Effects Of Driving Conditions On Diesel Exhaust Particulates

摘要

Four driving conditions were examined to characterize how speeds and loads of a medium-duty diesel engine affect resultant diesel exhaust particulates (DEPs) in terms of number concentrations(≤400 nm),size distribution,persistent free radicals,elemental carbon (EC),and organic carbon (OC).At the medium engine load (60%),DEPs surged in number concentrations at around 40-70 nm,whereas DEPs from the full engine load (100%) showed a distinctive bimodal distribution with a large population of 30-50 nm and 100-400 nm.Under the full engine load,engine speeds insignificantly affected resultant DEP number concentrations.When the engine load decreased from 100% to the medium level (60%),DEPs of ultrafine size and 100-400 nm decreased at least 1.4 times (from 5.6×10~8 to 4×10~8 #/cm~3) and more than 3 times (from 2.7×10~8 to 0.8×10~8 #/cm~3),respectively.The same reduction in the engine load significantly decreased persistent free radicals in DEPs up to approximately 30 times (from 123×10~(16) to 4×10~(16) #spin/g).Decreasing the engine load from 100 to 60% also concurrently reduced both EC and OC in total DEPs around 2 times,from 27.3 to 13.9 mg/m~3,and from 17.6 to 9.2 mg/m~3,respectively.For DEPs smaller than 1 μm,under the full engine load,EC and OC consistently peaked at 170-330 nm under an engine speed of 1800 rpm or 94-170 nm under an engine speed of 3000 rpm,reflecting processes of nu-cleation,cluster-cluster agglomeration,and condensation.Decreasing the engine load from 100 to 60% reduced EC and OC in DEPs (smaller than 1μm) at least 3 times (0.6 to 0.2 mg/m~3) and 2 times (0.4 to 0.2 mg/m~3),respectively.Taken together,decreasing the full engine load to a medium (60%) level effectively reduced the number concentrations (≤400 nm),persistent free radicals,EC,and OC of total DEPs,as well as the concentration of EC and OC in ultrafine and accumulation-mode DEPs.