Investigation of Particle Reduction Efficiency of a Flow-Through Filter, 03-R8247
Inclusive Dates: 08/01/11 – 012/01/11
Background — Flow-through filters (FTF) can be a
cost-effective emissions control technology to reduce particulate matter (PM)
from diesel engine exhaust, though they have a lower reduction efficiency than a
typical, more expensive wall-flow diesel particulate filter (DPF). A FTF system
usually consists of an upstream diesel oxidation catalyst (DOC) and a downstream
FTF. The DOC has two main functions: 1) oxidize nitric oxide (NO) to nitrogen
dioxide (NO2), and 2) reduce the soluble organic fraction (SOF) of the PM. In
addition, the DOC can also effectively reduce carbon monoxide (CO) and
hydrocarbons (HC) emitted by the diesel engine. In the downstream FTF, the solid
portion of the PM, represented as elemental carbon (EC), is oxidized by NO2.
Therefore, the FTF system can reduce both SOF and EC. It was the intent of this
project to benchmark the PM and particle number (PN) reduction efficiency, and
the potential for soot blow-off, of a FTF system in order to determine FTF
viability for various emissions regulations.
Approach — A supplier-provided FTF system was instrumented for temperature and pressure measurements. Reduction efficiencies of NO, particulate mass, and PN were then measured over the World-Harmonized Steady-State Cycle (WHSC). Using this data, soot loading and blow-off cycles were developed from the WHSC operating modes. After triplicates of each pertinent emission species were sampled, the FTF was then loaded to approximately 3.0 and 5.0 g/L, respectively. A blow-off cycle was then performed each time to measure PM and PN efficiencies in this worst-case scenario.
Accomplishments — PM and PN reduction efficiencies over the WHSC were approximately 85.0 and 62.0 percent, respectively. The tailpipe PN emission over the WHSC cycle was estimated to be 3.76x1013 #/kW-hr. This result does not meet the EURO 5+/6 regulations of 6x1011 #/kW-hr. In addition, when the FTF was loaded with soot, maximum instantaneous PN emission during a harsh acceleration event was approximately 25 percent higher than the highest portion of the WHSC cycle on a clean FTF. The results indicate that as the FTF is loaded with soot, PN emissions increase. This behavior is the opposite of a properly functioning wall-flow DPF whose PM/PN emissions decrease with soot loading. Steps will have to be taken in-cylinder to lower engine-out PM/PN rates before a FTF can be a viable solution for sufficient PM/PN reduction to meet upcoming emission regulations.