The control of exhaust emissions from modern vehicles is primarily based on the use of after-treatment devices, typically consisting in different types of catalysts. The efficiency of catalytic systems however strictly depends on their temperature, achieving certain effectiveness in reducing emissions only above the light-off temperature. Moreover, the enrichment of the air/fuel mixture during cold-start engine operation, in order to compensate for the reduced fuel vaporization and elevated engine components friction, leads to incomplete fuel combustion. These two factors generally contribute to elevated emissions during cold-start operation, especially under low ambient temperatures. We investigated the gaseous emission performance of thirteen late technology vehicles over the New European Driving Cycle (NEDC), at 22 ¡ãC and ?7 ¡ãC test cell temperatures. The test fleet included gasoline vehicles both Port Fuel Injection (PFI) and Gasoline Direct Injection (G-DI) as well as diesel vehicles, amongst which a fully Euro 6 compliant vehicle equipped with a Selective Catalytic Reduction (SCR) system.
The test results showed that carbon monoxide (CO) and total hydrocarbon (HC) emissions of gasoline vehicles increased from 2.3 to 11.3 times at ?7 ¡ãC over the Urban Driving Cycle (UDC), remaining however below the current legislative limits by 45 % and 65 % respectively. Nitrogen oxides (NOx) emissions of gasoline vehicles at ?7 ¡ãC turned out to be either higher or lower than at 22 ¡ãC, depending on the catalyst¡¯s performance and engine injection strategy. Diesel vehicles without any NOx after-treatment system exhibited increased NOx emissions over both the UDC and Extra Urban Driving Cycle (EUDC) when tested at ?7 ¡ãC. The diesel car with the SCR system showed superior NOx performance only over the second half of the NEDC.
