Comparison of CO2, NOx, and VOCs emissions between CNG and E10 fueled light-duty vehicles

In China, natural gas (NG) is the main vehicle fuel after gasoline and diesel, and the number of NG vehicles ranks first in the world. At present, there are many studies on the conventional gaseous pollutants and particulate matter of NG vehicles, but very few studies on their VOCs. In this study, the chassis dynamometer is used to test CNG/E10 bi-fuel light-duty vehicles, analyze the advantages of CNG in CO2, fuel thermal efficiency, and cost, and discuss its disadvantages in NOx emission. Most importantly, the emission characteristics and ozone formation potential of VOCs in the exhaust of CNG vehicles were analyzed in the study. Compared with E10, CNG fuel can reduce CO2 emission by about 20 %, improve thermal efficiency by about 13 %, and save fuel costs by about 50 %. However, it will increase NOx and NO2 emissions by about 10 % and 13 % respectively. As for VOCs, the emission factor of VOCs from CNG fuel is about 54 % of E10 fuel. The VOCs group with the highest proportion in the exhaust of CNG-fueled vehicles is alkanes, >80%. while the alkanes and alkeneswith the highest proportion in E10 fuel are 30% and 23% respectively. C2 VOCs emitted by CNG account for >70 %, while C2 VOCs emitted by E10 are <60 %, followed by C4 VOCs, about 10% - 30 %. The OFPs of VOCs in CNG exhaust is about 13.7% of E10. Alkenes contribute the most to ozone, and the OFPs of alkenes in CNG and E10 vehicle exhaust accounts for about 55.3 % and 78.8 % of TVOCs respectively. The results of this study are helpful to improve people's understanding of the environmental value of using NG vehicles.

Automated summary

This study analyzes the advantages and disadvantages of CNG/E10 bi-fuel light-duty vehicles and the characteristics of VOCs and ozone formation potential in CNG vehicle exhaust. The results show that CNG fuel can reduce CO2 emissions, improve thermal efficiency, and save fuel costs compared to E10. However, it also increases NOx and NO2 emissions. The VOCs emitted by CNG vehicles are mainly alkanes, while E10 contains high proportions of alkanes and alkenes. These findings help enhance understanding of the environmental value of using NG vehicles.