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Bachman, K. C.
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Control of Automotive Sulfate Emissions

Exxon Research and Engineering Company-E. L. Holt, K. C. Bachman, W. R. Leppard, E. E. Wigg
U. S. Environmental Protection Agency-J. H. Somers
Published 1975-02-01 by SAE International in United States
A study has been made of potential methods for controlling SO4= emissions from oxidation catalyst-equipped vehicles. The methods considered included operating condition and catalyst changes, as well as the use of a vehicle trap for SO4=. Emissions of SO4= from non-catalyst cars were also measured.The only engine operating variable we found to significantly lower SO4= emission was exhaust gas O2 level. Limiting air pump use reduced SO4= emissions by factors of 5 to 7 over the FTP, and by factors of 2 to more than 10 at 96 km/h. Some increase in CO and HC emissions was observed when the greatest SO4= reductions were achieved, but it appears that properly modulated carburetion could overcome this problem. Limited excess air shows great promise as a means of minimizing SO4= emissions. Use of a three-way or oxidation catalyst system with closed-loop fuel metering control achieved very low levels of SO4=, while simultaneously controlling CO and HC, at the stoichiometric A/F ratio and slightly leaner than stoichiometric.Pelleted catalysts emitted lower amounts of SO4= during low speed operation than…
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