Soot Volume Fraction Measurements in the Soot-forming Regions of Ethylene-AirTurbulent Partially-premixed Flames

This paper reports an investigation of soot formation in ethylene-air partially premixed flames over a wide range of premixedness. An axisymmetric co-flow configuration is chosen to establish partially premixed flames from the fully non-premixed to fully premixed conditions. Reducing the fuel flow rate as a percentage of the maximum from the core stream and supplying the same to the annular stream leads to stratification of the reactant concentrations. The thermal power, overall equivalence ratio, and the average velocity in the both streams are maintained constant under all conditions. The soot volume fraction is estimated by light attenuation method, and laser induced incandescence is performed to map the soot distribution in the flow field. The soot volume fraction is observed to exhibit a ‘S’-type trend as the conditions are traversed from near the premixed to the non-premixed regimes. That is, when traversing from the non-premixed to near-premixed regime, below 60% fuel flow rate in core, the soot volume fraction drops drastically. The onset of sooting in the partially premixed flames is clearly seen to be at the tip of the rich-premixed flame branch of their triple flame structure, which advances upstream towards the base of the flame as the premixing is reduced. The ‘S’-type variation is clearly the effect of partial premixing, more specifically due to the presence of the lean premixed flame branch of the triple flame. Laser induced incandescence intensities are insufficient to capture the upstream advance of the soot onset with decreased premixedness. So, a quick and inexpensive technique to isolate soot luminescence through flame imaging is presented in the paper involving quasi-simultaneous imaging with a 650 nm and a BG-3 filter using a normal color camera.

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Formation of Soot in Ethylene–Air Partially Premixed Flames Over a Wide Range of Premixedness

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4037580 ◽

2017 ◽

Vol 139 (12) ◽

Author(s):

Aritra Chakraborty ◽

Satya R. Chakravarthy

Keyword(s):

Flow Rate ◽

Volume Fraction ◽

Premixed Flames ◽

Soot Volume Fraction ◽

Premixed Flame ◽

Fuel Flow Rate ◽

Fuel Flow ◽

Wide Range ◽

Partially Premixed Flames ◽

Partially Premixed

This paper reports an investigation of soot formation in ethylene–air partially premixed flames (PPFs) over a wide range of premixedness. An axisymmetric co-flow configuration is chosen to establish PPFs from the fully nonpremixed to fully premixed conditions. Reducing the fuel flow rate as a percentage of the maximum from the core stream and supplying the same to the annular stream leads to stratification of the reactant concentrations. The thermal power, overall equivalence ratio, and the average velocity in both the streams are maintained constant under all conditions. The soot volume fraction is estimated by light attenuation method, and laser-induced incandescence (LII) is performed to map the soot distribution in the flow field. The soot volume fraction is observed to exhibit an “S”-type trend as the conditions are traversed from near the premixed to the nonpremixed regimes. That is, when traversing from the nonpremixed to near-premixed regime, below 60% fuel flow rate in core, the soot volume fraction drops drastically. The onset of sooting in the PPFs is clearly seen to be at the tip of the rich-premixed flame (RPF) branch of their triple flame structure, which advances upstream toward the base of the flame as the premixing is reduced. The S-type variation is clearly the effect of partial premixing, more specifically due to the presence of the lean premixed flame (LPF) branch of the triple flame. LII intensities are insufficient to capture the upstream advance of the soot onset with decreased premixedness. So, a quick and inexpensive technique to isolate soot luminescence through flame imaging is presented in the paper involving quasi-simultaneous imaging with a 650 nm and a BG-3 filter using a normal color camera.

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Dilution and Suppression of Partially Premixed Flames in Normal and Microgravity for Different Fuels

Heat Transfer, Volume 2 ◽

10.1115/imece2006-14641 ◽

2006 ◽

Author(s):

Andrew J. Lock ◽

Alejandro Briones ◽

Suresh K. Aggarwal ◽

Ishwar K. Puri ◽

Uday G. Hegde

Keyword(s):

Volume Fraction ◽

Premixed Flames ◽

Dilution Effect ◽

Critical Volume ◽

Area Of Interest ◽

Air Stream ◽

Partially Premixed Flames ◽

Critical Volume Fraction ◽

Partially Premixed ◽

Fuel Stream

The suppression of fires and flames is an important area of interest for both terrestrial and space based applications. In this investigation we elucidate the relative efficacy of fuel and air stream inert diluents for suppressing laminar partially premixed flames. A comparison of the effects of fuel and air stream dilution are also made with other fuels. Both counterflow and coflow flames are investigated, with both normal and zerogravity conditions considered for coflow flames. Simulations are conducted for both the counterflow and coflow flames, while experimental observations are made on the coflowing flames. With fuel or air stream dilution, coflow flames are observed to move downstream from the burner after overcoming initial heat transfer coupling. Further increases in diluent result in increases in the flame liftoff height until blow off occurs. The flame liftoff height and the critical volume fraction of extinguishing agent at blow out vary with both equivalence ratio and with the stream in which diluents are introduced. Nonpremixed methane-air flames are more difficult to extinguish than partially premixed flames with fuel stream dilution; whereas, partially premixed methane-air flames are more resistant to extinction than nonpremixed flames with air stream dilution. This difference in efficacy of the fuel and air stream dilution is attributed to the action of the diluent. In leaner partially premixed flames with fuel stream dilution and richer partially premixed flames with air stream dilution the effect of the diluent is to replace the deficient reactant in the system, thus starving the flame. In leaner partially premixed flames with air stream dilution and richer partially premixed flames with fuel stream dilution the effect of the diluent is purely thermal in that it absorbs heat from the flame, until combustion may no longer be sustained. The dilution effect is more effective than the thermal effect. When gravity is eliminated from the 2-D flame the liftoff height decreases and the critical volume fraction of diluent for blow off is also decreased.

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Structure and Extinction of Heptane/Air Partially Premixed Flames

AIAA Journal ◽

10.2514/2.1565 ◽

2002 ◽

Vol 40 (11) ◽

pp. 2289-2297 ◽

Cited By ~ 10

Author(s):

Hongshe Xue ◽

Suresh K. Aggarwal

Keyword(s):

Premixed Flames ◽

Partially Premixed Flames ◽

Partially Premixed

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Simulation of turbulent non-premixed and partially premixed flames using a look-up table

Journal of Thermal Science and Technology ◽

10.1299/jtst.2014jtst0003 ◽

2014 ◽

Vol 9 (1) ◽

pp. JTST0003-JTST0003 ◽

Cited By ~ 1

Author(s):

Kazui FUKUMOTO ◽

Yoshifumi OGAMI

Keyword(s):

Premixed Flames ◽

Look Up Table ◽

Partially Premixed Flames ◽

Partially Premixed

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Numerical Analysis of Equivalence Ratio Fluctuations in a Partially Premixed Gas Turbine Combustor Using Large Eddy Simulations

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4041656 ◽

2018 ◽

Vol 141 (4) ◽

Author(s):

Ping Wang ◽

Qian Yu ◽

Prashant Shrotriya ◽

Mingmin Chen

Keyword(s):

Reaction Mechanism ◽

Equivalence Ratio ◽

Flame Temperature ◽

Premixed Flames ◽

Large Eddy Simulations ◽

Combustion Model ◽

Inlet Channel ◽

Large Eddy ◽

Partially Premixed Flames ◽

Partially Premixed

In the present work, the fluctuations of equivalence ratio in the PRECCINSTA combustor are investigated via large eddy simulations (LES). Four isothermal flow cases with different combinations of global equivalence ratios (0.7 or 0.83) and grids (1.2 or 1.8 million cells) are simulated to study the mixing process of air with methane, which is injected into the inlet channel through small holes. It is shown that the fluctuations of equivalence ratio are very large, and their ranges are [0.4, 1.3] and [0.3, 1.2] for cases 0.83 and 0.7, respectively. For simulating turbulent partially premixed flames in this burner with the well-known dynamically thickened flame (DTF) combustion model, a suitable multistep reaction mechanism should be chosen aforehand. To do that, laminar premixed flames of 15 different equivalence ratios are calculated using three different methane/air reaction mechanisms: 2S_CH4_BFER, 2sCM2 reduced mechanisms and GRI-Mech 3.0 detailed reaction mechanism. The variations of flame temperature, flame speed and thickness of the laminar flames with the equivalence ratios are compared in detail. It is demonstrated that the applicative equivalence ratio range for the 2S_CH4_BFER mechanism is [0.5, 1.3], which is larger than that of the 2sCM2 mechanism [0.5, 1.2]. Therefore, it is recommended to use the 2S_CH4_BFER scheme to simulate the partially premixed flames in the PRECCINSTA combustion chamber.

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STRUCTURE AND NOx EMISSION PROPERTIES OF PARTIALLY PREMIXED FLAMES

Advances in Chemical Propulsion ◽

10.1201/9781420040685-29 ◽

2001 ◽

pp. 473-486

Keyword(s):

Premixed Flames ◽

Nox Emission ◽

Emission Properties ◽

Partially Premixed Flames ◽

Partially Premixed

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Time and Space Series Analysis of Spectral Radiation Intensities for a Partially Premixed Turbulent Flame

Heat Transfer: Volume 2 ◽

10.1115/ht2003-47579 ◽

2003 ◽

Author(s):

Yuan Zheng ◽

Jay P. Gore

Keyword(s):

Single Point ◽

Turbulent Flame ◽

Premixed Flames ◽

Model Parameters ◽

Time And Space ◽

Spectral Radiation ◽

Series Analysis ◽

Partially Premixed Flames ◽

Partially Premixed ◽

Premixed Turbulent Flame

A recently developed technique called time and space series analysis was used to calculate the mean and fluctuating spectral radiation intensities leaving diametric and chord-like paths in turbulent partially premixed flames. A standard flame (Flame D) from Sandia Workshop on Turbulent Non-premixed Flames was selected to allow an evaluation of the radiation calculations at least at the single point statistics level. Measurements of spectral radiation intensities using a fast infrared array spectrometer provide an evaluation of the computations and also allow estimation of the length and time scales of scalar fluctuations, which appear as model parameters in the time and space series analysis modeling.

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