Evaluation of the Oxidation Reactivity and Behavior of Exhaust Soot Particles from Diesel Engines with Different Emission Levels

The aim of this study was to investigate the oxidation reactivity and behavior of exhaust particulate matter(PM)from diesel engines.PM samples from two diesel engines(1K,CY4102)with different emission levels were collected by a thermophoretic system and a quartz filter.The oxidation reactivity,oxidation behaviors,and physicochemical properties of the PM samples were analyzed using thermogravimetric analysis(TGA),high-resolution transmission electron microscopy(HRTEM),Fourier-transform infrared spectrometry(FTIR),and Raman spectroscopy.The results showed that there was a great difference in the oxidation reactivity of soot particles emitted by the two different diesel engines.A qualitative analysis of the factors influencing oxidation reactivity showed that the nanostructure,degree of graphitization,and relative concentration of aliphatic C—H functional groups were the most important factors,whereas no significant correlation was found between the primary particle size and activation energy of the diesel soot.Based on the oxidation behavior analysis,the diesel soot particles exhibited both internal and surface oxidation modes during the oxidation process.Surface oxidation was dominant during the initial stage,and as oxidation progressed,the mode gradually changed to internal oxidation.Internal oxidation mode of soot particles from the 1K engine was significantly higher than that of CY4102.

Numerical Analysis on the Characteristics of Soot Particles in C2H4/CO2/O2/N2 Combustion

The purpose of this study is to investigate the characteristics of soot particles in C2H4/CO2/O2/N2 com- bustion at equivalence ratio of 3.0-5.0. As the oxidant is switched from conventional air to CO2/O2/N2 mixture, the key species C2H2, C3H3 responsible for formation of first aromatic ring, the apical aromatics and 4zring aromatics total production rate all decrease greatly. In addition, with CO2 mole fraction from 0.2 to 0.5 in the mixture, the soot particle number density, volume fraction, surface area density, which are three most important parameters to soot oarticle orooertv, are suooressed obviously. Furthermore, the increasing content of C02 in the oxidizer influences mostly H, OH radical concentrations by two reactins CO ＋ OH == CO2＋ H and H ＋ O2===O＋ OH, and the procluction rate ofvo reactions declined, which revealed that C02 in mixture has an inhibiting ef- fect on soot particle generation.

Soot particle distributions inside a diesel particulate filter during soot loading in plateau environment

A three-dimensional diesel particulate filter(DPF)simulation model was developed by using AVL software FIRE to study the effects of four factors on soot particle distributions along the axial and radial directions in the DPF after the model accuracy was validated.An orthogonal test method was used to determine the importance and weights of the design of experiments(DoE)factors such as the expanding angle,the number of channels per square inch,and the exhaust mass flow rate.The effects of these factors on the uniformity of the soot particle distributions were also analyzed.The results show that when the soot loading time was 400 s,the soot particles inside the DPF along the axial direction exhibited a bowl shape,which was high on the both ends and low in the middle.The uniformity of the axial distribution of soot particles reduces significantly with an increase in the number of channels per square inch.The uniformity of the radial distribution reduced with an increase in the expanding angle of the divergent tube.Based on the impacts on the axial uniformity,the three most influencing factors in a descending order are the number of channels per square inch,the exhaust mass flow rate,and the expanding angle of the divergent tube.

Variations in surface functional groups, carbon chemical state and graphitization degree during thermal deactivation of diesel soot particles

The thermal deactivation of diesel soot particles exerts a significant influence on the control strategy for the regeneration of diesel particulate filters(DPFs).This work focused on the changes in the surface functional groups,carbon chemical state,and graphitization degree during thermal treatment in an inert gas environment at intermediate temperatures of 600℃,800℃,and 1000℃ and explore the chemical species that were desorbed from the diesel soot surface during thermal treatment using a thermogravimetric analyser coupled with a gas-chromatograph mass spectrometer(TGA-GC/MS).The surface functional groups and carbon chemical statewere characterized using Fourier transform infrared spectroscopy(FT-IR)and X-ray photoelectron spectroscopy(XPS).The graphitization degree was evaluated by means of Raman spectroscopy(RS).The concentrations of aliphatic C–H,C–OH,C=O,and O–C=O groups are reduced for diesel soot and carbon black when increasing the thermal treatment temperature,while the sp^(2)/sp^(3) hybridized ratio and graphitization degree enhance.These results provide comprehensive evidence of the decreased reactivity of soot samples.Among oxygenated functional groups,the percentage reduction during thermal treatment is the largest for the O–C=O groups owing to its worst thermodynamic stability.TGA-GC/MS results show that the aliphatic and aromatic chains and oxygenated species would be desorbed from the soot surface during 1000℃ thermal treatment of diesel soot.

Comparison of light absorption and oxidative potential of biodiesel/diesel and chemicals/diesel blends soot particles

Soot particles,mainly coming from fuel combustion,affect climate forcing through absorbing light and also result in adverse human health outcomes.Though biodiesel or additives blending with diesel was considered environmentally friendly,the understanding on absorbing and oxidative capacity of soot emitted from them are still unclear.The watersoluble organic carbon(WSOC)content,surface chemical structure,light absorption and oxidative potential(OPDTT)of soot from biodiesel/diesel and chemicals/diesel blends were investigated utilizing total organic carbon analyzer,X-ray photoelectron spectrometer,ultraviolet–visible spectrophotometry and dithiothreitol(DTT)assay.The differences and correlations between soot properties were statistically analyzed.Chemicals/diesel blends soot owned significantly higher WSOC content,ratio of mass absorbing efficiency(MAE)in250 and 365 nm(E2/E3),OPDTT,and higher surface carbonyl content.Coconut biodiesel/diesel blends soot contained evidently higher aromatic carbon–oxygen single bond(ArC–O)content,and higher MAE365.The individual comparison of biodiesel/diesel blends showed20%coconut biodiesel blend owned the lowest WSOC,E2/E3 and OPDTT,while highest ArC–O and MAE365,representing strongest absorbing properties.Association analysis showed OPDTTwas significantly positively correlated with WSOC.Further,the evident negative correlation between MAE365 and OPDTT was observed.Our results showed coconut biodiesel/diesel blends soot induced lower levels of oxidative potential,whereas absorption of light was higher,which have far reaching consequences on climate forcing.Therefore,it is important to evaluate the balance point between light-absorbing properties and oxidative potential,under the wide use of biodiesel.

Effects of Magnetic Fields on Morphology and Nanostructure Evolution of Incipient Soot Particles from n-heptane/2,5-dimethylfuran Inverse Diffusion Flames

Differences of the morphology and nanostructure evolution of incipient soot particles generated in n-heptane/2,5-dimethylfuran(DMF)inverse diffusion flames(IDFs)with/without magnetic fields were investigated.Utilizing a high resolution transmission electron spectroscopy,the morphology and nanostructures of soot sampled from spatial locations at different heights in IDFs were analyzed.The graphitization and the oxidation reactivity of soot were tested by an X-ray diffraction and a thermogravimetric analyzer,respectively.Results demonstrated that the magnetic force on paramagnetic species,such as oxygen molecules,can modify the soot formation and oxidation.More incipient soot particles with larger diameters appeared in chains or branches or tufted forms on the flame wing region and the higher position than that on the flame centerline region and the lower position.With magnetic fields,greater amounts of clustered soot particles displayed more crowded distribution and larger diameters.Soot particles with typical structures of the core-shell were promoted to own more orderly bordered lamellae with longer fringe length and smaller fringe tortuosity by the magnetic force acting on oxygen at the same sample position.These modifications resulted in relatively larger diffraction angle of the peak,higher graphitization degree and slightly lower oxidation reactivity of soot.

SOOT PARTICLES ANALYSIS IN LAMINAR PREMIXED PROPANE/OXYGEN(C_(3)H_(8)/O_(2))FLAMES USING PUBLISHED MEASUREMENT DATA

A laminar premixed Propane/Air flame with a fuel equivalence ratio of 2.1 was employed for analysis of soot particles. Zeroth-order lognormal distributions (ZOLD) were used in the analysis of experimental distribution phe-nomena at different residence times during soot formation in the flame. Rayleigh抯 theory and Mie抯 scattering theory were combined with agglomerate analysis using scattering and extinction data to determine the following soot charac-teristics: agglomerate parameters, volumetric fractions, mass flow rates and surface growth rate. Soot density meas-urements were carried out to determine density variations at different stages of growth. The measured results show that for long residence times the soot clearly crystallizes with higher density (up to 1.8 g.cm-3). The increases of soot volu-metric fraction and mass flow rate indicate that the surface growth rate of soot particles exceeds the oxidation rates in the flame studied. The data obtained in this work would be used to study soot oxidation rate under flaming condition.

Soot reduction by addition of dimethyl carbonate in normal and inverse ethylene diffusion flames:Nanostructural evidence

Oxygenated fuel represents an attractive alternative as an additive for reducing soot emissions.Dimethyl carbonate（DMC） is an oxygenated compound which is a good option to reduce soot,but the detailed characteristics of soot produced from combustion of hydrocarbon fuels blended with DMC are still lacking. The present research studied the nanostructure and reactivity of soot particles in ethylene/DMC normal and inverse diffusion flames. High resolution transmission electron microscopy（HRTEM）, X-ray diffraction（XRD）, and thermogravimetric analysis（TGA）were used to analyze the nanostructure and reactivity of soot. It was found that DMC addition was effective in decreasing the average weights of soot formed in flames. The results of HRTEM images showed that soot particles obtained with DMC addition showed liquid-like material and tight bonding, and exhibited more highly disorganized layers, which give it higher reactivity than soot obtained without DMC addition. Furthermore, HRTEM was used to analyze soot fringe characteristics consisting of fringe tortuosity, fringe length, and fringe separation. XRD was used to crosscheck the results for fringe separation, and was consistent with HRTEM results. In addition, the mass loss curve of TGA experiments showed that DMC addition could enhance the reactivity of soot particles.

Optical properties of chain-like soot with water coatings

In a moist atmosphere,the ageing process of aerosol can make the agglomerated soot particles compact,and cause them to be covered by a water coating.Based on the cluster‒cluster aggregation(CCA)algorithm,the models of chain-like soot with water coatings(Models A to E)were generated in this study.The superposition T-matrix method was employed to calculate their optical properties at 337,550,860,and 1060 nm wavelengths,with a focus on the impact of the soot inclusion morphology and water coating.Our results indicate that for particles with a looser soot-inclusion structure,there is a larger difference in the scattering phase function between them and the corresponding particles with a spherical soot core.The largest relative difference reached 51.8%at 337 nm.Impacted by the size parameter,the extinction cross section(Cext),absorption cross section(Cabs),scattering cross section(Csca),and single scattering albedo(SSA)increased as the water coating radius(Rwater)increased and incidence wavelength decreased.The traditional assumption of a spherical soot core can cause the Cext,Cabs,and Csca to be overestimated,and cause the SSA to be underestimated when the incident wavelength is 337 nm.At 1060 nm,the assumption can cause the Cext,Cabs,and Csca to be underestimated,and lead the SSA to be overestimated.When the fractal dimension(Df)of chain-like soot inclusion increased from 1.8 to 2.6,the SSA of the particles with a Rwater of 0.20μm significantly decreased from 0.784 to 0.764 at 1060 nm.Moreover,the thickness of the water coating had a stronger effect on the particles with chain-like soot inclusion at 337 nm than that at 1060 nm.For the 337 nm wavelength,the difference between the Cext and Csca in Model B when Rwater=0.30 and 0.20μm was 0.588 and 0.587μm2,respectively.The differences were only 0.096 and 0.095μm2,respectively,for the 1060 nm wavelength.Based on the results calculated by the superposition T-matrix method,the ratios of P22(Θ)/P11(Θ)for chain-like soot with water coatings are not absolutely equal to 100%.When the Df value of aggregated soot inclusion is a constant,P22(Θ)/P11(Θ)decreased as the volume ratio of soot inclusion to the water droplet increased.Therefore,the ratio of P22(Θ)/P11(Θ)can be potentially used as an optical indicator to describe the morphology of non-spherical and/or inhomogeneous particles(or inclusion)for internal aerosol,fog,or cloud particles.Generally,although the thickness of the water coating,to a large extent,dominates the optical properties of the internal mixtures,the morphology of aggregated soot inclusion is a key factor for causing uncertainties in optical parameters.This is especially so when the volume ratio of the soot inclusion and water droplet is large,and the structure of the soot inclusion is loose.