Toward a better understanding of 2-butanone oxidation: Detailed species measurements and kinetic modeling

In view of a desired transition from fossil fuels to sustainably produced biofuels that should contribute to a net reduction of CO2 emissions, promising fuel candidates have been identified including 2-butanone (methyl ethyl ketone, MEK) that is qualified for use in spark-ignition (SI) engines. To support a potential, rapid integration of such biofuels into the existing infrastructure, fundamental studies of their combustion and emission behavior are highly important. In the case of 2-butanone specifically, only very few fundamental combustion experiments have been performed to date, with a notable shortage of detailed speciation data. For predictive model development, accurate and reliable species measurements are needed to describe the oxidation and combustion of 2-butanone and to elucidate the kinetic mechanism. The present study relies on three different experiments: a laminar flow reactor coupled with molecular-beam mass spectrometry (MBMS, Bielefeld), a rapid compression machine (RCM, Aachen), and a shock tube using advanced laser absorption techniques (Stanford). This combination ensured coverage of a wide regime in temperature, pressure, and mixture composition while providing numerous species profiles. The species measurements in the flow reactor were performed at stoichiometric (Phi = 1.0) and fuel-rich (Phi = 2.0) equivalence ratios at temperatures between about 800-1100 K with an argon dilution of 95%. Ignition delay times in the RCM were measured in air for equivalence ratios of 0.5, 2.0 in the temperature range of 840-945 K to reflect application-relevant conditions. Shock tube measurements were performed at stoichiometric conditions at 1303-1509 K in argon. To provide insight into the oxidation mechanism of 2-butanone, the newly measured experimental data was used to develop and validate a detailed chemical kinetic model. To this end, the reactions for the low-temperature regime, especially concerning early fuel consumption, radical formation, and subsequent low-temperature oxidation, were examined in detail, and used to extend and adapt an existing reaction mechanism (Burke et al., 2016 [231) to more accurately predict the new low-temperature conditions studied. The resulting model that incorporates the latest theoretical kinetic calculations available in the literature was compared to the measurements presented here as well as validated using literature data. To the authors' knowledge, the present model represents the most robustly validated mechanism available for the prediction of 2-butanone combustion targets to date. (C) 2017 The Combustion Institute. Published by Elsevier Inc. All rights reserved.