Continued efforts to reduce the total emissions of harmful exhaust gases and greenhouse gases feature a reduction from the personal transportation sector as a central strategy. Ambitious long-term targets planned for the EU would reduce the emission factors of HCs, CO, NO* and PM to very low levels, approaching a combined mass of 1 g/km for SI and well under 1 g/km for CI. Such targets may not deliver concrete air quality improvement if low ambient temperatures continue to cause such large excess start-up emissions. Somewhere in the region of (1-2)×1011 cool and cold starts are performed annually within the EU alone. A significant proportion of these occur at low ambient temperatures; a smaller but yet significant subset will occur at subzero temperatures. While EU legislation recognizes the effect of a low ambient temperature on the emission factors, the type-approval temperature of 7 °C is in no way representative of the lower limit of operation for passenger cars. To obtain a more accurate figure for real-world on-road emissions, a climate-specific weighted mean could perhaps be used from tests performed at various temperatures, to be more representative of real climatic conditions in a given country. Regarding regulated emissions, Euro 5 SI vehicles show significantly lower excess emissions at -7 °C than Euro 4 vehicles do, but no real improvement was observed regarding the fuel consumption. The fleet average data presented here confirm that CI engines suffer overall lower excess emissions following a cold start and that their fuel consumption at -7 °C may be comparable with SI fuel consumption at 24 °C. Efforts to improve the fuel economies of both vehicle types should take low-temperature cold-start operation into account. Cold-start behaviour is controlled by a wide range of factors: the engine design, the fuel and lubricant properties, the thermal management, and the catalyst functionality. Research must be forthcoming in all these areas in order to address the problem of excess emission from cold starts and to enable further reductions in the real-world fuel consumption.
The effect of a low ambient temperature on the cold-start emissions and fuel consumption of passenger cars
2011
12 Seiten, 9 Bilder, 3 Tabellen, 26 Quellen
Article (Journal)
English
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