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

Abstract

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.