Impact of Ambient Temperatures on Exhaust Thermal Characteristics during Cold Start for Real World SI Car Urban Driving Tests

Thermal characteristics of SI engine exhaust during cold start and warm up period were investigated for different ambient temperatures (-2 to 32 °C). A Euro 1 emission compliance SI car was tested using a real world urban driving cycle to represent typical city driving patterns and simulate ECE15 urban driving cycle. The test car was equipped with 27 thermocouples along the engine and exhaust pipes so as to measure metal and exhaust gas temperatures along the engine, exhaust and catalyst. The characteristics of thermal properties of engine, exhaust system and catalyst were studied as a function of warm up time and ambient temperature. The temperature and time of the light-off of catalyst were investigated so as to evaluate the effect of thermal properties of the catalyst on emissions.

The results show that the coolant water reached the full warm up about 5 minutes in summer and 9 minutes in winter after a cold start. Lubricating oil reached the full warm up in 10 minutes in summer and 14 minutes in winter after a cold start. The light-off time of TWC was about 3 minutes in summer and 6 minutes in winter in terms of catalyst substrate temperatures. The determination of catalyst light off has been studied and discussed in terms of catalyst substrate temperatures and gas temperatures. The ambient temperature had little influence on engine out exhaust gas temperatures. The heat loss from the engine out to the catalyst was at highest level in the first 5∼6 minutes and after this point the heat available at the catalyst was relatively stable.

The thermal properties of the engine and exhaust system had significant influence on emissions. The results indicate that in some urban driving conditions such as short journeys in cities especially under cold weather conditions, the function of catalysts for emission reductions is very limited.