Relationships between diesel fuel ignition quality indicators and composition

Relationships between fuel composition and four secondary measures of diesel fuel ignition quality have been established. Composition has been defined in terms of the fractions of 13C n.m.r. intensity attributable to n-alkyl carbon (Cn) and aromatic carbon (Car). The indicators of diesel ignition quality are: a secondary engine test based on an Institute of Petroleum standard (IP41); an index calculated using boiling point and specific gravity data based on ASTM D976; a calculated index based on aniline point; and a diesel index (IP21) calculated from aniline point and specific gravity. It has been found that all four cetane quality indicators can be adequately described by a very simple property-composition relationship of the form, P = aCn + bCar + c, where P is the property in question and a, b and c are coefficients determined by multiple linear regression using a sample set deriving from a diverse range of petroleum and synthetic fuel sources. The cetane quality indicator based on ASTM D976 has been found to give a distinctly pessimistic view of ignition quality for highly naphthenic diesel fuels, such as are produced via coal liquefaction.