Experimental and Modeling Study of the Low-Temperature Oxidation of Large Alkanes

Abstract

This paper presents an experimental and modeling study of the oxidation of large linear akanes (from C 10 ) representative from diesel fuel from low to intermediate temperature (550-1100 K) including the negative temperature coefficient (NTC) zone. The experimental study has been performed in a jet-stirred reactor at atmospheric pressure for n-decane and a n-decane/n-hexadecane blend. Detailed kinetic mechanisms have been developed using computer-aided generation (EXGAS) with improved rules for writing reactions of primary products. These mechanisms have allowed a correct simulation of the experimental results obtained. Data from the literature for the oxidation of n-decane, in a jet-stirred reactor at 10 bar and in shock tubes, and of n-dodecane in a pressurized flow reactor have also been correctly modeled. A considerable improvement of the prediction of the formation of products is obtained compared to our previous models. Flow rates and sensitivity analyses have been performed in 1 * E-Mail : Frederique.Battin-Leclerc@ensic.inpl-nancy.fr, Tel : 33 3 83175125, Fax : 33 3 83378120 order to better understand the influence of reactions of primary products. A modeling comparison between linear alkanes for C 8 to C 16 in terms of ignition delay times and the formation of light products is also discussed.

Experimental and modeling investigation of the low-temperature oxidation of n-heptane

“…Theoretical calculations were performed for the three most probable C 7 H 12 O 2 isomers: 1,3-heptadione, 2,4-heptadione and 3,5-heptadione. These species have the two carbonyl functions separated by a CH 2 group and are expected to be formed in larger amounts than other isomers because the isomerizations of ROO• radicals into •QOOH radicals through six membered ring transition states are the easiest isomerization channels [31,32]. Computed ionization energies are 9.32, 9.40 and 9.37 eV for 1,3-heptadione, 2,4-heptadione and 3,5-heptadione, respectively (Table 2).…”

“…The reactions which consume these products are written in a global way in order to promote the formation of species which are already included in the primary mechanism and in the C 0 -C 2 reaction base. As an example, the lumped C 7 H 14 O 3 ketohydroperoxide will decompose in one step into a CO molecule, an OH radical, a n-propyl radical and a propanal molecule [31]. The rate constant for this global reaction is the one corresponding to the breaking of the weak O-O bond.…”

“…Reaction 3b was added to the model generated using software EXGAS [31] (reactions (1) and (2) and (3a) were already included in the generated model) with the rate constants proposed by Le Crâne et al [66]. In reaction 3b, the formation of ozone was replaced by that of an oxygen molecule and a O-atom.…”

“…In 1989, Westbrook et al [25] proposed the first detailed kinetic model accounting for the low-and high-temperature oxidation of n-heptane. Since then several low-and high-temperature oxidation models were proposed for this species [26][27][28][29][30][31][32]. All these models were constructed using the commonly accepted low-temperature branchedchain mechanism via the formation of degenerate branching agent (hydroperoxide species) for the oxidation of hydrocarbons (Figure 1) [35].…”

“…The purpose of this paper is to extend the same approach to a larger n-alkane: nheptane. The experimental results obtained with both methods of analysis have been confronted and experimental data have been compared with simulation results computed using a detailed kinetic model generated with software EXGAS [31].…”