PAH and other emissions from burning of JP-8 and diesel fuels in diffusion flames

Jet fuel JP-8 is of technical interest to the military aviation industry. JP-8 is now the single battlefield fuel for all US Army and Air Force equipment, replacing gasoline altogether and gradually replacing diesel fuel. Hence, emissions from the combustion of this fuel are the subject for this investigation. The emissions from the combustion of JP-8 fuel are examined and are compared to those from diesel fuel No. 2, burned under identical conditions. Combustion occurred inside a laboratory furnace in sooty diffusion flames, under adverse conditions that typically emit large amounts of products of incomplete combustion (PIC). Under such conditions, even compounds that otherwise might appear only in trace amounts were present in sufficient quantities for detection. The study reports on emissions of CO, light volatile organic compounds, semi-volatile organic compounds with an emphasis on polycyclic aromatic hydrocarbons (PAH), particulate emissions, oxides of nitrogen (NO_x) and oxides of sulfur (SO₂). Some PAH compounds are suspected of posing a threat to human health, benzo[a]pyrene being listed as a bio-accumulative toxin by the EPA. An afterburner was also used to examine the effects of longer furnace residence time. Results have demonstrated that PAH emissions from the combustion of diesel fuel were higher than those of JP-8, under most conditions examined. Moreover, as the temperature of the primary furnace was increased, in the range of 600–1000 °C, most of the emissions from both fuels increased. Particulate emissions were reduced by the afterburner, which was operated at 1000 °C, only when the primary furnace was operated at the lowest temperature (600 °C), but that condition increased the CO emissions. Overall, transient combustion of these two fuels, burning in laminar and sooty diffusion flames, did not reveal major differences in the emissions of the following PIC: C1–C4 light aliphatic hydrocarbons, PAH, CO and particulate matter.     

Examining the Relationship Between Black Carbon and Soot in Flames and Engine Exhaust

This article investigates the black carbon (BC) content of soot formed in premixed and diffusion flames and emitted by light duty gasoline and diesel vehicles. BC is measured photoacoustically and compared with particulate mass collected by filter and calculated from particle size distributions. The BC fraction of soot from rich premixed ethylene flames increases with height above the burner, but can remain well below unity in modestly sooting flames. The BC fraction produced by a propane diffusion flame soot generator (combustion aerosol standard, CAST) falls as the fuel is diluted with nitrogen, the principal means used to adjust the desired particle size. Thermally treating the soot to remove possible condensed semivolatile species does little to change these trends. Transmission electron microscopy (TEM) images show that despite low BC content, these particles display the characteristic fractal-like agglomerate morphology of soot. Particle mass spectra reveal polycyclic aromatic hydrocarbon (PAH) and fullerene fragments associated with low BC soot, which disappear as the BC fraction approaches unity. The results suggest that low BC content reflects immature solid soot that has not carbonized. Particulate matter (PM) measurements from current technology diesel and gasoline vehicles exhibit a high, >80% BC fraction. This is attributed to effective soot carbonization during the expansion and exhaust strokes of the engine, and to the substantial reductions of condensable hydrocarbons by catalytic aftertreatment. These results are discussed with respect to using light absorption-based instruments to monitor engine exhaust PM and using flame-generated soot for PM instrument calibration.     

乙苯脱氢催化剂焙烧工艺的改进

以乙苯脱氢制苯乙烯催化剂为研究对象,对采用连续式回转炉和马弗炉焙烧的催化剂分别进行了物性分析和活性评价。结果表明,采用回转炉焙烧的催化剂样品在外观、强度、比表面积、孔容、孔径、晶粒形貌和催化活性等均优于马弗炉焙烧的催化剂,可用连续式回转炉代替马弗炉。     

Polycyclic aromatic hydrocarbons (PAHs) in soot produced by combustion of polystyrene,polypropylene, and wood

The smoke and soot produced by the combustion of plastics or wood in a domestic stove or fireplace contain many poisonous compounds, including the polycyclic aromatic hydrocarbons (PAHs), many of which are carcinogenic. PAHs were selected as the subject of our study to gain a better sense of the hazards of burning plastics. Small samples of polystyrene, polypropylene, and wood underwent combustion in a tubular oven at 700°C; in addition, polystyrene and wood were combusted at room temperature. After their extraction and purification, the PAHs were analyzed by gas chromatography and mass spectrometry. Conditions in the hot oven promoted soot production, whereas combustion at room temperature led to somewhat more complete combustion. The PAH profiles of the examined materials resembled each other to some extent, though the original chemical structure of the polymeric materials varied a great deal. However, clear differences between the materials could be detected from the soot extracts, the soot of polystyrene being especially rich in compounds containing remnants of the polymer structure. Carcinogenic activity caused by the PAHs can be assumed to be of the same order of magnitude as soot from the combustion of wood.     

Combustion synthesis of fullerenes and fullerenic nanostructures

Samples of condensable material collected from low-pressure premixed and diffusion benzene/oxygen/argon flames were analyzed chemically to determine fullerene yield and by high-resolution transmission electron microscopy to characterize the fullerenic material on and within the soot particles. Results show that fullerene formation is sensitive to changes in operating conditions, such as fuel/oxygen ratio, chamber pressure, and inert gas dilution, and that the formation of amorphous and fullerenic carbon occurs early in the flame, with the structures becoming more curved with greater residence time. All flames exhibit a fullerene maximum with the premixed flame showing two distinct regions of formation. Additionally, the fullerene maximum in the diffusion flames is always just above the stoichiometric flame surface and a maximum is observed with increasing dilution due to competing dilution effects. Image analysis data show that the curvatures and diameters of the structures are consistent with the chemical analysis and that nanostructures, found at greater residence times than fullerenes, are formed directly from curved structures in the soot. These data complement previous fullerene studies and shed light on several proposed mechanisms for fullerene formation in combustion.     

Characterization of a new miniCAST with diffusion flame and premixed flame options: Generation of particles with high EC content in the size range 30 nm to 200 nm

Flame-generated soot from miniCAST burners is increasingly being used in academia and industry as engine exhaust soot surrogate for atmospheric studies and instrument calibration. Previous studies have found that elemental carbon (EC) content of miniCAST soot is proportional to the mean particle size. Here, the characterization of a prototype miniCAST generator (5201 Type BC), which was designed to decouple the soot composition from the particle size and produce soot particles with high EC and BC content in a large size range, is reported. This prototype may operate either in a diffusion-flame or a partially premixed-flame mode, an option that was not available in former models. It was confirmed that soot properties, such as EC content and Ångström absorption exponent (AAE), were linked to the overall flame composition. In particular, combustion under fuel-rich conditions provided particles with size coupled to the EC fraction and AAE, i.e. smaller particles exhibited a lower EC fraction and higher AAE. In contrast, with fuel-lean diffusion flames and especially with premixed flames under near overall stoichiometric conditions small particles (down to 30?nm) with high EC/TC ratios (>60%) and low AAE (≈1.4) could be generated even without any thermal after-treatment. This new source might thus serve in the future as a useful surrogate for engine exhaust emissions and help to improve calibration procedures of common aerosol instruments.

Copyright © 2018 The Author(s). Published with license by Taylor & Francis Group, LLC     

Growth characteristics of polycyclic aromatic hydrocarbons in dimethyl ether diffusion flame

The growth characteristics of polycyclic aromatic hydrocarbons (PAHs) in laminar dimethyl ether (DME) diffusion flame were investigated experimentally, and we assumed that the growth of PAHs within the flame was predominantly due to methyl addition/cyclization (MAC) mechanism. Methane and propane laminar diffusion flames were also investigated for comparison, and their PAHs growth characteristics had been explained by reactions concerning acetylene and propargyl radical. Laser-induced fluorescence (LIF) and laser-induced incandescence (LII) techniques were used to measure the relative concentration of soot and PAHs, respectively. Two-dimensional images of the OH-LIF, PAHs-LIF, and LII from soot were measured in the test flames. Furthermore, to investigate the growth characteristics of the PAHs in the flames, the fluorescence spectra of the PAHs were measured at several heights in the flames, using a spectrograph. The molecular size of the PAHs was estimated based on an emission wavelength region of the PAHs-LIF that varied along with the PAH size. The results show that although the PAHs were widely distributed within the unburned region similar to that of the methane and propane flames, the intensity and detection region of LII were much smaller than that of the methane and propane flames. The PAHs-LIF spectra indicated that the growth of the PAHs within the DME flame was much slower than the methane and propane flames, and thus a large number of small PAHs were discharged into the OH region distributed around the outer edge of the flame.     

Identification of large polycyclic aromatic hydrocarbons in carbon particulates formed in a fuel-rich premixed ethylene flame

Large polycyclic aromatic hydrocarbons were identified in carbon particulate sampled in a fuel-rich premixed ethylene flame. The particulate was extracted with dichloromethane (DCM) in order to separate the soluble organic species (DCM-extract) from the solid carbon (soot). After DCM extraction soot was re-extracted with N-methyl pyrrolidone (NMP) obtaining the NMP-extract. Both the DCM-extract and NMP-extract were further fractionated by size exclusion chromatography in selected molecular weight (MW) ranges. Large polycyclic aromatic hydrocarbons obtained by regular incorporation of C₂ and/or C₂H₂ unit (24/26 rule) occurring in both odd and even series of carbon atom number of polycyclic aromatic hydrocarbons, were identified by laser desorption ionization–mass spectrometry (LDI–MS) analysis of the lighter MW fractions of both the DCM-extract and NMP-extract (100–400 u MW of the DCM-extract and 200–600 u fractions of the NMP-extract). The LDI–MS spectra of the heaviest MW fractions of DCM-extract and NMP-extract (600–2000 u and 600–5000 u fraction) showed a continuous spectrum of masses typical of polymeric structures. The UV–visible absorption and emission spectral analysis corroborated the assignment of lighter and of heavier fractions of DCM-extract and NMP-extract to PAH and to polymeric aromatic structures, respectively.     

不同石化燃料燃烧烟尘的来源辨识

利用固相微萃取-气质联用(SPME-GC-MS)技术,对汽油、柴油、聚苯乙烯、ABS 4种石化燃料进行燃烧烟尘的特征组分分析,对其特征组分谱图中的保留时间进行归纳总结.对获得的20×35的数学矩阵,进行了主成分分析,得到了3个主成分,其累计率达到了92％,表明主成分所组成的二维数学坐标以及三维坐标系能较好地将不同比例的...     

Experimental and artificial neural network modeling study on soot formation in premixed hydrocarbon flames

The formation of soot in premixed flames of methane, ethane, propane, and butane was studied at three different equivalence ratios. Soot particle sizes, number densities, and volume fractions were determined using classical light scattering measurement techniques. The experimental data revealed that the soot properties were sensitive to the fuel type and combustion parameter equivalence ratio. Increase in equivalence ratio increased the amount of soot formed for each fuel. In addition, methane flames showed larger particle diameters at higher distances above the burner surface and propane, ethane, and butane flames came after the methane flames, respectively. Three-layer, feed-forward type artificial neural networks having seven input neurons, one output neuron, and five hidden neurons for soot particle diameter predictions and seven hidden neurons for volume fraction predictions were used to model the soot properties. The network could not be trained and tested with sufficient accuracy to predict the number density due to a large data range and greater uncertainty in determination of this parameter. The number of complete data set used in the model was 156. There was a good agreement between the experimental and predicted values, and neural networks performed better when predicting output parameters (i.e. soot particle diameters and volume fractions) within the limits of the training data.     

Effect of ethanol on the chemistry of formation of precursors of polyaromatic hydrocarbons in a fuel-rich ethylene flame at atmospheric pressure

The effect of the addition of ethanol (EtOH) to the initial combustible mixture on the concentration of various compounds, in particular, those preceding the formation of polyaromatic hydrocarbons in a fuel-rich (equivalence ratio of fuel ? = 1.7) flat premixed ethylene/oxygen/argon flame at atmospheric pressure was studied experimentally and by numerical modeling using a detailed mechanism of chemical reactions. Concentrations of various stable and labile species, including reactants, major combustion products, and intermediates in C₂H₄/O₂/Ar and C₂H₄/EtOH/O₂/Ar flames were measured along the height above the burner using molecular beam mass spectrometry. Experimental mole fraction profiles were compared with those calculated using the previously proposed mechanisms of chemical reactions. This mechanism was analyzed to determine the cause of the ethanol effect on the flame concentration of propargyl, the main precursor of polyaromatic hydrocarbons.     

Laser and Probe Diagnostics in Fundamental Combustion Research

Combustion diagnostics using lasers has matured considerably during the last decade. By now, lasers are routinely relied upon in many practical applications where direct inspection of the combustion process is necessary. Quantitative information, however, may still be a major challenge. In this article, some essential features of laser techniques for fundamental combustion research are discussed in view of their potential and limitations. Laser methods are complemented by molecular beam mass spectrometry. Applications include diagnostics in laminar and turbulent diffusion flames, in fuel-rich and sooting flames, and in combustion chemical vapor deposition (CVD) of thin diamond films. Avenues for further research will be discussed.     

Soot Formation in Combustion Processes (Review)

A review is given of recent papers on the phenomenology, kinetics, and mechanism of soot formation in hydrocarbon combustion; the effects of various factors on the formation of polycyclic aromatic hydrocarbons, fullerenes, and soot, low-temperature soot formation in cool flames, combustion in electric field, and the paramagnetism of soot particles from an ecological viewpoint are considered. __________ Translated from Fizika Goreniya i Vzryva, Vol. 41, No. 6, pp. 137–156, November–December, 2005.     

Formation of flame ions, clusters, nanotubes, and soot in hydrocarbon flames

The actual work deals with the present state of research on flame ions, polyaromatic hydrocarbons, nanotubes, fullerenes, and soot particles in premixed flames. Experimental arrangements for detection and quantitative investigation of flame ions are presented. In addition, the influence of ions on flame chemistry and on formation of carbon particles under non-sooting and sooting conditions is discussed. The study also focuses on the formation pathway from flat polyatomic hydrocarbons to fullerenes, nanotubes, and soot particles. In this connection, the features of arched “aromers,” which are high reactive metastable species and leading candidates for soot precursors and fullerene formation, are reported. These aromers seem to be a kind of “switch” capable of producing either fullerenes or soot particles, depending on the reaction conditions. At lower flame temperatures and a high number density of small unsaturated hydrocarbons, bimolecular reactions are favored, and the formation of soot particles exceeds that of fullerenes. It is also shown how the further growth of soot particles can be described, namely, by soot mass growth and by coagulation processes in strong sooting flames. Typical values for soot volume fractions and particle diameters under various reaction conditions are given. __________ Translated from Fizika Goreniya i Vzryva, Vol. 42, No. 6, pp. 82–88, November–December, 2006.     

电场控制火焰中细颗粒生成及分布的研究进展

以碳黑为主的燃烧源可吸入颗粒物的形成与控制是关系地球环境及人类健康的重要问题.目前对该课题的研究主要集中在颗粒生成后的控制方法上,而对如何在燃烧源内部控制颗粒物的生成尚处在初步探索阶段.介绍了电场对火焰中细颗粒控制的影响因素,对国内外研究现状进行了评述,并从生成、团聚和污染物协同控制三个方面总结了以往实验研究的成果.研究表明,在电场作用下,碳黑颗粒的质量浓度最高可减小90%;而在电场和催化金属的作用下,则可生成结构紧凑的碳纳米管束.最后提出了进一步研究的重点和方向.     

Online Characterization of Syngas Particulates Using Aerosol Mass Spectrometry in Entrained-Flow Biomass Gasification

Entrained flow gasification is a promising technique where biomass is converted to a synthesis gas (syngas) under fuel-rich conditions. In contrast to combustion, where the fuel is converted to heat, CO₂, and H₂O, the syngas from gasification is rich in energetic gases such as CO and H₂. These compounds (CO and H₂) represent the building blocks for further catalytic synthesis to chemicals or biofuels. Impurities in the syngas, such as particulates, need to be reduced to different levels depending on the syngas application. The objective of this work was to evaluate the amount of particulates; the particle size distribution and the particle composition from entrained flow gasification of pine stem wood at different operating conditions of the gasifier. For this purpose, online time resolved measurements were performed with a soot particle aerosol mass spectrometer (SP-AMS) and a scanning mobility particle sizer (SMPS). The main advantage of SP-AMS compared to other techniques is that the particle composition (soot, PAH, organics, and ash forming elements) can be obtained with high time resolution and thus studied as a direct effect of the gasifier-operating conditions. The results suggest that syngas particulates were essentially composed of soot at these tested process temperatures in the reactor (1200–1400°C). Furthermore, the AMS analysis showed a clear correlation between the amounts of polycyclic aromatic hydrocarbons (PAH) and soot in the raw syngas. Minimization of soot and PAH yields from entrained flow gasification of wood proved to be possible by further increasing the O₂ addition.

Copyright 2014 American Association for Aerosol Research     

Effects of oxygenate concentration on species mole fractions in premixed n-heptane flames

Atmospheric pressure, laminar, premixed, fuel-rich flames of n-heptane/oxygen/argon and n-heptane/oxygenate/oxygen/argon were studied at an equivalence ratio of 1.97 to determine the effects of oxygenate concentration on species mole fractions. The oxygen weight percents in n-heptane/oxygenate mixtures were 2.7 and 3.4. Three different fuel oxygenates (i.e. MTBE, methanol, and ethanol) were tested. A heated quartz micro-probe coupled to an on-line gas chromatography/mass spectrometry has been used to establish the identities and absolute concentrations of stable major, minor, and trace species by the direct analysis of samples, withdrawn from the flames. The oxygenate addition has increased the maximum flame temperatures and reduced the mole fractions of CO, low-molecular-weight hydrocarbons, aromatics, and polycyclic aromatic hydrocarbons. The reduction in mole fractions of aromatic and polycyclic aromatic hydrocarbon species by an increase in oxygenate concentration was more significant.     

The mechanism of the formation of soot and other pollutants during the co-firing of coal and pine wood in a fixed bed combustor

The co-firing of coal and biomass reduces the emission of pollutants by a mechanism which has been extensively studied but is still uncertain. Emissions were collected during the combustion in a fixed-bed furnace of Polish bituminous coal and pine wood, both individually and together, and it was observed that biomass produced less soot and burned at a lower temperature. Complementary analytical-scale combustion and pyrolysis experiments were carried out. The results of the analysis of emissions and reaction products, mainly by gas chromatography–mass spectrometry (GC–MS), but for large molecules by size exclusion chromatography (SEC), were interpreted so as to construct a reaction scheme for pollutant formation during co-firing. Evidence for three main routes to pollutant formation during co-combustion was adduced. Firstly, the presence of high MW material (from SEC) indicates escape of devolatilisation products round the outside of the flame. Secondly, the emission factors (ef) of PAH, alkyl-PAH, oxygen-containing PAH (O-PAC) and phenols are consistent with partial pyrolysis, while the high concentrations of the two-ring (naphthalenes and indene) PAH precursors evidently arise through radical reactions involving cyclopentadiene intermediates from phenols generated by pyrolysis of both coal and of biomass lignin. Thirdly, the concentrations of larger PAH are consistent with contributions from a hydrogen abstraction carbon addition (HACA) mechanism in which acetylene or butadiene formed in the flame are added to smaller PAH radicals. A kinetic model was applied to coal, biomass and coal/biomass co-combustion and highlighted the role of HACA in soot production during biomass combustion, but this route to soot was insufficient to model the higher yields of soot observed during coal combustion. In this latter case radical reactions involving either cyclopentadiene or condensation reactions of smaller PAH molecules initially formed in the pyrolysis stage to give ‘aromers’ are more important.     

内在矿物质对煤焦燃烧特性影响的动力学研究（Ⅰ）等温热重研究

选择宁夏地区2种烟煤和2种无烟煤作为实验煤样,用浮沉法得到灰分在30％左右的煤粉在马弗炉上900℃制焦,然后用化学脱灰法处理煤焦样,得到超低灰煤焦样。在WCT-2型热重分析仪上,在消除内、外扩散影响的条件下对高灰煤焦和脱灰煤焦进行等温热重实验。动力学分析的结果表明：2种烟煤焦脱灰后的活化能降低,2种无烟煤焦脱灰后的活化能升高;烟煤中的矿物质对烟煤的燃烧有阻碍作用,无烟煤中的矿物质对烟煤的燃烧有促进作用。     

Diesel soot combustion on potassium promoted hydrotalcite-based mixed oxide catalysts

KNO₃ or K₂CO₃ supported Mg–Al hydrotalcite-based mixed oxide catalysts were investigated for the catalytic combustion of diesel soot. The activity of the catalysts before and after reactions with soot was conducted under the flow of air and high purity He gas. It has been found that K shows a great promotion of the catalytic activity, and deactivation was not detected after the reaction with soot in a muffle furnace in a static air atmosphere. The active phases were examined by XRD. The high activity is found to be due to an interaction between K and Mg(Al), which may weaken the Mg(Al)–O bonds, thus facilitating the mobility of the O species.