Study On Characteristics Of Ultrafine Particles Emitted From Compression Ignition Engines And Its Pollution Features In Real World

With the rapid increase of the vehicle population in China, the vehicle emission pollution have been becoming as the major pollution source in the urban atmosphere. Many toxicological studies reported that ultrafine particles (Dp<100 nm) contain considerable trace amounts of toxic substances and organic pollutants, which can penetrate deep into the lung and enter interstitial tissues, causing severe respiratory inflammation and acute pulmonary toxicity. Therefore, the ultrafine particles from vehicle have attracted extensive attention.The aim of this study is to evaluate the effects of engine factors on ultrafine particles from engines and atmospheric factors on dispersion of ultrafine particles during exhuast dilution. Using a single-stage dilution tunnel and SMPS particle size analyse instrument, author conducted engine rig test, roadside measurement and CFD simulation.Effect of oxygen content of fuel on the exhuast particle number concentration and size distribution was studied. The results indicate that, with the increase of oxygen content of fuel, number concentration in the accumulation mode decreases obviously, number concentration in the nucleation mode increases significantly. Meanwhile, with the increase of oxygen content of fuel, number concentration of total particles (10~487nm) increases, mass concentration of total particles decreases obviously. Also, with the increase of oxygen content of fuel, the mass content of DS decreases significantly. However, the mass contents of SOF and ester increase evidently with oxygen content of oxygenated diesel.Number size distributions (NSDs, 10-487nm) and composition of nanoparticle emitted from an engine fuelled with ordinary diesel (OD) and low sulfur diesel (LSD) fuel were comparatively studied. The results indicate that, compared with the OD, the LSD is found to slightly reduce the mass concentration, and significantly reduce the number concentration of the total particles (10-487 nm), and the reduction of number increases with the speed and load of engine. Under the same engine conditions, the nucleation mode for LSD fuel is significantly lower than those of ordinary diesel. However, the accumulation mode for the two fuels shows little difference. The elements composition of exhaust particles include C, O, Cl, S, Si, Ca, Na, Al and K. The S element is not detected in LSD fuel case. The main components of soluble organic fraction (SOF) of exhaust particles for the two fuels include saturated alkane (C15-C26), ester and polycyclic aromatic hydrocarbons (PAHs). However PAHs are not found in LSD fuel case.Effects of fuel supply advance angle , injection pressure , and simulated exhaust gas recirculation (EGR) on NSDs of exhaust particles emitted from a DI diesel engine were experimentally investigated. The results show that increase fuel supply advance angle slightly reduces the total exhasust particle. Increasing injection pressure is found to reduce the accumulation mode particle number and favour the formation of nucleation mode particles. With the increase of CO2 concention of the engine intake manifold, number concentration in the accumulation mode increases, but number concentration in the nucleation mode decreases evidently.Effect of combustion modes (including compression ignition direct injection (CIDI), homogeneous charge compression ignition (HCCI) and compound charge compression ignition combustion (CCCI)) on NSDs of exhaust particles from engines fuelled with n-heptane and dimethyl ether (DME) was studied. The results indicate that the structure of NSDs for n-heptane changes with rp obviously. Accumulation mode dominantes in CIDI case. With the increase of premixed ratio(rp), the accumulation mode decreases, the nucleation mode increases significantly. In HCCI case, nucleation mode occupies the dominant part of the total particles, and the number concentration of accumulation mode is very low. And the total exhaust particles number concentrations for CCCI and HCCI are obviously higher than those of CIDI. In addition, the number concentration of nucleation mode is highly correlation with HC concentrations. The results of combustion mode study for DME indicate that the structure of NSDs for DME shows less change with rp at all test engine conditions. In all cases, nucleation mode occupies the dominant part of the total particles, and the number concentration of accumulation mode is very low. Under the same engine condition, the total exhaust particles number concentrations for CCCI are slightly lower than those of HCCI, but higher than those of CIDI significantly. The number concentrations of nucleation mode particles and total particles have a significantly positive correlation with HC concentrations.Field measurements of particle number and mass concentrations, CO concentration, and PM1 mass concentration were performed at 3 typical roads in Shanghai at daytime of 7:30~19:30. Mean diurnal variations show that the ultrafine particles concentrations, PM1 and CO concentrations change obviously with traffic situation. The total number and mass concentrations of particles increase with the traffic volume. Also, the mean particles concentrations in morning rush hour are evindently higher than those of afternoon rush hour for three cases. The CO average concentration and PM1 average concentration are highly correlation with total particle number average concentration (Ntotal). Moreover, the mean emission factor per vehicle was calculated, which is about 4.52×1014~8.50×1014 particles Km-1Vehicle-1.Transverse distribution characteristic of ultrafine particles at the downwind of a major road (Highway A4)were investigated. CFD numerical simulation coupling with the wind direction frequency weighted (WDFW) method was carried out based on the actual conditions. The results indicate that the peak concentrations of NSDs and MSDs decrease significantly with the increase of the distance. However, the diameters of peak concentration are in the same range. For NSDs, the peak concentration and the diameters of peak concentration of accumulation mode show less change. Meantime, it is found that the mean diameter of NSDs increases with the increase of the distance. The mean diameter for NSDs at 106m sampling site is 12nm larger than that of 17m sampling site. The CO average concentration is highly correlation with Ntotal(R2=0.78). From the results of CFD simulation, it was concluded that the decay rates of Ntotal and M total in field measurement case are larger than those of simulation case. And the number concentration decay mainly reflect the dacay of nucleation mode. The decay rates of simulated result and experimetal data can be described by a power function.