With increasing energy demand and the goal of 2-pentanone reducing global warming, there is a need to transition away from fossil fuel combustion in the transport sector to second-generation biofuels, as it could ultimately contribute to reducing net carbon emissions. As representatives of such fuels, small molecule methyl ketones such as acetone (RON=110-117 [1], [2]) and 2-butanone (RON=117 [3]) show impressive antiknock sex. For example, 2-butanone was tested in a SI engine as a neat fuel and showed lower emissions of soot, NOx and unburned hydrocarbons compared to a RON 95 blend, ethanol and 2-methylfuran [3]. Nevertheless, few studies have been conducted on the combustion behavior and properties of 2-pentanone (methyl propyl ketone, MPK), while the symmetrical isomer 3-pentanone (diethyl ketone, DEK) has received more attention [4 ], [5], [6]. Compared with 2-butanone and 3-pentanone, which have one or two ethyl side chains, respectively, 2-pentanone has a propyl side chain, which may lead to the underlying kinetic changes and reduces the effect of the carbonyl. C5 ketones with higher energy density may be preferred in engine applications, but the formation of toxic and hazardous substances is unknown. Although, to the best of our knowledge, pathways for (large-scale) production of 2-pentanone from biomass remain to be developed, this study sought to further understand the combustion behavior of small methyl ketones.

In a premixed flame study [7], 2-butanone was shown to have very low emissions of oxygenated intermediates and soot precursors. The linear alkyl chain with three carbon atoms in 2-pentanone can increase the formation of soot precursors such as C3H3. Minwegan et al. [8] measured the ignition delay times for a series of small linear ketones, including 2-pentanone, at 20 bar and 40 bar in a shock tube. The pyrometry of the reaction of small linear ketones with OH at 1-2 atmospheres was performed by Lam et al. [9]. In addition, Badra et al. [10] experimentally studied the H-abstraction of the OH of a series of larger ketones. In the theoretical work of Hudzik and Bozzelli [11], the thermochemistry and bond dissociation energies of ketones were calculated.

In this study, 2-pentanone was quantitatively analyzed by vacuum-ultraviolet photoionization molecular beam mass spectrometry (VUV-PI-MBMS) in a laminar premixed low-pressure (40 mbar) fuel-rich (φ=1.6) planar flame. To facilitate comparison with published 2-butanone data [7], the same conditions (settings, stoichiometry, pressure, argon dilution) were chosen. For 2-pentanone, for the first time, 47 substances were measured and quantified, with possible separation of the isomers.

As a complement to the experimental dataset, a kinetic model representing high-temperature chemistry is presented here. For this kinetic model, the thermochemistry (heat of formation, entropy, and heat capacity) of the fuel and corresponding fuel radicals is determined by ab initio quantum mechanical calculations.