Cetane ratings by ASTM D 613 method are not very accurate. Moreover, the standard deviation for ratings varies according to the properties of the fuel tested. An investigation of combustion in the CFR cetane rating engine has revealed pronounced combustion instability at the standard rating conditions. Changes to the operating conditions can stabilize the combustion and thus potentially improve rating accuracy.
A new cetane rating technique, using the CFR engine, has been developed and tested in a correlation program involving six engines and five fuels. This has shown that the modified rating method gives improvements of 25% in repeatability and reproducibility standard deviation compared with the ASTM method, and gives the same value for cetane number. The new method uses the same equipment as the standard method, is easier to operate, and lends itself to automation