Gasoline fuels contain varying amounts of sulphur. Sulphur has a great influence on the emissions from catalyst equipped cars. Standard catalysts of European-type have been investigated regarding sulphur storage and release during different operating conditions. Papers presented earlier on H2S problems from three-way catalyst equipped cars have not illustrated the dependence upon catalyst age and driving conditions. This paper will discuss tests and results of H2S release in connection with closed throttle operations and evaporative canister purging.
Test have been performed on passenger cars, driven both on the test track and on highways in a repeatible way. The fuel has had varying amounts of sulphur.
By varying temperature and air-fuel ratio, the conditions necessary for sulphur storage and release in closed-looped fuel injected catalyst equipped engines have been demonstrated.
It is shown that the storage is increased by leaner fuel mixtures and that the release of H2S requires an inlet temperature of 450° C for a fresh catalyst and over 550° C for an aged catalyst.
If temperature conditions are fulfilled, H2S release is possible during:
Closed throttle operation and canister purging are frequent conditions in stop-and-go traffic. It is also shown that the ability of catalysts to form H2S declines after some 1000 miles. The explanation of this phenomen is partially to be found in the decreased oxygen storage capacity of the catalyst.