Electrically Heated Catalysts and Reformulated Gasolines

A 1991 Volvo model 960 equipped with an electrically heated catalytic converter system (EHC) was evaluated in multiple FTP tests with three different gasolines: current certification fuel, the Auto/Oil industry average fuel (RF-A), and a fuel that meets the 1996 California Phase II reformulated gasoline standards. Tests of each fuel were run with a low-mileage EHC located upstream of either a low-mileage stock main converter or a stock converter that had been road aged for 100,000 miles under European driving conditions. Test results with EHC operation showed significant variations in NMHC, CO, and NO_X emissions with the three test fuels. NMHC emissions were 2-2.5 times lower for the Phase II fuel versus RF-A, with the certification fuel intermediate in NMHC emissions. Tests with the EHC/high-mileage converter system exhibited higher overall FTP emissions compared to the EHC/low-mileage main converter system, as expected. Fuel trends with respect to NMHC and CO were the same for both of these EHC/main converter systems. Expected differences in engine-out emissions for these three fuels, air/fuel stoichiometry during cold start-up, and the relatively cool exhaust temperatures during cold starts associated with this vehicle's underfloor converter system location contribute to the observed effects of fuel composition on emission performance.