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Authors
J.F. Thomas, S.A. Lewis, Sr., B.G. Bunting, J.M. Storey, R.L. Graves, P.W. Park
Publication
SAE
Paper 2005-01-1082, Society of Automotive Engineers, 2005
Abstract
Previously
reported work with a full-scale ethanol-SCR system featuring a
Ag-Al2O3 catalyst demonstrated that this
particular system has potential to reduce NOx emissions
80-90% for engine operating conditions that allow catalyst temperatures
above 340°C. A concept explored was utilization of a fuel-borne
reductant, in this case ethanol “stripped” from an
ethanol-diesel micro-emulsion fuel. Increased tailpipe-out emissions of
hydrocarbons, acetaldehyde and ammonia were measured, but very little
N2O was detected. In the current increment of work, a number
of light alcohols and other hydrocarbons were used in experiments to map
their performance with the same Ag-Al2O3 catalyst. These exploratory tests are aimed at identification of
compounds or organic functional groups that could be candidates for
fuel-borne reductants in a compression ignition fuel, or could be
produced by some workable method of fuel reforming. A second important
goal was to improve understanding of the possible reaction mechanisms
and other phenomena that influence performance of this SCR system. Test
results revealed that diesel engine exhaust NOx emissions can be reduced
by more than 80%, utilizing ethanol as the reductant for a space
velocity near 50,000/h and catalyst temperatures between 330 and
490°C. Similar results were achieved for 1-propanol, 2-propanol and
1-butanol, with a (desirable) shift to a lower temperature range seen
for the primary alcohols. Heavier alcohols and other oxygenated
organics were also tested as reductants showing a range of less
successful results. Non-oxygenated hydrocarbons and the selected
secondary and tertiary alcohols proved to be very poor reductants for
this system. Some discussion concerning the possible mechanisms behind
the results is offered. |
