The effect of variations in external temperature on pollutant emissions and energy consumption of warmed-up passenger cars was investigated. Existing emission and fuel data from the warm phases stabilised and hot transient, of the FTP driving cycle, at ambient temperatures ranging from -20ŸC to +20ŸC were reviewed. The relationships of emissions and of fuel consumption with ambient temperature were analysed by linear regression methods. The fuel data yielded a negative temperature relationship, with lowered temperature entailing increased fuel consumption. CO of non-catalyst cars also exhibited a statistically sound negative temperature dependence. HC and NOx emissions of non-catalyst vehicles had small positive temperature dependences, while all catalyst car values were slightly negative. In view of the large measures of uncertainty associated with the slopes obtained, however, it was deduced that no safe conclusions, regarding covariation with temperature of these parameters could be drawn. Increases at low temperatures in air density, as well as in rolling resistance etc, of the wheel axle not on the rollers, may lead to underestimations of fuel consumption, and consequently of HC, CO and NOx, in dynamometer measurements. These effects need to be investigated. (A)
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