Energy Fuels 2010, 24, 1668–1676 Published on Web 02/17/2010
: DOI:10.1021/ef9015526
Kinetics of Oxidation of Commercial and Surrogate Diesel Fuels in a Jet-Stirred Reactor: Experimental and Modeling Studies H. P. Ramirez L.,† K. Hadj-Ali,† P. Dievart,†,‡ G. Moreac,§ and P. Dagaut*,† † ‡
Centre National de la Recherche Scientifique (CNRS), 1c, Ave. de la Recherche, Scientifique, 45071 Orl eans Cedex 2, France, Facult e des Sciences, University of Orl eans, 45067 Orl eans Cedex 2, France, and §Renault SAS, TCR LAB 0 12, 1 av. du Golf, 78288 Guyancourt Cedex, France Received December 17, 2009. Revised Manuscript Received February 3, 2010
The oxidation of a commercial diesel fuel and a diesel surrogate fuel (70% n-decane/30% 1-methylnaphthalene in moles) was performed using a fused-silica jet-stirred reactor under the same initial experimental conditions (560-1030 K, 6 and 10 atm, equivalence ratios of 0.25-1.5, and 10 300 ppm of carbon). The results of this series of experiments consisting of concentration profiles of reactants, stable intermediates, and products as a function of the temperature were compared to each other, confirming that the 70/30% mixture n-decane/1-methylnaphthalene in moles is an excellent simple diesel fuel surrogate. A chemical kinetic model consisting of 4762 reactions involving 1124 species was proposed on the basis of previous chemical mechanisms for the oxidation of n-decane and 1-methylnaphthalene in similar conditions. The kinetic modeling showed reasonable agreement between the present data and computations over the entire range of conditions considered in this study.
A surrogate diesel fuel called the Integrated Development on Engine Action (IDEA) fuel, consisting of 70% n-decane and 30% 1-methyl naphthalene, was formulated previously as part of the IDEA program.5 This fuel mixture matches both the physicochemical properties and combustion behavior of a conventional diesel fuel. The IDEA fuel has properties similar to those of a conventional diesel fuel; i.e., it has a normal density of 798 kg/m3 at 20 °C, a cetane number (CN) of ca. 53, and hydrogen/carbon ratio of 1.8. The kinetic oxidation mechanisms of large n-paraffins and aromatics have been developed separately in several fundamental studies6,7 and merged to simulate the oxidation of surrogate gasoline, kerosene, and diesel fuels.3,4,8 A long carbon chain n-paraffin compound is highly suitable for representing the paraffinic fraction of a diesel fuel because of the high concentration of these chemicals in this kind of fuel.3 On the other hand, aromatic hydrocarbons play an important role in soot formation reactions and must be used in diesel surrogate mixtures. They also contribute to the reduction of the cool-flame oxidation of long-chain n-alkanes.9 In this study, the kinetics of oxidation of a commercial diesel fuel and a surrogate diesel fuel (the IDEA fuel) were measured and compared. These experiments were performed in a jet-stirred reactor (JSR) to (1) verify the agreement between the chemical kinetics of oxidation of the surrogate (IDEA fuel) and a commercial diesel fuel, (2) provide new
1. Introduction To meet the emission regulation targets, it is necessary to improve diesel engine combustion. To this end, the modeling of combustion in engines is extensively used. It requires good kinetic models for the combustion of diesel fuels. Also, the development of diesel fuel surrogates along with detailed descriptions of the oxidation kinetic mechanisms should allow for quantitative characterization of the chemistry of the diesel fuel ignition process.1 With the development of efficient computational tools, chemical kinetics and computational fluid dynamics may be coupled to rapidly design high-efficiency and low-emission engines. However, there are still significant uncertainties in our knowledge of these combustion processes2 do to the lack of kinetic data and validated models. A conventional diesel fuel consists of a complex mixture of thousands of medium-high molecular-weight hydrocarbons3 that participate in thousands of chemical reactions. Therefore, surrogates3,4 are employed to represent diesel fuel with a limited number of components, allowing for a molecular level understanding of diesel oxidation processes. Surrogate fuels can contain more than one component that exhibits physicochemical characteristics similar to those of real fuel components. Thus, n-alkanes and naphthenic and aromatic hydrocarbons are often used to chemically represent a diesel fuel.4 *To whom correspondence should be addressed. E-mail: dagaut@ cnrs-orleans.fr. (1) Hernandez, J. J.; Sanzargent, J.; Benajes, J.; Molina, S. Fuel 2008, 87, 655. (2) Farrell, J. T.; Cernansky, N. P.; Dryer, F. L.; Friend, D.; Hergart, C.-A.; Law, C. K.; McDavid, R. M.; Mueller, C. J.; Patel, A.; Pitsch, H. SAE Tech. Pap. 2007-01-0201, 2007. (3) Dagaut, P. Phys. Chem. Chem. Phys. 2002, 4, 2079. (4) Mati, K.; Ristori, A.; Gail, S.; Pengloan, G.; Dagaut, P. Proc. Combust. Inst. 2007, 31, 2939. r 2010 American Chemical Society
(5) Hentschel, W.; Schindler, K.-P.; Haahtele, O. SAE Tech. Pap. 941954, 1994. (6) Ristori, A.; Dagaut, P.; Cathonnet, M. Combust. Flame 2001, 125, 1128. (7) Battin-Leclerc, F.; Fournet, R.; Glaude, P. A.; Judenherc, B.; Warth, V.; C^ ome, G. M.; Scacchi, G. Proc. Combust. Inst. 2000, 28, 1597. (8) Yahyaoui, M.; Djebaili-Chaumeix, N.; Dagaut, P.; Paillard, C. E.; Gail, S. Proc. Combust. Inst. 2007, 31, 385. (9) Moriue, O.; Eigenbrod, C.; Rath, H. J.; Sato, J.; Okai, K.; Tsue, M.; Kono, M. Proc. Combust. Inst. 2000, 28, 969.
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pubs.acs.org/EF
Energy Fuels 2010, 24, 1668–1676
: DOI:10.1021/ef9015526
Ramirez L. et al.
3. Computational Methods
Table 1. Experimental Conditions in the JSR
The computations were performed using the PSR computer code.12 The detailed chemical kinetic mechanism used here is based on previous studies of the oxidation of n-decane and large alkanes3,4,13 and of that of 1-methylnaphtalene.11 In addition, cross-reactions describing the interactions between the two fuels components were added (Table 2). They include metathesis reactions of n-decane with phenyl, benzyl, 1-naphtylmethyl, 1-naphtyl, and indenyl radicals. Reactions of C10H21O2 with toluene, 1-methylnaphtalene, 1-naphtylmethyl, 1-naphtaldehyde, benzyl, phenyl, and 1-naphtyl were also added. Finally, reactions of 1-vinylnaphtalene with HO2 and reactions of decyl radicals with 1-naphtaldehyde were added. The kinetics of these added reactions were assumed on the basis of similar reactions used in the kinetic base set6 and the literature.14 The proposed kinetic reaction mechanism consisting of 4762 reversible reactions involving 1124 species is available from the authors. The rate constants for the reverse reactions were computed from the forward rate constants and the equilibrium constants calculated using the appropriate thermochemical data.4,11,15
initial concentrations (in ppm for the fuel and in mol fraction for O2 and N2) diesel
n-decane C11H10
650 650 650 650 700 700 700 700
300 300 300 300
O2
N2
j
P (atm)
0.0597 0.0299 0.0149 0.0100 0.0596 0.0298 0.0149 0.0099
0.9396 0.9695 0.9844 0.9894 0.9394 0.9692 0.9841 0.9891
0.25 0.5 1 1.5 0.25 0.5 1 1.5
10 10 10 10 10 6, 10 6, 10 10
information on the kinetic of oxidation of diesel fuels over a wide range of conditions, and (3) propose and validate a detailed kinetic reaction mechanism for the oxidation of a diesel fuel from low to high temperatures. 2. Experimental Section The JSR used here is similar to that used earlier.4,10,11 It consists of a fused silica (to minimize wall catalytic reactions) sphere of 33 cm3 in volume, equipped with four nozzles of 1 mm diameter for the injection of the gases achieving the stirring. A nitrogen flow of 100 L/h was used to dilute the fuel and avoid its pyrolysis before admission in the reactor. All gases were preheated before injection to minimize temperature gradients inside the JSR. The liquid fuel was atomized and vaporized before injection into the reactor. The fuel and oxygen were diluted by a flow of nitrogen (
