Particle Emissions from a Small Two-Stroke Engine:Effects of Fuel,Lubricating Oil,and Exhaust Aftertreatment on Particle Characteristics

摘要

The effects of fuel and lubricating oil formulation and exhaust catalytic aftertreatment on physical and chemical characteristics of two-stroke engine exhaust particles were studied.The exhaust particles were produced with a professional chainsaw engine.The employed fuels were a 98-octane oxygenated,low-sulfur,low-aromatic reformulated gasoline,which served as a reference,and a 95-octane nonoxygenated alkylate gasoline that had no aro-matics and olefins.The applied lubricating oils were a semisyn-thetic mineral-based oil and a biodegradable ester-based oil.In total eight fuel-lubricating oil-catalyst combinations were studied.The test runs were conducted on a test bench and exhaust was diluted in a full-flow dilution tunnel.The size and number emissions of the exhaust particles were measured with a scanning mobility particle sizer (SMPS).The organic carbon (OC) and elemental carbon (EC) composition of the particles were analyzed with a thermal-optical transmission analyzer (TOT).In addition,the inorganic ion and metal composition of the particles were quantified,and the gaseous total hydrocarbon (THC),carbon monoxide (CO),and nitrogen oxide (NO_x) emissions were measured.The volatility characteristics of the exhaust particles were studied with a thermal desorption unit combined with the SMPS.The particle mass (PM) emissions ranged without catalyst from 2.9 to 3.4 g/kWh and with catalyst from 1.7 to 2.4 g/kWh,the catalytic converter thus reducing PM emissions by 19-50.Without catalyst the alkylate fuel-biodegradable oil combination gave the highest particle mass emissions,but with catalyst with the same fuel-oil mixture the emissions were the lowest.The count median diameter (CMD) of the particles ranged from 57 to 123 nm.Without catalyst,the alkylate fuel-biodegradable oil combination gave the lowest number emissions,but with catalyst with the same fuel-oil combination the emissions were the highest.The catalytic converter reduced the particle size by 22-56 nm,but it also increased the number emissions by a factor of 1.3-2.6.In thermal analysis 88-98 of the exhaust particle volume proved to be volatile,the solid fraction consisting of elemental carbon and metal residues.With the mineral-based lubricating oil,the metal residues appeared in two modes at the evaporation temperatures of 350degC and higher,while in the particles produced with the biodegradable oil the residues were unimodally distributed.