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 (R-2 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.

Automated summary

This study quantitatively evaluated the correlation between ambient temperature and CO2 emission by testing two light-duty gasoline vehicles under different temperatures. The results showed that the increased CO2 emission under cold ambient temperature is mainly caused by increased internal resistance. Furthermore, CO2 emission from larger engines is more sensitive to temperature variation, while that from smaller engines is more sensitive to load variation. The findings can be used to improve CO2 models and regulations.