised: 2015
  • Method reapproved: None
  • REF/ISBN: IP498-2937259
  • Status: Current
  • First printed in STM books: February 2015


This European Standard specifies a test method for the quantitative determination of ignition delay of middle distillate fuels intended for use in compression ignition engines. The method utilizes a constant volume combustion chamber designed for operation by compression ignition, and employing direct injection of fuel into compressed air that is controlled to a specified pressure and temperature. An equation is given to calculate the derived cetane number (DCN) from the ignition delay measurement.

This European Standard is applicable to diesel fuels, including those containing fatty acid methyl esters (FAME) up to 30 % (V/V ). The method is also applicable to middle distillate fuels of nonpetroleum origin, oilsands based fuels, blends of fuel containing biodiesel material, diesel fuel oils containing cetane number improver additives and low-sulfur diesel fuel oils.

However, users applying this standard especially to unconventional distillate fuels are warned that the relationship between derived cetane number and combustion behaviour in real engines is not yet fully understood. The test method is also applicable to the quantitative determination of the ignition characteristics of FAME, especially the ignition delay. However the correlation data available were inconclusive about the precision of the equation. So the determination of derived cetane number for FAME fuel, also known as B100, has not been included in the precision determination as in Clause 122).

This European Standard covers the ignition delay range from 2,8 ms to 6,3 ms (71 DCN to 34 DCN). The combustion analyser can measure shorter or longer ignition delays, but precision is not known. For these shorter or longer ignition delays the correlation equation for DCN is given in Annex D.

NOTE 1 There is no information about how DCNs outside the 34 to 71 range compares to EN ISO 5165.

NOTE 2 For the purpose of this European Standard, the expression “% (V/V)” is used to represent the volume fraction and “% (m/m)” the mass fraction.

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