Soot measurements by two angle scattering and extinction in an N2-diluted ethylene/air counterflow diffusion flame from 2 to 5 atm

Amin, Hafiz M.F.; Roberts, William L.

doi:10.1016/j.proci.2016.06.044

Cited by 41 publications

(20 citation statements)

References 28 publications

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“…The SVF drops to a negligible level before reaching the stagnation plane, consistent with the fact that SFO flames typically do not emit soot. In contrast, the SVF profile in SF flame is highly skewed toward the fuel side, characterized by a sharp decrease across the stagnation plane, a phenomenon observed also in several other studies [78,281,529,530]. This is because the particles have very low diffusivity and cannot effectively penetrate through the stagnation plane, so they eventually leak out of the flame in the radial direction.…”

Section: Sooting Structures Of Cdfs and Comparison With Coflow Diffusion Flamesmentioning

confidence: 70%

“…Amin and Roberts [529] pioneered in-situ determination of the morphology of soot particles in CDFs at elevated pressures. Specifically, laser light extinction and two-angle scattering were used to measure SVF, primary particle size, and number density, along with aggregate size (average radius were all increased, but the primary particle number density (c) decreased.…”

Section: Effects Of Pressure On Soot Formationmentioning

confidence: 99%

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Soot formation in laminar counterflow flames

Wang

Chung

2019

Progress in Energy and Combustion Science

336

116

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Many practical soot-emitting combustion systems such as diesel and jet engines rely on diffusion flames for efficient and reliable operation. Efforts to mitigate soot emissions from these systems are dependent on fundamental understanding of the physicochemical pathways leading from fuel to soot in laminar diffusion flames. Existing diffusion flame−based soot studies focused primarily on overventilated coflow flame where the fuel gas (or vapor) issues from a cylindrical tube into a co-flowing oxidizer, and counterflow flame, where a reacting zone is established between two opposing streams of fuel and oxidizer. As a canonical diffusion flame configuration, laminar counterflow diffusion flames have been widely used as a highly controllable environment for soot research, enabling significant progress in the understanding of soot formation for several decades. In view of the possibility of fuel/oxidizer premixing in practical systems, counterflow partially premixed flames have also been studied. In the present work we intend to provide a comprehensive review of the researches on various aspects of soot formation utilizing counterflow flames. Major processes of soot formation (formation of gas phase soot precursors, soot inception and surface reactions, as well as particle-particle interactions) are examined first, with focus on the most recent (post-2010) research progress. Experimental techniques and associated challenges for the measurement of soot-related properties (some knowledge of which is helpful for full appreciation of the experimental data to be reviewed) are then introduced. This is followed by a detailed description of soot evolution in counterflow flames, which is complemented by a discussion on the similarity and differences of the sooting structures between counterflow and coflow diffusion flames. Parametric studies of the effects of fuel molecular structure, fuel additive, partial-premixing, pressure, temperature, stoichiometric mixture fraction, and residence time on soot formation in counterflow flames will then be addressed in detail. This review concludes with a summary of the knowledge and challenges gathered and demonstrated through decades of research, and an outlook on opportunities for future counterflow flame−based soot research towards a more complete understanding of soot formation and the development of novel techniques for soot mitigation in practical combustion devices.

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Section: Sooting Structures Of Cdfs and Comparison With Coflow Diffusion Flamesmentioning

confidence: 70%

Section: Effects Of Pressure On Soot Formationmentioning

confidence: 99%

Soot formation in laminar counterflow flames

Wang

Chung

2019

Progress in Energy and Combustion Science

336

116

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“…This fact together with CDF's unique sooting characteristics has motivated various research groups to perform detailed CDF-based soot investigations, mostly using optical measurement techniques. Among these, Amin and Roberts [43] combined extinction and two-angle scattering with a 514.5 nm beam to measure both soot volume fraction and morphology in N 2 -diluted ethylene/air CDFs at elevated pressures. Similarly, Wang and Chung [44] studied the sooting characteristics of ethylene CDFs with CO 2 dilution using light extinction at 514.5 nm.…”

Section: Soot Volume Fraction (F V )mentioning

confidence: 99%

An experimental study on the spectral dependence of light extinction in sooting ethylene counterflow diffusion flames

Yan

Zhou

et al. 2019

Experimental Thermal and Fluid Science

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A light extinction technique is widely-adopted for quantitative measurement of soot volume fractions. The measurement accuracy is dependent on the optical properties of soot, which are expected to vary with the wavelength of incident light and physicochemical environments in which soot is formed. In the present study, a diode laser based light extinction setup, capable of providing light with variable wavelengths ranging from 405 to 1064 nm, was utilized to investigate the in-situ spectral dependence of light absorption for soot formed in counterflow diffusion flames. Soot volume fractions (F V) were inferred from the extinction level of these laser beams for a series of flames parameterized by oxygen/fuel mole fractions, nozzle exit velocities, and fuel types. Special attention was given to distinguish between the soot formation (SF) and soot formation/oxidation (SFO) flames, considering their notable differences in soot evolutions. It was found that the inferred F V as measured with visible light (405670 nm) was always significantly higher than those measured with near-infrared light (> 780 nm). In addition, the quantitative decrease of F V with the increase in light wavelength (λ) was found to be different for soot particles formed at different flame locations and/or flame conditions, even in the spectral range above 780 nm for which polycyclic aromatic hydrocarbon (PAH) interferences are expected to be minimal. This confirms the wavelength dependence of the soot optical property E(m). In particular, the value of E(m) tends to decrease with increasing wavelength and the rate of decrease is lower for more mature soot particles. Furthermore, by fitting the extinction coefficient with wavelength in the near-infrared range, the quantitative relation of E(m) with λ was derived and compared among various flame conditions. The present study demonstrates that soot formed at different conditions have different optical properties. The results are also expected to provide essential information for uncertainty evaluation in literature F V data in counterflow diffusion flames as measured with light extinction, especially for those performed with visible light sources where PAH interference may not be negligible.

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“…The width of the concentric slit for shield nitrogen was 9 mm. The pressure vessel had four optical windows providing 160° of optical access, whose details were reported previously [33]. An electronic back-pressure regulator controlled the vessel pressure within 2% fluctuations at a setpoint.…”

Section: Experiments and Simulationsmentioning

confidence: 99%

Effect of dimethyl ether (DME) addition on sooting limits in counterflow diffusion flames of ethylene at elevated pressures

Amin

Liu

et al. 2018

Combustion and Flame

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The effects of dimethyl ether (DME) addition to ethylene fuel on sooting tendencies with varying pressure were investigated in counterflow diffusion flames by using a laser scattering technique. Sooting limit maps were determined in the fuel (XF) and oxygen (XO) mole fraction plane, separating sooting and non-sooting regions. The results showed that when DME is mixed to ethylene, the sooting region was appreciably shrank, especially in the cases of soot formation/oxidation (SFO) flames as compared with the cases of soot formation (SF) flames. This indicated an inhibiting role of DME on sooting. An interesting observation was that the critical XO required for sooting initially decreased and then increased with the DME mixing ratio to ethylene β for the cases of SF flames, exhibiting a non-monotonic behavior. This implied a promoting role of DME on sooting when small amount of DME is mixed to ethylene. As the pressure increased, the sooting region generally expanded. Specifically, the range of β in promoting soot formation extended with pressure. This implies that a strategy in reducing soot by adding DME to ethylene at high pressures required a large amount of DME addition. To interpret the observed phenomena, kinetic simulations including reaction pathway and sensitivity analyses were conducted with the opposed-flow flames model using the KAUST-Aramco PAH Mech. The results showed that the thermal effect of DME addition on sooting tendency monotonically decreases with . The chemical effect was found to be the main contributor to the DME addition effect on sooting tendency, resulting in the non-monotonic sooting limt behavior. The pathway analysis showed the role of methyl radicals generated from DME promoted incipient benzene ring formtion when small amount of DME was added, which can be attributed to the soot promoting role of DME addition for small β.

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Soot measurements by two angle scattering and extinction in an N2-diluted ethylene/air counterflow diffusion flame from 2 to 5 atm

Cited by 41 publications

References 28 publications

Soot formation in laminar counterflow flames

Soot formation in laminar counterflow flames

An experimental study on the spectral dependence of light extinction in sooting ethylene counterflow diffusion flames

Effect of dimethyl ether (DME) addition on sooting limits in counterflow diffusion flames of ethylene at elevated pressures

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