Originally Posted by RichH
Additives will help 'boosting the Cetane rating' of the fuel
... if your engine is 'old' it was designed for diesel fuel that had much higher cetane (think octane in gasoline) rating than present ... higher cetane, slower fuel burn and less 'knocking' under load.
I think you need to go back and re read what you have written. Octane and Cetane are diametrically opposed as far as what they do inside the combustion chamber.
From Wikipedia;Cetane number or CN is a measure of a fuel's ignition delay; the time period between the start of injection and the first identifiable pressure increase during combustion of the fuel. In a particular diesel engine, higher cetane fuels will have shorter ignition delay periods than lower cetane fuels. The higher the Cetane number the more easily the fuel will combust in a compression setting (such as a diesel engine).