Investigation of Polycyclic Aromatic Hydrocarbons in Gas
Inclusive Dates: 06/19/01 - 10/20/01
Background - Polycyclic aromatic hydrocarbons (PAHs) in diesel exhaust have been reported, but very little data exist on PAHs in gas turbine exhaust. PAHs are found both in the vapor phase and condensed onto particulates; some of these PAHs are known carcinogens.
Approach - A combustor from a modern gas turbine engine was operated at idle, cruise, and takeoff conditions in the Institute's pressurized combustor facility. The exhaust was sampled with a dilution probe to collect particulates and organic samples. The dilution ratio was determined by comparing the CO2 concentration with that of an undiluted exhaust sample. The particulates were collected on a fluorocarbon-coated glass-fiber filter. The volatile organic compounds that passed through the particulate filter were adsorbed onto a PUF/XAD-2 filter. These two filters were solvent washed to extract the organic material. After preparation, this extract was analyzed for 21 PAH compounds using GC/MS/SIM (selected ion monitoring) by SwRI's Department of Analytical and Environmental Chemistry. The jet fuel burned in the experiments was also analyzed for PAHs for comparison.
Accomplishments - The samples were obtained and successfully speciated for PAHs. The fraction of PAHs collected from the particulates depended upon the temperature of the exhaust sample at the filter, which could be controlled by the dilution ratio. The only PAHs found in the fuel sample were the various naphthalenes plus some bi-phenyl, i.e., compounds with only two rings. The exhaust contained compounds with as many as six rings, many of which are carcinogenic. This increase shows that the exhaust PAHs are combustion generated. In general, only the more volatile, noncarcinogenic compounds were found in the volatile fraction, whereas all the compounds were found on the particulates. The fraction of carcinogens increased at the higher power. The methodology can be used to evaluate fuel additives and composition to improve air quality in and around airports.