Design of Inlet Conditions for High Pressure NOx Measurements in Lean Premixed Combustors

1995 ◽  
Author(s):  
Jon P. McDonald ◽  
Arthur M. Mellor
Keyword(s):  
Sensitivity Analysis ◽  
Natural Gas ◽  
Equivalence Ratio ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
Oxides Of Nitrogen ◽  
Nox Formation ◽  
Lean Premixed ◽  
Inlet Conditions

Semi–empirical characteristic time models (CTMs) for NOx emissions index (EI) and lean blowoff are used in the design of an inlet condition matrix for measurement of NOxEI from a lean premixed combustor. Such models relate either NOxEI or the weak extinction limit to times representing relevant physical and chemical processes in the combustor. Lean premixed (LP) natural gas/air combustion is considered for the following conditions: inlet temperature, 300–800 K; combustor pressure, 1–30 atm; and equivalence ratio, 0.5–0.7. The NOx model is used to determine combinations of inlet conditions corresponding to greatest NOx sensitivity. A dependence of NOx emissions on pressure is included in the model. Emissions of oxides of nitrogen are found to he most sensitive to variations in inlet temperature and combustor pressure, in the 560–800 K and 20–30 atm ranges, respectively, while sensitivity to variations in equivalence ratio is substantial over the entire range considered. Thus it is found that operating conditions for high thermal efficiency in LP turbine combustors conflict with the goal of lowering NOx emissions, a result consistent with thermal NOx from conventional, diffusion flame combustors. A lean blowoff model is used to estimate the lowest equivalence ratio at which a flame can he held, as well as to determine whether a flame can be stabilised at the operating conditions suggested by the NOx sensitivity analysis. The results suggest a nominal lower limit on equivalence ratio of 0.4, and that a flame can be held for most of the combinations of inlet conditions suggested by the NOx sensitivity analysis. Autoignition of the fuel/air mixture is also considered in relation to the location and/or design of the premixing system. The current NOx CTM is applied to LP natural gas fired data from the literature. A model modification, thought to better represent the fluid mechanics relevant to LP NOx formation, is applied, and its implications discussed.

Engine Testing of a Natural Gas-Fired, Low-NOx, Variable Geometry Gas Turbine Combustor for a Small Gas Turbine

1996 ◽  
Author(s):  
Shigeru Hayashi ◽  
Hideshi Yamada ◽  
Kazuo Shimodaira
Keyword(s):  
Natural Gas ◽  
Gas Turbine ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
Variable Geometry ◽  
Wide Range ◽  
Lean Premixed ◽  
Full Power ◽  
Engine Testing

The development of a variable geometry lean-premixed combustor is in progress at NAL. Engine testing has been cooducted by using a natural gas-fueled 210-kW gas turbine to demonstrate the capability of ultra-low NOx emissions over a wide range of eogine operation. This paper describes the effort of engine testing of the combustor to achieve NOx emissions of the 10-ppm level. Fuel was staged to the non-premixed pilot and premixed main burners. A butterfly valve air splitting system was employed to maintain both low NOx emissions and high efficieocy over a wide operating range of the engine. The engioe was operated in the lean-premixed, low NOx emissions mode from idle to full power. Over the whole operating conditions from idle to full power, NOx emissions were reduced to levels less than 25 ppm (15% O2 dry). The NOx emissions level for a nearly constant combustion efficiency decreased with increasing power or turbine inlet temperature. At operating conditions of 90% to full power, NOx emissions levels of 12 to 8 ppm (15% O2 dry) were measured with combustion efficiencies of 99.7 to 99.1%.

A Literature Review of NOx Formation Kinetics and a Prediction Method for Lean-Burn, Two-Stroke Natural Gas Engines

2019 ◽  
Author(s):  
Taylor F. Linker ◽  
Mark Patterson ◽  
Greg Beshouri ◽  
Abdullah U. Bajwa ◽  
Timothy J. Jacobs
Keyword(s):  
Natural Gas ◽  
Chemical Properties ◽  
Prediction Method ◽  
Operating Conditions ◽  
Combustion Mechanism ◽  
Nox Emissions ◽  
Lean Burn ◽  
Nox Formation ◽  
Gas Combustion ◽  
No2 Formation

Abstract The increased production of natural gas harvested from unconventional sources, such as shale, has led to fluctuations in the species composition of natural gas moving through pipelines. These variations alter the chemical properties of the bulk gas mixture and, consequently, affect the operation of pipeline compressor engines which use the gas as fuel. Among several possible ramifications of these variations is that of unacceptably high engine-out NOx emissions. Therefore, engine controller enhancements which can account for fuel variability are necessary for maintaining emissions compliance. Having the means to predict NOx emissions from a field engine can inform the development of such control schemes. There are several types of compressor engines; however, this study considers a large bore, lean-burn, two-stroke, integral compressor engine. This class of engine has unique operating conditions which make the formation of engine-out NOx different from typical automotive spark-ignited engines. For this reason, automotive-based methods for predicting NOx emissions are not sufficiently accurate. In this study, an investigation is performed on the possible NO and NO2 formation pathways which could be contributing to exhaust emissions. Additionally, a modeling method is proposed to predict engine-out NOx emissions using a 0-D/1-D model of a Cooper-Bessemer GMWH-10C compressor engine. Predictions are achieved with GRI-Mech3.0, a natural gas combustion mechanism, which allows for simulated formation of NOx species. The implemented technique is tuned using experimental data from a field engine to better predict emissions over a range of engine operating conditions. Tuning the model led to acceptable agreement across operating points varying in both load and trapped equivalence ratio.

A NOx Prediction Scheme for Lean-Premixed Gas Turbine Combustion Based on Detailed Chemical Kinetics

1996 ◽  
Vol 118 (4) ◽  
pp. 765-772 ◽  
Author(s):  
W. Polifke ◽  
K. Do¨bbeling ◽  
T. Sattelmayer ◽  
D. G. Nicol ◽  
P. C. Malte
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Concentration Field ◽  
Operating Conditions ◽  
Chemical Mechanism ◽  
Reacting Flow ◽  
Oxides Of Nitrogen ◽  
Detailed Chemical Kinetics ◽  
Nox Formation ◽  
Lean Premixed

The lean-premixed technique has proven very efficient in reducing the emissions of oxides of nitrogen (NOx) from gas turbine combustors. The numerical prediction of NOx levels in such combustors with multidimensional CFD codes has only met with limited success so far. This is to some extent due to the complexity of the NOx formation chemistry in lean-premixed combustion, i.e., all three known NOx formation routes (Zeldovich, nitrous, and prompt) can contribute significantly. Furthermore, NOx formation occurs almost exclusively in the flame zone, where radical concentrations significantly above equilibrium values are observed. A relatively large chemical mechanism is therefore required to predict radical concentrations and NOx formation rates under such conditions. These difficulties have prompted the development of a NOx postprocessing scheme, where rate and concentration information necessary to predict NOx formation is taken from one-dimensional combustion models with detailed chemistry and provided—via look-up tables—to the multidimensional CFD code. The look-up tables are prepared beforehand in accordance with the operating conditions and are based on CO concentrations, which are indicative of free radical chemistry. Once the reacting flow field has been computed with the main CFD code, the chemical source terms of the NO transport equation, i.e., local NO formation rates, are determined from the reacting flow field and the tabulated chemical data. Then the main code is turned on again to compute the NO concentration field. This NOx submodel has no adjustable parameters and converges very quickly. Good agreement with experiment has been observed and interesting conclusions concerning superequilibrium O-atom concentrations and fluctuations of temperature could be drawn.

Using Multi-Dimensional Combustion Simulations of a Natural Gas/Diesel Dual Fuel Engine to Investigate NOx Trends With Air-Fuel Ratio

2017 ◽  
Author(s):  
Andrew Hockett ◽  
Michael Flory ◽  
Joel Hiltner ◽  
Scott Fiveland
Keyword(s):  
Natural Gas ◽  
Oil And Gas ◽  
Operating Conditions ◽  
Dual Fuel ◽  
Nox Emissions ◽  
Nox Formation ◽  
Jet Flame ◽  
Gas Drilling ◽  
Fuel Ratio ◽  
Wide Range

Natural gas/diesel dual fuel engines used in oil and gas drilling operations must be able to meet NOx emissions limits across a wide range of substitution percentage, which affects the air to natural gas ratio or gas lambda. In a dual fuel engine operating at high substitution, premixed, propagating natural gas flames occur and the NOx formed in such premixed flames is known to be a strong function of gas lambda. Consequently there is interest in understanding how NOx formation in a dual fuel engine is affected by gas lambda. However, NOx formation in a dual fuel engine is complicated by the interaction with the non-premixed diesel jet flame. As a result, previous studies have shown that enriching the air-fuel ratio can either increase or decrease NOx emissions depending on the operating conditions investigated. This study presents multi-dimensional combustion simulations of an air-fuel ratio sweep from gas lambda 2.0 to 1.5 at 80% substitution, which exhibited a minimum in NOx emissions at a natural gas lambda of 1.75. Images from the simulations are used to provide detailed explanations of the physical processes responsible for the minimum NOx trend with natural gas lambda.

CFD Simulation of Humid Air Premixed Flame Combustion Chamber for Evaporative Gas Turbine Cycles

2001 ◽  
Author(s):  
M. Bianco ◽  
S. M. Camporeale ◽  
B. Fortunato
Keyword(s):  
Combustion Chamber ◽  
Equivalence Ratio ◽  
Flame Temperature ◽  
Oxidation Mechanism ◽  
Premixed Flame ◽  
Inlet Temperature ◽  
Nox Emissions ◽  
Humid Air ◽  
Nox Formation ◽  
Operation Conditions

Evaporative cycles, such as Recuperated Water lnjected (RWI) cycle, Humid Air Turbine (HAT) cycle, Cascaded Humidified Advanced Turbine (CHAT) offer the attractive possibility to increase plant efficiency without the use of a steam turbine, necessary for gas-steam combined cycles, appearing, therefore, as an interesting solution for industrial power applications such as electric utilities and independent power producers. It is expected that water addition may contribute to reduce NOx emissions in premixed flame combustors. In order to analyse this solution, a lean-bum combustor, fed with an homogeneous mixture formed by methane and humid air, has been analysed through CFD simulations, in order to predict velocity field, temperatures and emissions. The study has been carried out under the hypothesis of a two-dimensional, axisymmetric combustion chamber assuming, as set of operation conditions, atmospheric pressure, inlet temperature of 650 K, fuel-air equivalence ratio of the methane-air mixture ranging from 0.5 to 0.7 and water-air mass ratio varying from 0% to 5%. In the simulation, the presence of turbulence in the flow has been taken into account using a RNG k-ε model, whilst the chemical behaviour of the system has been described by means of a five-step global reduced mechanism including the oxidation mechanism and the NOx formation mechanism. The analysis of the results shows that the moisture in the premixed flow reduces both NOx and CO emissions at constant equivalence ratio; moreover the lean blow-out limit is shifted toward higher equivalence ratio. The main effect of the water seems to be the increase of the specific heat the mixture which causes a reduction in flame temperature, slowing the chemical reactions responsible of NOx formation. The reasonable agreement has been found between the simulation results concerning NOx emissions and recent experimental results carried out on premixed flamed with humid air. A discussion is also provided about the adopted turbulence models and their influence on the emission results.

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.

scholarly journals A NOx Prediction Scheme for Lean-Premixed Gas Turbine Combustion Based on Detailed Chemical Kinetics

1995 ◽  
Author(s):  
Wolfgang Polifke ◽  
Klaus Döbbeling ◽  
Thomas Sattelmayer ◽  
David G. Nicol ◽  
Philip C. Malte
Keyword(s):  
Flow Field ◽  
Gas Turbine ◽  
Concentration Field ◽  
Operating Conditions ◽  
Chemical Mechanism ◽  
Reacting Flow ◽  
Oxides Of Nitrogen ◽  
Nox Formation ◽  
Processing Scheme ◽  
Lean Premixed

The lean-premixed technique has proven very efficient in reducing the emissions of oxides of nitrogen (NOx) from gas turbine combustors. The numerical prediction of NOx-levels in such combustors with multidimensional CFD codes has only met with limited success so far. This is at least to some extent due to the complexity of the NOx formation chemistry in lean-premixed combustion, i.e. all three known NOx formation routes (Zeldovich, nitrous and prompt) can contribute significantly. Furthermore, NOx formation occurs almost exclusively in the flame zone, where radical concentrations significantly above equilibrium values are observed. A relatively large chemical mechanism is therefore required to predict radical concentrations and NOx formation rates under such conditions. These difficulties have prompted the development of a NOx post-processing scheme, where rate and concentration information necessary to predict NOx formation is taken from one-dimensional combustion models with detailed chemistry and provided — via look-up tables — to the multi-dimensional CFD code. The look-up tables are prepared beforehand in accordance with the operating conditions and are based on CO concentrations, which are indicative of free radical chemistry. Once the reacting flow field has been computed with the main CFD code, the chemical source terms of the NO transport equation, i.e. local NO formation rates, are determined from the reacting flow field and the tabulated chemical data. Then the main code is turned on again to compute the NO concentration field. This NOx sub-model has no adjustable parameters and converges very quickly. Good agreement with experiment has been observed and interesting conclusions concerning superequilibrium O-atom concentrations and fluctuations of temperature could be drawn.

Influence of Pressure and Steam Dilution on NOx and CO Emissions in a Premixed Natural Gas Flame

2013 ◽  
Author(s):  
Sebastian Göke ◽  
Sebastian Schimek ◽  
Steffen Terhaar ◽  
Thoralf Reichel ◽  
Katharina Göckeler ◽  
...  
Keyword(s):  
Natural Gas ◽  
Scaling Laws ◽  
Combustion Process ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Nox Formation ◽  
Combustion Chemistry ◽  
Air Mass ◽  
Gas Flame ◽  
Reactor Network

In the current study, the influence of pressure and steam on the emission formation in a premixed natural gas flame is investigated at pressures between 1.5 bar and 9 bar. A premixed, swirl-stabilized combustor is developed that provides a stable flame up to very high steam contents. Combustion tests are conducted at different pressure levels for equivalence ratios from lean blowout to near-stoichiometric conditions and steam-to-air mass ratios from 0% to 25%. A reactor network is developed to model the combustion process. The simulation results match the measured NOx and CO concentrations very well for all operating conditions. The reactor network is used for a detailed investigation of the influence of steam and pressure on the NOx formation pathways. In the experiments, adding 20% steam reduces NOx and CO emissions to below 10 ppm at all tested pressures up to near-stoichiometric conditions. Pressure scaling laws are derived: CO changes with a pressure exponent of approximately −0.5 that is not noticeably affected by the steam. For the NOx emissions, the exponent increases with equivalence ratio from 0.1 to 0.65 at dry conditions. At a steam-to-air mass ratio of 20%, the NOx pressure exponent is reduced to −0.1 to +0.25. The numerical analysis reveals that steam has a strong effect on the combustion chemistry. The reduction in NOx emissions is mainly caused by lower concentrations of atomic oxygen at steam-diluted conditions, constraining the thermal pathway.

Influence of Pressure and Steam Dilution on NOx and CO Emissions in a Premixed Natural Gas Flame

2014 ◽  
Vol 136 (9) ◽  
Author(s):  
Sebastian Göke ◽  
Sebastian Schimek ◽  
Steffen Terhaar ◽  
Thoralf Reichel ◽  
Katharina Göckeler ◽  
...  
Keyword(s):  
Natural Gas ◽  
Scaling Laws ◽  
Combustion Process ◽  
Operating Conditions ◽  
Nox Emissions ◽  
Nox Formation ◽  
Combustion Chemistry ◽  
Air Mass ◽  
Gas Flame ◽  
Reactor Network

In the current study, the influence of pressure and steam on the emission formation in a premixed natural gas flame is investigated at pressures between 1.5 bar and 9 bar. A premixed, swirl-stabilized combustor is developed that provides a stable flame up to very high steam contents. Combustion tests are conducted at different pressure levels for equivalence ratios from lean blowout to near-stoichiometric conditions and steam-to-air mass ratios from 0% to 25%. A reactor network is developed to model the combustion process. The simulation results match the measured NOx and CO concentrations very well for all operating conditions. The reactor network is used for a detailed investigation of the influence of steam and pressure on the NOx formation pathways. In the experiments, adding 20% steam reduces NOx and CO emissions to below 10 ppm at all tested pressures up to near-stoichiometric conditions. Pressure scaling laws are derived: CO changes with a pressure exponent of approximately −0.5 that is not noticeably affected by the steam. For the NOx emissions, the exponent increases with equivalence ratio from 0.1 to 0.65 at dry conditions. At a steam-to-air mass ratio of 20%, the NOx pressure exponent is reduced to −0.1 to +0.25. The numerical analysis reveals that steam has a strong effect on the combustion chemistry. The reduction in NOx emissions is mainly caused by lower concentrations of atomic oxygen at steam-diluted conditions, constraining the thermal pathway.

scholarly journals Performance and Sensitivity analysis of Factors Affecting NOx Emissions from Hydrogen Fueled SI Engine

2016 ◽  
Vol 6 (2) ◽  
pp. 47-74
Author(s):  
Eiman Ali Eh. Sheet
Keyword(s):  
Sensitivity Analysis ◽  
Equivalence Ratio ◽  
Engine Speed ◽  
Simulation Software ◽  
Spark Ignition Engine ◽  
P Value ◽  
Nox Emissions ◽  
Oxides Of Nitrogen ◽  
Factors Affecting ◽  
Performance And Emission

An Analysis of Variance (ANOVA) sensitivity analysis using suitable MATLAB code onthe factors affecting oxides of Nitrogen (NOx) emissions of a hydrogen powered 4-stroke,water-cooled spark-ignition engine was conducted in this work. This was done usingspecialized engine performance and emission simulation software. The parameters studiedwere the engine speed, air-fuel equivalence ratio, spark plug location in addition to some othercombustion parameters like combustion duration, heat loss besides some other usefulperformance parameters. It was found that NOx formation is minimum at peripheral sparklocation, slightly lean (PHI=0.9), and less advance timing is needed. Further, based onANOVA analysis, the combination of engine speed and spark location has more significance(effect based on P-value) compared with engine speed and equivalence ratio. The combinationof engine speed and ignition timing has more significance (effect based on P-value) comparedwith engine speed and equivalence ratio. Also found that NOx emissions behavior is moreclear at lean mixture (PHI = 0.7), central spark location (XSP = 0.5) and retarded ignitiontiming (IGN near zero).

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