An Autoignition Study of iso-Butanol: Experiments and Modeling

The demand for a clean, renewable biofuel increases as new benchmarks are legislated amid increased pressure to reduce the world’s dependence on fossil fuels for energy and chemicals. Biobutanol is considered an advanced biofuel - superior to ethanol in terms of higher energy density, lower vapor pressure and lower hygroscopicity, with several practical positive effects on combustion engines. Because of the potential advantages of butanol over current generation biofuels, companies have begun to commercialize butanol from biological sources. In particular one butanol isomer - iso-butanol - has gained popularity because of its high octane rating and ease of industrial scale production, as demonstrated by Gevo Inc. and others.

Because of the recent interest in determining the combustion properties of butanol, many kinetic models have been constructed. Substantial progress has been made in the last few years to improve the ability of models to predict combustion phenomena at extreme conditions, improving predictions of low temperature, high pressure ignition delays by several orders of magnitude, for example. These types of extreme conditions are important for models to faithfully predict because they are the ranges in which new advanced engine concepts will operate. Nevertheless, despite the rapid improvement of the modeling of butanol combustion, the ability of existing models to predict new experimental data is often lacking. Existing models often struggle to predict a priori the autoignition of the butanol isomers under off-stoichiometric conditions at high pressure and low temperature. Further work is still needed to develop truly predictive models.

In this work, new ignition delay measurements of the autoignition of iso-butanol acquired in a heated Rapid Compression Machine (RCM) are presented. The conditions presented in this work are selected to complement previous studies in the RCM. In particular, conditions at 15 and 30 bar pressure for equivalence ratios of ϕ=0.5 and 2.0 are presented. In addition, a model for iso-butanol combustion is built using the open-source software, Reaction Mechanism Generator (RMG). The model is compared with the new and existing experimental data and discussion of the important pathways of iso-butanol decomposition is presented.