Innovative particulate emission measurements were performed on three different natural gas-fired spark-ignited reciprocating internal combustion engines at a natural gas production facility:

  • A 4-stroke rich burn (4SRB) engine equipped with non-selective catalytic reduction for emissions control.

  • A 4-stroke lean burn (4SLB) engine with no emission controls.

  • A 2-stroke lean burn (2SLB) engine equipped with precombustion chambers for emissions control.

Emission measurements were made in the exhaust duct downstream of the engine and emissions controls systems using an innovative dilution sampling protocol and using traditional stationary source test methods with hot filters/iced impingers. A compact dilution sampler design, intended to be practical for routine stationary source stack emissions sampling, embodies the concept of dilution followed by aging developed by others, but with faster mixing, shorter residence time and lower sample flow rate. A broad suite of speciation measurements was applied to determine chemical and physical characteristics of primary PM2.5 (particles smaller than 2.5 micrometers in aerodynamic diameter) and PM2.5 precursor emissions. PM2.5 mass, ions, elements, organic carbon (OC) and elemental carbon (EC), particulate carbon and precursor species and ultrafine particle size distribution were determined. PM2.5 mass concentration measured by dilution sampling is approximately half that measured by traditional hot filter/iced impinger methods, although the difference is not significant at the 95 percent confidence level due to the variability of the results. The results suggest potential for positive bias in the organic condensable particulate measurement by iced impinger methods. Particulate speciation results from the dilution sampler show 80 to 90 percent of PM2.5 emissions are accounted for by OC, with smaller amounts of iron (Fe), silica (Si) and other inorganic compounds, for the 4-stroke engines. OC accounted for 98 percent of PM2.5 for the 2-stroke engine. Only a small portion of the OC was accounted for by identified organic species, which is not surprising (e.g., Zheng et al., 2002; Schauer et al., 1996). Polycyclic aromatic hydrocarbon (PAH) measurements indicate more than 99 percent of the organic carbon is most likely due to semivolatile organic compounds (SVOC) other than PAH. Preliminary measurements of ultrafine particle size distribution show peak particle number concentrations in the diluted exhaust at 40 to 50 nanometers, and particles between 10 and 400 nanometers account for 7 to 49 percent of total PM2.5 mass.

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