Performance evaluation of diesel particulate filters on heavy-duty vehicles

Abstract

Diesel particulate filters, or DPFs, are exhaust aftertreatment devices used to reduce exhaust emissions from diesel powered vehicles. Typical designs have a wall flow filter element downstream of an oxidation catalyst, which oxidizes a portion of the NO present in the exhaust stream to form NO 2. The resulting NO 2 aides in the combustion of the soot collected in the wall flow filter element allowing for the complete breakdown of the soot within typical diesel exhaust temperatures, thus limiting the required maintenance on the filter elements to the removal of non-combustible ash. Three aspects of DPF performance were investigated: cold start performance, filter durability, and general efficiencies. The cold start performance evaluation determined that the filter elements trapped particulate matter prior to the DPF light-off temperature being reached, however there was no significant impact on white smoke emissions at any temperature range. The DPF light-off temperature was determined to be between 330°F and 450°F for the Engelhard DPX and between 375°F and 450°F for the Johnson-Matthey CRT. The filter durability study showed a slight degeneration of DPF performance as age and accumulated mileage increased. However, a definitive DPF life span could not be determined due to inconsistencies in the data from one testing round to the next. In the general efficiencies evaluation, CO emissions were reduced by greater than 84% for both DPF styles tested. HC emissions were reduced by 76% with the Engelhard DPX and by 81% with the Johnson-Matthey CRT. PM emissions were reduced by 94% and 82% by the Engelhard DPX and the Johnson-Matthey CRT respectively. No significant changes were recorded for total NO X (NO + NO2) or CO 2 emissions. Virginia University (WVU), the Washington Metropolitan Area Transit Authority (WMATA), the Westchester County Transit Authority (WCTA), the New York City Department of Sanitation (NYCDOS), and Ralph's Grocery fleet in Riverside, California. Multiple driving schedules were utilized through out this testing. Most driving schedules were cycles or routes developed to simulate the duty cycle of a specific fleet, although some driving schedules were standard cycles, such as the Central Business District (CBD) cycle. Details pertaining to the test vehicles, the driving schedules, and experimental results are given in Chapter 4 of this thesis, Test Vehicles, Driving Schedules, and Results. Conclusions drawn from this data about the performance of diesel particulate filters are shown in Chapter 5-Conclusions.