Effect of Fuel System Impedance Mismatch on Combustion Dynamics

2008 ◽  
Vol 130 (1) ◽  
Author(s):  
Geo A. Richards ◽  
Edward H. Robey
Keyword(s):  
Dynamic Response ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Stable Operation ◽  
Base Line ◽  
Fuel System ◽  
Fuel Injector ◽  
Impedance Mismatch ◽  
Combustion Dynamics ◽  
Fuel Injectors

Combustion dynamics are a challenging problem in the design and operation of premixed gas turbine combustors. In premixed combustors, pressure oscillations created by the flame dynamic response can lead to damage. These dynamics are typically controlled by designing the combustor to achieve a stable operation for planned conditions, but dynamics may still occur with minor changes in ambient operating conditions or fuel composition. In these situations, pilot flames or adjustment to fuel flow splits can be used to stabilize the combustor, but often with a compromise in emission performance. As an alternative to purely passive design changes, prior studies have demonstrated that adjustment to the fuel system impedance can be used to stabilize combustion. Prior studies have considered just the response of an individual fuel injector and combustor. However, in practical combustion systems, multiple fuel injectors are used. In this situation, individual injector impedance can be modified to produce a different dynamic response from individual flames. The resulting impedance mismatch prevents all injectors from strongly coupling to the same acoustic mode. In principle, this mismatch should reduce the amplitude of dynamics and may expand the operating margin for stable combustion conditions. In this paper, a 30kW laboratory combustor with two premixed fuel injectors is used to study the effect of impedance mismatch on combustion stability. The two fuel injectors are equipped with variable geometry resonators that allow a survey of dynamic stability while changing the impedance of the individual fuel systems. Results demonstrate that a wide variation in dynamic response can be achieved by combining different impedance fuel injectors. A base line 7% rms pressure oscillation was reduced to less than 3% by mismatching the fuel impedance.

Effect of Fuel System Impedance Mismatch on Combustion Dynamics

2005 ◽  
Author(s):  
Geo A. Richards ◽  
Edward H. Robey
Keyword(s):  
Dynamic Response ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Stable Operation ◽  
Fuel System ◽  
Fuel Injector ◽  
Pressure Oscillations ◽  
Impedance Mismatch ◽  
Combustion Dynamics ◽  
Fuel Injectors

Combustion dynamics are a challenging problem in the design and operation of premixed gas turbine combustors. In premixed combustors, pressure oscillations created by the flame dynamic response can lead to damaging pressure oscillations. These dynamics are typically controlled by designing the combustor to achieve stable operation for planned conditions, but dynamics may still occur with minor changes in ambient operating conditions, or fuel composition. In these situations, pilot flames, or adjustment to fuel flow splits can be used to stabilize the combustor, but often with a compromise in emissions performance. As an alternative to purely passive design changes, prior studies have demonstrated that adjustment to the fuel system impedance can be used to stabilize combustion. Prior studies have considered just the response of individual fuel injector and combustor. However, in practical combustion systems, multiple fuel injectors are used. In this situation, individual injector impedance can be modified to produce a different dynamic response from individual flames. The resulting impedance mismatch prevents all injectors from strongly coupling to the same acoustic mode. In principle, this mismatch should reduce the amplitude of dynamics, and may expand the operating margin for stable combustion conditions. In this paper, a 30 kW laboratory combustor with two premixed fuel injectors is used to study the effect of impedance mismatch on combustion stability. The two fuel injectors are equipped with variable geometry resonators that allow a survey of dynamic stability while changing the impedance of the individual fuel systems. Results demonstrate that a wide variation in dynamic response can be achieved by combining different impedence fuel injectors. A baseline 7% RMS pressure oscillation was reduced to less than 3% by mismatching the fuel impedance.

Lean-Burn Characteristics of a Heavy-Duty Diesel Engine Retrofitted to Natural Gas Spark Ignition

2018 ◽  
Author(s):  
Jinlong Liu ◽  
Cosmin E. Dumitrescu
Keyword(s):  
Natural Gas ◽  
Combustion Chamber ◽  
Spark Ignition ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Fuel Injector ◽  
Heavy Duty ◽  
Lean Burn ◽  
Spark Timing ◽  
Heavy Duty Diesel

Increased utilization of natural-gas (NG) in the transportation sector can decrease the use of petroleum-based fuels and reduce greenhouse-gas emissions. Heavy-duty diesel engines retrofitted to NG spark ignition (SI) can achieve higher efficiencies and low NOx, CO, and HC emissions when operated under lean-burn conditions. To investigate the SI lean-burn combustion phenomena in a bowl-in-piston combustion chamber, a conventional heavy-duty direct-injection CI engine was converted to SI operation by replacing the fuel injector with a spark plug and by fumigating NG in the intake manifold. Steady-state engine experiments and numerical simulations were performed at several operating conditions that changed spark timing, engine speed, and mixture equivalence ratio. Results suggested a two-zone NG combustion inside the diesel-like combustion chamber. More frequent and significant late burn (including double-peak heat release rate) was observed for advanced spark timing. This was due to the chamber geometry affecting the local flame speed, which resulted in a faster and thicker flame in the bowl but a slower and thinner flame in the squish volume. Good combustion stability (COVIMEP < 3 %), moderate rate of pressure rise, and lack of knocking showed promise for heavy-duty CI engines converted to NG SI operation.

Lean-Burn Characteristics of a Heavy-Duty Diesel Engine Retrofitted to Natural-Gas Spark Ignition

2019 ◽  
Vol 141 (7) ◽  
Author(s):  
Jinlong Liu ◽  
Cosmin Emil Dumitrescu
Keyword(s):  
Natural Gas ◽  
Combustion Chamber ◽  
Spark Ignition ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Fuel Injector ◽  
Heavy Duty ◽  
Lean Burn ◽  
Heavy Duty Diesel ◽  
Ci Engines

Increased utilization of natural gas (NG) in the transportation sector can decrease the use of petroleum-based fuels and reduced greenhouse gas emissions. Heavy-duty diesel engines retrofitted to NG spark ignition (SI) can achieve higher efficiencies and low NOX, CO, and hydrocarbon (HC) emissions when operated under lean-burn conditions. To investigate the SI lean-burn combustion phenomena in a bowl-in-piston combustion chamber, a conventional heavy-duty direct-injection CI engine was converted to SI operation by replacing the fuel injector with a spark plug and by fumigating NG in the intake manifold. Steady-state engine experiments and numerical simulations were performed at several operating conditions that changed spark timing (ST), engine speed, and mixture equivalence ratio. Results suggested a two-zone NG combustion inside the diesel-like combustion chamber. More frequent and significant late-burn (including double-peak heat release rate) was observed for advanced ST. This was due to the chamber geometry affecting the local flame speed, which resulted in a faster and thicker flame in the bowl but a slower and thinner flame in the squish volume. Good combustion stability (COVIMEP < 3%), moderate rate of pressure-rise, and lack of knocking showed promise for heavy-duty CI engines converted to NG SI operation.

Modeling and Control of Combustion Dynamics in Industrial Gas Turbines

2004 ◽  
Author(s):  
Keith McManus ◽  
Fei Han ◽  
Wayne Dunstan ◽  
Corneliu Barbu ◽  
Minesh Shah
Keyword(s):  
Gas Turbine ◽  
Gas Turbines ◽  
Pressure Oscillation ◽  
Fast Response ◽  
Operating Conditions ◽  
Fuel System ◽  
Combustion Dynamics ◽  
Modeling And Control ◽  
Persistent Excitation ◽  
Industrial Gas Turbines

The thermoacoustic response of an industrial-scale gas turbine combustor to fuel flow perturbations is examined. Experimental measurements in a laboratory combustor along with numerical modeling results are used to identify the dynamic behavior of the combustor over a variety of operating conditions. A fast-response actuator was coupled to the fuel system to apply continuous sinusoidal perturbations to the total fuel mass flow rate. The effects of these perturbations on the combustor pressure oscillation characteristics as well as overall operability of the system are described. The results of this work suggest that persistent excitation of the fuel system may present a viable means of controlling combustion dynamics in industrial gas turbine and, in turn, enhance their performance.

Control of Combustion Dynamics Using Fuel System Impedance

2003 ◽  
Author(s):  
Geo Richards ◽  
Doug Straub ◽  
Ed Robey
Keyword(s):  
Active Control ◽  
High Frequency ◽  
Operating Conditions ◽  
Design Parameters ◽  
Fuel System ◽  
Combustion Dynamics ◽  
Design Variables ◽  
Low Emission ◽  
Wide Range ◽  
Significant Attenuation

Combustion oscillations (dynamics) have become a major challenge in the development of low-emission premix combustors. In this paper, a variable impedance fuel system is used to modulate the phase and magnitude of the combustion response in a laboratory scale 30 kW combustor. With the proper choice of design parameters, this technique demonstrates significant attenuation of dynamics pressures, over a wide range of operating conditions. The technique is similar to active control, but does not require high frequency actuators. The paper will report on the key design variables that should be considered when using this concept to improve dynamic stability.

Dynamic Response of a Premix Fuel Injector

2001 ◽  
Author(s):  
Geo. A. Richards ◽  
Douglas L. Straub ◽  
Edward H. Robey
Keyword(s):  
Dynamic Response ◽  
Transfer Matrix ◽  
Reduced Order Model ◽  
Phase Response ◽  
Acoustic Properties ◽  
Variable Geometry ◽  
Fuel System ◽  
Fuel Injector ◽  
Order Model ◽  
Reduced Order

Combustion oscillations (dynamics) have become a major challenge in the development of low-emission premix combustors. Numerous recent papers have considered the various mechanisms that drive oscillations, as well as acoustic features of the combustor and fuel system that participate in sustaining unwanted oscillations. The acoustic transfer matrix technique has been used in a number of recent analyses of both the combustion and fuel injection process. In this paper, the transfer matrix analysis is combined with a reduced order model of the fuel supply to calculate the magnitude and phase of the fuel system response to imposed pressure perturbations. The analysis is used to determine if a variable geometry resonator in the fuel system can be used to adjust the phase and gain of the fuel response to enhance stability. Experimental data recorded in a research premix fuel injector show that the reduced order model accurately describes the dynamic response of the fuel entering the premix passage. Using measured acoustic properties it is also shown that the variable geometry resonator studied here can produce a phase response for fuel delivery over a range of 70 degrees, with appreciable modulation of the main fuel flow. It is suggested that this variable phase response could be used to adjust the stability properties of a given combustor.

Experimental Investigation of Spray and Combustion Performances of a Fuel-Staged Low Emission Combustor: Part II — Effects of Venturi Angle

2018 ◽  
Author(s):  
Cunxi Liu ◽  
Fuqiang Liu ◽  
Jinhu Yang ◽  
Yong Mu ◽  
Gang Xu
Keyword(s):  
Flow Field ◽  
High Altitude ◽  
Gas Turbines ◽  
Fuel Injection ◽  
Operating Conditions ◽  
Combustion Stability ◽  
Main Stage ◽  
Fuel Injector ◽  
Lean Burn ◽  
Low Emission

In order to reduce NOx emissions, modern gas turbines are often equipped with lean burn combustion systems, where the high-velocity fuel-lean conditions that limit NOx formation in combustors also inhibit the ability of ignition, high altitude relight, and lean combustion stability. To face these issues, an internally staged scheme of fuel injection is proposed. The pilot and main fuel staging enable fuel distribution control and high turn-down ratio, multi-injections of main fuel leads to a fast and efficient fuel/air mixing. A fuel-staged low emission combustor in the framework of lean burn combustion is developed in the present study, the central pilot stage of fuel injector working singly at low power operating conditions is swirl-cup prefilming atomization and main stage is jet-in-crossflow multi-injection atomization, a combination of pilot and main stage injection is provided for higher power operating conditions. A significant amount of the air mass flow utilised for fuel preparation and initiation is adverse to the operability specifications, such as ignition, lean blow-out, and high-altitude relight etc. The spray characteristics of pilot spray and flow field are one of the key factors affecting combustion operability. This work investigates the effects of the venturi angle on combustion operability, the ignition and lean blow-out performances were evaluated in a single dome rectangular combustor. Furthermore, the spray patterns and flow field are characterized by kerosene-planar laser induced fluorescence and particle image velocimetry to provide insight into the correlation between spray, flow field and combustion operability performances.

Using CFD for Time-Delay Modeling of Premix Flames

2001 ◽  
Author(s):  
Peter Flohr ◽  
Christian Oliver Paschereit ◽  
Bart van Roon ◽  
Bruno Schuermans
Keyword(s):  
Time Delay ◽  
Heat Release ◽  
Time Delays ◽  
Flame Temperature ◽  
Model Fitting ◽  
Operating Conditions ◽  
Fuel Injector ◽  
Fuel Injectors ◽  
Flame Shape ◽  
Good Agreement

This paper presents a refined model of the transfer function of a premix burner, compares the model with experiments, and discusses how the model can be used to map stability characteristics of a combustion system. The model is based on the assumption that acoustic velocity fluctuations cause modulations of fuel concentration at the fuel injector which, after a time delay, result in fluctuating heat release rates at the flame. Here, the time delay is modeled as a multitude of single time delays. The distribution of these time delays can be found either from model fitting to experimental data, or can be obtained directly from numerical simulations of the burner. The effect of distributed time delays is caused by axially distributed fuel injectors, turbulent diffusion, and a non-planar flame shape. As a consequence, heat release fluctuations at higher frequencies cancel, an effect which is also observed experimentally. It is found that the model is generally in good agreement with experiments. It is also demonstrated that the model can be used to map the burner stability charactistics for various operating conditions, e.g. for variations in power and flame temperature. A stability analysis is performed by incorporating the flame model into a combustor network model.

3D LES Modeling of Combustion Dynamics in Lean Premixed Combustors

2001 ◽  
Author(s):  
Steven M. Cannon ◽  
Virgil Adumitroaie ◽  
Clifford E. Smith
Keyword(s):  
Turbulence Model ◽  
Time Lag ◽  
Pressure Oscillation ◽  
Operating Conditions ◽  
Pressure Amplitude ◽  
Fuel Injector ◽  
Turbulent Structures ◽  
Combustion Dynamics ◽  
Lean Premixed ◽  
Unsteady Rans

A lean premixed fuel injector/combustor typical of industrial gas turbine combustors has been analyzed using 3D Large Eddy Simulation (LES) methods. The objective of the study was to evaluate the 3D LES modeling approach for predicting combustion dynamics and compare it with simpler unsteady Reynolds Averaged Navier Stokes (RANS) methods using 2D and 3D analyses. Large amplitude pressure oscillations were observed experimentally at the modeled operating conditions, and previous 2D axisymmetric unsteady RANS analysis has shown reasonable, but not perfect, engineering agreement with pressure measurements. Although the pressure amplitude was accurately predicted, the frequency was substantially in error. This study sought to see if 3D modeling would improve the agreement. 2D axisymmetric and full 3D calculations were performed with a state-of-the-art, unstructured-grid, parallel (domain decomposition) CFD code. For the unsteady RANS calculations, the RNG k-ε turbulence model was employed, while for the LES calculation the Smagorinsky subgrid turbulence model was employed. Surprisingly, the 2D unsteady RANS, 3D unsteady RANS, and 3D LES calculations gave nearly identical pressure oscillation predictions, and all calculations had the oscillation frequency around 280 Hertz. This work has shown that smaller turbulent structures captured with 3D LES have very little effect on capturing combustion instability driven primarily by a fuel time-lag.

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