Quantification of the Fraction of Particulate Matter Derived from a Range of ¹³C‑Labeled 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 (¹³C) labeling experiment, in which the fuel of interest was enriched with ¹³C to serve as an atomic tracer. Measurement of the ¹³C/¹²C 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 °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 “submolecular” 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 (∼60%) of the total particulate was derived from the lubrication oil