Characteristics Of Carbonaceous Particles Emitted From A Diesel Engine Fueled With Oxygenated Fuels

Diesel engines emit large amounts of gas and carbonaceous particle,and exhaust particle from diesel vehicles have become a major source of urban atmospheric PM_2.5.The development and promotion of oxygenated fuels such as diesel fuel blended with biodiesel and alcohol has a great potential in the field of diesel combustion with the increasing air pollution and energy crisis.The effects of oxygenated fuels on the distribution of particle size and organic carbon/elemental carbon?OC/EC?,as well as the emissions of polycyclic aromatic hydrocarbons/oxy-derivate PAHs/nitro-derivate PAHs?PAHs/OPAHs/NPAHs?of diesel fuel?D100?in blends either with 20%biodiesel?DB20?,or 50%biodiesel?DB50?,or 100%biodiesel?B100?,or 13%ethanol?E13?,or 20%n-butanol?NB20?,or 20%iso-butanol?IB20?,or 25%n-pentanol?P25?by volume in a 4-cylinder direct injection diesel engine were compared and analyzed under three different engine loads,respectively.Firstly,the experiment of effect of oxygenated fuels on the combustion characteristics and economy of diesel engine was conducted.It was shown that the maximum explosive pressure of diesel blended with biodiesel increased,the peak of heat release rate decreased slightly,while the ignition delay decreased comparing with China V diesel.The peak of cylinder pressure increased,while the heat release rate decreased slightly with the increase of the proportion of biodiesel.The brake specific fuel consumption?BSFC?of mixed fuel was higher than that of pure diesel,and the value inceased with the increase of diesel blending biodiesel.Compared with China V diesel,higher peak heat release rate,longer ignition delay and shorter combustion duration had been observed with the alcohol additions,the variations were more evident for higher alcohol blends?i.e.,NB20,IB20and P25?compared with lower alcohol blend?E13?,the peak heat release rate of IB20 was significantly higher than that of NB20 and P25 due to its lower cetane number,lower boiling point and more hydrocarbon branching of isobutanol.BSFC of mixed fuel was higher than that of China V diesel,and BSFC of IB20 was higher than E13,NB20 and P25.Secondaly,the effects of oxygenated fuels on gas and particulate emissions were studied by gas analyser,scanning mobility particle sizer?SMPS?and thermo-optical carbon analyzers.With the increase of biodiesel blending ratio,the emission of CO and NOx increased,while the HC emission decreased.Particle number emission decreased with the increase of biodiesel blending ratio,and the particle size distribution was shifted to the smaller particle size,which was more obvious at medium and high loads.EC specific emission of diesel-biodiesel blends was significantly lower than that of China V diesel,and the emission decreased with the increase of biodiesel blending ratio.Whereas the variation of OC emissions depended on engine load.The emission of CO and HC increased with the addition of alcohol,while the NOx emission maintained the same level.There was a significant difference in particle emissions although the oxygen contents of the four alcohol-diesel blends were at the same level.The order of EC emissions were E13>P25>NB20>IB20,which was identical to the order of particle number emissions.Thirdly,the effects of oxygenated fuels on the characteristics of diesel engine exhaust particulate PAHs,OPAHs and NPAHs were further analyzed by Gas Chromatography/MassSpectrometry?GC/MS?.The emission of low molecular weight PAHs decreased significantly with the increase of biodiesel belnding ratio under the same engine load.The total PAHs emissions were higher at low and high loads than those at medium load.Alcohol could significantly reduce PAHs emissions,especially at low and medium loads.E13 inhibited PAHs more strongly than those of higher alcohol blends for the four alcohol-diesel blends.The particulate OPAHs emission levels for bioblended fuels were comparable to those of PAHs,while NPAHs emission levels were one order lower than those of PAHs and OPAHs.The fractions of parent PAHs gradually decreased with increasing alcohol blending ratio,on the contrary,the corresponding OPAHs and NPAHs observably increased.