The study of aldehydes in diesel exhaust is important because
of their relationship to diesel odor, to air pollution, and to the development
of a theory of combustion. Therefore, a study is made
of the low order aliphatic aldehydes using gas chromatography in
conjunction with standard wet chemical tests.
The engine is a two stroke-cycle GMC 3-71 RC diesel, with
standard injectors, connected to an eddy current dynomometer. A
special ten foot insulated exhaust pipe is used for the sample collection.
Engine load and exhaust pipe length are used as variables, two
probes 6. 7 feet apart being sampled simultaneously.
For the gas chromatographic analysis the aldehydes are converted
to 2, 4-dinitrophenylhydrazone derivatives in special tall form
bubblers. The precipitates are then volumetrically dissolved in
carbon disulfide in preparation for the chromatographic separation.
The columns are ten percent SF 96 on 60-80 mesh acid washed
DMCS treated Chromosorb W in 6 feet by 0. 085 inch I. D. stainless
steel. Nitrogen at 60 ml per minute is used as the carrier gas and
the hydrogen flow for the flame ionization detector is 35 ml per
minute. The column temperature is 230°C and the injector temperature
270°C. The sample injection size is 10μ.
The chromotropic acid test is used as a wet test for the
formaldehyde concentration in the exhaust, the MBTH test being
used for total aliphatic aldehydes. The wet tests are used for correlation
studies with the gas chromatograph and for comparison with
No correlation was found between the chromatograph and wet
tests, the wet tests usually giving higher values. Both tests, however,
indicate the concentration of aldehydes in the exhaust increases
The average molecular weight of the lower molecular weight
aldehydes in the diesel exhaust is found by gas chromatographic
analysis to be approximately 35, 75-80 mole percent of the total
aldehydes being formaldehyde. The average molecular weight decreases
with probe length, as predicted by theory, and the concentration