carbon residue of a fuel is the tendency to form carbon deposits under high
temperature conditions in an inert atmosphere, and may be expressed commonly as
Micro Carbon Residue (MCR) or alternatively Conradson Carbon Residue (CCR). It
should be noted that numerically MCR is effectively the same as CCR.
The overall relationship between actual diesel engine performance and carbon residue is poor, however, the carbon residue value is considered by some to give an indication of the combustibility and carbonaceous deposit forming tendencies of a fuel.
The carbon residue provides information on the carbonaceous deposits which will result from combustion of the fuel. For fuels with a high carbon- high carbon/hydrogen ratio, it is proved more difficult to burn them fully, which results in increased deposits in the combustion and exhaust spaces. Fuels with a high carbon residue value may cause problems in older engines when they are operating under part load conditions. The carbon residue value of a fuel depends on the refinery processes employed in its manufacture.