First-stage
and overall ignition delay times of dimethyl ether
(DME) were measured in a high-pressure shock tube for various mixtures
containing high amounts of CO2. The data are available
for DME/air mixtures diluted with 40% CO2 as well as for
the mixture of DME and oxidizer containing 20.5% O2 and
79.5% CO2. As a reference, data were also collected for
mixtures containing the corresponding amounts of N2. Measurements
were conducted for pressures of 15, 35, and 50 bar and a range of
temperatures (744–1316 K). For the DME/air mixture diluted
with CO2, the equivalence ratio was varied in the range
of 0.5–2.0. The results demonstrate that CO2 dilution
has a strong effect on ignition delay times in the NTC (negative temperature
coefficient) region. The kinetic study that was conducted showed that
this phenomenon can be attributed to a thermal effect resulting from
the high heat capacity of CO2. In low and high temperature
ranges, the effect of CO2 is less pronounced. Additionally,
a chemical effect was identified. At high temperatures this effect
can be attributed mostly to the influence of CO2 on third-body
reactions and leads to slight acceleration of ignition. Various chemical-kinetic
models available were evaluated with respect to their accuracy in
prediction of ignition delay times for mixtures containing DME and
large amounts of CO2.
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