Experiments on Lean Blowout and NOx Emissions of a Premixed Trapped Vortex Combustor With High G-Loading

2011 ◽  
Author(s):  
Jong Guen Lee ◽  
Jeffrey P. Armstrong ◽  
Domenic A. Santavicca
Keyword(s):  
Residence Time ◽  
Equivalence Ratio ◽  
Reaction Rates ◽  
Vortex Chamber ◽  
Nox Emissions ◽  
Lower Mass ◽  
Lean Blowout ◽  
Wide Range ◽  
Gas Flame ◽  
Trapped Vortex

The feasibility of a novel combustor concept (‘g-load’ combustion with trapped-vortex chamber) to extend the premixed lean-blowout (LBO) limit and to decrease NOx emissions was experimentally determined in a scaled-modular rig that simulated a commercial 250 kilowatt microturbine combustor. The effect of a wide range of g-load’s (770–5050) on the flame regime was identified. The natural gas flame was found to be stabilized in the trapped-vortex cavity (TVC) when the equivalence ratio was within a certain range near the lean blowout limits. The TVC extended the LBO limits to marginally lower mass-based equivalence ratio levels (5%). The LBO limits were found to decrease as the g-loads decrease and the residence time increases, indicating the increase of flame mixing and reaction rates with respect to g-load is not the reason for the extension of LBO limits. The increase of residence time of mixture in the TVC was the reason for the improvement of LBO limits. The new combustor concept would enable operation at lower equivalence ratios, reducing the NOx emissions as much as much as 30%. It also showed that when the flame is contained in the trapped vortex cavity, NOx is reduced compared to baseline combustion concept without TVC.

Impact of Cooling Air Injection on the Combustion Stability of a Premixed Swirl Burner Near Lean Blowout

2013 ◽  
Vol 135 (11) ◽  
Author(s):  
A. Marosky ◽  
V. Seidel ◽  
T. Sattelmayer ◽  
F. Magni ◽  
W. Geng
Keyword(s):  
Flame Front ◽  
Equivalence Ratio ◽  
Flame Stabilization ◽  
Air Injection ◽  
Combustion Stability ◽  
Nox Emissions ◽  
Test Rig ◽  
Lean Blowout ◽  
Burner Exit ◽  
Cooling Air

In most dry, low-NOx combustor designs of stationary gas turbines, the front panel impingement cooling air is directly injected into the combustor primary zone. This air partially mixes with the swirling flow of premixed reactants from the burner and reduces the effective equivalence ratio in the flame. However, local unmixedness and the lean equivalence ratio are supposed to have a major impact on combustion performance. The overall goal of this investigation is to answer the question of whether the cooling air injection into the primary combustor zone has a beneficial effect on combustion stability and NOx emissions or not. The flame stabilization of a typical swirl burner with and without front panel cooling air injection is studied in detail under atmospheric conditions close to the lean blowout limit (LBO) in a full-scale, single-burner combustion test rig. Based on previous isothermal investigations, a typical injection configuration is implemented for the combustion tests. Isothermal results of experimental studies in a water test rig adopting high-speed planar laser-induced fluorescence (HSPLIF) reveal the spatial and temporal mixing characteristics for the experimental setup studied under atmospheric combustion. This paper focuses on the effects of cooling air injection on both flame dynamics and emissions in the reacting case. To reveal dependencies of cooling air injection on combustion stability and NOx emissions, the amount of injected cooling air is varied. OH*-chemiluminescence measurements are applied to characterize the impact of cooling air injection on the flame front. Emissions are collected for different cooling air concentrations, both global measurements at the chamber exit, and local measurements in the region of the flame front close to the burner exit. The effect of cooling air injection on pulsation level is investigated by evaluating the dynamic pressure in the combustor. The flame stabilization at the burner exit changes with an increasing degree of dilution with cooling air. Depending on the amount of cooling, only a specific share of the additional air participates in the combustion process.

NOx Emissions of a Premixed Partially Vaporized Kerosene Spray Flame

2006 ◽  
Author(s):  
Stefan Baessler ◽  
Klaus G. Mo¨sl ◽  
Thomas Sattelmayer
Keyword(s):  
Equivalence Ratio ◽  
Glass Tube ◽  
Gas Analysis ◽  
Test Case ◽  
Nox Emissions ◽  
Air Temperatures ◽  
Spray Flames ◽  
Wide Range ◽  
Phase Doppler Anemometer ◽  
Analysis System

An important question for future aero-engine combustors is how partial vaporization influences the NOx emissions of spray flames. In order to address this question an experimental study of the combustion of partially vaporized kerosene/air mixtures was conducted, which assesses the influence of the degree of fuel vaporization on the NOx emissions in a wide range of equivalence ratios covering the entire lean burning regime. The tests were performed at atmospheric pressure, inlet air temperatures of 313 to 376K, a reference mean air velocity of 1.35m/s, and equivalence ratios of 0.6, 0.7 and 0.9 using Jet A1 fuel. An ultrasonic atomizer was used to generate a fuel spray with a Sauter Mean Diameter of approximately 50μm. The spray and the heated air were mixed in a glass tube of 71mm diameter and a variable length of 0.5 to 1m. The temperature of the mixing air and the length of the preheater tube were used for the control of the degree of vaporization. Downstream of the vaporizing section, the mixture was ignited and the flame was stabilized with a hot wire ring that is electrically heated. For local exhaust measurements a temperature controlled suction probe in combination with a conventional gas analysis system were used. The vaporized ratio of the injected fuel was determined by a Phase Doppler Anemometer (PDA). In order to optimize the accuracy of these measurements, extensive validation tests with a patternator method were performed and a calibration curve was derived. The data collected in this study illustrates the effect of the vaporization rate Ψ upstream of the flame front on the NOx emissions, which changes with varying equivalence ratio and degree of vaporization. In the test case with low pre-vaporization, the equivalence ratio only has a minor influence on the NOx emissions. Experiments made with air preheat and higher degrees of vaporization show two effects: With increasing preheat air temperature, NOx emissions increase due to higher effective flame temperatures. However, with an increasing degree of vaporization, emissions become lower due to the dropping number and size of burning droplets, which act as hot spots. A correction for the effect of the preheat temperature was developed. It reveals the effect of the degree of pre-vaporization and shows that the NOx emissions are almost independent of Ψ for near-stoichiometric operation. At overall lean conditions the NOx emissions drop nonlinearly with Ψ. This leads to the conclusion that a high degree of vaporization is required in order to achieve substantial NOx abatement.

Experimental Characterization of the Combustion in Fuel Flexible Humid Power Cycles

2021 ◽  
Author(s):  
Simeon Dybe ◽  
Felix Güthe ◽  
Michael Bartlett ◽  
Panagiotis Stathopoulos ◽  
Christian Oliver Paschereit
Keyword(s):  
Natural Gas ◽  
Equivalence Ratio ◽  
High Efficiency ◽  
Full Potential ◽  
Nox Emissions ◽  
Nox Formation ◽  
Fuel Blend ◽  
Power Cycles ◽  
Wide Range ◽  
Renewable Electricity Generation

Abstract Modified humid power cycles provide the necessary boundary condition for combustion to operate on a wide fuel spectrum in a steam-rich atmosphere comprising hydrogen and syngas from gasification besides natural gas as fuels. Thus, these cycles with their high efficiency and flexibility fit in a carbon-free energy market dominated by renewable electricity generation, providing dispatchable heat and electric power. To realize their full potential, the combustor utilized in such power cycles must fulfill the emission limits as well as demands of stable combustion over a wide range of fuel and steam ratios. The operation is limited by the risk of lean blowout for highly diluted syngas with low reactivity, and flashback for highly reactive hydrogen. Further, the gasification product gas can contain unwanted pollutants such as tars and nitrogen containing species like ammonia (NH3). Tars carry a considerable portion of the feedstock’s energy but are associated with detrimental operational behavior. The presence of ammonia in the combustion increases the risk of high NOx-emission at already small ammonia concentrations in the fuel. In this work, humid hydrogen flames are analyzed for their stability and emissions. Stable hydrogen flames were produced over a wide equivalence ratio and steam ratio range at negligible NOx-emissions. Further, natural gas, and a fuel blend substituting bio-syngas, was doped with ammonia. The combustion is analyzed with a focus on emissions and flame position and stability. The addition of ammonia causes high NOx-formation from fuel bound nitrogen (FBN), which highly increases NOx-emissions. The latter decrease with increasing NH3 content and increasing equivalence ratio.

Impact of Cooling Air Injection on the Combustion Stability of a Premixed Swirl Burner Near Lean Blowout

2013 ◽  
Author(s):  
A. Marosky ◽  
V. Seidel ◽  
T. Sattelmayer ◽  
F. Magni ◽  
W. Geng
Keyword(s):  
Flame Front ◽  
Equivalence Ratio ◽  
Flame Stabilization ◽  
Air Injection ◽  
Combustion Stability ◽  
Nox Emissions ◽  
Test Rig ◽  
Lean Blowout ◽  
Burner Exit ◽  
Cooling Air

In most dry low NOx combustor designs of stationary gas turbines the front panel impingement cooling air is directly injected into the combustor primary zone. This air partially mixes with the swirling flow of premixed reactants from the burner and reduces the effective equivalence ratio in the flame. However, local unmixedness and the lean equivalence ratio are supposed to have a major impact on combustion performance. Overall goal of this investigation is to answer the question whether the cooling air injection into the primary combustor zone has a beneficial effect on combustion stability and NOx emissions or not. The flame stabilization of a typical swirl burner with and without front panel cooling air injection is studied in detail under atmospheric conditions close to the lean blowout limit (LBO) in a full scale single burner combustion test rig. Based on previous isothermal investigations a typical injection configuration is implemented for the combustion tests. Isothermal results of experimental studies in a water test rig adopting high speed planar laser-induced fluorescence (HSPLIF) reveal the spatial and temporal mixing characteristics for the experimental setup studied under atmospheric combustion. This paper focuses on the effects of cooling air injection on both flame dynamics and emissions in the reacting case. To reveal dependencies of cooling air injection on combustion stability and NOx emissions, the amount of injected cooling air is varied. OH*-chemiluminescence measurements are applied to characterize the impact of cooling air injection on the flame front. Emissions are collected for different cooling air concentrations, both global measurements at the chamber exit and local measurements in the region of the flame front close to the burner exit. The effect of cooling air injection on pulsation level is investigated by evaluating the dynamic pressure in the combustor. The flame stabilization at the burner exit changes with an increasing degree of dilution with cooling air. Depending on the amount of cooling only a specific share of the additional air participates in the combustion process.

scholarly journals Numerical study of flame/vortex interactions in 2-D Trapped Vortex Combustor

2014 ◽  
Vol 18 (4) ◽  
pp. 1373-1387 ◽  
Author(s):  
Prasad Mishra ◽  
Renganathan Sudharshan ◽  
Kumar Ezhil
Keyword(s):  
Numerical Study ◽  
Flame Structure ◽  
Reaction Rates ◽  
Operating Conditions ◽  
Navier Stokes ◽  
Base Case ◽  
Primary Vortex ◽  
Vortex Interactions ◽  
Wide Range ◽  
Trapped Vortex

The interactions between flame and vortex in a 2-D Trapped Vortex Combustor are investigated by simulating the Reynolds Averaged Navier Stokes (RANS) equations, for the following five cases namely (i) non-reacting (base) case, (ii) post-vortex ignition without premixing, (iii) post-vortex ignition with premixing, (iv) pre-vortex ignition without premixing and (v) pre-vortex ignition with premixing. For the post-vortex ignition without premixing case, the reactants are mixed well in the cavity resulting in a stable ?C? shaped flame along the vortex edge. Further, there is insignificant change in the vorticity due to chemical reactions. In contrast, for the pre-vortex ignition case (no premixing); the flame gets stabilized at the interface of two counter rotating vortices resulting in reduced reaction rates. There is a noticeable change in the location and size of the primary vortex as compared to case (ii). When the mainstream air is premixed with fuel, there is a further reduction in the reaction rates and thus structure of cavity flame gets altered significantly for case (v). Pilot flame established for cases (ii) and (iii) are well shielded from main flow and hence the flame structure and reaction rates do not change appreciably. Hence, it is expected that cases (ii) and (iii) can perform well over a wide range of operating conditions.

Lean Blowout Limits and NOx Emissions of Turbulent, Lean Premixed, Hydrogen-Enriched Methane/Air Flames at High Pressure

2006 ◽  
Author(s):  
P. Griebel ◽  
E. Boschek ◽  
P. Jansohn
Keyword(s):  
High Pressure ◽  
Nox Reduction ◽  
Flame Temperature ◽  
Operating Conditions ◽  
Flame Stability ◽  
Nox Emissions ◽  
Lean Blowout ◽  
Wide Range ◽  
Pure Methane ◽  
Lean Premixed

Flame stability is a crucial issue in low NOx combustion systems operating at extremely lean conditions. Hydrogen enrichment seems to be a promising option to extend lean blowout limits of natural gas combustion. This experimental study addresses flame stability enhancement and NOx reduction in turbulent, high-pressure, lean premixed methane/air flames in a generic combustor, capable of a wide range of operating conditions. Lean blowout limits (LBO) and NOx emissions are presented for pressures up to 14 bars, bulk velocities in the range of 32–80 m/s, two different preheating temperatures (673 K, 773 K), and a range of fuel mixtures from pure methane to 20% H2/80% CH4 by volume. The influence of turbulence on LBO limits is discussed, too. In addition to the investigation of perfectly premixed H2-enriched flames, LBO and NOx are also discussed for hydrogen piloting. Experiments have revealed that a mixture of 20% hydrogen and 80% methane, by volume, can typically extend the lean blowout limit by roughly 10% compared to pure methane. The flame temperature at LBO is approximately 60 K lower resulting in the reduction of NOx concentration by ≈ 35% (0.5 → 0.3 ppm/15% O2).

Prediction of the NOx-Emissions of a Swirl Burner in Partially and Fully Premixed Mode on the Basis of Water Channel LIF and PIV Measurements

2013 ◽  
Author(s):  
J. Sangl ◽  
C. Mayer ◽  
T. Sattelmayer
Keyword(s):  
Equivalence Ratio ◽  
Fuel Injection ◽  
Water Channel ◽  
Premixed Combustion ◽  
Nox Emissions ◽  
Swirl Burner ◽  
Engine Operation ◽  
Measured Velocity ◽  
Wide Range ◽  
Air Mixing

The paper describes the development and validation of an efficient and cost effective method for the prediction of the NOx emissions of turbulent gas turbine burners in the early burner design phases which are usually focused on the optimization of the swirler aerodynamics and the fuel air mixing. As the method solely relies on non-reacting tests of burner models in the water channel it can be applied before any test equipment for combustion experiments exists. In order to achieve optimum similarity of fuel air mixing in the water channel tests with engine operation the model is operated at the engine momentum ratio. During the LIF measurements the water flow representing the fuel is doped with fluorescent dye, a plane perpendicular to the length axis near the burner exit plane is illuminated with a 5W Ar-Ion Laser and the fluorescence is recorded with a video camera from downstream. From the video sequences the local probability density functions (PDF) of the dye concentration fluctuations are calculated from the data. Furthermore, the time mean velocity fields are measured with PIV. From the LIF data the PDFs of the local equivalence ratio are derived. Assuming flamelets, the NOx generation in the entire equivalence ratio range observed in the water channel tests is computed using the unstrained freely propagating one-dimensional flame model in Cantera and the GRI3.0 reaction scheme. Although neither flame stretch nor post flame NOx generation were considered the NOx values computed were in excellent agreement with the experimental data from perfectly premixed combustion experiments. The local time averaged NOx mole fraction is obtained by integrating the flamelet NOx over the mixture PDF. Finally the global NOx emission of the burner at the considered operating point is obtained by spatial integration considering the measured velocity field. The method was validated using a conical swirl burner with two fuel injection stages, allowing the degree of premixedness to be adjusted over a wide range depending on the specific fuel injection scenario. For the case with fuel injection along the air inlet slots NOx values slightly above the minimum NOx limit for perfectly premixed combustion were computed. This is consistent with the emission measurements and indicates finite mixing quality of this injection method. In the partially premixed regime the configurations with potential for low NOx emissions were reliably identified with the LIF and PIV based water channel method. The method also shows the steep increase of the NOx emissions with decreasing degree of premixing observed in the experiments but quantitative predictions would have required a postprocessing of the data from the LIF mixing study with a higher spacial resolution than available.

N O x Emissions of a Premixed Partially Vaporized Kerosene Spray Flame

2006 ◽  
Vol 129 (3) ◽  
pp. 695-702 ◽  
Author(s):  
Stefan Baessler ◽  
Klaus G. Mösl ◽  
Thomas Sattelmayer
Keyword(s):  
Equivalence Ratio ◽  
Glass Tube ◽  
Gas Analysis ◽  
Test Case ◽  
Nox Emissions ◽  
Air Temperatures ◽  
Spray Flames ◽  
Wide Range ◽  
Phase Doppler Anemometer ◽  
Analysis System

An important question for future aeroengine combustors is how partial vaporization influences the NOx emissions of spray flames. In order to address this question an experimental study of the combustion of partially vaporized kerosene/air mixtures was conducted. This assesses the influence of the degree of fuel vaporization on the NOx emissions in a wide range of equivalence ratios covering the entire lean burning regime. The tests were performed at atmospheric pressure, inlet air temperatures of 313–376K, a reference mean air velocity of 1.35m∕s, and equivalence ratios of 0.6, 0.7, and 0.9 using Jet A1 fuel. An ultrasonic atomizer was used to generate a fuel spray with a Sauter Mean Diameter of approximately 50μm. The spray and the heated air were mixed in a glass tube of 71mm diameter and a variable length of 0.5–1m. The temperature of the mixing air and the length of the preheater tube were used for the control of the degree of vaporization. Downstream of the vaporizing section, the mixture was ignited and the flame was stabilized with a hot wire ring that was electrically heated. For local exhaust measurements a temperature controlled suction probe in combination with a conventional gas analysis system were used. The vaporized ratio of the injected fuel was determined by a Phase Doppler Anemometer (PDA). In order to optimize the accuracy of these measurements extensive validation tests with a patternator method were performed and a calibration curve was derived. The data collected in this study illustrates the effect of the vaporization rate ψ upstream of the flame front on the NOx emissions which changes with varying equivalence ratio and degree of vaporization. In the test case with low prevaporization the equivalence ratio only has a minor influence on the NOx emissions. Experiments made with air preheat and higher degrees of vaporization show two effects: With increasing preheat air temperature, NOx emissions increase due to higher effective flame temperatures. However, with an increasing degree of vaporization, emissions become lower due to the dropping number and size of burning droplets, which act as hot spots. A correction for the effect of the preheat temperature was developed. It reveals the effect of the degree of prevaporization and shows that the NOx emissions are almost independent of ψ for near-stoichiometric operation. At overall lean conditions the NOx emissions drop nonlinearly with ψ. This leads to the conclusion that a high degree of vaporization is required in order to achieve substantial NOx abatement.

Lean Blowout Limits and NOx Emissions of Turbulent, Lean Premixed, Hydrogen-Enriched Methane/Air Flames at High Pressure

2006 ◽  
Vol 129 (2) ◽  
pp. 404-410 ◽  
Author(s):  
P. Griebel ◽  
E. Boschek ◽  
P. Jansohn
Keyword(s):  
High Pressure ◽  
Nox Reduction ◽  
Flame Temperature ◽  
Operating Conditions ◽  
Flame Stability ◽  
Nox Emissions ◽  
Lean Blowout ◽  
Wide Range ◽  
Pure Methane ◽  
Lean Premixed

Flame stability is a crucial issue in low NOx combustion systems operating at extremely lean conditions. Hydrogen enrichment seems to be a promising option to extend lean blowout limits (LBO) of natural gas combustion. This experimental study addresses flame stability enhancement and NOx reduction in turbulent, high-pressure, lean premixed methane/air flames in a generic combustor capable of a wide range of operating conditions. Lean blowout limits and NOx emissions are presented for pressures up to 14bar, bulk velocities in the range of 32–80m∕s, two different preheating temperatures (673K, 773K), and a range of fuel mixtures from pure methane to 20% H2∕80%CH4 by volume. The influence of turbulence on LBO limits is also discussed. In addition to the investigation of perfectly premixed H2-enriched flames, LBO and NOx are also discussed for hydrogen piloting. Experiments have revealed that a mixture of 20% hydrogen and 80% methane, by volume, can typically extend the lean blowout limit by ∼10% compared to pure methane. The flame temperature at LBO is ∼60K lower resulting in the reduction of NOx concentration by ≈35%(0.5→0.3ppm∕15%O2).

Compact Combustion Systems Using a Combination of Trapped Vortex and High-G Combustor Technologies

2008 ◽  
Author(s):  
J. Zelina ◽  
W. Anderson ◽  
P. Koch ◽  
D. T. Shouse
Keyword(s):  
High Performance ◽  
Combustion Efficiency ◽  
Operating Conditions ◽  
Fuel Injector ◽  
Flammability Limits ◽  
Turbine Engine ◽  
Lean Blowout ◽  
Wide Range ◽  
Combustion Systems ◽  
Trapped Vortex

Major advances in combustor technology are required to meet the conflicting challenges of improving performance, increasing durability and maintaining cost. Ultra-short combustors to minimize residence time, with special flame-holding mechanisms to cope with increased through-velocities are likely in the future. This paper focuses on vortex-stabilized combustor technologies that can enable the design of compact, high-performance combustion systems. Compact combustors weigh less and take up less volume in space-limited turbine engine for aero applications. This paper presents the UCC, a novel design based on TVC work that uses high swirl in a circumferential cavity to enhance mixing rates via high cavity g-loading on the order of 3000 g’s. The UCC design integrates compressor and turbine features which will enable a shorter and potentially less complex gas turbine engine. Ultimately, it is envisioned that this type of combustion system can be used as the main combustor and/or as a secondary combustor between the high pressure and low pressure turbine to operate as a reheat cycle engine. The focus on this paper includes experimental results of the UCC for a variety of conditions: (1) the addition of turbine vanes in the combustor flowpath, (2) a comparison of JP-8 and FT fuel performance in the combustor, (3) the use of trapped-vortex-like air addition to increase combustor flammability limits, and (4) combustor performance related to two different fuel injector designs. Lean blowout fuel-air ratio limits at 20% the value of current systems were demonstrated. Combustion efficiency was measured over a wide range of UCC operating conditions. This data begins to build the design space required for future engine designs that may use these novel, compact, high-g combustion systems.

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