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A gas chromatographic technique was used to determine the vapor pressures of blends of six candidate diesel fuel oxygenates with three diesel fuels at 0, 5, 10, 30, and 100 percent blend levels. Both the oxygenates and the diesel fuels were selected to represent a variety of chemical compositions. The vapor pressures were determined over a range of temperatures from -30 C to +30 C. In each case the fraction of the vapor pressure derived from the oxygenate and the fuel was identified. The vapor pressure results showed that there were significant deviations from ideality, leading to both higher and lower vapor pressures than would be predicted from Raoult's Law. These results are significant for fire safety and evaporative emissions as well as for a more basic understanding of the behavior of these blends. Data were also obtained on the heats of vaporization for each of the blends.

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.

In 1992, a Round Robin was sponsored by the CRC's Emissions Analysis Round Robin Subcommittee, to provide an opportunity for automotive emissions laboratories to compare their analytical methodologies with those used in other laboratories. Compressed gas samples were provided to participants to test hydrocarbon methodologies, while liquid samples were used for alcohol and carbonyl analyses. The results of this study were published in SAE 950780 and SAE 941944. A second Round Robin study was conducted in 1995, using the same basic structure as the first study. The results of the carbonyl analyses have been published separately (SAE 971609). The purpose of this paper is to compare methods used for hydrocarbon speciation of emissions by gas chromatography. As in the 1992 study, cylinders of a synthetic exhaust were prepared by using a fuel base, and adding components that would be expected as typical combustion products.