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Abstract
This work (and the companion paper, Part II) presents new experimental data for the combustion of n-C3–C6 alcohols (n-propanol, n-butanol, n-pentanol, n-hexanol) and a lumped kinetic model to describe their pyrolysis and oxidation. The kinetic subsets for alcohol pyrolysis and oxidation from the CRECK kinetic model have been systematically updated to describe the pyrolysis and high- and low-temperature oxidation of this series of fuels. Using the reaction class approach, the reference kinetic parameters have been determined based on experimental, theoretical, and kinetic modeling studies previously reported in the literature, providing a consistent set of rate rules that allow easy extension and good predictive capability. The modeling approach is based on the assumption of an alkane-like and alcohol-specific moiety for the alcohol fuel molecules. A thorough review and discussion of the information available in the literature supports the selection of the kinetic parameters that are then applied to the n-C3–C6 alcohol series and extended for further proof to describe n-octanol oxidation. Because of space limitations, the large amount of information, and the comprehensive character of this study, the manuscript has been divided into two parts. Part I describes the kinetic model as well as the lumping techniques and provides a synoptic synthesis of its wide range validation made possible also by newly obtained experimental data. These include speciation measurements performed in a jet-stirred reactor (p = 107 kPa, T = 550–1100 K, φ = 0.5, 1.0, 2.0) for n-butanol, n-pentanol, and n-hexanol and ignition delay times of ethanol, n-propanol, n-butanol, n-pentanol/air mixtures measured in a rapid compression machine at φ = 1.0, p = 10 and 30 bar, and T = 704–935 K. These data are presented and discussed in detail in Part II, together with detailed comparisons with model predictions and a deep kinetic discussion. This work provides new experimental targets that are useful for kinetic model development and validation (Part II), as well as an extensively validated kinetic model (Part I), which also contains subsets of other reference components for real fuels, thus allowing the assessment of combustion properties of new sustainable fuels and fuel mixtures.
Highlights
Alcohols are promising alternative fuels, from the perspective of carbon footprint reduction in the transport sector, as well as being blending fuel components for internal combustion engines
The resistance to ignition, or the antiknocking propensity, of a fuel is characterized by its octane rating, which can be measured as the research octane number (RON) and/or the motor octane number (MON)
Considering new experimental measurements that have been performed in this work, as well as the large amount of experimental data on alcohol pyrolysis and combustion available in the literature, the alcohol subset of the CRECK kinetic model developed in previous kinetics studies[51−53] has been updated and systematically extended to describe the low-temperature oxidation of n-butanol, npentanol, and n-hexanol at low temperatures
Summary
Alcohols are promising alternative fuels, from the perspective of carbon footprint reduction in the transport sector, as well as being blending fuel components for internal combustion engines. The development of detailed and predictive combustion kinetic models provides a very efficient tool for the synergistic design of fuels and engines,[18] allowing parametric analyses to explore, interpolate, and extrapolate the propensity for (or the resistance to) ignition of different fuels and fuel blends.[19] Generally, the reactivity of oxygenated biofuels (e.g., alcohols, aldehydes, organic acids) is largely influenced by the presence of an oxygenated functional group that modifies bond dissociation energies and enhances, inhibits, and triggers different reaction pathways compared to the parent fuel molecule (e.g., alkane).[20] The recent interest in biofuels and bio-oils from the fast pyrolysis of biomass has motivated systematic experimental and modeling investigations of different chemical families such as aldehydes,[21−25] acids,[26] and oxygenated aromatics[27−29] to unravel the effects of different oxygenated functional groups on fuel kinetics Beyond their application as surrogate fuel components,[30] such species are important intermediates in the oxidation of alternative or conventional hydrocarbon fuels, because they are implicit in the hierarchical nature of complex combustion kinetic models. For a more-detailed discussion on model validations and performances, the reader is referred to Part II of this study.[56]
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