The Influence of Premixed Combustion Flame Stabilizer Geometry on Flame Stability and Emissions

1981 ◽  
Vol 103 (4) ◽  
pp. 749-758 ◽  
Author(s):  
N. A. Al Dabbagh ◽  
G. E. Andrews
Keyword(s):  
Gas Turbines ◽  
Recirculation Zone ◽  
Combustion Efficiency ◽  
Premixed Combustion ◽  
Major Influence ◽  
Flame Stability ◽  
Zone Size ◽  
Recirculation Zones ◽  
Combustion Systems ◽  
Ultimate Objective

Premixed combustion systems for gas turbines offer the possibility of low-pollution, high-combustion efficiency and good temperature distribution. They form a basis by which other well-mixed combustion systems may be assessed. The ultimate objective of this work is the development of nonpremixed rapid mixing combustion systems. Different geometries of baffle flame stabilizers are tested to study the influence of recirculation zone size and number of recirculation zones on flame stability, combustion efficiency and NOx. The results show that the flame stabilizer geometry has a major influence on combustion efficiency and flame stability but a lesser influence on NOx. Optimum equivalence ratios are identified for good combustion efficiency and low NOx at simulated low and high-power engine conditions.

Computational Modelling of Self-Excited Combustion Instabilities

2000 ◽  
Author(s):  
Steve J. Brookes ◽  
R. Stewart Cant ◽  
Iain D. J. Dupere ◽  
Ann P. Dowling
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Release ◽  
Large Scale ◽  
Computational Modelling ◽  
Combustion Efficiency ◽  
Design Tool ◽  
Premixed Combustion ◽  
Combustion Instabilities ◽  
Combustion Systems

It is well known that lean premixed combustion systems potentially offer better emissions performance than conventional non-premixed designs. However, premixed combustion systems are more susceptible to combustion instabilities than non-premixed systems. Combustion instabilities (large-scale oscillations in heat release and pressure) have a deleterious effect on equipment, and also tend to decrease combustion efficiency. Designing out combustion instabilities is a difficult process and, particularly if many large-scale experiments are required, also very costly. Computational fluid dynamics (CFD) is now an established design tool in many areas of gas turbine design. However, its accuracy in the prediction of combustion instabilities is not yet proven. Unsteady heat release will generally be coupled to unsteady flow conditions within the combustor. In principle, computational fluid dynamics should be capable of modelling this coupled process. The present work assesses the ability of CFD to model self-excited combustion instabilities occurring within a model combustor. The accuracy of CFD in predicting both the onset and the nature of the instability is reported.

Chemical Kinetic Modeling of Ignition and Emissions From Natural Gas and LNG Fueled Gas Turbines

2012 ◽  
Author(s):  
P. Gokulakrishnan ◽  
C. C. Fuller ◽  
R. G. Joklik ◽  
M. S. Klassen
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Chemical Kinetic ◽  
Higher Order ◽  
Premixed Combustion ◽  
Nox Emissions ◽  
Lean Premixed Combustion ◽  
Lean Premixed ◽  
Combustion Systems

Single digit NOx emission targets as part of gas turbine design criteria require highly accurate modeling of the various NOx formation pathways. The concept of lean, premixed combustion is adopted in various gas turbine combustor designs, which achieves lower NOx levels by primarily lowering the flame temperature. At these conditions, the post-flame thermal-NOx pathway contribution to the total NOx can be relatively small compared to that from the prompt-NOx and the N2O-route, which are enhanced by the super-equilibrium radical pathway at the flame front. In addition, new sources of natural gas fuel (e.g., imported LNG) with widely varying chemical compositions including higher order hydrocarbon components, impact flame stability, lean blow-out limits and emissions in existing lean premixed combustion systems. Also, the presence of higher order hydrocarbons can increase the risk of flashback induced by autoignition in the premixing section of the combustor. In this work a detailed chemical kinetic model was developed for natural gas fuels that consist of CH4, C2H6, C3H8, nC4H10, iC4H10, and small amounts of nC5H12, iC5H12 and nC6H14 in order to predict ignition behavior at typical gas turbine premixing conditions and to predict CO and NOx emissions at lean premixed combustion conditions. The model was validated for different NOx-pathways using low and high pressure laminar premixed flame data. The model was also extended to include a vitiated kinetic scheme to account for the influence of exhaust gas recirculation on fuel oxidation. The model was employed in a chemical reactor network to simulate a laboratory scale lean premixed combustion system to predict CO and NOx. The current kinetic mechanism demonstrates good predictive capability for NOx emissions at lower temperatures typical of practical lean premixed combustion systems.

Computational Modeling of Self-Excited Combustion Instabilities

2001 ◽  
Vol 123 (2) ◽  
pp. 322-326 ◽  
Author(s):  
S. J. Brookes ◽  
R. S. Cant ◽  
I. D. J. Dupere ◽  
A. P. Dowling
Keyword(s):  
Fluid Dynamics ◽  
Computational Fluid Dynamics ◽  
Heat Release ◽  
Large Scale ◽  
Combustion Efficiency ◽  
Design Tool ◽  
Premixed Combustion ◽  
Combustion Instabilities ◽  
Lean Premixed Combustion ◽  
Combustion Systems

It is well known that lean premixed combustion systems potentially offer better emissions performance than conventional non-premixed designs. However, premixed combustion systems are more susceptible to combustion instabilities than non-premixed systems. Combustion instabilities (large-scale oscillations in heat release and pressure) have a deleterious effect on equipment, and also tend to decrease combustion efficiency. Designing out combustion instabilities is a difficult process and, particularly if many large-scale experiments are required, also very costly. Computational fluid dynamics (CFD) is now an established design tool in many areas of gas turbine design. However, its accuracy in the prediction of combustion instabilities is not yet proven. Unsteady heat release will generally be coupled to unsteady flow conditions within the combustor. In principle, computational fluid dynamics should be capable of modeling this coupled process. The present work assesses the ability of CFD to model self-excited combustion instabilities occurring within a model combustor. The accuracy of CFD in predicting both the onset and the nature of the instability is reported.

scholarly journals Ultra Low NOx Emissions for Gas and Liquid Fuels Using Radial Swirlers

1989 ◽  
Author(s):  
H. S. Alkabie ◽  
G. E. Andrews
Keyword(s):  
Gas Turbines ◽  
Fuel Injection ◽  
Air Flow ◽  
Combustion Efficiency ◽  
Liquid Fuels ◽  
Inlet Temperature ◽  
Flame Stability ◽  
Nox Emissions ◽  
Gas Oil ◽  
Industrial Gas Turbines

Curved blade radial swirlers using all the primary air were investigated with applications to lean burning gas turbine combustor primary zones with low NOx emissions. Two modes of fuel injection were compared, central and radial swirler pássage injection for gaseous and liquid fuels. Both fuel systems produced low NOx emissions but the upstream mixing in the swirler passages resulted in ultra low NOx emissions. A 140mm diameter atmospheric pressure combustor was used with 43% of the combustor air flow into the primary zone through the radial swirler. Radial gas composition measurements at various axial distances were made and these showed that the flame stability and NOx emissions were controlled by differences in local mixing at the base of the swirling shear layer downstream of the swirler outlet. For radial passage fuel injection it was found that a very high combustion efficiency was obtained for both propane and liquid fuels at 400K and 600K inlet temperatures. The flame stability, although worse than for central fuel injection was considerably better than for a premixed system. The NOx emissions at one bar pressure and 600K inlet temperature, compatible with a high combustion efficiency, for propane and kerosene were 3 and 6 ppm at 15% oxygen. For Gas Oil the NOx emissions were higher, but were still very low at 12ppm. Assuming a square root dependence of NOx on pressure these results indicate that NOx emissions of 48ppm for Gas Oil and less than 12ppm for gaseous fuels could be achieved at 16 bar pressure, which is typical of recent industrial gas turbines. High air flow radial swirlers with passage fuel injection have the potential for a dry solution to the NOx emissions regulations.

Lean Low NOx Primary Zones Using Radial Swirlers

1988 ◽  
Author(s):  
H. S. Alkabie ◽  
G. E. Andrews ◽  
N. T. Ahmad
Keyword(s):  
Natural Gas ◽  
Recirculation Zone ◽  
Fuel Injection ◽  
Swirling Flow ◽  
Combustion Efficiency ◽  
Flame Stability ◽  
Nox Emissions ◽  
Primary Zone ◽  
Outer Expansion ◽  
Curved Blade

Swirling flow primary zones with between 30% and 60% simulated primary zone air flow were investigated using curved blade radial swirlers. Two radial swirlers were compared with the same open area but different outlet diameters, d, giving different expansion ratios, D/d, from the swirler to the combustor diameter, D. Two combustors were used, 76 mm and 140 mm diameter, the larger one corresponding to the size of several gas turbine can combustors. There was no influence of D/d on the weak extinction. It was demonstrated that an adequate efficiency was not achieved in the weak region until there was a significant outer expansion and associated recirculation zone. It was shown that these systems with central gaseous fuel injection had good flame stability with very low NOx emissions. Propane and natural gas were compared and the NOx emissions were 50% lower with natural gas. The optimum NOx emissions, compatible with a high combustion efficiency, were close to 10 ppm NOx emissions corrected to 15% oxygen.

scholarly journals Mixing and Fuel Atomisation Effects on Premixed Combustion Performance

1983 ◽  
Author(s):  
G. E. Andrews ◽  
M. M. Abdul Aziz ◽  
N. A. Al-Dabbagh
Keyword(s):  
Liquid Fuel ◽  
Fuel Injection ◽  
Constant Pressure ◽  
Combustion Efficiency ◽  
Premixed Combustion ◽  
Flame Stability ◽  
Nox Emissions ◽  
Jet Mixing ◽  
Mixing Effects ◽  
Single Droplets

The main objective was to compare a flame stabiliser at constant pressure loss and identical isothermal aerodynamics with three modes of fuel injection: premixed, direct propane injection and direct kerosene injection. A Jet Mixing type of flame stabiliser was used at simulated gas turbine primary conditions. The influence of gaseous mixing effects was to deteriorate the combustion efficiency solely by increasing the CO emissions and to increase the NOx emissions. The flame stability was increased and low CO emissions were achieved at weaker mixtures. Liquid fuel atomisation effects resulted in a further deterioration in combustion efficiency due solely to un-burnt hydrocarbons. However, the NOx emissions were reduced indicating that local stoichiometric burning around single droplets does not occur.

scholarly journals Numerical Investigation of Pressure Influence on the Confined Turbulent Boundary Layer Flashback Process

Fluids ◽  
2019 ◽  
Vol 4 (3) ◽  
pp. 146 ◽  
Author(s):  
Aaron Endres ◽  
Thomas Sattelmayer
Keyword(s):  
Boundary Layer ◽  
Gas Turbines ◽  
Separation Zone ◽  
Turbulent Flame ◽  
Pressure Rise ◽  
Flame Speed ◽  
Zone Size ◽  
Detailed Chemical Kinetics ◽  
Turbulent Flame Speed ◽  
Quenching Distance

Boundary layer flashback from the combustion chamber into the premixing section is a threat associated with the premixed combustion of hydrogen-containing fuels in gas turbines. In this study, the effect of pressure on the confined flashback behaviour of hydrogen-air flames was investigated numerically. This was done by means of large eddy simulations with finite rate chemistry as well as detailed chemical kinetics and diffusion models at pressures between 0 . 5 and 3 . It was found that the flashback propensity increases with increasing pressure. The separation zone size and the turbulent flame speed at flashback conditions decrease with increasing pressure, which decreases flashback propensity. At the same time the quenching distance decreases with increasing pressure, which increases flashback propensity. It is not possible to predict the occurrence of boundary layer flashback based on the turbulent flame speed or the ratio of separation zone size to quenching distance alone. Instead the interaction of all effects has to be accounted for when modelling boundary layer flashback. It was further found that the pressure rise ahead of the flame cannot be approximated by one-dimensional analyses and that the assumptions of the boundary layer theory are not satisfied during confined boundary layer flashback.

Flow recirculation zone length and shear rate are differentially affected by stenosis severity in human coronary arteries

2013 ◽  
Vol 304 (4) ◽  
pp. H559-H566 ◽  
Author(s):  
Ashkan Javadzadegan ◽  
Andy S. C. Yong ◽  
Michael Chang ◽  
Austin C. C. Ng ◽  
John Yiannikas ◽  
...  
Keyword(s):  
Shear Rate ◽  
Coronary Arteries ◽  
Recirculation Zone ◽  
Fluid Dynamic ◽  
Zone Length ◽  
Flow Recirculation ◽  
Stenosis Severity ◽  
Recirculation Zones ◽  
The Relationship

Flow recirculation zones and shear rate are associated with distinct pathogenic biological pathways relevant to thrombosis and atherogenesis. The interaction between stenosis severity and lesion eccentricity in determining the length of flow recirculation zones and peak shear rate in human coronary arteries in vivo is unclear. Computational fluid dynamic simulations were performed under resting and hyperemic conditions on computer-generated models and three-dimensional (3-D) reconstructions of coronary arteriograms of 25 patients. Boundary conditions for 3-D reconstructions simulations were obtained by direct measurements using a pressure-temperature sensor guidewire. In the computer-generated models, stenosis severity and lesion eccentricity were strongly associated with recirculation zone length and maximum shear rate. In the 3-D reconstructions, eccentricity increased recirculation zone length and shear rate when lesions of the same stenosis severity were compared. However, across the whole population of coronary lesions, eccentricity did not correlate with recirculation zone length or shear rate ( P = not signficant for both), whereas stenosis severity correlated strongly with both parameters ( r = 0.97, P < 0.001, and r = 0.96, P < 0.001, respectively). Nonlinear regression analyses demonstrated that the relationship between stenosis severity and peak shear was exponential, whereas the relationship between stenosis severity and recirculation zone length was sigmoidal, with an apparent threshold effect, demonstrating a steep increase in recirculation zone length between 40% and 60% diameter stenosis. Increasing stenosis severity and lesion eccentricity can both increase flow recirculation and shear rate in human coronary arteries. Flow recirculation is much more sensitive to mild changes in the severity of intermediate stenoses than is peak shear.

scholarly journals Measurement of Air-Fuel Ratio Fluctuations Caused by Combustor Driven Oscillations

1998 ◽  
Author(s):  
Rajiv Mongia ◽  
Robert Dibble ◽  
Jeff Lovett
Keyword(s):  
Power Spectrum ◽  
Mole Fraction ◽  
Gas Turbines ◽  
Operating Conditions ◽  
Premixed Combustion ◽  
Pollutant Emissions ◽  
Combustion Instabilities ◽  
Pressure Oscillations ◽  
Lean Premixed Combustion ◽  
Lean Premixed

Lean premixed combustion has emerged as a method of achieving low pollutant emissions from gas turbines. A common problem of lean premixed combustion is combustion instability. As conditions inside lean premixed combustors approach the lean flammability limit, large pressure variations are encountered. As a consequence, certain desirable gas turbine operating regimes are not approachable. In minimizing these regimes, combustor designers must rely upon trial and error because combustion instabilities are not well understood (and thus difficult to model). When they occur, pressure oscillations in the combustor can induce fluctuations in fuel mole fraction that can augment the pressure oscillations (undesirable) or dampen the pressure oscillations (desirable). In this paper, we demonstrate a method for measuring the fuel mole fraction oscillations which occur in the premixing section during combustion instabilities produced in the combustor that is downstream of the premixer. The fuel mole fraction in the premixer is measured with kHz resolution by the absorption of light from a 3.39 μm He-Ne laser. A sudden expansion combustor is constructed to demonstrate this fuel mole fraction measurement technique. Under several operating conditions, we measure significant fuel mole fraction fluctuations that are caused by pressure oscillations in the combustion chamber. Since the fuel mole fraction is sampled continuously, a power spectrum is easily generated. The fuel mole fraction power spectrum clearly indicates fuel mole fraction fluctuation frequencies are the same as the pressure fluctuation frequencies under some operating conditions.

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