Modeling the non-Arrhenius ignition behavior of 2‐butanol: A detailed theoretical and experimental study

Abstract

2-butanol is a promising alternative to fossil fuels for which production pathways are already established and which was proven to be suitable for usage within modern internal combustion engines. It is a potential octane booster for gasoline fuels, can be used in diesel engines to reduce soot production, and is applicable as a stand-alone fuel. In the present study, the previously not discussed non-Arrhenius ignition behavior of 2-butanol was revealed by recalculating and adjusting the thermodynamic properties of the fuel and its most important radicals. All relevant fuel consumption reaction rate coefficients were replaced by a consistent set of analogies without any further modifications of the rate parameters. The existing spectrum of validation targets for 2-butanol was extended by new high-pressure Rapid Compression Machine (RCM) experiments for end-of-compression pressures of peoc = 20, 30, 40, and 50 bar with high resolution of temperature to highlight the non-Arrhenius ignition behavior and to study the model performance in more detail. The kinetic model proposed in the present study can reproduce the observed non-Arrhenius behavior within the RCM regime. Kinetic analysis demonstrated that simulated Ignition Delay Times (IDTs) are very sensitive to the equilibria of the R. + O2 reactions for all 2-hydroxybutyl radicals. With the newly determined thermodynamic properties, the equilibria of the R. + O2 reactions are moved towards lower temperatures, enabling low-temperature chain branching. The shift of the equilibrium from the RO.2 side to R. + O2 within the temperature regime covered by the RCM experiments could be identified as the main reason for the observed non-Arrhenius behavior.