Effects of oxygen-enrichment and fuel unsaturation on soot and NO  emissions in ethylene, propane, and propene flames

Kalvakala, Krishna C.; Katta, Viswanath R.; Aggarwal, Suresh K.

doi:10.1016/j.combustflame.2017.09.015

Cited by 50 publications

(20 citation statements)

References 41 publications

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“…In many recent models for soot formation, soot inception was modelled as the physical collision of large PAHs such as pyrene [282,[375][376][377], or an ensemble of larger aromatics up to coronene [111,140,378]. In these studies, nucleation reactions were generally assumed to be irreversible with zero activation energy [198].…”

Section: Models Of 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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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: Models Of 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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“…Therefore, for a quantitative prediction of soot formation, many existing soot inception models are typically developed based on the dimerization of different-sized PAHs [72][73][74][75]. In particular, the present work utilized the wellestablished models based on dimerization of large PAHs (4 rings and larger), which has been used widely by various research groups [34,76,77] and successful in explaining many experimental observations. We nevertheless note more work needs to be done to improve the model to account for most recent fundamental development in soot inception mechanisms.…”

Section: Numerical Modelingmentioning

confidence: 99%

“…An alternative would be to employ a quasi-one-dimensional counterflow diffusion flame (CDF). Due primarily to its simpler flow field and relative ease of modeling, CDF is particularly suitable for studying the fundamental chemistry of soot evolution [33][34][35][36], e.g., the fuel mixing effects on soot formation [37,38] as performed in this work. Additional benefits of CDF include its relevance to the laminar flamelet model [39], its resistance to buoyancydriven instability especially under high-pressure conditions [40], its capability to provide a sooting zone without interference from soot oxidation [41,42].…”

Section: Introductionmentioning

confidence: 99%

Chemical effects of hydrogen addition on soot formation in counterflow diffusion flames: Dependence on fuel type and oxidizer composition

Yan

Wang

et al. 2020

Combustion and Flame

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We experimentally studied and kinetically modeled the effects of hydrogen addition on soot formation in methane and ethylene counterflow diffusion flames (CDFs). To isolate the chemical effects of hydrogen in such flames, we also ran a set of experiments on flames of the same base fuels but with the addition of helium. Specifically, we measured the soot volume fractions of the flames using the planar laser-induced incandescence technique. We simulated detailed sooting structures by coupling the gas-phase chemistry with the polycyclic aromatic hydrocarbon (PAH)-based soot model, using a sectional method to resolve the soot particle dynamics. Our experimental and numerical results show that hydrogen chemically inhibits soot formation in ethylene CDFs. While in methane flames, it is interesting to observe that the difference in soot production between the hydrogen-and helium-doped cases became much smaller when the oxygen concentration in the oxidizer stream (XO) was reduced.This suggests that for methane CDFs the chemical soot-inhibiting effects of hydrogen was highly dependent on oxidizer composition (i.e., XO). Explanations are provided through detailed kinetic analysis concerning the effects of hydrogen addition on the growth of PAH, soot inception, and soot surface growth processes. Our results suggest that hydrogen's chemical role in soot formation not only depends on fuel type (ethylene or methane), it also may be sensitive to oxidizer composition.

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“…Du et al [47] reported that the change in flame structure associated with an increase in Zstoi resulted in a shift of the OH concentration towards the high-temperature region, leading to a narrower soot-inception region. In a recent study, Kalvakala et al [50] showed that reduction of soot at larger Zstoi was achieved through both flame structure and hydrodynamic effects. As Zstoi increased, the concentrations of soot precursor species, i.e., acetylene, benzene and pyrene, became decreased, which inhibited soot formation.…”

Section: Introductionmentioning

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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Effects of oxygen-enrichment and fuel unsaturation on soot and NO emissions in ethylene, propane, and propene flames

Cited by 50 publications

References 41 publications

Soot formation in laminar counterflow flames

Soot formation in laminar counterflow flames

Chemical effects of hydrogen addition on soot formation in counterflow diffusion flames: Dependence on fuel type and oxidizer composition

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

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