General estimation method for lower flammability limits of organic compounds: The simpler the better

Abstract

Due to the lack of well-established procedures to estimate the lower flammability limit (LFL) of arbitrary fuel-air mixtures, we report therein a simple method derived from a relationship introduced over 80 years ago for C–H–O molecules and presently extended to molecules containing C–H–N–O–F–Cl–Br–I–Si–P–S elements. The LFL was usually found to represent a constant fraction α≃1/2 of the stoichiometric concentration of fuel, except for halogen compounds for which α increases with the fraction of halogen atoms in the fuel molecules. Interestingly, this extremely simple scheme, which could be then easily integrated into any molecule design workflow, indicates that LFL values are mainly determined by the element count on the fuel structure, in sharp contrast with the premises underlying quantitative structure–property relationship (QSPR) and group contribution (GC) approaches.