The Effect of Gasoline Composition on Vehicle Tailpipe Emissions at Low Ambient Temperature

The tailpipe emissions of seven 1991-92 model years vehicles were measured at two different ambient temperatures (-7, 25°C) with three different base fuels. As expected, the emissions of the first bag were most dominant over the whole FTP cycle at the lower temperature. For the whole fleet, the HC, CO and NO_x, emissions at -7°C were 3.8, 4.9 and 1.2 times respectively higher compared with the emissions at 25°C, while for the first bag of the FTP cycle, they were 5.1, 6.9 and 1.3 times higher. The increase in emissions at low temperature was found to be mainly vehicle dependent. Tests performed at 25°C showed good agreement with the Auto/Oil AQlRP results regarding the HC and CO emissions but showed some difference with respect to the NO_x, emissions. However, the vehicle responses to the fuels were significantly different between the two temperatures. Some fuel effects on the carbon monoxide and oxides of nitrogen emissions were found to be directionally different at the two temperatures. The effects on hydrocarbon emissions were directionally the same at both temperatures although the magnitudes of the changes were found to be different.