An investigation into the conversion of specific carbon atoms in oleic acid and methyl oleate to particulate matter in a diesel engine and tube reactor. (1st August 2015)

• Record Type: Journal Article
• Authors: Eveleigh, Aaron; Ladommatos, Nicos; Hellier, Paul; Jourdan, Anne-Lise
• Is Part Of: Fuel. Volume 153(2015)
• Page Start: 604
• Page End: 611
• Publication Date: 2015-08-01
• Subjects: Oleic acid -- Methyl oleate -- Isotope tracing -- Carbon-13 -- IRMS; Fuel -- Periodicals; Coal -- Periodicals; Coal; Fuel; Periodicals; 662.6
• DOI: 10.1016/j.fuel.2015.03.037
• Languages: English
• ISSNs: 0016-2361

Abstract

Highlights: The 13 C isotope has been used to trace specific carbon atoms during combustion. Two molecules were investigated, the biofuels oleic acid and methyl oleate. The double bonded C in oleic acid forms particulate at about the same rate as the average carbon atom. The carbonyl carbon in methyl oleate and oleic acid does not convert to particulate. Abstract: The paper is concerned with particulate formation from the fuels oleic acid and methyl oleate. In particular the paper reports, quantitatively, the propensity of individual carbon atoms in these two molecules in being converted to particulate. The conversion of individual carbon atoms to particulate was traced by 'labelling' individual carbon atoms in those two fuel molecules with isotopic carbon-13 ( 13 C) and then measuring how many of the labelled atoms was found in the particulate. This allowed the measuring of the conversion rates of individual fuel carbon atoms to particulate. In the case of oleic acid, three carbon atoms were selected as being particularly relevant to particulate formation, and 13 C labelled. One of the carbon atoms was double bonded to the oxygen atom on the carboxylic acid group; and the other two were part of the oleic acid molecule alkyl chain and double bonded to each other. In the case of the methyl oleate, one carbon atom was 13 C labelled. This was the carbon atom that was double bonded to one of the oxygen atoms of the ester group. Experimental results are presented for particulate matter (PM) formed in a laminar flow tube reactor, and also in a direct injection compression ignition engine. The tube reactor has been used for the pyrolysis of oleic acid and methyl oleate at 1300 °C, under oxygen-free conditions and at air–fuel equivalence ratios ( λ ) of 0.1, and 0.2. Samples of PM were also collected from the compression ignition engine at an intermediate engine load. Isotope ratio mass spectrometry (IRMS) has been used to determine the relative abundance of 13 C in the initial fuel and in the resulting PM. Significant differences in the relative conversion rates of individual carbon atoms are reported; a negligible contribution to PM from the carbon atom directly bonded to two oxygen atoms was found in both the engine and reactor. The labelling technique used in this paper requires low quantities of 13 C labelled molecules to enrich otherwise unlabelled oleic acid; enrichment is at volumetric concentrations typically less than 0.7% (v/v). In addition, emissions data from the engine and tube reactor, including unburned hydrocarbons, CO, CO2, NO x, and PM size and number distributions measured by differential mobility spectrometer, are also presented.