| Driving behavior data collected for 40 cars driven for a week in March of 1992 in Baltimore and Spokane indicate that roughly 15% of real-world driving time involves driving that is outside the speed/acceleration limits of the Federal Test Procedure (FTP). The FTP is the official protocol for testing new car compliance with the federal tailpipe emissions standards. High-power driving episodes form a subset of this "off-cycle" driving behavior and are responsible in part for the fact that average real-world tailpipe emission rates are several times the current standards.; A simple model for second-by-second automobile exhaust emissions of CO, HC, and NO{dollar}rmsb{lcub}x{rcub}{dollar} that depends only on the instantaneous fuel consumption rate is developed and applied to the Baltimore/Spokane driving behavior data, and an estimate is made of the effect of high-power driving episodes on real-world emissions. The model is a simple algebraic expression that describes engine-out emissions and the action of the catalyst; it is derived from an analysis of detailed dynamometer emissions tests of 13 1992-94 model-year cars collected in 1993-94 for the FTP Revision Project. The estimates for the extra g/mile tailpipe emission rates for an average, properly-functioning, early 1990's passenger car resulting from high-power driving episodes are 2.8 g/mile for CO, 0.05 g/mile for HC, and 0.09 g/mile for NO{dollar}rmsb{lcub}x{rcub}.{dollar}; The model is also used to evaluate the potential impact of the new Supplemental FTP (SFTP) on in-use emissions. It is found that the CO emission standard is strict when applied to the SFTP, and it will require manufacturers to eliminate practically all use of fuel enrichment during the SFTP in order to meet the standard. Fuel enrichment is typically used during high-power driving episodes to supply maximum power, cool the engine and catalyst, reduce the probability of knock, and to ensure drivability. If command enrichment is reduced altogether, then the in-use emission rates of CO and HC will drop by up to 2.8 g/mile and 0.05 g/mile, respectively, for properly-functioning cars. |
