Quantitative study of vehicle CO₂ emission at various temperatures and road loads

Vehicle CO₂ emissions have been long studied, but the relationship between ambient temperature and CO₂ emission has never been quantified. To quantitatively evaluate the correlation between ambient temperature and CO₂ emission, two light-duty gasoline vehicles were tested over WLTC (Worldwide-harmonized Light vehicles Test Cycle) under four temperatures, −10 ℃, 0 ℃, 23 ℃, and 40 ℃. Obtained results proved that the dominant reason for the increased CO₂ emission under cold ambient temperature is the increased internal resistance rather than fuel enrichments. CO₂ emission from large engines is more sensitive to temperature variation while that from small engines are more sensitive to load variation. The usage of the air-conditioner increased the distance-specific CO₂ emission by 23.07% and 22.49% for vehicle 1 and vehicle 2 respectively. The strong correlation (R² greater than 0.98) between cumulated CO₂ emission/coolant temperature and transient CO₂ emission means the cumulated CO₂ emission/coolant temperature could be used to describe the engine warm-up status and to improve the transient CO₂ model. For the laboratory tests, using the coolant temperature to describe the engine warm-up needs more verification due to the uneven engine temperature field. This study helps understand the CO₂ emission at various temperatures and the results in this study could be used for microscopic CO₂ modeling & CO₂-related regulations.