Real-world emission characteristics of natural gas-gasoline bi-fuel vehicles
天然气-汽油双燃料车实际道路排放特性研究

The CO2, CO, NOx and total hydrocarbon(THC) emissions of 25 compressed natural gas (CNG)-gasoline bi-fuel taxies were tested by portable emissions measurement system (PEMS) to investigate the impact of CNG on the emissions of light-duty vehicles. Results showed that CO2 and CO emissions from original equipment manufacturer (OEM) vehicles on average were reduced by 22% and 24%, respectively, when the fuel was switched from gasoline to CNG. In comparison, NOx and THC emissions increased by 27% and 22%, respectively, as a result of fuel switch. Using CNG for converted vehicles led to decrease of CO2 and CO emissions by 25% and 32% respectively, but increase of NOx and THC emissions by about 200% compared to gasoline. Changes of CO, NOx and THC emissions with gasoline-to-CNG switch may be related to the conversion of engines, exhaust composition and the performance of three way catalysts.