Effect of Sulfur Content of Gasoline on Exhaust Emissions

Researchers in the U. S. Auto/Oil Joint Research Program (AQIRP) have reported as one of results of their study that a reduced sulfur content in gasoline causes a decrease in the three exhaust emissions, i.e. hydrocarbon (HC), carbon mono-oxide (CO) and nitrogen oxides (NOx). On the basis of these results, the State of California has enforced a regulation that the sulfur content of phase 2 reformulated gasoline be 80 ppmw maximum and 30 ppmw on average as shown in Table 1. The EPA's Reformulated gasoline regulation (Complex Model) includes the sulfur content in fuel-related elements. Thus, the influence of gasoline sulfur content was drawn into attention. Against this background, we have been studying the influence of the sulfur content on the exhaust emissions and have made an interim report. This time, to allow further detailed analysis, we conducted tests while varying the sulfur content of the fuel between 2 and 300 ppmw. The test cycle was repeated in the LA#4 mode of the 1975 Federal Test Procedure ('75 FTP) to evaluate changes in the exhaust gas, individual HC components in the exhaust gas, and the catalyst conversion rate on an engine bench. The tests revealed three facts. First, the exhaust emission level changes immediately when the sulfur content of the fuel is changes. Secondly, when the sulfur content of the gasoline changed, the mass emission changes, but the kind of individual hydrocarbon components in the emissions, i.e. the specific ozone reactivity of emissions, remains unchanged. thirdly, the change in exhaust emission level is caused by the deterioration of the catalyst conversion performance which is due to the sulfur in the gasoline