(480e) A Study of Unexpected Autoignition Temperature Trends for Pure N-Alkanes

An experimental study of minimum autoignition temperatures (AIT) reveals unexpected behavior of pure, high-carbon-number n-alkanes (C16 and larger) not predicted by current AIT prediction methods. The well-documented behavior of n-alkanes shows AIT starting higher for the smaller members of the family and then decreasing to a roughly constant value with little change between members of the family from C7 and larger. Our measurements show that values start to increase again at C16 and show a dramatic increase between C25 and C26.

Measured values for several n-alkanes using the ASTM E-659 method are reported and compared to data from other sources. The impact of measurement method on AIT values is discussed. A mechanistic explanation of the unexpected behavior is proposed. Finally, the implications of this behavior on estimation techniques and on the trend with carbon number for other chemical families are discussed.