Excess Emissions and Fuel Consumption of Modern Spark Ignition Passenger Cars at Low Ambient Temperatures

Cold starts are demanding events for spark-ignition (SI) internal combustion engines. When the temperatures of the engine oil, coolant and the engine block are close to the ambient temperature, start-up can be difficult to achieve without fuel enrichment, which results in significant excesses in exhaust emissions and fuel consumption. In general, the lower the ambient temperature, the more substantial these problems are. Many nations frequently experience sub-zero ambient temperatures, and the European Union (among others) has specified an emissions test at low ambient temperature (-7°C). Passenger cars typically experience one to two cold start events per day, and so both cold starts and the warm-up period that follows are significant in terms of exhaust emissions. This paper examines emissions at low ambient temperatures with a special focus on cold start; emissions are also compared to start-up at a higher ambient temperature (24°C). The causes of excess emissions and fuel consumption are briefly discussed. A series of tests were performed on European passenger cars on a chassis dynamometer within an advanced climate-controlled test laboratory at BOSMAL Automotive Research and Development Institute, Poland. Emissions data obtained over the Urban Driving Cycle by testing at 24°C and at -7°C, are presented for a selection of modern Euro 5 gasoline vehicles representative of the European passenger car fleet. A full modal emissions analysis was also conducted at 24°C and at -7°C over the New European Driving Cycle. Emissions and fuel consumption were substantially higher at -7°C than at 24°C.