This paper applies the D 2-law to a group of heterogeneous size of bio-diesel drops in order to determine the time evolution of the drop-size distribution and its burnout time. The drop-size distribution has been first transformed into a dimensionless form before its time evolution distributions and the evaporation time are analyzed. Experiment to verify the measurement procedures proposed have been performed on a bio-diesel spray issuing from a small scale industrial burner. It can be found that the D 2-law for evaporation of a droplet can be adapted well to calculate the time evolution of distribution of the group of drops and their burnout time. The dimensionless evaporation time is shortest for a single size drop distribution. For a broader drop-size distribution the dimensionless evaporation time takes longer time. The results of this paper are confined to the analyses of evaporation time obtained from line-of-sight measurement data.