In addition, one of these negative coefficients in Table , Num_of Atoms, is not orthogonal, as indicated earlier, which restricts the increase of NC and NH. The other negative coefficient, NumAromaticRings, is unwanted, as aromatic compounds produced 88% more soot formation than cycloalkanes due to incomplete combustion . Consequently, the coefficients reported in Table The agreement between the predicted and the literature NHOC values of the compounds is excellent. Most of the compounds are along a straight line except for a small number of compounds in Fig. and), with minor discrepancies as indicated in the oval.