The high-temperature autoignition of biodiesels and biodiesel components

Ignition delay time measurements are reported for two reference fatty-acid methyl ester biodiesel fuels, derived from methanol-based transesterification of soybean oil and animal fats, and four primary constituents of all methyl ester biodiesels: methyl palmitate, methyl stearate, methyl oleate, and methyl linoleate. Experiments were carried out behind reflected shock waves for gaseous fuel/air mixtures at temperatures ranging from 900 to 1350 K and at pressures around 10 and 20 atm. Ignition delay times were determined by monitoring pressure and ultraviolet chemiluminescence from electronically-excited OH radicals. The results show similarity in ignition delay times for all methyl ester fuels considered, irrespective of the variations in organic structure, at the high-temperature conditions studied and also similarity in high-temperature ignition delay times for methyl esters and n-alkanes. Comparisons with recent kinetic model efforts are encouraging, showing deviations of at most a factor of two and in many cases significantly less.