Investigations of microwave stimulation of a turbulent low-swirl flame

Ehn, Andreas; Petersson, Per; Zhu, Jiajian; Li, Z.S.; Aldén, Marcus; Nilsson, Erik; Larfeldt, Jenny; Larsson, Anders; Hurtig, Tomas; Zettervall, Niklas; Fureby, Christer

doi:10.1016/j.proci.2016.06.164

Cited by 33 publications

(18 citation statements)

References 32 publications

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“…Experimental details for similar conditions have been presented in a previous publication by Ehn et al, 37 and experimental data and LES were further discussed in another publication by the same group. 38 The authors presented averaged OH-and CH 2 O-PLIF data in this publication showing a distinct increase in OH-PLIF signal with microwave stimulation, as well as a broadening of the flame. Furthermore, the averaged PLIF images indicated that the flame was displaced with microwave stimulation, in that it moved closer to the burner nozzle.…”

Section: Energy and Fuelsmentioning

confidence: 95%

“…Planar laser-induced fluorescence data from OH and CH 2 O show that the flame is shifted closer to the burner nozzle when the flame absorbs microwave energy. 38 The temperature increase and the shift in flame position indicate an increase in flame speed for the turbulent flame as microwaves are applied to the flame. Development of numerical simulation models for studying electrical aspects of flames is a broad and active research area.…”

Section: Introductionmentioning

confidence: 99%

“…In addition, the microwave radiation has been showed to lower the lean extinction limit, and therefore the technique of microwave-stimulation show promising results. Most investigations of microwave-stimulated combustion have been performed experimentally, and only a few simulation A recent study by the authors of the present work 38 include both experiments and simulations of a turbulent low-swirl flame close to the lean blow-off limit, subjected to microwave stimulation. It was shown that microwave stimulation affects flame stabilization, increase the turbulent flame speed, and the kinetics analysis indicate that singlet oxygen molecules are the dominant flame-enhancing species.…”

Section: Introductionmentioning

confidence: 99%

“…As a first step in investigating the effect of turbulence, LES without and with microwave-stimulation of premixed flames in homogeneous isotropic turbulence at different Reynolds numbers is studied. Finally, the low-swirl flame from our previous work 38 is analyzed with a new approach to yield information on increase of turbulent flame speed from experiments, as well as simulations. A discussion is comprised focusing on analyzing the results in comparison with the existing experimental data and the assumptions and simplifications made in order to develop this model.…”

Section: Introductionmentioning

confidence: 99%

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Skeletal Methane–Air Reaction Mechanism for Large Eddy Simulation of Turbulent Microwave-Assisted Combustion

et al. 2017

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Irradiating a flame via microwave radiation is a plasma-assisted combustion (PAC) technology that can be used to modify the combustion chemical kinetics in order to improve flame stability and to delay lean blow-out. One practical implication is that combustion engines may be able to operate with leaner fuel mixtures and have an improved fuel flexibility capability including biofuels. Furthermore, this technology may assist in reducing thermoacoustic instabilities, which is a phenomenon that may severely damage the engine and increase NO X production. To further understand microwave-assisted combustion, a skeletal kinetic reaction mechanism for methane−air combustion is developed and presented. The mechanism is detailed enough to take into account relevant features, but sufficiently small to be implemented in large eddy simulations (LES) of turbulent combustion. The mechanism consists of a proposed skeletal methane−air reaction mechanism accompanied by subsets for ozone, singlet oxygen, chemionization, and electron impact reactions. The baseline skeletal methane−air mechanism contains 17 species and 42 reactions, and it predicts the ignition delay time, flame temperature, flame speed, major species, and most minor species well, in addition to the extinction strain, compared to the detailed GRI 3.0 reaction mechanism. The amended skeletal reaction mechanism consists of 27 species and 80 reactions and is developed for a reduced electric field E/N below the critical field strength (of ∼125 Td) for the formation of a microwave breakdown plasma. Both laminar and turbulent flame simulation studies are carried out with the proposed skeletal reaction mechanism. The turbulent flame studies consist of propagating planar flames in homogeneous isotropic turbulence in the reaction sheets and the flamelets in eddies regimes, and a turbulent low-swirl flame. A comparison with experimental data is performed for a turbulent low-swirl flame. The results suggest that we can influence both laminar and turbulent flames by nonthermal plasmas, based on microwave irradiation. The laminar flame speed increases more than the turbulent flame speed, but the radical pool created by the microwave irradiation significantly increases the lean blow-out limits of the turbulent flame, thus making it less vulnerable to thermoacoustic combustion oscillations. Apart from the experimental results from low-swirl flame presented here, experimental data for validation of the simulated trends are scarce, and conclusions build largely on simulation results. Analysis of chemical kinetics from simulations of laminar flames and LES on turbulent flames reveal that singlet oxygen molecule is of key importance for the increased reactivity, accompanied by production of radicals such as O and OH.

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Section: Energy and Fuelsmentioning

confidence: 95%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

Skeletal Methane–Air Reaction Mechanism for Large Eddy Simulation of Turbulent Microwave-Assisted Combustion

et al. 2017

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“…The experiments also focused on turbulent flames, temperature fields at ignition, burning velocity and changes in the flame position under pulsed microwave input. [6] Ju et al made a sensitivity analysis of the free electron number for different equivalence ratios. Their results indicated that the exhaust gas could possibly absorb the majority of the microwave electron heating.…”

Section: Introductionmentioning

confidence: 99%

Microwave influenced laminar premixed hydrocarbon flames: Spectroscopic investigations

Eckart

Behrend

Krause

2019

Proceedings 17th International Conference on Microwave and High Frequency Heating

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Low laminar burning velocity’s and slow reactions propagation are among a key problem in combustion processes with low calorific gas mixtures. The mixtures have a laminar burning velocity of 10 cm/s to 15 cm/s or even below which is 37% of natural gas. Thermal use of these gases could save considerable amounts of fossil fuel and reduce CO2 emissions. Due to low burning velocities and low enthalpy of combustion, ignition and stable combustion is complex, often preventing utilization of these gases. Microwave-assisted combustion can help to solve these problems. With microwave assistance, these gas mixtures could be burned with a higher burning velocity without preheating or co-firing. Therefore, this effect could be used for flame stabilization processes in industry applications. Microwaves could also change the combustion properties, for example radical formation and flame thickness. In this paper, we explore a possibility of using microwaves to increase the burning velocity of propane as one component in low calorific gas mixtures and also show higher productions of OH* and CH* radicals with an increase of the input microwave power. Different compositions of low calorific fuels were tested within a range of equivalence ratios from φ= 0.8 to φ= 1.3 for initial temperatures of 298 K and atmospheric conditions and microwave powers from 120 W to 600 W. For the experiments, a standard WR340 waveguide was modified with a port for burner installation and filter elements allowing for flue gas exhaust and optical access from the side. A 2.45 GHz CW magnetron was used as microwave source, microwave measurements were carried out with a 6-port- reflectometer with integrated three stub tuner. An axisymmetric premixed burner was designed to generate a steady conical laminar premixed flame stabilized on the outlet of a contoured nozzle under atmospheric pressure. The burner was operated with a propane mass flow of 0.2-0.4 nl/min at an equivalence ratio of φ= 0.8 to φ= 1.3. The optical techniques used in the current study are based on the flame contours detection by using the OH* chemiluminescence image technique. For every experimental case, 150 pictures were taken and averaged. Additionally, spectroscopic analysis of the flames was undertaken. The results suggest that production of OH* radicals in the flame front increases with microwave power. For evaluation, a picture based OH* chemiluminescence and a spectrographic method was used. In addition, a 9.9% increase of the burning velocity was observed in the premixed propane-air mixture for a 66 Watt absorbed microwave power. This effect is attributed to the increased OH* (~310nm) and CH* (~420nm) radical formation, which also reduces the flame thickness. It was found that absorption of microwaves in flames is generally low, but could be improved by a customized applicator design.

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Assessment of Finite Rate Chemistry Large Eddy Simulation Combustion Models

Fedina

Fureby

Bulat

et al. 2017

Flow Turbulence Combust

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Large Eddy Simulations (LES) of a swirl-stabilized natural gas-air flame in a laboratory gas turbine combustor is performed using six different LES combustion models to provide a head-to-head comparative study. More specifically, six finite rate chemistry models, including the thickened flame model, the partially stirred reactor model, the approximate deconvolution model and the stochastic fields model have been studied. The LES predictions are compared against experimental data including velocity, temperature and major species concentrations measured using Particle Image Velocimetry (PIV), OH Planar Laser-Induced Fluorescence (OH-PLIF), OH chemiluminescence imaging and one-dimensional laser Raman scattering. Based on previous results a skeletal methane-air reaction mechanism based on the well-known Smooke and Giovangigli mechanism was used in this work. Two computational grids of about 7 and 56 million cells, respectively, are used to quantify the influence of grid resolution. The overall flow and flame structures appear similar for all LES combustion models studied and agree well with experimental still and video images. Takeno flame index and chemical explosives mode analysis suggest that the flame is premixed and resides within the thin reaction zone. The LES results show good agreement with the experimental data for the axial velocity, temperature and major species, but differences due to the choice of LES combustion model are observed and discussed. Furthermore, the intrinsic flame structure and the flame dynamics are similarly predicted by all LES combustion models examined. Within this range of models, there is no strong case for deciding which model performs the best.

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Investigations of microwave stimulation of a turbulent low-swirl flame

Cited by 33 publications

References 32 publications

Skeletal Methane–Air Reaction Mechanism for Large Eddy Simulation of Turbulent Microwave-Assisted Combustion

Skeletal Methane–Air Reaction Mechanism for Large Eddy Simulation of Turbulent Microwave-Assisted Combustion

Microwave influenced laminar premixed hydrocarbon flames: Spectroscopic investigations

Assessment of Finite Rate Chemistry Large Eddy Simulation Combustion Models

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