On-road and laboratory evaluation of combustion aerosols—Part1: Summary of diesel engine results

The objective was to characterize diesel exhaust aerosols on road and to duplicate the results in the laboratory without altering the physical characteristics of the nuclei mode. On-road emissions from four, heavy-duty diesel truck engines were measured. The same engines were reevaluated in the manufacturers’ laboratories. For highway cruise and acceleration conditions, all engines produced bimodal size distributions with the nuclei mode ranging in size from 6 to 11 nm and the accumulation mode from 52 to 62 nm. On-road size distribution measurements nearly always showed a nuclei mode while laboratory measurements showed a nuclei mode under many, but not all conditions. Laboratory studies showed that nuclei mode particles consisted mainly of heavy hydrocarbons. More than 97% of the volume of 12 and 30 nm particles disappeared on heating to 400 °C. The volatility resembled that of C24–C32 n-alkanes implying a significant contribution from lubricating oil.     

Development of a novel simulated diesel particulate matter generator system

We introduce a simulated diesel particulate matter (DPM) generator which can resolve the disadvantages of conventional soot generators and be helpful in studying reduction mechanism of DPM in DPM reduction devices. Considering characteristics of DPM, the nucleation mode was reproduced with H₂SO₄ and benzene saturators, which can produce particles in the size range 15–30 nm. The accumulation mode, which consists of particles in the size range 70–100 nm, was reproduced with a carbon spark discharge generator and a benzene saturator. In our system, bimodal distributions, which commonly occur during the idling and light load operations of diesel vehicles, could be simulated at the laboratory scale by simply changing the flow rates of the carrier gas and of H₂SO₄. The accumulation mode, which is mainly generated at heavy engine loads without a diesel oxidation catalyst (DOC) and at light engine loads with a DOC, was also simulated by changing the applied voltage at a carbon spark discharge generator or the flow rates of the carrier gas containing the carbon particles. To evaluate the performance of the DPM generator, we measured the chemical components and morphology, and compared the size distributions of the emitted particles with them of real DPM under various engine operating conditions and sulphur contents of fuel.     

TEM study on volatility and potential presence of solid cores in nucleation mode particles from diesel powered passenger cars

Nucleation mode particles were investigated for their morphology using TEM and the presence or absence of solid cores was addressed. At cold start idle nucleation particles were observed in the exhaust of a diesel passenger car. These particles occurred with both low and high S fuel and were only partly volatile in a thermodenuder, which indicates that the composition was not sulfate and as derived from TEM/EDX (transmission electron microscopy/energy dispersive X-ray analysis) probably not ash. It could be high boiling hydrocarbons, or primary soot particles. With all fuels at warm idle no nucleation particles and only soot particles were observed in the SMPS and the TEM. With 3.0×10¹¹ s^?1 the total soot particle number during idle was much less than during driving, e.g. at 120 km h^?1 the emission rate was 6.7×10¹² s^?1.At high load and high S fuel 10–20 nm nucleation particles were observed by SMPS and TEM. A thermodenuder at 280 °C and TEM showed that all nucleation particles were volatile. EDX gave a weak S-signal only. Some nucleation particles contained smaller spots (1–3 nm) with a very high contrast, which might be due to heavy elements. However, under the electron beam of the TEM these spots disappeared and EDX analysis was not possible. With low S fuel at 120 km h^?1 only soot particles and no nucleation particles were observed.     

Influence of fuel ash composition on high temperature aerosol formation in fixed bed combustion of woody biomass pellets

In this work, the influence of fuel ash composition on high temperature aerosol formation during fixed bed combustion of woody biomass (two wood pellets and one bark pellets) were investigated experimentally in a laboratory reactor and theoretically through chemical equilibrium model calculations. For all fuels, the particle mass size distribution in the PM_2.5 region was bimodal, with one fine mode and one coarse mode. Early in the flame, the fine mode was dominated by particles from incomplete combustion and these particles were rapidly oxidised in the post flame zone. After the hot flame, the fine mode concentration and the particle diameter increases gradually when the temperature decreases due to condensation of vaporised inorganic matter, K, Na, S, Cl, and Zn. For two of the fuels also P could be found in the fine particles. The coarse mode consisted of carbon, refractory metals and considerable amount of alkali. Further, the initial fuel alkali concentration and the alkali to silicon ratio (K + Na)/Si influenced the amount of vaporised aerosol forming alkali matter. Finally, the present study shows that, combustion temperature and fuel ash composition is of major importance for the formation of high temperature aerosols in fixed bed combustion of woody biomass pellets.     

Macroporous rubber gels as reusable sorbents for the removal of oil from surface waters

Macroporous organogels were prepared by solution crosslinking various rubbers in benzene at ?18 °C. Butyl rubber (PIB), cis-polybutadiene (CBR) and styrene–butadiene rubber (SBR) were used as the rubber components, while sulfur monochloride was the crosslinker in the gel preparation. The organogel networks consist of large pores of 10¹–10² μm in size caused by the benzene crystals acting as a template during gelation. The networks formed by CBR and SBR showed an aligned porous structure consisting of regular pores, whereas those derived from PIB had irregular pores with a broad pore size distribution due to the phase separation of PIB chains at low temperatures. All organogels were very tough and could be completely compressed without any crack development. Sorption tests showed that the organogels were efficient at removing crude oil, gasoline, diesel, fuel oil and olive oil. The organogels are reusable once they are squeezed, leading to continuous sorption capacities of CBR or SBR gels for crude oil and olive oil of 33–38 g/g and 24–27 g/g, respectively. These sorption capacities are two to three times the capacity of the gels derived from PIB.     

Effect of atomization methods on the size and morphology of Gd0.1Ce0.9O2−δ powder synthesized by aerosol flame synthesis

Nano-sized gadolinium doped ceria (GDC) powders were successfully synthesized by aerosol flame deposition (AFD) with two different atomization methods; ultrasonic and electrostatic atomization. The effect of the atomization method on the size and morphology of GDC particles were investigated. It was observed that the diameter range of the GDC small primary particles synthesized by the ultrasonic atomization method was 10–50 nm while with the electrostatic method was 5–25 nm. In addition, the size of primary large particle found to be decreased from 200 nm to 50 nm with increasing electric field up to 15 kV. The GDC powder synthesized by the electrostatic atomization exhibited reduced crystallite size, particle size, and similar electrical conductivity compared to GDC powder synthesized by ultrasonic atomization. This work demonstrated the benefits of the electrostatic atomization for producing smaller-sized GDC nanopowders for the application in intermediate temperature solid oxide fuel cells.     

Abundance and size distribution of HULIS in ambient aerosols at a rural site in South China

HUmic-LIke Substances (HULIS) comprise a significant fraction of the water-soluble organic aerosol mass and influence the water uptake properties of aerosols in the atmosphere. In this work, the abundance and size distributions of HULIS in ambient aerosols were measured in a rural location in South China at a time with a visible presence of crop residue burning. PM_2.5 samples of fresh smoke from burning rice straw and sugar cane leaves were also collected and analyzed for HULIS and major aerosol constituents. HULIS were abundant in both ambient samples and in fresh biomass burning emissions, accounting for ～60% of the water-soluble organic carbon in the ambient aerosols and ～30% in the fresh biomass burning aerosols. In the particles in the range of 0.32–1.8 μm, the abundance of HULIS was 40–90% of the combined abundance of sulfate and ammonium, suggesting that HULIS should be considered when quantifying the role of sulfate aerosols serving as cloud condensation nuclei. The size distribution of HULIS was characterized by a dominant droplet mode with a mass median aerodynamic diameter (MMAD) in the range of 0.63–0.87 μm, accounting for 81% of the total HULIS mass, a minor condensation mode (12%, MMAD: 0.23–0.28 μm) and a coarse mode (7%, MMAD: 4.0–5.7 μm). The small amount of HULIS in the coarse mode indicated that soil-derived HULIS was a very minor source. On the basis of the size distribution characteristics, HULIS were postulated to have multiple sources, including secondary formation in cloud droplets, secondary formation through heterogeneous reactions or aerosol-phase reactions, and primary emissions from biomass burning.     

Aerosol synthesis of silicon nanoparticles with narrow size distribution—Part 1: Experimental investigations

A study on the feasibility of aerosol processing of nearly monodisperse silicon nanoparticles via pyrolysis of monosilane in a hot wall reactor is presented. For optimal conditions silicon nanoparticles with a geometric standard deviation of 1.06 were synthesized at a production rate of 0.7 g/h. The size of the particles could be precisely controlled in the range of 20–40 nm, whilst maintaining a geometric standard deviation in the range of 1.06–1.08, by proper choice of the governing parameters temperature, residence time and precursor concentration. The results show that narrow particle size distributions can only be obtained in the temperature range between 900 and 1100 °C, as long as both the initial silane concentration (1 mbar silane partial pressure) and the reactor total pressure are low (25 mbar). This regime for the production of narrow particle size distributions has not been identified in prior work on the thermal decomposition of silane. Narrowly distributed particles can be obtained under conditions where nucleation and particle growth are separated and the agglomeration rates are negligible.     

Aircraft-based operation of an aerosol mass spectrometer: Measurements of tropospheric aerosol composition

The Aerodyne quadrupole aerosol mass spectrometer was deployed on the Falcon twin jet research aircraft operated by Deutsches Zentrum für Luft- und Raumfahrt (DLR). This was the first deployment of an AMS in a jet aircraft. Aerosol mass concentration measurements in the troposphere up to altitudes of about 11 km were performed within two measurement flights on 12 and 14 May 2003 over southern Germany. Background aerosol data were gained up to 6 km, while aircraft exhaust aerosol was be sampled at higher altitudes on 14 May, indicating the presence of sulfuric acid and unburned hydrocarbons in the exhaust particles. The boundary layer aerosol on 12 May was found to be composed of 49% organics, 12% sulfate, 15% ammonium, and 24% nitrate by mass. The upper edge of the boundary layer was marked by a sharp decrease of nitrate and ammonium at an altitude of 3 km, while sulfate and organics decreased to a much lesser degree. On 14 May, the boundary layer aerosol was composed of 23% organics, 20% sulfate, 24% ammonium, and 33% nitrate by mass, and the boundary layer reached up to about 5000 m and had no sharp upper edge. The size distributions indicated internal mixtures of ammonium sulfate and –nitrate in the boundary layer, while the organics were externally mixed. Additionally, a smaller mode consisting only of ammonium sulfate, was detected. This bimodal structure of ammonium sulfate was also detected above the boundary layer in 6 km altitude on 14 May.     

Transesterification of soybean oil and analysis of bioproduct

Biodiesel produced by the transesterification reaction of soybean oil using potassium hydroxide (KOH) catalytic is a promising alternative fuel to diesel regarding the limited resources of fossil fuel and the environmental concerns. In order to decrease the operational temperature and increase the conversion efficiency of methanol, a novel idea was presented in which a co-solvent dichloromethane was added to the reactants. The results showed that the yield of methyl ester was improved when dichloromethane was coexistence. The effects of the co-solvent, molar ratio of methanol/oil, reaction temperature, and catalyst on the biodiesel conversion were investigated. With the optimal reaction temperature of 45 °C, methanol to oil ratio of 4.5:1, co-solvent dichloromethane of 4.0%, a 96% yield of methyl esters was observed in 2.0 h at the condition with 1.0 wt.% potassium hydroxide. The characterization and analysis of biodiesel were obtained by FT-IR, gas chromatograph and inductively coupled plasma atomic emission (ICP–OES) spectroscopy methods. The cetane number, flash point, cold filter plugging point, acid number, water content, ash content and total glycerol content were investigated.     

Determination of the ratio of diffusion charging-based surface area to geometric surface area for spherical particles in the size range of 100–900 nm

Diffusion charging-based surface area for spherical particles was measured and compared with geometric surface area in the submicrometer size ranging from 100 to 900 nm. Spherical aerosol particles (polystyrene latex particles (PSL) and droplets of diethylhexyl sebacate (DEHS)) were generated by electrosprays for 100–600 nm particles and by a condensation generator for 700–900 nm particles. Two commercially available diffusion chargers (DCs) (DC2000CE, Ecochem, USA; LQ1-DC, Matter Engineering, Switzerland) were challenged with monodisperse uncharged spherical aerosols. Results showed that the surface areas measured by the two DCs were proportional to mobility diameter to power 1.22 and 1.38, respectively, in the size range from 100 to 900 nm. Comparison of the DC-based surface area with theoretical active surface area resulted in reasonable agreement within ±30%, indicating that the DCs underestimate geometric surface area of particles. The deviation of the DC-based surface area from the geometric surface area was quantitatively measured and was found to be up to 94% in the size range studied. Three types of aerosol particles were used to validate the correction of the DC deviation from the geometric surface area for particles larger than 100 nm based on the fit obtained for spherical particles in this study: spherical silver particles, carbon nanofibers, and titanium dioxide agglomerates. Comparison of the corrected DC-based surface area to Brunauer–Emmett–Teller (BET)-measured surface area indicated that the DC surface area reasonably agrees with the BET value for the particles tested except carbon nanofibers with 300 nm modal diameter.     

Filtration of fly ash using fluidized bed at 300–500 °C

The filtration of the coal-burning fly ash using fluidized beds with silica sand of 770 μm under temperatures of 36, 300, 400, and 500 °C was studied. The variations of the outlet concentration and particle size distribution (PSD) with time were measured to evaluate the dynamic characteristics of the process. Experimental results showed that the overall collection efficiency decayed with the operation time, revealed the effect of the elutriation of fly ash on particle filtration. The collection efficiency rose when the temperature increased from 36 °C to 500 °C. The strong attrition at high temperature released more small particles than that at room temperature, increased the concentration of the particles less than 10 μm (PM₁₀) at high temperature. The removal efficiency of the particles in a size of 4–7 μm, not the submicron particles, is the lowest because they are most easily elutriated from fluidized beds.     

Coal–oil–water multiphase fuel: Rheological behavior and prediction of optimum particle size

As the coal–oil–water slurry is gaining importance in place of fuel oil, a better understanding of handling characteristics is in demand. Therefore, experimental investigations have been carried out to investigate the rheological properties of coal–oil–water suspension containing coal particles of different sizes. Different coal stocks with average particle sizes of 108 μm, 75.7 μm and 62.9 μm have been used. The concentration of solid for the experiment varies from 10% to 50% by weight. All experiments have been carried out in a cup and bob type coaxial cylindrical viscometer. Newtonian, shear thinning and shear thickening behavior of suspension has been observed depending on component content and operating conditions. Study with different particle sizes shows that it is possible to achieve an optimum particle size for better handling of such suspension. A generalized correlation has been developed to predict the apparent viscosity of coal–oil–water suspension incorporating the coal concentration, oil concentration, torque and particle diameter. The experimental data are in well agreement with proposed correlation.     

Performance evaluation of long differential mobility analyzer (LDMA) in measurements of nanoparticles

Performance of a long differential mobility analyzer (LDMA) in measurements of nanoparticles was evaluated experimentally and numerically. In the evaluation of the LDMA measurements, silver particles in a size range of 5–30 nm were used under an increased flow rate. The numerical calculation method was used for calculating the particle trajectory in the LDMA, and the results were used for a comparison with Stolzenburg's transfer function. Using the CFD method, the flow around the aerosol inlet slit was analyzed, and the resulting particle mobility distribution was compared with that for an ideal flow. The resulting flow effect on the penetration efficiency caused by the inlet and exit slits were negligible when a well-designed system was used. The experimental measurements of mobility distributions were in good agreement with the theoretical prediction of particle size ranges over 10 nm, but some discrepancies were observed when particle size ranges were below 10 nm in size. The numerical calculation estimated the discrepancy found below the 10 nm particle size ranges.     

Relationships derived from physical properties of vegetable oil and biodiesel fuels

The aim of this study was to estimate mathematical relationships between higher heating value (HHV) and viscosity, density or flash point measurements of various biodiesel fuels. The HHV is an important property defining the energy content and thereby efficiency of fuels, such as vegetable oils and biodiesels. The biodiesels were characterized for their physical and main fuel properties including viscosity, density, flash point and higher heating value. The viscosities of biodiesels (2.8–5.1 mm²/s or cSt at 311 K) were much less than those of pure oils (23–53 mm²/s at 311 K), and their HHVs of approximately 41 MJ/kg were 10% less than those of petrodiesel fules (～46 MJ/kg). Compared to No. 2 diesel fuel, all of the vegetable oil methyl esters were slightly viscous. The density and flash point values of vegetable oil methyl esters are highly lower than those of vegetable oils. The HHVs of vegetable oils and their biodiesels were measured and correlated using linear least square regression analysis. There is high regression between viscosity and higher heating value for vegetable oil and biodiesel samples. An increase in density from 848 to 885 g/L for biodiesels increases the viscosity from 2.8 to 5.1 cSt and the increases are highly regular. There is high regression between density and viscosity values vegetable oil methyl esters. The relationships between viscosity and flash point for vegetable oil methyl esters are considerably regular.     

Study of fuel consumption when introducing DME or ethanol into diesel engine

An investigation of the effect of DME or ethanol on fuel consumption is conducted in a four-stroke, one-cylinder, direct-injection diesel engine. DME or ethanol is first heated to pyrolyze and then the resultant product gas is introduced into air intake. Brake Specific Fuel Consumption (BSFC) can be reduced a lot, when emulsified fuel (diesel fuel emulsified with water) is fueled to diesel engine and DME is heated to about 1000 K before its being introduced into air intake. Results show that BSFC can be decreased by about 10% and diesel fuel consumption can be decreased by 18%. High saving rate of BSFC up to 10% is also acquired using ethanol instead of DME. To achieve high saving rate of BSFC, the heating temperature of about 1000 K is needed for DME operation, while the diesel engine exhaust temperature of about 750 K is enough for pyrolyzing ethanol. Hydrogen produced in DME or ethanol pyrolysis is considered as the main reason for the excellent fuel saving. The technique adopted in the present work is extremely easy to utilize, and may be firstly adopted on diesel engines for power plants, trains, ships, etc.     

COAGULATION OF CIGARETTE SMOKE PARTICLES

Experimental measurements on the deposition of cigarette smoke particles (CSP) in the human airways have produced results that are inconsistent with typical deposition data based on particle size. Previous work relating to hygroscopic growth indicates that hygroscopicity alone can not account for this discrepancy. The present study investigates coagulation of CSP modeled as a polydisperse-charged aerosol as a possible explanation. The results of the model more accurately predict the experimental coagulation data for mainstream CSP than models that treat CSP as a monodisperse or polydisperse-uncharged aerosol. An aerosol with an initial charge distribution based on Boltzmann equilibrium yields slightly larger coagulation rates than the mainstream CSP polydisperse-charged model. The numerical results indicate that the size and charge distribution of sidestream CSP, with a concentration of 10⁶ particles cm^-3, remain stable. In 2 s, the size distribution of mainstream CSP, with a concentration of 10⁹ particles cm^-3, shifts to a larger size while becoming flatter and wider. The diameter of average mass increases from 0.29 to 0.5 μm. Numerical results confirm experimental reports for mainstream CSP, which indicate that the total number of charged particles increases with time and, in the early stages of coagulation, the amount of charge per particle cannot be estimated based on the particle size. This study shows that polydisperse-charged CSP, allowed to coagulate for 2 s in the mouth, will not produce size distributions that yield the observed deposition of CSP. However, additional coagulation will take place as the CSP travels through the respiratory tract, which will be investigated in future work.     

Dense CO2 antisolvent precipitation of levothyroxine sodium: A comparative study of GAS and ARISE techniques based on morphology and particle size distributions

Morphology and particle size distribution of levothyroxine sodium are experimentally investigated by comparing gas antisolvent (GAS) and atomized rapid injection for solvent extraction (ARISE) techniques using dense CO₂. Precipitation of levothyroxine sodium from ethanol was carried out at 25, 40 and 50 °C, with pressure in the 90–120 bar range and different concentrations of the organic solution. Particles produced by the GAS process are nanospheres whereas ARISE processed particles are either spherical or rod-like micro and nanoparticles. Particle size and size distributions of GAS processed levothyroxine sodium are in the 370–500 nm range, while the ARISE process produced particles in the 360–1200 nm range. In most cases, both techniques produced bimodal size distributions, due to particle agglomeration. The different morphological characteristics and particle size distributions of levothyroxine sodium obtained using GAS and ARISE at different operating conditions can be useful depending on the type of drug formulation chosen, as well as the route of drug administration and delivery system.     

Penetration of freeway ultrafine particles into indoor environments

High concentrations of ultrafine particles have been reported to exist near major freeways. Many urban residences are located in close proximity to high-density roadways. Consequently, indoor environments near freeways may experience significant concentrations of outdoor ultrafine particles. Given that people spend over 80% of their time indoors, understanding transport of ultrafine particles from outdoor to indoor environments is important for assessing the impact of exposure to outdoor particulate matter on human health. Four two-bedroom apartments within 60 m from the center of the 405 Freeway in Los Angeles, CA were used for this study. Indoor and outdoor ultrafine particle size distributions in the size range of 6–220 nm were measured concurrently under different ventilation conditions without indoor aerosol generation sources. The size distributions of indoor aerosols showed less variability than the adjacent outdoor aerosols. Indoor to outdoor ratios for ultrafine particle number concentrations depended strongly on particle size. Indoor/outdoor (I/O) ratios also showed dependence on the nature of indoor ventilation mechanisms. Under infiltration conditions with air exchange rates ranging from 0.31 to 1.11  ${\mathrm{h}}^{-1}$, the highest I/O ratios (0.6–0.9) were usually found for larger ultrafine particles (70–100 nm), while the lowest I/O ratios (0.1–0.4) were observed for particulate matter of 10–20 nm. Data collected under infiltration conditions were fitted into a dynamic mass balance model. Size-specific penetration factors and deposition rates were determined for all studied residences. Results from this research have implications concerning personal exposure to freeway-related ultrafine particles and possible associated health consequences.     

Experimental study on particulate emission of a diesel engine fueled with blended ethanol–dodecanol–diesel

Experiments were conducted on a 4-cylinder direct-injection diesel engine which has a compressing ratio of 19, using ultra low sulfur diesel blended with ethanol using 1–1.5% by volume of 1-dodecanol as the solvent to investigate the particulate emissions of the engine under five engine loads and at engine speeds of 1800 and 2400 rev/min. Blended fuels containing 6.1%, 12.2%, 18.2% and 24.2% by volume of ethanol, corresponding to 2%, 4%, 6% and 8% by mass of oxygen in the blended fuel, were used. At both engine speeds, with an increase in ethanol in the fuel, the smoke opacity, the particulate mass concentration and the total number of nano-size particles are all reduced. A diesel oxidation catalyst (Finnkat) was used and found to further reduce particulate emission. The smoke opacity, the particulate mass concentration and the total number concentration at 2400 rev/min are higher than those at 1800 rev/min.