Laser microprobe analysis of soot precursor particles and carbonaceous soot

doi:10.1016/0010-2180(94)00047-V

Combustion and Flame

Volume 100, Issues 1–2, January 1995, Pages 301-309

https://doi.org/10.1016/0010-2180(94)00047-V Get rights and content

Abstract

Samples of soot precursor particles and carbonaceous soot from a nonsmoking ethene diffusion flame have been analyzed by means of laser microprobe mass spectrometry (LMMS). The mass spectra of soot precursor particles from the lower flame display many peaks in the 200–300-amu range that are characteristic of polycyclic aromatic hydrocarbons (PAHs). The most prominent of these are the masses 252, 276, and 300, which correspond to the isomers of C₂₀H₁₂, C₂₂H₁₂, and C₂₄H₁₂, respectively. These masses are among those predicted by Stein and Fahr to be the most thermodynamically stable (“stabilomers”) under typical hydrocarbon flame conditions, and they have been previously reported as components of soot collected from a variety of fuels and combustion configurations. Carbonaceous soot from the upper region of the flame yields mass spectra composed of carbon-hydrogen clusters, C_xH_y with x = 3 to 24 and y usually 0, 1 or 2. Smaller amounts of PAH-like species with masses in the 418 to 444 amu range are also found. These results suggest that the carbonization process observed in this flame is the dehydrogenation of the PAH species formed in the lower flame unaccompanied by polymeric growth. The LMMS technique provides a lower bound value of the hydrogen mole fraction X_H of 0.36 ( $C H = 1.8$ ) for precursor particles from the lower diffusion flame and 0.15 ( $C H = 5.6$ ) for carbonaceous soot aggregates.

References (38)

S.C. Graham
B.L. Wersborg et al.
A.J. Hurd et al.
J. Colloid Interface Sci.
(1988)
U.O. Köylü et al.
Combust. Flame
(1992)
R. Puri et al.
Combust. Flame
(1994)
R.J. Santoro et al.
Combust. Flame
(1983)
T. Mauney
Anal. Chim. Acta
(1987)
R.A. Dobbins et al.
R.A. Dobbins
A. D'Alesio et al.

A. D'Alesio et al.

C.W. Sweitzer et al.

Rubber World

(1954)

G. Prado et al.

Carbon

(1974)

G.S. Jackson et al.

R.A. Dobbins et al.

Langmuir

(1987)

C.M. Megaridis

C.M. Megaridis et al.

Combust. Sci. Technol.

(1989)

C.M. Megaridis et al.

Combust. Sci. Technol.

(1990)

C.M. Megaridis et al.

Cited by (161)

Soot particles formed by n-heptane and n-heptane/oxymethylene ether-3 in an inverse diffusion flame: A comparative analysis of chemical features
2024, Fuel
Oxymethylene ether-3 (OME₃) is a promising synthetic e-fuel and alternative fuel for diesel engines. In contrast to diesel fuel, the use of OME₃ leads to a distinct combustion process in which soot particles are generated, which leads to changes in the chemical properties of these particles. These chemical properties are intricately connected to both the concentration and availability of potential radical sites, which, in turn, exert a substantial influence on soot oxidation during diesel particulate filter (DPF) regeneration. Hence, it is crucial to investigate the chemical features of soot samples. Nevertheless, a thorough investigation into the chemical features of n-heptane/OME₃ soot samples has not been fully understood. Here, X-ray photoelectron spectroscopy (XPS), Fourier transform infrared spectroscopy (FT-IR), elemental analyser, and thermogravimetric analysis (TGA) were used to examine the impact of blending OME₃ on chemical features of soot particles at various flame heights of an inverse n-heptane-OME₃ flame. XPS results from C1s and O1s peaks showed that OME₃ incorporation enhanced the concentrations of C = O, C–O, and O = C–O groups, especially C = O groups, with the percentage increase ranging from 11.93 % to 49.74 %. Similarly, the content of aliphatic C − H groups, along with O and H, increased with higher levels of OME₃ blending. Moreover, it was discovered that blending OME₃ altered the spatial distribution of hybridisation orbitals of carbon atoms, leading to a decrease in the sp²/sp³ ratio by as much as 40 % with the increase in the OME₃ blending ratio. The alteration in these chemical properties due to the addition of OME₃ enhanced the oxidative reactivity of soot particles, as manifested by up to a 15 % reduction in the measured activation energy. These findings are useful to optimise control strategies of DPF regeneration with the more widespread use of e-fuel.
Variations in surface functional groups, carbon chemical state and graphitization degree during thermal deactivation of diesel soot particles
2023, Journal of Environmental Sciences (China)
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°C, 800°C, and 1000°C 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 state were 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 sp²/sp³ 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°C thermal treatment of diesel soot.
Jet-entrainment sampling: A new method for extracting particles from flames
2023, Proceedings of the Combustion Institute
We have developed a new method for extracting particulates and gas-phase species from flames. This technique involves directing a small jet of inert gas through the flame to entrain the sample, which is then collected by a probe on the other side of the flame. This sampling technique does not require inserting a probe or sampling surface into the flame and thus avoids effects on the flame due to conductive cooling by the probe and recombination, quenching, and deposition reactions at the sampling surface in contact with the flame. This approach thus allows for quenching and diluting the sample during extraction while minimizing the perturbations to the flame that have a substantial impact on flame chemistry. It also circumvents clogging of the probe with soot, a problem that commonly occurs when a probe is inserted into a hydrocarbon-rich premixed or diffusion flame. In this paper, we present experimental results demonstrating the application of this technique to the extraction of soot particles from a co-flow ethylene/air diffusion flame. The extracted samples were analyzed using transmission electron microscopy (TEM), and the results are compared with measurements using in situ diagnostics, i.e., laser-induced incandescence and small-angle X-ray scattering. We also compare TEM images of particles sampled using this approach with those sampled using rapid-insertion thermophoretic sampling, a common technique for extracting particles from flames. In addition, we have performed detailed numerical simulations of the flow field associated with this new sampling approach to assess the impact it has on the flame structure and sample following extraction. The results presented in this paper demonstrate that this jet-entrainment sampling technique has significant advantages over other common sample-extraction methods.
Morphology and electronic properties of incipient soot by scanning tunneling microscopy and spectroscopy
2022, Combustion and Flame
Citation Excerpt :
The quasi one-dimensional nature of the flame enables the temperature and species concentrations to vary only along the height above the burner, i.e., the flame residence time. Particles were collected thermophoretically by rapid insertion (insertion time 30 ms) using a pneumatic actuator; a procedure used in numerous earlier flame soot investigations [16,43-53]. Incipient soot was collected immediately behind the flame front at a distance of a few millimeters from the burner surface.
Soot nucleation is one of the most complex and debated steps of the soot formation process in combustion. In this work, we used scanning tunneling microscopy (STM) and spectroscopy (STS) to probe morphological and electronic properties of incipient soot particles formed right behind the flame front of a lightly sooting laminar premixed flame of ethylene and air. Particles were thermophoretically sampled on an atomically flat gold film on a mica substrate. High-resolution STM images of incipient soot particles were obtained for the first time showing the morphology of sub-5 nm incipient soot particles. High-resolution single-particle spectroscopic properties were measured confirming the semiconductor behavior of incipient soot particles with an electronic band gap ranging from 1.5 to 2 eV, consistent with earlier optical and spectroscopic observations.
Thermo-optical-transmission OC/EC and Raman spectroscopy analyses of flame-generated carbonaceous nanoparticles
2022, Fuel
Elemental and organic carbon content of flame-generated soot nanoparticles produced under different operating conditions of equivalence ratio and particle residence time is determined by thermo-optical-transmission measurements, while particle carbon structure is characterized by Raman spectroscopy analysis. The sampled soot nanoparticles are produced in slightly-rich, almost bluish, flames and comprise small 2–4 nm nascent soot nanoparticles, often neglected in the primary carbonaceous emissions from combustion systems, and larger 4–15 nm soot particles.
The application of the NIOSH-like protocol for the thermo-optical-transmission analysis allows the separation of the total carbon (TC) into fractions of organic carbon (OC), pyrolytic carbon (PC), and elemental carbon (EC). The lowest amount of elemental carbon is measured in young soot nanoparticles and it is progressively larger in mature soot particles. The organic carbon has the opposite trend and shows that it is the “pyrolyzable” carbon fraction of the young soot nanoparticles that transforms into elemental carbon in the primary soot.
Raman spectroscopy showed consistent results as compared to the thermo-optical-transmission analysis indicating a analogous trend in the graphitization order of the different soot particles. Most importantly, the logarithm of the intensity of the measured photoluminescence background shows a linear dependence with the OC/EC ratio.
Mass absorption coefficients (MAC) were retrieved by the thermo-optical-transmission analysis for the four soot samples; the estimated MAC coefficient ranged from 2 to 6 m²/g, dependently from the relative percentage of EC component. The data are in excellent agreement with currently available literature data and extend the determination of MACs to carbonaceous particles with a larger OC/TC content.
On-line fast analysis of light hydrocarbons, PAH and radicals by molecular-beam time of flight mass spectrometry
2021, Chemosphere
Volatile organic compounds (VOC) and polycyclic aromatic hydrocarbons (PAH), emitted in the environment from a wide range of combustion sources, are hazardous to human health and considered important precursors of both primary and secondary particulate pollutants. In the present work, light hydrocarbons up to C₉, as main components of combustion-derived VOC, and PAH produced in fuel-rich conditions of premixed ethylene flames were analyzed by implementing a molecular-beam time of flight mass spectrometer (MB-TOFMS), purposely built for on-line fast monitoring of the environmental impact of combustion systems. The reliability of the MB-TOFMS was preliminarily verified on a slightly-sooting flame, comparing the results with those obtained by batch sampling and gas chromatographic techniques. Electron ionization (EI) and multi-photon ionization (MPI) were used as MB-TOFMS sources and tested on combustion gases of a no-sooting premixed ethylene flame where VOC and PAH are present in traces not detectable with batch sampling and conventional analytical techniques. The mass identification accuracy was improved and guaranteed by systematically performing internal mass calibration, exploiting the formation of “in situ” clusters from combustion water in the molecular beam apparatus. Selective and sensitive monitoring of light hydrocarbons and PAH, derived from oxidation and pyrolysis reactions featuring combustion, was shown to be especially effective when using the MB-TOFMS equipped with MPI source. This technique showed to be effective also for the detection of radical species that are important for the risk assessment of aerosol and fundamental understanding of aerosol chemistry at a molecular level.

View all citing articles on Scopus

^☆: Presented at the Twenty-Fifth Symposium (International) on Combustion, Irvine, California, 31 July–5 August 1994.

^☆☆: This work has been supported at Brown University by the Army Research Officer under Grant No. DAAL03-92-G-0023. The temperature measurements were conducted by Mr. George J. Govatzidakis. The LAMMA-500 is located at NIST in the Microanallysis Research Group.

View full text

Laser microprobe analysis of soot precursor particles and carbonaceous soot☆,☆☆

Abstract

J. Colloid Interface Sci.

Combust. Flame

Combust. Flame

Combust. Flame

Anal. Chim. Acta

Rubber World

Carbon

Langmuir

Combust. Sci. Technol.

Combust. Sci. Technol.