Cold start and full cycle emissions from a flexible fuel vehicle operating with natural gas, ethanol and gasoline

• Natural gas produces lower carbon monoxide emission than gasoline and ethanol.
• Natural gas produces lower carbon dioxide emission than gasoline and ethanol.
• Natural gas produces lower oxides of nitrogen emissions than gasoline and ethanol.
• Natural gas produces lower fuel consumption than gasoline and ethanol.
• Natural gas requires improvements for methane and hydrocarbon reduction.

This paper describes a comparative study between the pollutant emissions produced by a spark ignition engine operating with three different fuels: commercial gasoline with 22% of ethanol (E22), compressed natural gas (CNG) and hydrous ethanol. The emission levels of oxides of nitrogen (NOx), carbon monoxide (CO), carbon dioxide (CO2), total hydrocarbons (HC), and methane (CH4) produced by a flexible fuel engine operating according to the US 1975 Federal Test Procedure (FTP 75) were analyzed. Tests were performed with a mid-size sedan powered by 1.4-L spark ignition engine on a chassis dynamometer. The results for the cold start tests demonstrate that E22 produced the lowest CO and HC emissions, while CNG produced the lowest NOx emissions. Considering the full test cycle, CNG emitted the lowest CO, NOx and CO2 concentrations, and the lowest fuel consumption. Gasoline presented the lowest emission levels of HC and CH4. Ethanol showed the highest fuel consumption and higher pollutant emission levels than the other fuels, except for CO2, which was higher than CNG and lower than gasoline.