The Emission of a Diesel Engine in Different Coolant Temperature during Cold Start at High Altitude

Emissions of diesel engine have been received much more attention since the Volkswagen Emission Scandal. The Euro VI emission standard has already included cold start emissions in the legislative emission driving cycles which is one of the hardest part of emission control. High altitude performance is also considered in the latest regulations which will be stricter in the future. Heating the coolant is one of the most common method to improve the cold start performance. But researches focus on the emission of a diesel engine in different coolant temperature at high altitude which up to 4500m have not been seen. The present research investigated the effect of coolant temperature on performance and exhaust emissions (gaseous and particulate emissions) during the cold start of a diesel engine. A plateau simulation system controlled the inlet and exhaust pressure to create altitude environments from 0m to 4500m, and the coolant temperature was controlled from 20°C to 60°C. The engine started up faster with as coolant temperature increased at each altitude. As the coolant temperature increased, the CO and THC emissions reached a higher peak and a lower total emission during the first 30 seconds. The CO₂ emission did not change obviously at different coolant temperatures. The NO_X emission was decreased as the coolant temperature increased, but went much higher when it was up to 60°C, which was just opposite of the particulate number (PN) and particulate number (PN) emission characteristics. At the same coolant temperature, higher gaseous and particulate emissions were observed at higher altitude. The PN and PM diameter distributions were analyzed and the relationship between PN and PM during cold start at different coolant temperature and altitude were established. Coolant temperature affects the engine transient emission and cold start performance obviously.