Comparison of Heavy-Duty Truck Diesel Particulate Matter Measurement:TEOM and Traditional Filter 2005-01-2153
The Tapered Element Oscillating Microbalance (TEOM) measures captured particle mass continuously on a small filter held on an oscillating element. In addition to traditional filter-based particulate matter (PM) measurement, a TEOM was used to characterize PM from the dilute exhaust of trucks examined in two phases (Phase 1.5 and Phase 2) of the Coordinating Research Council (CRC) Heavy-Duty Vehicle Emissions Inventory Project E-55/E-59. Test schedules employed were the Heavy Heavy-Duty Diesel Truck (HHDDT) test schedule that consists of four modes (Idle, Creep, Transient and Cruise), the HHDDT Short (HHDDT_S) which represents high-speed freeway operation, and the Heavy-Duty Urban Dynamometer Driving Schedule (UDDS). TEOM results were on average 6% lower than those from traditional particulate filter weighing. Data (in units of g/cycle) were examined by plotting cycle-averaged TEOM mass against filter mass. Regression (R2) values for these plots were from 0.88 to 0.99. The TEOM/filter mass ratio varied most, and correlation was the worst, for the Idle and the HHDDT_S but it was steady for the UDDS, Creep, Transient, and Cruise cycles. In the case of Idle, poor correlation may be attributed to the variation in organic fraction of the PM between vehicles, coupled with differences in filter face temperatures between the TEOM and traditional filter. Slopes and intercepts varied only slightly between the UDDS, Creep, Transient, and Cruise, and between vehicle test weights. This implies that TEOM data may be used with some confidence to report PM mass from a portion of a test schedule, and that TEOM data can act as a check on, or early screen for, PM filter data when multiple runs are not performed. For the case of the HHDDT_S, it was found using TEOM data that the cruising section of the schedule had distance-specific PM emissions that were 10% lower than for the whole schedule. The acceleration and deceleration portions of the schedule had PM emissions that were 33% higher than for the whole schedule. In this way, modal behavior can be extracted. In previous research, when TEOM data were not available, the authors used continuous carbon monoxide (CO) data to proportion PM over a cycle. Although there was no overall (fleet) relationship between CO and PM integrated over the test schedule, data taken from a single truck executed through six different schedules showed a strong relationship between CO and PM. In this case, it is likely that higher CO production is in sympathy with higher elemental carbon production in the cylinder.