Smoke points of fuel-fuel and fuel-inert mixtures

Laminar smoke points are important fuel properties for understanding soot processes in fires and flames. Several past studies have measured laminar smoke points of fuel-fuel and fuel-inert mixtures, but scaling laws for these smoke points have been lacking and thus are considered here. To supplement published data from 8 past studies, smoke points are measured for ethylene-inert mixtures. The resulting dataset includes 160 smoke points for fuel-fuel mixtures and 78 for fuel-inert mixtures. For fuel-fuel mixtures, the most successful scaling equates mixture smoke point to the reciprocal of the sum of the constituent mass fractions divided by their smoke points. This scaling is also reasonably successful for fuel-inert mixtures (except those involving Ar) when infinite smoke points are assumed for the inerts. The effectiveness ranking of the inerts to increase smoke points is, by volume: SO2>CO2>N2>Ar>He, and by mass: He>CO2≈SO2>N2>Ar. Argon's unusual behavior and low effectiveness is attributed to its low heat capacity.