1989-02-01

Predictability of Emissions from In-use vehicles at Low-Ambient Temperature and Alternate Driving Cycle Based on Standard Tests 890625

Exhaust emission data were generated from a fleet of 24 late model fuel-injected vehicles at ambient temperatures of 75°, 50°, and 20°F using a commercial gasoline with Reid vapor pressure (RVP) of 11.8 psi. Tests were conducted using the standard FTP and a low-speed cold- and hot-start test cycle. The in-use vehicles were tested in an as-received condition without engine adjustment or modification.
Data analysis included statistical treatment of CO emissions, with emphasis on: 1) the predictability of CO emissions at low-ambient temperatures based upon FTP data generated at 75°F, 2) predictability of CO emissions from low-speed hot- and cold-start tests at 20°, 50°, and 75°F ambient temperature based upon data from FTP tests, and 3) predictability of CO emissions from low-speed cold- and hot-start tests at low-ambient temperature based on similar tests conducted at 75°F.
Data analysis shows that vehicles producing comparatively low emissions at 75°F do not necessarily produce low emissions at lower temperature and conversely, vehicles producing relatively high emissions at 75°F do not necessarily produce relatively high emissions at lower temperatures.
Data analysis suggests that CO emissions from the FTP at low-ambient temperature cannot be estimated from tests at 75°F using the standard FTP test cycle. The data also suggest that CO emissions from low-speed cold-and hot-start test cycles at low-ambient temperatures cannot be predicted from FTP emissions. Further, the data suggest that prediction of CO emissions from low-speed cold- and hot-start test cycles at low temperatures cannot be made based upon data from similar tests conducted at 75°F.
Analysis of this data suggests that estimation of CO emissions at low-ambient temperatures or low-speed test cycles is not practical without testing at those conditions. Specifically, testing at low-ambient temperature is necessary in order to estimate the CO emissions at low temperature, and further, testing using low-speed test cycles is necessary to estimate the CO emissions at low speeds.

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