Sooting limits of non-premixed counterflow ethylene/oxygen/inert flames using LII: Effects of flow strain rate and pressure (up to 30 atm)

Sarnacki, Brendyn; Chelliah, Harsha K.

doi:10.1016/j.combustflame.2018.03.029

Cited by 32 publications

(9 citation statements)

References 65 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: 71%

“…The authors rationalized the similarity between C3H8 and C2H4 flames by pointing out that C2H4 was among the primary products of fuel-side propane pyrolysis. Sarnacki and Chelliah [530] performed absolute irradiance-calibrated time-resolved LII and PIV measurements to quantify SVF and flow fields, respectively, in ethylene CDFs up to 30 atm.…”

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

360

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: 71%

Section: Effects Of Pressure On Soot Formationmentioning

confidence: 99%

Soot formation in laminar counterflow flames

Wang

Chung

2019

Progress in Energy and Combustion Science

360

116

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“…The nozzle exit velocities for both the fuel and oxidizer streams were maintained at U0 = 20 cm/s. Thus, the global strain rate αg was maintained at ag = 100 s 1 based on 4U0/L [14]. The nozzle outlet temperature and pressure were maintained at ambient conditions.…”

Section: Methodsmentioning

confidence: 99%

Experimental and soot modeling studies of ethylene counterflow diffusion flames: Non-monotonic influence of the oxidizer composition on soot formation

Yan

Zhou

et al. 2018

Combustion and Flame

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Chung SH (2018) Experimental and soot modeling studies of ethylene counterflow diffusion flames: Non-monotonic influence of the oxidizer composition on soot formation. Combustion and Flame 197: 304-318. Available: http:// dx. AbstractPrevious soot studies in counterflow diffusion flames revealed that the sooting limit curve in regions with large oxygen mole fractions (XO) exhibited marked bending behaviors that indicated a non-monotonic variation of sooting tendency with oxygen concentration. The underlying mechanisms of this bending behavior remained unclear. In this regard, the present study systematically investigated the effect of oxygen mole fraction in the oxidizer stream on the sooting characteristics of ethylene counterflow diffusion flames. We used the near-infrared light extinction technique to measure the soot volume fractions of two types of flames that significantly differed in sooting structures: soot formation oxidation (SFO) flames with a fixed fuel mole fraction (XF) of 0.28 and varying XO between 0.5 and 1.0 and soot formation (SF) flames with pure ethylene (XF = 1.0) in the fuel stream and varied XO from 0.250.3. We also conducted detailed soot modeling studies by combining the gas-phase chemistry with a sectional soot model that accounted for soot inception, soot mass growth, particle coagulation as well as soot oxidation. Our experimental and modeling results demonstrated the non-monotonic relationship between the soot volume fractions with XO in SFO flames. A detailed analysis of the evolutionary process of soot formation revealed that the suppression of soot inception and the enhancement of the soot oxidation process with increasing XO led to a reduction of soot volume fraction. On the contrary, the surface growth rates increased with XO, resulting in an increase in soot mass concentration. These competing effects led to the nonmonotonic variation of soot volume fractions with XO for SFO flames. On the other hand, in SF flames the inception and surface growth of soot both increased as XO increased, resulting in the observed monotonic relationship between soot volume fraction and XO. We also analyzed the soot zone structures and made comparisons between SFO and SF flames.

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“…SVF is commonly measured using optical methods, including the light extinction (LE) method (Yan et al, 2019b), laser-induced incandescence (LII) (Sarnacki and Chelliah, 2018), and soot spectral emission (SSE) (Kholghy et al, 2017). LII utilizes the decay radiation signal of soot particles being heated up to ∼4,000K by a high-energy laser pulse to infer the SVF.…”

Section: Introductionmentioning

confidence: 99%

Planar Light Extinction Measurement of Soot Volume Fraction in Laminar Counterflow Diffusion Flames

Zhou

et al. 2021

Front. Mech. Eng.

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A cost-effective and straightforward light extinction method has been extensively used for measurement of soot volume fraction (SVF) in sooting flames. The traditional pointwise measurement with translation stage suffers from relatively time-consuming operation and low spatial resolution. In the current study, the planar light extinction method is processed by utilizing a CMOS camera to image the combustion field of counterflow diffusion flame (CDF) backlit with the lamp. Collimated and diffuse optical layouts were adopted to explore the feasibility. Investigations of beam-steering effects are presented and discussed through a combination of computational fluid dynamics (CFD) and ray tracing simulations. Measured SVF are compared to the well-validated laser-induced incandescence (LII) measurements. Current measurements show that the diffuse optical layout is feasible and robust to provide accurate and more efficient measurement of the SVF in CDF with superior spatial resolution (21.65 μm).

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Sooting limits of non-premixed counterflow ethylene/oxygen/inert flames using LII: Effects of flow strain rate and pressure (up to 30 atm)

Cited by 32 publications

References 65 publications

Soot formation in laminar counterflow flames

Soot formation in laminar counterflow flames

Experimental and soot modeling studies of ethylene counterflow diffusion flames: Non-monotonic influence of the oxidizer composition on soot formation

Planar Light Extinction Measurement of Soot Volume Fraction in Laminar Counterflow Diffusion Flames

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