A shock tube and laser absorption study of ignition delay times and OH reaction rates of ketones: 2-Butanone and 3-buten-2-one Jihad Badra a , Ahmed E. Elwardany a , Fethi Khaled a , Subith S. Vasu b , Aamir Farooq a,⇑ a Clean Combustion Research Center, Division of Physical Sciences and Engineering, King Abdullah University of Science and Technology (KAUST), Thuwal 23955, Saudi Arabia b Mechanical and Aerospace Engineering Department, University of Central Florida, Orlando, FL 32816, USA article info Article history: Received 29 July 2013 Received in revised form 1 October 2013 Accepted 1 October 2013 Available online 20 October 2013 Keywords: Ketones Ignition delay times Shock tube Reaction rates Hydroxyl radical abstract Ketones are potential biofuel candidates and are also formed as intermediate products during the oxidation of large hydrocarbons or oxygenated fuels, such as alcohols and esters. This paper presents shock tube ignition delay times and OH reaction rates of 2-butanone (C 2 H 5 COCH 3 ) and 3-buten-2-one (C 2 H 3 COCH 3 ). Ignition delay measurements were carried out over temperatures of 1100–1400 K, pressures of 3–6.5 atm, and at equivalence ratios (U) of 0.5 and 1. Ignition delay times were monitored using two differ- ent techniques: pressure time history and OH absorption near 306 nm. The reaction rates of hydroxyl rad- icals (OH) with these two ketones were measured over the temperature range of 950–1400 K near 1.5 atm. The OH profiles were monitored by the narrow-line-width ring-dye laser absorption of the well-character- ized R 1 (5) line in the OH A–X (0, 0) band near 306.69 nm. We found that the ignition delay times of 2-buta- none and 3-buten-2-one mixtures scale with pressure as P 0.42 and P 0.52 , respectively. The ignition delay times of 3-buten-2-one were longer than that of 2-butanone for stoichiometric mixtures, however, for lean mixtures (U = 0.5), 2-butanone had longer ignition delay times. The chemical kinetic mechanism of Serinyel et al. [1] over-predicted the ignition delay times of 2-butanone at all tested conditions, however, the dis- crepancies were smaller at higher pressures. The mechanism was updated with recent rate measurements to decrease discrepancy with the experimental data. A detailed chemistry for the oxidation of 3-buten-2- one was developed using rate estimation method and reasonable agreements were obtained with the mea- sured ignition delay data. The measured reaction rate of 2-butanone with OH agreed well with the literature data, while we present the first high-temperature measurements for the reaction of OH with 3-buten-2- one. The following Arrhenius expressions are suggested over the temperature range of 950–1450 K: k C 2 H 5 COCH 3 þOH ¼ 6:78  10 13 expð2534=TÞcm 3 mol 1 s 1 k C 2 H 3 COCH 3 þOH ¼ 4:17  10 13 expð2350=T Þcm 3 mol 1 s 1 Ó 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved. 1. Introduction Biofuels will be a significant part of future energy portfolio and recently there have been many innovative methods to produce bio- fuels from biomass [2–4]. One promising platform for cellulosic biofuel generation is to harness the metabolic processes of endo- phytic fungi that directly convert lignocellulosic material into a variety of volatile organic compounds including various types of saturated and unsaturated ketones [5–9]. Ketones are also consid- ered as contributors to pollution and because significant amounts of ketones are emitted into the atmosphere from several natural sources, their kinetic behavior needs to be well-understood. Even though, there have been increased interest in the combustion of ketones [1,5–8,10–18], the oxidation chemistry and ignition char- acteristics of ketones are not well-known. Previous combustion investigations have mostly focused on smaller ketones. The smallest ketone, acetone, has drawn a lot of attention where its ignition delay times at a wide range of temper- atures have been investigated thoroughly. Black et al. [13] mea- sured ignition delay times and stretch-free laminar flame speed of acetone using shock tube and spherical bomb, and also devel- oped a kinetic model for acetone. Pichon et al. [19] and Davidson et al. [20] studied the ignition delay times of acetone at relatively high temperatures 1600–2200 K. Along with ignition delay times and flame speed measurements, quite a bit of attention went to- wards measuring the highly important ketone + OH reaction rate. Starting in 1991, Bott and Cohen [21] measured the rate constant of the reaction: acetone + OH. Subsequent to that, many research- ers focused on measuring this reaction rate [15,16,18,22–26]. In 0010-2180/$ - see front matter Ó 2013 The Combustion Institute. Published by Elsevier Inc. All rights reserved. http://dx.doi.org/10.1016/j.combustflame.2013.10.001 ⇑ Corresponding author. E-mail address: aamir.farooq@kaust.edu.sa (A. Farooq). Combustion and Flame 161 (2014) 725–734 Contents lists available at ScienceDirect Combustion and Flame journal homepage: www.elsevier.com/locate/combustflame