Creation and Evaluation of a Medium Heavy-Duty Truck Test Cycle 2003-01-3284

The California Air Resources Board (ARB) developed a Medium Heavy-Duty Truck (MHDT) schedule by selecting and joining microtrips from real-world MHDT. The MHDT consisted of three modes; namely, a Lower Speed Transient, a Higher Speed Transient, and a Cruise mode. The maximum speeds of these modes were 28.9, 58.2 and 66.0 mph, respectively. Each mode represented statistically selected truck behavior patterns in California. The MHDT is intended to be applied to emissions characterization of trucks (14,001 to 33,000lb gross vehicle weight) exercised on a chassis dynamometer. This paper presents the creation of the MHDT and an examination of repeatability of emissions data from MHDT driven through this schedule. Two trucks were procured to acquire data using the MHDT schedule. The first, a GMC truck with an 8.2-liter Isuzu engine and a standard transmission, was tested at laden weight (90% GVW, 17,550lb) and at unladen weight (50% GVW, 9,750lb). The second, a Freightliner with a 7.2-liter Caterpillar engine and an automatic transmission, was tested only at 13,000lb (50% GVW). The test runs were performed using the West Virginia University (WVU) medium-duty chassis dynamometer, located in Riverside, CA. Vehicle inertia was mimicked using a flywheel set, and tire and wind drag were mimicked using an eddy current power absorber. The truck exhaust was ducted to a full-scale dilution tunnel, with HEPA filtered dilution air, and a flow rate of approximately 1,500scfm. Particulate matter (PM) mass was found gravimetrically, using filtration, while carbon dioxide (CO₂), carbon monoxide (CO), oxides of nitrogen (NO_X) and hydrocarbons (HC) were measured using research grade analyzers. Data were computed in units of g/cycle, g/mile, g/ahp-hr, g/gallon and g/minute, and were examined most carefully in units of g/mile. Preliminary runs showed that the GMC truck did deviate from the target trace when tested at laden weight, and the completed distance for the MHDT Lower Speed Transient mode varied from 0.906 to 0.954 miles. Laden data from the GMC truck demonstrated that emissions were repeatable for all three modes of the MHDT schedule. Averaged GMC truck results for all laden runs of the Lower Speed Transient mode were 8.99g/mile NO_X and 0.26g/mile PM results for the Higher Speed Transient mode were 6.50g/mile NO_X and 0.20g/mile PM and for the Cruise mode were 4.73g/mile NO_X and 0.09g/mile PM. Unladen data from the GMC truck also showed acceptable repeatability, with emissions of NO_X that were about 87% of the laden values. The Freightliner, with an automatic transmission, produced 16.39g/mile NO_X and 0.33g/mile PM on the Lower Speed Transient mode, 12.59g/mile NOX and 0.25g/mile PM on the Higher Speed Transient mode, 7.93g/mile NO_X and 0.14g/mile PM on the Cruise mode and 7.57g/mile NO_X and 0.19g/mile PM on the UDDS (Test D). when three runs of thee same mode were run back-to-back, the standard deviation of NO_X values for six sequences of runs were under 4% of the average for all three modes on both the manual transmission truck at laden test weight and the automatic transmission truck at unladen weight. CO₂ variation was under 4% as well, except in one instance. In two of the six sequences PM variability exceeded 10%. The researchers concluded that the MHDT was suitable for characterizing the emissions from trucks in future inventory research. Data also showed that emissions from a mode were unaffected by whichever mode was run previously.