Development of a Solid Exhaust Particle Number Measurement System Using a Catalytic Stripper Technology 2011-01-0635

A solid particle number measurement system (SPNMS) was developed using a catalytic stripper (CS) technology instead of an evaporation tube (ET). The ET is used in commercially available systems, compliant with the Particle Measurement Program (PMP) protocol developed for European Union (EU) solid particle number regulations. The catalytic stripper consists of a small core of a diesel exhaust oxidation catalyst. The SPNMS/CS met all performance requirements under the PMP protocol. It showed a much better performance in removing large volatile tetracontane particles down to a size well below the PMP lower cut-size of 23 nm, compared to a SPNMS equipped with an ET instead of a CS. The SPNMS/CS also showed a similar performance to a commercially available system when used on a gasoline direct injection (GDI) engine exhaust.

While both the SPNMS/CS and the SPNMS/ET will likely perform similarly when used within the confinement of Euro 6/VI regulations, the SPNMS/CS has some advantages over an SPNMS/ET in its ability to evaporate and oxidize the volatile hydrocarbon materials instead of simply transferring them to the gas phase as done with the ET. Oxidizing the volatile hydrocarbon species promotes faster droplet evaporation and reduces any potential artifact particle formation downstream of the CS, as compared with the ET, during dilution and/or cooling. This performance characteristic may give the SPNMS/CS a wider flexibility for measuring solid particle number from various combustion sources with high volatile particulate matter, well beyond the current scope of regulatory requirements. Relative to the potential sulfuric acid formation downstream of the CS, we were able to demonstrate in previous work that sulfuric acid formation does not occur at the CS operating temperature of 300°C. In addition, using synthetic gas containing high concentration of SO₂ in air (~80 ppm), this CS showed high adsorption of SO₂ with no sign of SO₃ formation at its operating temperature of 300°C.