Impact of Ambient Temperature Conditions on Cold Start Combustion, Gaseous and Particle Emissions from Gasoline Engines

Ambient temperature conditions, engine design, fuel, lubricant and fuel injection strategies influence the cold start performance of gasoline engines. Despite the cold start period is only a very small portion in the legislative emission driving cycle, but it accounts for a major portion of the overall driving cycle emissions. The start ability tests were carried out in the weather controlled transient dynamometer - engine test cell at different ambient conditions for investigating the cold start behavior of a modern generation multi-point fuel injection system spark ignition engine. The combustion data were analyzed for the first 200 cycles and the engine performance and emissions were analyzed for 300 s from key-on. It is observed that cumulative fuel consumption of the engine during the first 60 s of engine cold starting at 10 °C was 60% higher than at 25 °C and resulted in 8% increase in the value of peak speed of the engine. The rate of pressure rise was significantly higher and prolonged for a number of cycles at 10°C compared to 25 °C and 45 °C. The cycle-to-cycle variation in the cylinder pressure at 10 °C was three times higher than at 25 °C. The first 60 sec of the cold start cumulative CO emission at 10 °C was approximately 3 times higher; cumulative HC emission was 3.5 times higher; cumulative NOx emission was 50% lower than that of at 25 °C. The particles in the size range of 50-200 nm are accounted for 60% at 10 °C and 6-8% at 25 °C & 45 °C ambient temperature conditions. The exhaust particles at the low ambient temperatures increased the exhaust particulate mass by 30 times at 10 °C in comparison with that of at 25 °C. The accumulated unburned fuel during the cold start period combusted abruptly and caused for the higher peak speed and exhaust emissions.