CHARACTERIZATION AND ANALYSIS OF DIESEL EXHAUST ODOR

An instrumental method known as the Diesel Odor Analysis System or DOAS, has been developed at A. D. Little, Inc. for measuring diesel exhaust odor. This method is based on the correlation found between the exhaust odor intensity, as measured by an odor panel, and the UV response of the oxygenated fraction of the exhaust.; It was of interest to determine which compound or compounds in the oxygenated fraction of the exhaust were primarily responsible for the odor correlation as developed at A. D. Little, Inc. This was accomplished by observing how the measurement of the exhaust odor intensity and number of chemical constituents of the oxygenate fraction were changing with respect to the odor values as measured by the DOAS.; Exhaust from a single cylinder IDI-CFR diesel engine operated over a wide range of test conditions was sampled and analyzed by the current DOAS methodology. The oxygenated fractions were obtained by separation of the exhaust samples on a silica Sep-Pak cartridge and analyzed by capillary gas chromatography. Computerized GC profiles were produced from which character impact peaks were chosen for correlations with odor as measured by the DOAS method. Peaks were also found that correlated with engine air to fuel ratio.; Benzaldehyde was found to give the best correlation (R = 0.98) with odor. A quantitative relationship between exhaust odor as measured by the total intensity of aroma (TIA) and the benzaldehyde concentration (B) in ppm in the exhaust is given by:; TIA = 1.11 log(,10) (B) + 4.10; This correlation was supported by results obtained from two other diesel engine exhaust sources. A methyl benzaldehyde isomer also yielded a good correlation (R = 0.90) with odor. Air to fuel ratio correlations were determined for the tentatively identified compounds, cinnamaldehyde (R = 0.94) and a C2 - benzaldehyde isomer (R = 0.94).; Sampling effects were studied by using chemical and C-14 labeled tracer compounds and GC profiling. Results showed that each tracer compound had its own particular breakthrough and recovery pattern which could be dependent on the sampling rate and sample volume collected. GC profiles indicated that the majority of organic compounds measured by the DOAs are low molecular weight oxygenates.