Measurements of PM2.5 Mass and Species Emissions from Natural Gas-FiredReciprocating Internal Combustion Engines

摘要

Innovative particulate emission measurements were performedon three different natural gas-fired spark-ignited reciprocatinginternal combustion engines at a natural gas productionfacility:· A 4-stroke rich burn (4SRB) engine equipped withnon-selective catalytic reduction for emissionscontrol.· A 4-stroke lean burn (4SLB) engine with no emissioncontrols.· A 2-stroke lean burn (2SLB) engine equipped withprecombustion chambers for emissions control.Emission measurements were made in the exhaust ductdownstream of the engine and emissions controls systemsusing an innovative dilution sampling protocol and usingtraditional stationary source test methods with hot filters/icedimpingers. A compact dilution sampler design, intended to bepractical for routine stationary source stack emissionssampling, embodies the concept of dilution followed by agingdeveloped by others, but with faster mixing, shorter residencetime and lower sample flow rate. A broad suite of speciationmeasurements was applied to determine chemical and physicalcharacteristics of primary PM2.5 (particles smaller than 2.5micrometers in aerodynamic diameter) and PM2.5 precursoremissions. PM2.5 mass, ions, elements, organic carbon (OC)and elemental carbon (EC), particulate carbon and precursorspecies and ultrafine particle size distribution weredetermined. PM2.5 mass concentration measured by dilutionsampling is approximately half that measured by traditionalhot filter/iced impinger methods, although the difference is notsignificant at the 95 percent confidence level due to thevariability of the results. The results suggest potential forpositive bias in the organic condensable particulatemeasurement by iced impinger methods. Particulate speciation results from the dilution sampler show 80 to 90percent of PM2.5 emissions are accounted for by OC, withsmaller amounts of iron (Fe), silica (Si) and other inorganiccompounds, for the 4-stroke engines. OC accounted for 98percent of PM2.5 for the 2-stroke engine. Only a smallportion of the OC was accounted for by identified organicspecies, 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 organiccarbon is most likely due to semivolatile organic compounds(SVOC) other than PAH. Preliminary measurements ofultrafine particle size distribution show peak particle numberconcentrations in the diluted exhaust at 40 to 50 nanometers,and particles between 10 and 400 nanometers account for 7 to49 percent of total PM2.5 mass.