Numerical study of soot formation in laminar coflow methane/air diffusion flames doped by n- heptane/toluene and iso-octane/toluene blends

Consalvi, Jean-Louis; Liu, Fengshan; Kashif, Muhammad; Legros, Guillaume

doi:10.1016/j.combustflame.2017.03.002

Cited by 34 publications

(12 citation statements)

References 28 publications

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“…The aforementioned studies have shown that the composition of TRF (especially toluene) has a strong effect on the formation of PAHs and soot and that PAHs shows a synergistic effect with the increasing toluene ratio. , However, the difference of PAHs trend and flame structure between n -heptane and isooctane for the toluene addition needs to be further studied. Furthermore, the 1-D distribution features in counterflow diffusion flames has been reported, while the distribution characteristics of different size PAHs in 2-D flames commonly used in the study of soot is unknown.…”

Section: Introductionmentioning

confidence: 99%

“…They reported that, as the toluene content increases, the soot formation increases monotonically, while PAHs shows a synergistic effect. Consalvi et al 27 studied numerically the effect of adding n-heptane/toluene or isooctane/toluene binary mixtures to methane on the formation of PAHs and soot in laminar diffusion flames. They found that, as the toluene content in binary mixtures increases, soot formation increases monotonically, while the benzene and pyrene formation shows a nonmonotonic trend in methane diffusion flames.…”

Section: Introductionmentioning

confidence: 99%

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Effect of Toluene Addition on the PAH Formation in Laminar Coflow Diffusion Flames of n-Heptane and Isooctane

Liu

Hua

et al. 2018

Energy Fuels

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Characterization of soot formation is becoming more important for gasoline surrogate fuels, requiring a deeper understanding of the effect of toluene ratio on PAHs formation. In this work, the different size PAHs distribution in laminar diffusion flames was measured by PLIF technique, and the chemiluminescences of OH and CH radicals were recorded by ICCD coupled with band-pass filters. The effect of toluene addition to n-heptane and isooctane on the flame and PAHs formation was comparatively studied. Then, the chemical kinetic of PAHs was analyzed using the CHEMKIN Diffusion Flame model. The experimental results showed that the cool flame area ranks as n-heptane > isooctane > toluene may due to the NTC action. The OH intensity and flame lift-off height show a monotonous increasing trend with the toluene ratio. At the same toluene ratio, the peak OH intensity and flame lift-off height of n-heptane/toluene is lower than that of isooctane/toluene. The CH intensity in nheptane, isooctane, and toluene flames shows completely different distribution characteristics. As the toluene ratio increases, the 320 nm-LIF in n-heptane and isooctane flames shows a weakening monotonous increasing trend with different inflection points. The 360/400/450 nm-LIF in n-heptane and isooctane flames show a nonmonotonic trend with different peak points. The peak point is 50% toluene ratio in n-heptane/toluene flames and 40% in isooctane/toluene flames, and it corresponds exactly to the smoke point of the flame. The kinetic analysis showed that the benzyl has a significant effect on the formation of A2−A4 through the generation of C 10 H 9 , C 9 H 7 , and C 14 H 12 . A1 trend is dominated by C 6 H 5 CH 3 + H = A1 + CH 3 and A1 − + CH 4 → A1 + CH 3 . The trends of A2, A3 and A4 are mainly dominated by the reactions between their own dehydrogenation groups with H 2 .

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Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of Toluene Addition on the PAH Formation in Laminar Coflow Diffusion Flames of n-Heptane and Isooctane

Liu

Hua

et al. 2018

Energy Fuels

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“…This simulation, to a certain extent, underestimates the soot along the centerline, and the problem exists in other numerical simulations as well. 22 , 28 , 40 This deficiency in the soot formation prediction is quite likely caused by the oversimplified assumption that soot nucleation is initiated by the collision of two pyrene (A4) molecules, whereas the soot nucleation process involves multiple PAHs of different sizes in reality. The flame of n -heptane, which has the strongest NTC behavior, generates the least soot particles and the smallest soot distribution area.…”

Section: Resultsmentioning

confidence: 99%

“… 22 − 24 Aromatic hydrocarbon fuels, such as toluene, n -propyl benzene, and so forth, are easy to form PAHs and promote the soot nucleation. 25 − 28 Mechanisms for the formation of soot have also been extensively studied since the 1990s, 29 − 32 among which the hydrogen abstraction carbon addition (HACA) theory is widely accepted for the growth process from A1 to high-ring PAHs. 33 , 34 The mechanism argued that the first step in the soot formation process is the generation of the soot precursor, especially the generation of the first benzene ring (A1) trough C 4 H 4 + C 2 H 2 = C 6 H 6 and 2C 3 H 3 = C 6 H 6 , 35 and the speed of this step determines the subsequent soot generation.…”

Section: Introductionmentioning

confidence: 99%

Numerical Investigation of Negative Temperature Coefficient Effects on Sooting Characteristics in a Laminar Co-flow Diffusion Flame

Dong

et al. 2021

ACS Omega

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It is a common sense that diesel engines produce worse soot emission than gasoline engines, even though gasoline direct injection also brings about terrible sooting tendency. However, reports showed that diesel emits less soot than gasoline in laminar diffusion flames, which implies that soot emission is a combined effect of multiple factors, such as the combustion mode, physical properties of the fuel, and also fuel chemistry. This work, thus, conducted numerical calculations in laminar co-flow diffusion flames of fuels with different negative temperature coefficient (NTC) behaviors in an order of n -heptane > iso-octane > toluene to solely evaluate the chemical effect, especially the role of low-temperature combustion on soot formation. 2-Dimensional simulations were carried out to obtain the soot distributions, and 0-dimensional simulations were performed to analyze the chemical kinetics of polycyclic aromatic hydrocarbon (PAH) formation and low-temperature reaction sensitivities. The grids of the 2-D model converged at 80( r ) × 196( z ), and the boundary conditions of both models were set to eliminate the influence of physical factors as much as possible. The results showed that there were three main reactions associated to the formation of aromatic hydrocarbons A1 at the first-stage combustion in the n -heptane flame and the iso-octane flame, in which the reaction of C 7 H 15 + O 2 = C 7 H 15 O 2 enhances the NTC behavior. The first two reaction pathways generated larger molecular hydrocarbons and were unfavorable by A 1 formation and therefore inhabit the PAH formation, and 49.8% of C 7 H 16 reacted through the large molecular pathways, while the percentage for C 8 H 18 , with weaker NTC behavior, was only 37%. Toluene with even weaker NTC behavior showed no low-temperature oxidation. Therefore, in a more general case, fuels with stronger NTC behavior smoke less, and this conclusion could be promising potential to reduce soot emission in future.

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“…They found that, as the toluene content increases, the soot formation increases monotonically, while PAHs show a synergistic effect. Consalvi et al 36 studied the effect of nheptane/toluene or isooctane/toluene binary mixture addition on the formation of PAHs and soot in methane laminar diffusion flames. They found that, as the toluene content increases, soot formation increases monotonically, while the formation of benzene and pyrene shows a non-monotonic trend.…”

Section: Introductionmentioning

confidence: 99%

Experimental Evaluation of Various Gasoline Surrogates Based on Soot Formation Characteristics

Hua

Liu

et al. 2018

Energy Fuels

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The evaluation of soot tendency of gasoline surrogates in simple atmosphere environments is essential for understanding soot formation processes and developing accurate soot models to represent real fuel chemistry in computational fluid dynamics simulations of gasoline engines. In this work, several surrogates were evaluated on the basis of soot precursor and soot characteristics in laminar diffusion flames. The relative concentrations of polycyclic aromatic hydrocarbons (PAHs) with different ring sizes and soot were measured using laser-induced fluorescence (LIF) and laser-induced incandescence (LII) techniques. The OH and CH luminescence intensities were also recorded using an intensified charge-coupled device. The results showed that the gasoline surrogates failed to represent the formation characteristics of small-ring aromatics (320/360 nm) for gasoline flames but have certain characterization ability for large-ring aromatics (400/450 nm). The relationship between the PAH LIF signal and the toluene content is not monotonically increasing. On the basis of the relative concentrations of larger PAHs and soot, the surrogate ( 1 / 3 n-heptane, 1 / 3 isooctane, and 1 / 3 toluene) can characterize the formation characteristics of soot precursors and soot in gasoline laminar diffusion flames best. On the basis of the OH and CH luminescence intensities, the surrogate ( 1 / 3 n-heptane, 1 / 3 isooctane, and 1 / 3 toluene) can best characterize the flame structure and development of gasoline. The CH trend is consistent with the PAH trend, inferring that there exists a strong correlation between CH intensity and PAHs in the diffusion flames. As the aromatic ring number increases, its PAH LIF signal peaks at a higher position and the high concentration region gradually evolves from the flame center to the two wings of the flame, which eventually leads to the characteristic of the two-wing distribution of soot. For the binary mixture of n-heptane−toluene, the 320 nm PAH LIF signal increases monotonically with the toluene ratio. The maximum PAH LIF signals of 360−450 nm exhibit a non-monotonic tendency, which reach the peak at a 50% toluene ratio. Furthermore, there exists a tolerance in terms of the toluene mixing ratio (10%), below which the effect of toluene on larger ring aromatic (A4−A5) formation can be neglected.

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Numerical study of soot formation in laminar coflow methane/air diffusion flames doped by n- heptane/toluene and iso-octane/toluene blends

Cited by 34 publications

References 28 publications

Effect of Toluene Addition on the PAH Formation in Laminar Coflow Diffusion Flames of n-Heptane and Isooctane

Effect of Toluene Addition on the PAH Formation in Laminar Coflow Diffusion Flames of n-Heptane and Isooctane

Numerical Investigation of Negative Temperature Coefficient Effects on Sooting Characteristics in a Laminar Co-flow Diffusion Flame

Experimental Evaluation of Various Gasoline Surrogates Based on Soot Formation Characteristics

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