A New Method for Diesel HC Collection and Speciation 2000-01-2951
As interest in diesel emissions has grown, so has the importance of analyzing the components of the exhaust. These compounds include alkanes, aromatics and alkenes, ranging in carbon number from C1 - C24, and polycyclic aromatic hydrocarbons (PAHs). These hydrocarbons can be in gaseous, semi-volatile and particulate form and cannot be collected accurately by conventional Tedlar™ bag sampling due to deposition of condensing vapor on bag walls. There are some sorbent methods used currently for the speciation of this exhaust, which require either thermal desorption and/or solvent extraction equipment.
Automotive Testing Laboratories, Inc. (ATL) reports here on the use of a gas chromatography (GC) method designed to specifically look at hydrocarbons in the diesel (C9 - C24) range. Also described is the use of an impinger trapping method for collecting the hydrocarbons in diesel exhaust, a type of sampling which is most commonly used in the automotive emission community for the collection of alcohols and carbonyls. In the work described here, impingers filled with organic solvent were used to trap exhaust components, and this sample was subsequently concentrated by solvent evaporation and analyzed by GC.
An approximately one-hour GC method for diesel-range hydrocarbons has been developed, which allows a time-efficient, yet thorough analysis of hydrocarbons in the exhaust. Diesel fuel has been analyzed with this method, and the chromatogram exhibited comparable patterns to those described in the literature. The emissions sampling method described here collected a range of hydrocarbon species that were comparable to those collected with other sorbent methods, described in the literature as well.
Tests performed include sampling cold-start exhaust from a light-duty diesel truck during bag 1 of an FTP chassis-emissions test. Impinging using hexane was performed and species from C9 through C24 quantified. Heated flame ionization detector (FID) and non-heated FID results were recorded for total hydrocarbons. Gas-phase bag samples were taken for typical C1-C12 GC analysis for hydrocarbons. Comparison of C9 through C12 analyzed via the gas phase analysis versus that observed with the impinger method was made. Total hydrocarbon as determined from gas phase measured C1-C12 plus impinger phase C12 through C24, versus the total hydrocarbon observed with heated FID, is also discussed.