Effects of In-Use Driving Conditions and Vehicle/Engine Operating Parameters on “Off-Cycle” Events: Comparison with Federal Test Procedure Conditions

Abstract

This study provides a direct evaluation of real-time, on-road vehicle and engine operating parameters, and investigates their relationship to rich open-loop (or “off-cycle) emissions for a 1991 Ford Taurus driven in morning and evening commute hours over a matrix of eight freeway and eight urban routes in California’s South Coast Air Basin. Frequency of rich open-loop operation for these routes during commute hours 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 “aggressive” driving experiments for the same routes (0.44 percent freeway and 1.1 percent urban). The maximum frequency of rich open-loop operation occurred during off-peak hours, merging, and on a steep grade. The available data show there can be large variances in the frequency of open-loop operation between manufacturers, and ...