Autoignition reactivity of blends of diesel and biodiesel fuels with butanol isomers

The effect of n-butanol replacement by iso, sec or tert-butanol on the autoignition reactivity of diesel and biodiesel/butanol blends (the total alcohol content being 40% by vol.) was analysed. The study was performed in a constant volume combustion chamber under different initial temperatures (535 degrees C, similar to 600 degrees C and 650 degrees C) and n-butanol substitutions. Results show that the effect of the alcohol in both pseudo-binary (diesel fuel/normal, sec, iso or tert-butanol) and pseudo-ternary (diesel fuelin-butanol iso, sec or tert-butanol) blends is not that expected from the autoignition properties of the pure isomers. When blended either with diesel or biodiesel fuels, tert-butanol increases the autoignition reactivity of the blend while the other two isomers reduce it. The partial substitution of n-butanol by tert-butanol could be an attractive method for increasing the alcohol content while keeping safe engine operation. Partial substitutions with iso or sec-butanol would promote partially premixed combustion conditions with limited pressure gradient peaks. Chemical kinetics simulations corroborate that the different consumption rates of active radicals from the butanol isomers are responsible for the observed trends. Biodiesel blends are less sensitive to the isomer replacing n-butanol due to its higher number of secondary C-H bonds when compared to diesel fuel. (C) 2018 Energy Institute. Published by Elsevier Ltd. All rights reserved.