On Diluted-Fuel Combustion Issues in Burning Biogas Surrogates

2009 ◽  
Vol 131 (4) ◽  
Author(s):  
David A. Wilson ◽  
Kevin M. Lyons
Keyword(s):  
Carbon Dioxide ◽  
Equivalence Ratio ◽  
Burning Velocity ◽  
Fuel Combustion ◽  
Flame Stabilization ◽  
Stable Operation

This paper describes an analysis of the burning velocity of pure and diluted fuels, with implications for the development and operation of biogas-fueled combustors. Background work in the area of flame stabilization and propagation are introduced from the combustion literature. Fuels examined in this paper were methane and ethylene; the diluents were primarily nitrogen, as well as argon, carbon dioxide, and helium. Trends in terms of burning velocities as functions of equivalence ratio are reported for a variety of fuels. Additionally, flame temperatures and associated burning velocities as a function of diluent composition are reported. Implications for several flame stabilization theories are discussed, as well as point to potential issues in converting combustors to accept biogas as a fuel permitting stable operation.

Fundamental Combustion Characteristics of Lean and Stoichiometric Hydrogen Laminar Premixed Flames Diluted With Nitrogen or Carbon Dioxide

2016 ◽  
Vol 138 (11) ◽  
Author(s):  
Hong-Meng Li ◽  
Guo-Xiu Li ◽  
Zuo-Yu Sun ◽  
Zi-Hang Zhou ◽  
Yuan Li ◽  
...  
Keyword(s):  
Carbon Dioxide ◽  
Equivalence Ratio ◽  
Burning Velocity ◽  
Flame Temperature ◽  
Premixed Flames ◽  
Combustion Characteristics ◽  
Inert Gas ◽  
Chemical Effect ◽  
Laminar Burning Velocity ◽  
Suppression Effect

In this work, the laminar combustion characteristics of H2/N2/air (H2/CO2/air) were systematically investigated under different hydrogen ratios (40–100%) and equivalence ratios (0.4–1.0) in a closed combustion vessel using the spherical expanding flame method associated with Schlieren technology. The unstretched laminar burning velocities were compared with data from previous study, and the result indicates that excellent agreements are obtained. Numerical simulations were also conducted using GRI3.0 and USC II mechanisms to compare with the present experimental results. The Markstein length for H2/inert gas can be decreased by decreasing the equivalence ratio and hydrogen ratio. The results indicate that the H2/inert gas premixed flames tend to be more unstable with the decrease of equivalence ratio and hydrogen ratio. For H2/N2 mixture, the suppression effect on laminar burning velocity is caused by modified specific heat of mixtures and decreased heat release, which result in a decreased flame temperature. For H2/CO2 mixture, the carbon dioxide has stronger dilution effect than nitrogen in reducing laminar burning velocity owing to both thermal effect and chemical effect.

Impact of Equivalence Ratio on the Macrostructure of Premixed Swirling CH4/Air and CH4/O2/CO2 Flames

2015 ◽  
Author(s):  
Hirotatsu Watanabe ◽  
Santosh J. Shanbhogue ◽  
Ahmed F. Ghoniem
Keyword(s):  
Strain Rate ◽  
Shear Layer ◽  
Equivalence Ratio ◽  
Burning Velocity ◽  
Flame Temperature ◽  
Flame Stabilization ◽  
Sudden Expansion ◽  
Strain Rates ◽  
Cross Point ◽  
Extinction Strain Rate

Premixed CH4/O2/CO2 flames (oxy-flames) and CH4/air flames (air-flames) were experimentally studied in a swirl-stabilized combustor. For comparing oxy and air flames, the same equivalence ratio and adiabatic flame temperature were used. CO2 dilution was adjusted to attain the same adiabatic temperature for the oxy-flame and the corresponding air-flame while keeping the equivalence ratio and Reynolds number (=20,000) the same. For high equivalence ratios, we observed flames stabilized along the inner and outer shear layers of the swirling flow and sudden expansion, respectively, in both flames. However, one notable difference between the two flames appears as the equivalence ratio reaches 0.60. At this point, the outer shear layer flame disappears in the air-flame while it persists in the oxy-flame, despite the lower burning velocity of the oxy-flame. Prior PIV measurements (Ref. 9) showed that the strains along the outer shear layer are higher than along the inner shear layer. Therefore, the extinction strain rates in both flames were calculated using a counter-flow premixed twin flame configuration. Calculations at the equivalence ratio of 0.60 show that the extinction strain rate is higher in the oxy than in the air flame, which help explain why it persists on the outer shear layer with higher strain rate. It is likely that extinction strain rates contribute to the oxy-flame stabilization when air flame extinguish in the outer shear layer. However, the trend reverses at higher equivalence ratio, and the cross point of the extinction strain rate appears at equivalence ratio of 0.64.

Measurements of the Laminar Burning Velocities for Typical Syngas–Air Mixtures at Elevated Pressures

2011 ◽  
Vol 133 (3) ◽  
Author(s):  
Eliseu Monteiro ◽  
Abel Rouboa
Keyword(s):  
Energy Source ◽  
Equivalence Ratio ◽  
Functional Form ◽  
Burning Velocity ◽  
Biomass Gasification ◽  
Producer Gas ◽  
Volume Percentage ◽  
Elevated Pressures ◽  
Syngas Combustion ◽  
Heat Value

In the currently reported work, three typical mixtures of H2, CO, CH4, CO2, and N2 have been considered as representative of the producer gas (syngas) coming from biomass gasification. Syngas is being recognized as a viable energy source worldwide, particularly for stationary power generation. However, there are gaps in the fundamental understand of syngas combustion characteristics, especially at elevated pressures that are relevant to practical combustors. In this work, constant volume spherical expanding flames of three typical syngas compositions resulting from biomass gasification have been employed to measure the laminar burning velocities for pressures ranges between 1.0 and 20 bar tanking into account the stretch effect on burning velocity. Over the ranges studied, the burning velocities are fit by a functional form Su=Su0(T/T0)α(P/P0)β; and the dependencies of α and β upon the equivalence ratio of mixture are also given. Conclusion can be drawn that the burning velocity decreases with the increase of pressure. In opposite, an increase in temperature induces an increase of the burning velocity. The higher burning velocity value is obtained for downdraft syngas. This result is endorsed to the higher heat value, lower dilution and higher volume percentage of hydrogen in the downdraft syngas.

Characteristics of Flame Bases for V-Gutters Stabilized Premixed Flames

2013 ◽  
Author(s):  
Fan Gong ◽  
Yong Huang
Keyword(s):  
Thermal Conductivity ◽  
Temperature Gradient ◽  
Equivalence Ratio ◽  
Premixed Flames ◽  
Flame Stabilization ◽  
Operating Conditions ◽  
Inlet Temperature ◽  
Heat Conducting ◽  
Inlet Velocity ◽  
The Impact

The objective of this work is to investigate the flame stabilization mechanism and the impact of the operating conditions on the characteristics of the steady, lean premixed flames. It’s well known that the flame base is very important to the existence of a flame, such as the flame after a V-gutter, which is typically used in ramjet and turbojet or turbofan afterburners and laboratory experiments. We performed two-dimensional simulations of turbulent premixed flames anchored downstream of the heat-conducting V-gutters in a confined passage for kerosene-air combustion. The flame bases are symmetrically located in the shear layers of the recirculation zone immediately after the V-gutter’s trailing edge. The effects of equivalence ratio of inlet mixture, inlet temperature, V-gutter’s thermal conductivity and inlet velocity on the flame base movements are investigated. When the equivalence ratio is raised, the flame base moves upstream slightly and the temperature gradient dT/dx near the flame base increases, so the flame base is strengthened. When the inlet temperature is raised, the flame base moves upstream very slightly, and near the flame base dT/dx increases and dT/dy decreases, so the flame base is strengthened. As the V-gutter’s thermal conductivity increases, the flame base moves downstream, and the temperature gradient dT/dx near the flame base decreases, so the flame base is weakened. When the inlet velocity is raised, the flame base moves upstream, and the convection heat loss with inlet mixture increases, so the flame base is weakened.

The Effect of Transient Fuel Staging on Self-Excited Instabilities in a Multi-Nozzle Model Gas Turbine Combustor

2017 ◽  
Author(s):  
Wyatt Culler ◽  
Janith Samarasinghe ◽  
Bryan D. Quay ◽  
Domenic A. Santavicca ◽  
Jacqueline O’Connor
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
High Speed ◽  
Equivalence Ratio ◽  
Growth Time ◽  
Stable Operation ◽  
Time Constants ◽  
Decay Times ◽  
Fuel Staging ◽  
Passive Techniques

Combustion instability in gas turbines can be mitigated using active techniques or passive techniques, but passive techniques are almost exclusively used in industrial settings. While fuel staging, a common passive technique, is effective in reducing the amplitude of self-excited instabilities in gas turbine combustors at steady-state conditions, the effect of transients in fuel staging on self-excited instabilities is not well understood. This paper examines the effect of fuel staging transients on a laboratory-scale five-nozzle can combustor undergoing self-excited instabilities. The five nozzles are arranged in a four-around-one configuration and fuel staging is accomplished by increasing the center nozzle equivalence ratio. When the global equivalence ratio is φ = 0.70 and all nozzles are fueled equally, the combustor undergoes self-excited oscillations. These oscillations are suppressed when the center nozzle equivalence ratio is increased to φ = 0.80 or φ = 0.85. Two transient staging schedules are used, resulting in transitions from unstable to stable operation, and vice-versa. It is found that the characteristic instability decay times are dependent on the amount of fuel staging in the center nozzle. It is also found that the decay time constants differ from the growth time constants, indicating hysteresis in stability transition points. High speed CH* chemiluminescence images in combination with dynamic pressure measurements are used to determine the instantaneous phase difference between the heat release rate fluctuation and the combustor pressure fluctuation throughout the combustor. This analysis shows that the instability onset process is different from the instability decay process.

Determination of global kinetic parameters by optimization procedure using burning velocity measurements

2018 ◽  
Vol 13 (6) ◽  
pp. 50
Author(s):  
Gleb V. Grenkin ◽  
Alexander Yu. Chebotarev ◽  
Valeri I. Babushok ◽  
Sergey S. Minaev
Keyword(s):  
Kinetic Parameters ◽  
Equivalence Ratio ◽  
Reaction Rate ◽  
Functional Dependence ◽  
Burning Velocity ◽  
Optimization Procedure ◽  
Optimal Parameters ◽  
Velocity Measurements ◽  
Equilibrium Calculations

The optimization procedure was developed to derive the global kinetic parameters using experimental dependence of burning velocity on the equivalence ratio. The simple model of laminar premixed flame propagation with assumed constant parameters was used to demonstrate the features of the suggested procedure. The suggested method allows finding optimal parameters for the defined functional dependence of the reaction rate on the temperature and reactant concentrations. The dependence of combustion adiabatic temperature on equivalence ratio is assumed to be known from the flame equilibrium calculations. The global kinetic parameters of combustion reaction were determined for methane, ethylene and propane mixtures with air on the basis of experimental data on burning velocity as function of the equivalence ratio. The calculated overall kinetic parameters are compared with parameters obtained by other methods within similar global model.

Techno-Economic Evaluation of Pressurized Oxy-Fuel Combustion Systems

2010 ◽  
Author(s):  
Jongsup Hong ◽  
Ahmed F. Ghoniem ◽  
Randall Field ◽  
Marco Gazzino
Keyword(s):  
Carbon Dioxide ◽  
Carbon Dioxide Emissions ◽  
Power Plants ◽  
Carbon Dioxide Capture ◽  
Fuel Combustion ◽  
Economic Feasibility ◽  
Operating Conditions ◽  
Air Separation ◽  
Separation Unit ◽  
Coal Price

Oxy-fuel combustion coal-fired power plants can achieve significant reduction in carbon dioxide emissions, but at the cost of lowering their efficiency. Research and development are conducted to reduce the efficiency penalty and to improve their reliability. High-pressure oxy-fuel combustion has been shown to improve the overall performance by recuperating more of the fuel enthalpy into the power cycle. In our previous papers, we demonstrated how pressurized oxy-fuel combustion indeed achieves higher net efficiency than that of conventional atmospheric oxy-fuel power cycles. The system utilizes a cryogenic air separation unit, a carbon dioxide purification/compression unit, and flue gas recirculation system, adding to its cost. In this study, we perform a techno-economic feasibility study of pressurized oxy-fuel combustion power systems. A number of reports and papers have been used to develop reliable models which can predict the costs of power plant components, its operation, and carbon dioxide capture specific systems, etc. We evaluate different metrics including capital investments, cost of electricity, and CO2 avoidance costs. Based on our cost analysis, we show that the pressurized oxy-fuel power system is an effective solution in comparison to other carbon dioxide capture technologies. The higher heat recovery displaces some of the regeneration components of the feedwater system. Moreover, pressurized operating conditions lead to reduction in the size of several other critical components. Sensitivity analysis with respect to important parameters such as coal price and plant capacity is performed. The analysis suggests a guideline to operate pressurized oxy-fuel combustion power plants in a more cost-effective way.

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