CONRADSON CARBON RESIDUE OF PETROLEUM PRODUCTS: D189
(Equivalent Test Methods: IP 13, ISO 6615, DIN 51551, JIS K 2270, and AFNOR T60-116)
EXPLANATION
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 amyl nitrate is absent (or if it is present, provided the test is performed on the base fuel without additive) the carbon residue of diesel fuel correlates approximately with combustion chamber deposits.

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.

This test method covers the determination of the amount of carbon residue left after evaporation and pyrolysis of an oil, and is intended to provide some indication of relative coke-forming propensities. This test method is generally applicable to relatively nonvolatile petroleum products, which partially decompose on distillation at atmospheric pressure. Petroleum products containing ash-forming constituents will have an erroneously high carbon residue, depending upon the amount of ash formed.

TEST SUMMARY
A weighed quantity of sample is placed in a crucible and subjected to destructive distillation. The residue undergoes cracking and coking reactions during a fixed period of severe heating. At the end of the specified heating period, the test crucible containing the carbonaceous residue is cooled in a desiccator and weighed. The residue remaining is calculated as a percentage of the original sample, and reported as Conradson carbon residue.

TEST PRECISION
Repeatability and reproducibility of Test Method D189 should be within limits shown in Fig. 4.

CORRELATION WITH OTHER TESTS
No exact correlation between results of D189 and D524 exists because of the empirical nature of the two tests. However, an approximate correlation (Fig. 5) has been derived between these two methods. Also, Fig. 6 shows a direct correlation obtained between D189 and D4530 test methods.