Predicting cetane numbers of n-alcohols and methyl esters from their physical properties

Cetane numbers (C#) for the homologous series of straight-chain, saturated n-alcohols, C₅−C₁₂ and C₁₄, were determined according to ASTM D 613. Measured C# ranged from 18.2–80.8 and increased linearly with carbon number (CN). Regression analyses developed equations that related various physical properties or molecular characteristics of these alcohols to calculated C#. The degree of relationship between measured and calculated C# was expressed as R². The decreasing order of the precision with which these properties correlated with C# was: boiling point (bp)>melting point (mp)>CN>heat of combustion (HG)>refractive index (n²⁰ _D)>density (d). This ranking was based upon R² (0.99–0.96) and the Average % error (2.8–7.2%). C# were also determined for straight-chain homologs of saturated methyl esters with CN of 6, 10, 12, 14, 16 and 18. C# ranged from 18.0–75.6 and increased curvilinearly with CN. Equations were also developed that related physical properties of these esters to C#. The precision with which these properties correlated with C# was: bp>viscosity (V)>heat of vaporization (HV)>HG>CN>surface tension (ST)>mp>n²⁰ _D>d. R² ranged from 0.99 for bp to 0.98 for d. Equations for the alcohols were linear or quadratic, while equations for the esters were linear, quadratic or cubic based upon statistical considerations that included a Student’s t-test. With related physical properties and these equations, accurate predictions of C# can be made for saturated n-alcohols and methyl esters.