NO&lt;SUB&gt;x&lt;/SUB&gt; and CO emissions and soot presence in partially premixed acoustically excited flames

Ferreira, Daniel Silva; Lacava, Pedro Teixeira; Ferreira, Marco Aurélio Marques; Carvalho, João Andrade de

doi:10.1179/014426009x12448168549985

Cited by 11 publications

(11 citation statements)

References 4 publications

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“…In other words, the key effect of axial diffusion on the asymptotic characteristics of F is on the time averaged profiles of Z , specifically the inlet profilei.e., axial diffusion effects on the unsteady dynamics of Z have minor influences on F , although they have important influences on the downstream evolution of the flame position, as shown by Eq. (18).…”

Section: Heat Release Transfer Functions -High Strouhal Asymptotic Rementioning

confidence: 99%

“…As a result of the strong effect of forcing on the ambient/co-flowing air and its entrainment with the fuel jet, a number of studies have also noted significant influences on soot and NOx production from the flame [17][18][19] sensitivities which are much stronger in non-premixed flames than in premixed flames. For example, Saito et al [17] showed that soot can be suppressed in acoustically excited non-premixed flames, with reductions of up to 50% in a laminar flame, and 90% for a turbulent flame.…”

Section: Introductionmentioning

confidence: 99%

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Effect of axial diffusion on the response of diffusion flames to axial flow perturbations

Magina

Lieuwen

2016

Combustion and Flame

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This paper elucidates the behavior and dynamics of non-premixed flames responding to bulk fluctuations in flow velocity. It expands previous work on this problem by consistently incorporating finite Peclet number (0 / D f Pe U R ) effects, and differentiating inflow boundary and dynamical effects on the flame dynamics. For analytical tractability, prior treatments of this problem generally prescribe the inflow boundary conditions into the domain. This paper shows, however, that prescribed inflow conditions, such as a step or constant local diffusive flux boundary condition, neglect axial diffusion effects in the region where their effects are most important; i.e., in the near-burner exit region where high transverse gradients and mass burning rates control the heat release dynamics. As the burning rate of non-premixed flames are controlled by mixture fraction gradients, the influence of axial diffusion substantively influences several burning rate characteristics of the flame. In addition, these effects cause the leading edge position of the flame front to oscillate, even for infinitely fast chemistry. Even in Pe>>1 flames, axial diffusion introduces several fundamentally new features to the problem, resulting in exponentially decaying, dispersive flame wrinkle propagation with downstream distance. Also investigated here are asymptotic results for the heat release dynamics. It is shown that axial diffusion introduces a triple-zone asymptotic structure into the unsteady heat release characteristics, resulting in O(1) flame transfer function trends for St<<1 (to which an n-τ model is developed), O(1/St 1/2) for intermediate Strouhal numbers, and O(1/St) for high Strouhal numbers. Finally, it is shown that the phase of the heat release response is approximately half that of a premixed flame with the same length, due to the concentration of unsteady heat release near the burner outlet, where transverse gradients are largest.

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Section: Heat Release Transfer Functions -High Strouhal Asymptotic Rementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Effect of axial diffusion on the response of diffusion flames to axial flow perturbations

Magina

Lieuwen

2016

Combustion and Flame

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“…In general, acoustic excitation of flames has shown to increase turbulent intensity, enhance the transition from laminar to turbulent flow, increase the burn rate and affect emission formation. 13–17 Yoshida et al 14 showed that turbulence in turbulent jet diffusion flames is increased when they are subjected to acoustic excitation, significantly enhancing combustion rate, while shortening and broadening the flame.…”

Section: Introductionmentioning

confidence: 99%

“…It is generally accepted that through the increase of air–fuel mixing caused by acoustic excitation, there follows a reduction in soot formation and an enhancement of soot and CO oxidation. 13,16 Ferreira et al 13 argue that large oxygen concentrations in the flame due to increased mixing lead to decreased soot production, through the conversion of the hydrocarbon radical (RH) directly to carbon monoxide and not to C 2 H 2 , which is a main precursor for soot. Additionally, increased flame temperature and oxygen concentration due to enhanced mixing also lead to increased oxidation of soot and CO in acoustically excited flames.…”

Section: Introductionmentioning

confidence: 99%

Apparent effects of in-cylinder pressure oscillations and cycle-to-cycle variability on heat release rate and soot concentration under long ignition delay conditions in diesel engines

Kyrtatos

Hoyer

Obrecht

et al. 2013

International Journal of Engine Research

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In diesel engines, long ignition delay due to cold in-cylinder conditions has been shown to lead to high cycle-to-cycle variability, as well as result in pressure oscillations due to rapid localised pressure rise rates from the resulting premixed combustion. These pressure oscillations appear as superimposed pressure waves on the engine indication graph, with an oscillation frequency corresponding to the first radial vibration mode. In the current study, the influences of pressure oscillations on heat release rate and the progress of in-cylinder soot concentration are investigated. Results showed that cycles where pressure oscillations occur reach a higher peak pressure than average or low pressure oscillation cycles, as a result of increased diffusion combustion rate and apparent mixing rate. Additionally, using in-cylinder soot pyrometry, cycles with high pressure oscillations were shown to exhibit increased soot oxidation rates. The combination of the two above-mentioned observed effects leads to the conclusion that pressure oscillations in direct injection diesel engines result in more rapid mixing due to increased turbulent intensity.

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“…[7][8][9] External excitation of non-premixed flames by acoustic forcing has also been studied with the motivation of enhancing mixing 10 or decreasing pollutant emissions. 11 In non-premixed swirl combustion, Idahosa et al 12 conducted that Strouhal number approximate unit and large velocity perturbation are necessary to initiate and sustain high flame response. Investigation of flame heat-release response to acoustic forcing can benefit the analysis of thermoacoustic instability in the combustor.…”

Section: Introductionmentioning

confidence: 99%

Study of burner geometry effects on non-premixed flame response under acoustic excitation

Zhou

Meng

Tao

et al. 2018

Journal of Low Frequency Noise, Vibration and Active Control

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The study of the flame under the acoustic excitation contributes to the study of flame self-excited thermoacoustic instability. Although non-premixed combustion is widely used in industry, research on its combustion instability characteristics is relatively few. This paper experimentally studies the response of a non-premixed swirl flame under excitation. The geometry modifications are the length of the inlet section which is set to be 0.245 m, 0.345 m and 0.445 m and the installation of separation plates. Through the analysis of flame response behavior at different excitation frequencies, combined with the calculation of acoustic mode, we find that for the 0.245 m and 0.345 m inlet length cases, the maximum flame heat release fluctuation responds near 144 Hz. This mode is due to the resonance of the fuel pipe. For the 0.445 m inlet length cases, the maximum flame heat release responds near 134 Hz. This mode is a mixed mode of fuel pipe and combustion chamber. The maximum flame response occurs at the point where the pressure fluctuation reaches the maximum in the inlet section. The image analysis shows the same mode distinction trend between short and long inlet length. Besides, the removing of separation plates leads to a more stable response of the flame in low inlet airflow rate. However, at high airflow rate, the flame tends to be more unstable. Moreover, the higher acoustic forcing frequency than quarter-wave mode will cause the quarter-wave resonant frequency to appear. The results of our work can benefit the implications of thermoacoustic instability in non-premixed flame.

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NO<SUB>x</SUB> and CO emissions and soot presence in partially premixed acoustically excited flames

Cited by 11 publications

References 4 publications

Effect of axial diffusion on the response of diffusion flames to axial flow perturbations

Effect of axial diffusion on the response of diffusion flames to axial flow perturbations

Apparent effects of in-cylinder pressure oscillations and cycle-to-cycle variability on heat release rate and soot concentration under long ignition delay conditions in diesel engines

Study of burner geometry effects on non-premixed flame response under acoustic excitation

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