EFFECTS OF IN-USE DRIVING CONDITIONS AND VEHICLE ENGINE OPERATING PARAMETERS ON OFF-CYCLE EVENTS - COMPARISON WITH FEDERAL TEST PROCEDURE CONDITIONS

This study provides a direct evaluation of real-time, on-road vehicle and engine operating parameters, and investigates their relationship t o rich open-loop (or ''off-cycle'') emissions for a 1991 Ford Taurus d riven in morning and evening commute hours over a matrix of eight free way and eight urban routes in California's South Coast Air Basin. Freq uency of rich open-loop operation for these routes during commute hour s was 0.003 percent and 0.007 percent, respectively. The low frequency of rich open-loop operation on these routes was attributed to the low velocities and close vehicle proximity during ''gridlock'' conditions . Higher frequencies of open-loop operation were observed for ''aggres sive'' driving experiments for the same routes (0.44 percent freeway a nd 1.1 percent urban). The maximum frequency of rich open-loop operati on occurred during off-peak hours, merging, and on a steep grade, The available data show there can be large variances in the frequency of o pen-loop o pe ration between manufacturers, and from vehicle-to-vehicl e for the same manufacturer (even with the same engine). Comparison of modal analysis for the FTP and on-road routes found higher percentage s of time at stop (19.1 versus 12.7 percent), cruise (25.1 versus 1 8. 5 percent) and in hard decelerations (3.4 versus 1.9 percent); compara ble amounts of time in medium accelerations (0.85 versus 1.03 percent) and 0.7 percent of the time coasting in the FTP, whereas coasting was observed an average of 5.6 percent of the time on-road. Hard accelera tions (i.e., near or at wide open throttle) did not occur in the FTP b ut were observed 0.007 percent of the time on-road. Comparison of the on-road data to the FTP as a function of velocity, acceleration and pr obability, showed the FTP overestimated the time at stop and at cruise between 25 and 35 mph, but underestimated accelerations and cruise be tween 40 and 50 mph and above 60 mph. The fuel economy measured during the FTP underestimated the observed fuel economy for the freeway and urban driving for both conservative and aggressive driver behavior by 25 and 8 percent, respectively.