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Relationship between smoke point and hydrocarbon composition: The formation of carbon deposits is related to the hydrocarbon composition of the fuel being burned. Carbon deposits can be divided into hard carbon deposits and soft carbon deposits. The carbon deposits formed in high-temperature areas are the product of the high-temperature polycondensation of fuel; they are hard and brittle, have a low H/C ratio, and are substances similar to oil coke, known as hard carbon deposits. The carbon deposits that form in low-temperature areas, such as those at the top of the combustion chamber, are relatively soft in texture and have a high H/C ratio; they are known as soft carbon deposits. This type of soot with a relatively high H/C ratio is a mixture of heavy hydrocarbons formed by the polycondensation of carbon black, soot, and high-boiling-point fractions in the fuel during the combustion process. The lower the H/C ratio of a hydrocarbon, the greater its tendency to form carbon deposits. The tendency of various hydrocarbons to form carbon deposits is: polycyclic aromatics > monocyclic aromatics > aromatics with side chains > naphthenes > alkenes > alkanes. The content of aromatic hydrocarbons, particularly polycyclic aromatic hydrocarbons and gums, has the greatest impact on the smoke point; an increase in the amount of unsaturated hydrocarbons, as well as the density of the fractions, can also alter the smoke point value. Relationship between the smoke point of hydrocarbons and their composition. Hydrocarbons, Smoke point/mm, Tendency to form deposits, Degree of complete combustion, H/C. Aromatic hydrocarbons: ~18, ↑, ↓, ↓. Cycloalkanes: 12–24, ↑, ↓, ↓. Alkanes: 30–40, ↑, ↓, ↓. Last edited by ali2004 on 2007-12-17 at 21:53