Numerical Prediction of the Dynamic Behaviour of Premixed Flames Using Systematically Reduced Multi-Step Reaction Mechanisms

Environmental compatibility requires low emission burners for both gas turbine power plants and jet engines. In the past, significant progress has been made in the development of low NOx and CO burners by introducing lean premixed techniques. Unfortunately these burners often have a more pronounced tendency than conventional burner designs to produce combustion driven oscillations. The oscillations may be excited to such an extent that strong pulsation may occur, and this is associated with a risk of engine failure. In order to describe the acoustical behaviour of the complete burner system, it is crucial to determine the unit function response of the flame itself. Using a new method which was presented in 1996 by Bohn et al. [1] the dynamic flame behaviour can be predicted by means of a full Navier-Stokes-simulation of the complex combustion process for both the steady-state and transient case. The authors have successfully used this method to obtain the frequency response of turbulent diffusion flames which are mainly controlled by the mixing process. Chemical kinetics become dominant for premixed flames. Therefore, the combustion process of a premixed methane-air mixture is modelled using a systematically reduced 6-step reaction mechanism which takes account of a set of 25 elementary reactions. This reduced mechanism was implemented in the 3D-Navier-Stokes solver in order to perform a combined flow and combustion computation. The dynamic combustion process of a laminar premixed methane flame in a matrix burner configuration has been investigated. At first, the steady-state combustion process was simulated using the code described above. The results are compared with experimental data. Very good agreement over a wide range of equivalence ratios has been found for quantities such as laminar burning velocity or adiabatic flame temperature. The steady state results are then used as an operating point from which the transient flame behaviour after a sudden jump in the mass flow at the burner inlet has been obtained. Finally, these data lead to the unit function response which can be transferred into frequency space by a Laplace transformation. The frequency response of the premixed methane flame obtained by a Navier-Stokes simulation has been compared with both experimental as well as analytical solutions. It must be stressed that a pure delay time element which is often used as an analytical formulation is not suitable to describe the dynamic flame behaviour in detail. The frequency response shows the characteristics of a higher order delay time element with several important details. Parametric studies on the influence of equivalence ratio and the flow pattern of the internal burner fluid flow which are of interest for gas turbine applications, show the importance of the detailed knowledge of the dynamic flame behaviour for the stability analysis of a gas turbine combustor.

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Numerical Prediction of the Dynamic Behaviour of Turbulent Diffusion Flames

Volume 3: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations ◽

10.1115/96-gt-133 ◽

1996 ◽

Cited By ~ 1

Author(s):

Dieter Bohn ◽

Gregor Deutsch ◽

Uwe Krüger

Keyword(s):

Steady State ◽

Frequency Response ◽

Turbulent Diffusion ◽

Dynamic Behaviour ◽

Diffusion Flames ◽

Sudden Change ◽

Combustion Process ◽

Turbulent Diffusion Flames ◽

Time Element ◽

Flame Behaviour

Environmental compatibility requires low emission burners for gas turbine power plants as well as for jet engines. In the past significant progress has been made developing low NOx and CO burners. Unfortunately these burners often have a more pronounced tendency than conventional burner designs to produce combustion driven oscillations The oscillations may be excited to such an extent that pronounced pulsation may possibly occur; this is associated with a risk of engine failure. The stability of a burner system can be investigated by means of a stability analysis under the assumption of acoustical behaviour. The problem with all these algorithms is the transfer function of the flame. A new method is presented here to predict the dynamic flame behaviour by means of a full Navier-Stokes-simulation of the complex combustion process. The first step is to get a steady-state solution of a flame configuration. After that a transient simulation follows with a sudden change in the mass flow rate at the flame inlet. The time-dependent answer of the flame to this disturbance is then transformed into the frequency space by a Laplace Transformation. This leads, in turn, to the frequency response representing the dynamic behaviour of the flame. In principle, this method can be adapted for both diffusion as well as premixed flame systems. However, due to the fact that diffusion flames are more controlled by the mixing process than by the chemical kinetic, the method has first been used for the prediction of the dynamic behaviour of turbulent diffusion flames. The combustion has been modelled by a mixed-is-burnt model. The influence of the turbulence has been taken into account by a modified k-ε-model and the turbulence influences the combustion rate by presumed probability density functions (pdf). The steady-state as well as the transient results have been compared with experimental data for two different diffusion flame configurations. Although the burner configuration is relatively complex, the steady state results collaborate very well with the experiments for velocity, temperature and species distribution. The most important result is that the heat release which drives the oscillations can be modelled sufficiently accurately. The effect of using different pdf-models has been discussed and the best model has been used for the transient calculations of the dynamic flame behaviour. The results for the frequency response of the flame are very encouraging. The principal behaviour of the flame — higher order time element with a delay time — can be predicted with sufficient precision. In addition, the qualitative results collaborate fairly well with the experiments.

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Numerical Predication of the Dynamic Behavior of Turbulent Diffusion Flames

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.2818458 ◽

1998 ◽

Vol 120 (4) ◽

pp. 713-720 ◽

Cited By ~ 12

Author(s):

D. Bohn ◽

G. Deutsch ◽

U. Kru¨ger

Keyword(s):

Steady State ◽

Frequency Response ◽

Dynamic Behavior ◽

Turbulent Diffusion ◽

Diffusion Flames ◽

Sudden Change ◽

Combustion Process ◽

Turbulent Diffusion Flames ◽

Time Element ◽

Flame Behavior

Environmental compatibility requires low-emission burners for gas turbine power plants as well as for jet engines. In the Past, significant progress has been made developing low NOx and CO burners. Unfortunately, these burners often have a more pronounced tendency than conventional burner designs to produce combustion driven oscillations. The oscillations may be excited to such an extent that pronounced pulsation may possibly occur; this is associated with a risk of engine failure. The stability of a burner system can be investigated by means of a stability analysis under the assumption of acoustical behavior. The problem with all these algorithms is the transfer function of the flame. A new method is presented here to predict the dynamic flame behavior by means of a full Navier-Stokes simulation of the complex combustion process. The first step is to get a steady-state solution of a flame configuration. After that a transient simulation follows with a sudden change in the mass flow rate at the flame inlet. The time-dependent answer of the flame to this disturbance is then transformed into the frequency space by a Laplace Transformation. This leads, in turn, to the frequency response representing the dynamic behavior of the flame. In principle, this method can be adapted for both diffusion as well as premixed flame systems. However, due to the fact that diffusion flames are more controlled by the mixing process than by the chemical kinetic, the method has first been used for the prediction of the dynamic behavior of turbulent diffusion flames. The combustion has been modelled by a mixed-is-burnt model. The influence of the turbulence has been taken into account by a modified k-ε model and the turbulence influences the combustion rate by presumed probability density functions (pdf). The steady state as well as the transient results have been compared with experimental data for two different diffusion flame configurations. Although the burner configuration is relatively complex, the steady-state results collaborate very well with the experiments for velocity, temperature, and species distribution. The most important result is that the heat release that drives the oscillations can be modeled sufficiently accurately. The effect of using different pdf models has been discussed and the best model has been used for the transient calculations of the dynamic flame behavior. The results for the frequency response of the flame are very encouraging. The principal behavior of the flame—higher order time element with a delay time—can be predicted with sufficient precision. In addition, the qualitative results collaborate fairly well with the experiments.

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Influence of Turbulence on the Dynamic Behaviour of Premixed Flames

Volume 3: Coal, Biomass and Alternative Fuels; Combustion and Fuels; Oil and Gas Applications; Cycle Innovations ◽

10.1115/98-gt-323 ◽

1998 ◽

Cited By ~ 5

Author(s):

Uwe Krüger ◽

Stefan Hoffmann ◽

Werner Krebs ◽

Hans Judith ◽

Dieter Bohn ◽

...

Keyword(s):

Steady State ◽

Frequency Response ◽

Gas Turbines ◽

Power Plants ◽

Dynamic Behaviour ◽

Diffusion Flames ◽

Premixed Flames ◽

Combustion Process ◽

Turbulent Premixed Flame ◽

Improved Model

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Transient Performance Analysis of an Industrial Gas Turbine Operating on Low-Calorific Fuels

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4034942 ◽

2016 ◽

Vol 139 (5) ◽

Cited By ~ 1

Author(s):

Vrishika Singh ◽

Lars-Uno Axelsson ◽

W.P.J. Visser

Keyword(s):

Steady State ◽

Energy Density ◽

Gas Turbine ◽

Alternative Fuels ◽

Combustion Process ◽

Transient Behavior ◽

Performance Model ◽

Transient Performance ◽

Wide Range ◽

Industrial Gas Turbine

The demand for more environmentally friendly and economic power production has led to an increasing interest to utilize alternative fuels. In the past, several investigations focusing on the effect of low-calorific fuels on the combustion process and steady-state performance have been published. However, it is also important to consider the transient behavior of the gas turbine when operating on nonconventional fuels. The alternative fuels contain very often a large amount of dilutants resulting in a low energy density. Therefore, a higher fuel flow rate is required, which can impact the dynamic behavior of the gas turbine. This paper will present an investigation of the transient behavior of the all-radial OP16 gas turbine. The OP16 is an industrial gas turbine rated at 1.9 MW, which has the capability to burn a wide range of fuels including ultra-low-calorific gaseous fuels. The transient behavior is simulated using the commercial software GSP including the recently added thermal network modeling functionality. The steady-state and transient performance model is thoroughly validated using real engine test data. The developed model is used to simulate and analyze the physical behavior of the gas turbine when performing load sheds. From the simulations, it is found that the energy density of the fuel has a noticeable effect on the rotor over-speed and must be considered when designing the fuel control.

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Development and Assessment of Combustion Models for Gas Turbine and Aero-Engine Applications

Volume 4B: Combustion, Fuels and Emissions ◽

10.1115/gt2015-44122 ◽

2015 ◽

Author(s):

Jan E. Anker ◽

Dirk Wunsch ◽

Luigi Romagnosi ◽

Kilian Claramunt ◽

Charles Hirsch

Keyword(s):

Gas Turbine ◽

Combustion Process ◽

Measurement Data ◽

Point Of View ◽

Navier Stokes ◽

Flammability Limits ◽

Combustion Models ◽

Spray Flames ◽

Aero Engine ◽

Combustion Processes

The classical flamelet method, the new Flamelet Generated Manifolds method (FGM), and the hybrid BML/flamelet approach are assessed in the context of the Reynolds-averaged Navier-Stokes (RANS) equations on a large range of configurations for both gaseous and spray flames. The conceptual differences, advantages, and shortcomings of the models are discussed in detail both from a theoretical and a practical point of view. In order to assess the models under gas turbine like conditions, the reactive flow in TU Darmstadt’s Generic Gas Turbine (GGT), DLR Stuttgart’s PRECCINSTA burner, and a premixed industrial combustor are computed. The computational results are compared to available measurement data and are used to discuss the strengths and the weaknesses of each of the aforementioned combustion models. In the current study it is shown that the hybrid BML/flamelet method globally performs well, but that it can be difficult to obtain a burning solution with this method, especially when the combustion process is operated close to the flammability limits. While the flamelet method is very robust, it is outperformed by the FGM method even for purely non-premixed configurations. It is demonstrated that the FGM approach can be used for the whole range of combustion modes, from non-premixed over to premixed combustion processes. Since the model did not lead to any difficulties with attaining a burning solution, and is computationally as efficient as the flamelet approach, the authors recommend the usage of this model over the other models investigated.

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Transient Performance Analysis of an Industrial Gas Turbine Operating on Low-Calorific Fuels

Volume 8: Microturbines, Turbochargers and Small Turbomachines; Steam Turbines ◽

10.1115/gt2016-57523 ◽

2016 ◽

Author(s):

Vrishika Singh ◽

Lars-Uno Axelsson ◽

W. P. J. Visser

Keyword(s):

Steady State ◽

Energy Density ◽

Gas Turbine ◽

Alternative Fuels ◽

Combustion Process ◽

Transient Behavior ◽

Performance Model ◽

Transient Performance ◽

Wide Range ◽

Industrial Gas Turbine

The demand for more environmentally friendly and economic power production has led to an increasing interest to utilize alternative fuels. In the past, several investigations focusing on the effect of low-calorific fuels on the combustion process and steady-state performance have been published. However, it is also important to consider the transient behavior of the gas turbine when operating on non-conventional fuels. The alternative fuels contain very often a large amount of dilutants resulting in a low energy density. Therefore a higher fuel flow rate is required, which can impact the dynamic behavior of the gas turbine. This paper will present an investigation of the transient behavior of the all-radial OP16 gas turbine. The OP16 is an industrial gas turbine rated at 1.9 MW, which has the capability to burn a wide range of fuels including ultra-low-calorific gaseous fuels. The transient behavior is simulated using the commercial software GSP including the recently added thermal network modeling functionality. The steady-state and transient performance model is thoroughly validated using real engine test data. The developed model is used to simulate and analyze the physical behavior of the gas turbine when performing load sheds. From the simulations it is found that the energy density of the fuel has a noticeable effect of the rotor over-speed and must be considered when designing the fuel control.

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Experimental and Numerical Analysis of a Motorcycle Air Intake System Aerodynamics and Performance

International Journal of Automotive and Mechanical Engineering ◽

10.15282/ijame.17.1.2020.10.0565 ◽

2020 ◽

Vol 17 (1) ◽

Author(s):

M. A. Abd Halim ◽

N. A. R. Nik Mohd ◽

M. N. Mohd Nasir ◽

M. N. Dahalan

Keyword(s):

Combustion Process ◽

Three Dimensional ◽

Engine Performance ◽

Internal Flow ◽

Rapid Expansion ◽

Navier Stokes ◽

Turbulent Fluctuation ◽

Ansys Fluent ◽

Induction System ◽

Acceleration And Deceleration

Induction system or also known as the breathing system is a sub-component of the internal combustion system that supplies clean air for the combustion process. A good design of the induction system would be able to supply the air with adequate pressure, temperature and density for the combustion process to optimizing the engine performance. The induction system has an internal flow problem with a geometry that has rapid expansion or diverging and converging sections that may lead to sudden acceleration and deceleration of flow, flow separation and cause excessive turbulent fluctuation in the system. The aerodynamic performance of these induction systems influences the pressure drop effect and thus the engine performance. Therefore, in this work, the aerodynamics of motorcycle induction systems is to be investigated for a range of Cubic Feet per Minute (CFM). A three-dimensional simulation of the flow inside a generic 4-stroke motorcycle airbox were done using Reynolds-Averaged Navier Stokes (RANS) Computational Fluid Dynamics (CFD) solver in ANSYS Fluent version 11. The simulation results are validated by an experimental study performed using a flow bench. The study shows that the difference of the validation is 1.54% in average at the total pressure outlet. A potential improvement to the system have been observed and can be done to suit motorsports applications.

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Comprehensive Thermodynamic Analysis of the Humphrey Cycle for Gas Turbines with Pressure Gain Combustion

Energies ◽

10.3390/en11123521 ◽

2018 ◽

Vol 11 (12) ◽

pp. 3521 ◽

Cited By ~ 5

Author(s):

Panagiotis Stathopoulos

Keyword(s):

Gas Turbine ◽

Gas Turbines ◽

Combustion Process ◽

Ideal Gas ◽

Point Of View ◽

Pressure Gain Combustion ◽

Combustion Technology ◽

Secondary Air ◽

And Performance ◽

The Impact

Conventional gas turbines are approaching their efficiency limits and performance gains are becoming increasingly difficult to achieve. Pressure Gain Combustion (PGC) has emerged as a very promising technology in this respect, due to the higher thermal efficiency of the respective ideal gas turbine thermodynamic cycles. Up to date, only very simplified models of open cycle gas turbines with pressure gain combustion have been considered. However, the integration of a fundamentally different combustion technology will be inherently connected with additional losses. Entropy generation in the combustion process, combustor inlet pressure loss (a central issue for pressure gain combustors), and the impact of PGC on the secondary air system (especially blade cooling) are all very important parameters that have been neglected. The current work uses the Humphrey cycle in an attempt to address all these issues in order to provide gas turbine component designers with benchmark efficiency values for individual components of gas turbines with PGC. The analysis concludes with some recommendations for the best strategy to integrate turbine expanders with PGC combustors. This is done from a purely thermodynamic point of view, again with the goal to deliver design benchmark values for a more realistic interpretation of the cycle.

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Nonlinear filter properties of the thick ascending limb

AJP Renal Physiology ◽

10.1152/ajprenal.1997.273.4.f625 ◽

1997 ◽

Vol 273 (4) ◽

pp. F625-F634 ◽

Cited By ~ 20

Author(s):

H. E. Layton ◽

E. Bruce Pitman ◽

Leon C. Moore

Keyword(s):

Steady State ◽

Frequency Response ◽

Transit Time ◽

Concentration Profile ◽

Tubuloglomerular Feedback ◽

Thick Ascending Limb ◽

Transport Parameters ◽

Nodal Structure ◽

Nacl Concentration ◽

Fluid Transit Time

A mathematical model was used to investigate the filter properties of the thick ascending limb (TAL), that is, the response of TAL luminal NaCl concentration to oscillations in tubular fluid flow. For the special case of no transtubular NaCl backleak and for spatially homogeneous transport parameters, the model predicts that NaCl concentration in intratubular fluid at each location along the TAL depends only on the fluid transit time up the TAL to that location. This exact mathematical result has four important consequences: 1) when a sinusoidal component is added to steady-state TAL flow, the NaCl concentration at the macula densa (MD) undergoes oscillations that are bounded by a range interval envelope with magnitude that decreases as a function of oscillatory frequency; 2) the frequency response within the range envelope exhibits nodes at those frequencies where the oscillatory flow has a transit time to the MD that equals the steady-state fluid transit time (this nodal structure arises from the establishment of standing waves in luminal concentration, relative to the steady-state concentration profile, along the length of the TAL); 3) for any dynamically changing but positive TAL flow rate, the luminal TAL NaCl concentration profile along the TAL decreases monotonically as a function of TAL length; and 4) sinusoidal oscillations in TAL flow, except at nodal frequencies, result in nonsinusoidal oscillations in NaCl concentration at the MD. Numerical calculations that include NaCl backleak exhibit solutions with these same four properties. For parameters in the physiological range, the first few nodes in the frequency response curve are separated by antinodes of significant amplitude, and the nodes arise at frequencies well below the frequency of respiration in rat. Therefore, the nodal structure and nonsinusoidal oscillations should be detectable in experiments, and they may influence the dynamic behavior of the tubuloglomerular feedback system.

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