Development and Initial Use of a Heavy-Duty Diesel Truck Test Schedule for Emissions Characterization

In characterizing the emissions from mobile sources, it is essential that the vehicle be exercised in a way that reasonably represents typical in-use behavior. A heavy-heavy duty diesel truck (HHDDT) test schedule was developed from speed-time data gathered during two Air Resources Board-sponsored truck activity programs. The data were divided into four modes, termed Idle, Creep, Transient and Cruise Modes, in order of increasing speed. For the last three modes, speed-time schedules were created that represented all the data in that mode. Statistical parameters such as average speed, stops per unit distance, kinetic energy, maximum speed and acceleration and deceleration values were considered in arriving at these schedules. The schedules were evaluated using two Class 8 over-the-road tractors on a chassis dynamometer. Emissions were measured using a full-scale dilution tunnel, filtration for particulate matter (PM), and research grade analyzers for the gases. Test runs at different simulated weights showed that the weight influenced the ability of the truck to follow the trace closely. Emissions from Idle and Creep Modes were found to be variable due to varying auxiliary loads on the engine. A test protocol was developed for running the four modes in a sequence, and repeats of this whole sequence were performed to clarify test-to-test variability. For a test weight of 56,000 lbs. on a 400 hp 1995 Mack tractor, NOx emissions were 19.6 g/mile for the Transient Mode and 22.3 g/mile on the Cruise Mode, while the respective PM emissions were 0.56 g/mile and 0.14 g/mile. It was concluded that this test schedule of four modes was suitable for future HHDDT emissions characterization.