Wide range modeling study of dimethyl ether oxidation Page: 3 of 23
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A Wide Range Modeling Study of Dimethyl Ether Oxidation
H. J. Curran, W. J. Pitz, N. M. Marinov and C. K. Westbrook
Lawrence Livermore National Laboratory, Livermore, CA 94550
- P. Dagaut, J-C Boettner and M. Cathonnet
CNRS,
Laborutoire de Combustion et Systemes Riactifs,
45071 Orleans Cedex 2, France
Abstract
A detailed chemical kinetic model has been used to study dimethyl ether (DME) oxidation over a wide range of
conditions. Experimental results obtained in a jet-stirred reactor (JSR) at 1 and 10 atm, 0.2 < # < 2.5, and
800 < T < 1300 K were modeled, in addition to those generated in a shock tube at 13 and 40 bar, 0 = 1.0 and
650 < T < 1300 K. The JSR results are particularly valuable as they include concentration profiles of reactants,
intermediates and products pertinent to the oxidation of DME. These data test the kinetic model severely, as it
must be able to predict the correct distribution and concentrations of intermediate and final products formed in
the oxidation process. Additionally, the shock tube results are very useful, as they were taken at low temperatures
and at high pressures, and thus undergo negative temperature dependence (NTC) behaviour. This behaviour is
characteristic of the oxidation of saturated hydrocarbon fuels, (e.g. the primary reference fuels, n-heptane and iso-
octane) under similar conditions. The numerical model consists of 78 chemical species and 336 chemical reactions.
The thermodynamic properties of unknown species pertaining to DME oxidation were calculated using THERM.
Introduction
Legislative restrictions pertaining to the emission of particulates, volatile organic compounds and NO.
from internal combustion engines has been increasing in severity in the U.S., Europe and Japan over the
past decade. Engine makers and automotive companies have had to look at ways to decrease the emission
of these toxic pollutants. Fuel composition affects the tendency of a fuel to form soot particulates and
NO. during combustion; increasing the carbon to hydrogen ratio or the number of carbon-carbon bonds
increases the tendency of a fuel to form soot. Dimethyl ether (DME), CH30CH3, is the simplest linear
ether, has no carbon-carbon bonds and after methane, has the lowest possible carbon to hydrogen ratio.
It is a high cetane fuel with a cetane number of 55-60, is not prone to particulate formation and has a
low toxicity. Recently, therefore, diesel engines fueled with DME have been tested [1, 2]. It was found
that DME did indeed affect a decrease in the emission of CO, NO., formaldehyde, particulates and non-
methane hydrocarbons [1], compared with commercial diesel fuels. DME has also been successfully used
as a methanol ignition improver in diesel engines where it has been reported to dramatically reduce total
hydrocarbon emissions [3]. Finally, the technology required for DME handling and use in an engine is that
already developed for LPG.
There have been a number of studies which have described the pyrolysis of dimethyl ether [4]-[13] but
there have only been three reported kinetic analyses of DME oxidation in laboratory experiments. Sehested
et at. [14] have performed experiments in a 140 litre Pyrex reactor at 0.38-940 torr total pressure and at a
temperature of 296 K. These experiments are performed at room temperature and up to pressures slightly
greater than one atmosphere, but these conditions bear little resemblence to those in an operating diesel
engine. Dagaut et at. [15] obtained results in a jet-stirred reactor (JSR) at 1 and 10 atm, 0.2 < 0 < 2.5,
and 800 < T < 1300 K. Pfahl and coworkers [16] measured DME ignition delay times behind reflected1
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Pitz, W.J.; Marinov, N.M.; Westbrook, C.K.; Dagaut, P.; Boettner, J-C & Cathonnet, M. Wide range modeling study of dimethyl ether oxidation, article, April 1, 1997; California. (https://digital.library.unt.edu/ark:/67531/metadc685617/m1/3/: accessed May 10, 2024), University of North Texas Libraries, UNT Digital Library, https://digital.library.unt.edu; crediting UNT Libraries Government Documents Department.