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Quantification of the Fraction of Particulate Matter Derived from a Range of <sup>13</sup>CāLabeled Fuels Blended into Heptane, Studied in a Diesel Engine and Tube Reactor
This
paper presents the results of an experimental study that was
carried out to determine the conversion rates to particulate matter
(PM) of several liquid fuel hydrocarbon molecules and specific carbon
atoms within those molecules. The fuels investigated (ethanol, <i>n</i>-propanol, <i>i</i>-propanol, acetone, and toluene)
were blended in binary mixtures with <i>n</i>-heptane to
a level of 10 mol percent. The contribution of the additive molecules
to PM was quantified using a carbon-13 (<sup>13</sup>C) labeling experiment,
in which the fuel of interest was enriched with <sup>13</sup>C to
serve as an atomic tracer. Measurement of the <sup>13</sup>C/<sup>12</sup>C in the fuel and in the resulting PM was carried out using
isotope ratio mass spectrometry. The fuel binary mixtures were tested
under pyrolysis conditions in a tube reactor and also combusted in
a direct injection compression ignition engine. In the tube reactor,
samples were generated under oxygen-free pyrolysis conditions and
at a temperature of 1300 Ā°C, while the engine experiments were
carried out at an intermediate load. Both in the tube reactor and
in the engine it was found that, dependent on the fuel molecular structure,
there were significant differences in the overall conversion rates
to PM of the fuel molecules and of the āsubmolecularā
carbon atoms. A separate experiment was also carried out in the compression
ignition engine, with <i>n</i>-heptane as fuel, in order
to determine the contribution of the engine lubrication oil to exhaust
PM; the results showed that a significant portion (ā¼60%) of
the total particulate was derived from the lubrication oil