The carbon residue value of burner fuel serves as a
rough approximation of the tendency of the fuel to form
deposits in vaporizing pot-type and sleeve-type burners. Similarly,
provided alkyl nitrates are absent (or if present, provided
the test is performed on the base fuel without additive) the
carbon residue of diesel fuel correlates approximately with
combustion chamber deposits.
5.2 The carbon residue value of motor oil, while at one time
regarded as indicative of the amount of carbonaceous deposits
a motor oil would form in the combustion chamber of an
engine, is now considered to be of doubtful significance due to
the presence of additives in many oils. For example, an
ash-forming detergent additive may increase the carbon residue
value of an oil yet will generally reduce its tendency to form
deposits.
5.3 The carbon residue value of gas oil is useful as a guide
in the manufacture of gas from gas oil, while carbon residue
values of crude oil residuums, cylinder and bright stocks, are
useful in the manufacture of lubricants.