Chemical kinetic modeling of dimethyl carbonate in an opposed-flow diffusion flame

Abstract

Dimethyl carbonate (DMC) has been of interest as an oxygenate additive to diesel fuel because of its high oxygen content. In this study, a chemical kinetic mechanism for DMC was developed for the first time and used to understand its combustion under conditions in an opposed flow diffusion flame. Computed results were compared to experimental results from an opposed flow diffusion flame. It was found that the decomposition rate DMC => H 3 COC(=O)O. + CH 3 in the flame was much slower than originally thought because resonance stabilization in the H 3 COC(=O)O. radical was less than expected. Also, a new molecular elimination path for DMC is proposed and its rate calculated by quantum chemical methods. In the simulations of DMC in the flame, it was determined that much of the oxygen in dimethyl carbonate goes directly to CO 2. This characteristic indicates that DMC would not be an effective oxygenate additive for reducing soot emissions from diesel engines. In an ideal oxygenate additive for diesel fuel, each oxygen atom stays bonded to one carbon atom in the products thereby preventing the formation of carbon-carbon bonds that can lead to soot. When CO 2 is formed directly, two oxygen atoms are bonded to one carbon atom thereby wasting one oxygen atom in the oxygenate additive. To determine how much CO 2 is formed directly, the branching ratio of the key reaction, CH 3 OC.=O going to the products CH 3 + CO 2 or CH 3 O + CO was determined by ab initio methods. The Afactors of the rate constant of this reaction were found to be about 20 times higher than previous estimates. The new reaction rate constants obtained can be used as reaction rate rules for all oxygenates that contain the ester moiety including biodiesel.

Chemical Kinetic Modeling Study of the Effects of Oxygenated Hydrocarbons on Soot Emissions from Diesel Engines

“…In the case of DBM as the oxygenated species, nearly 90% of the analogous n-butoxy formyl radical produces CO 2 . Glaude et al 47 , McCunn et al 55 and Good and Francisco 56 have examined the methyl formyl decomposition reaction, using CBS-Q and CCSD(T) methods at the B3LYP level, and all three studies agreed that the energy barrier to the CH 3 + CO 2 product channel is about 14.7 kcal/mol, while the barrier to the CH 3 O + CO products is more than 22 kcal/mol, explaining why the CO 2 channel would be expected to dominate.…”

“…As in our previous mechanism developments 47 , thermodynamic parameters were estimated using quantum chemistry methods and group additivity [49][50][51] . For most species the enthalpy of formation was computed using CBS-Q methods with geometries optimized at the B3LYP/6-31G9(d,p) level following Bozzelli 52 , and other details of the techniques are described by Glaude et al 47 . All of these kinetic mechanisms are available on our web page 40 .…”

Characterization of the Methoxy Carbonyl Radical Formed via Photolysis of Methyl Chloroformate at 193.3 nm

“…The methoxy carbonyl radical is an intermediate in many combustion and atmospheric chemical reactions including the methoxy + CO reaction [1][2][3] (which is integral to the methane combustion mechanism), the combustion and atmospheric oxidation of dimethyl ether, 4,5 and the combustion of dimethyl carbonate. 6 Of particular interest in the above reactions is the development of oxygenated fuels that hinder soot production by forming CO and CO 2 as combustion products. Numerous theoretical and experimental studies have investigated the methoxy carbonyl radical as an intermediate in the oxidation of dimethyl ether, which is currently being investigated as an additive to conventional diesel fuels to reduce soot formation.…”

“…Other work by Glaude et al on the combustion of dimethyl carbonate, 6 also under consideration as a fuel additive, developed a kinetic mechanism for the reaction, which incorporated the methoxy carbonyl radical. The mechanism of Glaude et al indicates that most of the oxygen in the dimethyl carbonate goes into the direct production of CO 2 via dissociation of the methoxy carbonyl radical.…”

Proposta de emprego de conceitos de equilíbrio químico na descrição matemática da câmara de combustão de caldeira siderúrgica

“…Na literatura, diversas pesquisas usam esta metodologia para predizer a composição do sistema para a queima de diferentes combustíveis [2][3][4][5][6][7]. A cinética é definida como a ciência que estuda a velocidade das reações químicas dos processos e os fatores que as influenciam.…”