Combustion Oscillations in Bluff Body Stabilized Diffusion Flames With Variable Length Inlet

2009 ◽  
Vol 131 (5) ◽  
Author(s):  
M. Madanmohan ◽  
S. Pandey ◽  
A. Kushari ◽  
K. Ramamurthi
Keyword(s):  
Heat Release ◽  
Phase Angle ◽  
Bluff Body ◽  
Diffusion Flames ◽  
Combustion Process ◽  
Low Frequency ◽  
Pressure Oscillations ◽  
Pipe Length ◽  
Entry Length ◽  
Low Frequency Oscillations

This paper describes the results of an experimental study to understand the influence of inlet flow disturbances on the dynamics of combustion process in bluff body stabilized diffusion flames of liquid petroleum gas and air. The results show the influence of weak disturbances created by the change in incoming pipe length on the amplitude of pressure oscillations and the phase angle between pressure and heat release. It is seen that the phase delay increases as the entry length increases. The rms value of pressure, however, generally falls with the increase in length. The phase angle is seen to be in the second quadrant, showing that the heat release oscillations damp the pressure oscillations. Therefore, the decrease in the phase angle results in the reduction in damping and hence an increase in pressure fluctuations. The dominant frequencies of combustion oscillations are found to be the low frequency oscillations, and the frequency of oscillations increases with a decrease in the inlet pipe length and an increase in the flow Reynolds number. It is suggested that such low frequency oscillations are driven by vortex shedding at the wake of the bluff body, which energizes the diffusion and mixing process.

On the Use of Helmholtz Resonators for Damping Acoustic Pulsations in Industrial Gas Turbines

2001 ◽  
Author(s):  
Valter Bellucci ◽  
Christian Oliver Paschereit ◽  
Peter Flohr ◽  
Fulvio Magni
Keyword(s):  
Heat Release ◽  
Gas Turbine ◽  
Gas Turbines ◽  
Structural Integrity ◽  
Combustion Process ◽  
Low Frequency ◽  
Operating Regime ◽  
Pressure Pulsations ◽  
Helmholtz Resonators ◽  
Resonance Frequencies

In modern gas turbines operating with premix combustion flames, the suppression of pressure pulsations is an important task related to the quality of the combustion process and to the structural integrity of engines. High pressure pulsations may occur when the resonance frequencies of the system are excited by heat release fluctuations independent of the acoustic field (“loudspeaker” behavior of the flame). Heat release fluctuations are also generated by acoustic fluctuations in the premixed stream. The feedback mechanism inherent in such processes (“amplifier” behavior of the flame) may lead to combustion instabilities, the amplitude of pulsations being limited only by nonlinearities. In this work, the application of Helmholtz resonators for damping low-frequency pulsations in gas turbine combustion chambers is discussed. We present a nonlinear model for predicting the acoustic response of resonators including the effect of purging air. Atmospheric experiments are used to validate the model, which is employed to design a resonator arrangement for damping low-frequency pulsations in an ALSTOM GT11N2 gas turbine. The predicted damper impedances are used as the boundary condition in the three-dimensional analysis of the combustion chamber. The suggested arrangement leads to a significant extension of the low-pulsation operating regime of the engine.

Numerical Study on the Kinetic Effects of Hydrogen Addition on the Thermal Characteristics of Laminar Methane Diffusion Flames

2018 ◽  
Vol 16 (8) ◽  
Author(s):  
Long Wu ◽  
Noriyuki Kobayashi ◽  
Zhanyong Li
Keyword(s):  
Heat Release ◽  
Diffusion Flames ◽  
Numerical Study ◽  
Combustion Process ◽  
Thermal Characteristics ◽  
Detailed Chemical Kinetics ◽  
Increase Rate ◽  
Methane Diffusion ◽  
Kinetic Effects ◽  
Detailed Chemical

Abstract The kinetic effects of H2 addition on the thermal characteristics of laminar methane diffusion flames were numerically studied using a detailed chemical kinetics consisting of 53 species and 325 reactions. The variations in the heat release properties and relevant key reactions with H2 addition were analyzed. Results show that the reactions of H + O2 + H2O ⇔ HO2 + H2O (R35), H + HO2 ⇔ OH + OH (R46), H + CH3 (+ M) ⇔ CH4 (+ M) (R52) and OH + H2 ⇔ H + H2O (R84) present important roles in the global heat release and the contributions of these reactions significantly increased as H2 is added to CH4 stream. Moreover, the increase rate of contribution of R84 with H2 addition is much larger than those of the reactions of R35, R46 and R52. The H and OH are the two most important radicals for heat release in the combustion process of CH4-H2 diffusion flame. The reaction of R84 is one of the main contributors for production of H radical and the contribution of R84 significantly increased with H2 addition, while the reaction of H + O2 ⇔ O + OH (R38) dominates the contribution of production of OH, which contributes more than 50 %, no matter whether H2 is added to CH4 stream.

Modeling of Turbulent Combustion Process and Lean Blow Out Using Combined Approach

2008 ◽  
Author(s):  
Yu. G. Kutsenko ◽  
S. F. Onegin ◽  
L. Y. Gomzikov
Keyword(s):  
Combustion Chamber ◽  
Bluff Body ◽  
Diffusion Flames ◽  
Premixed Flames ◽  
Combustion Process ◽  
Flame Stabilization ◽  
Combustion Model ◽  
Main Zone ◽  
Lean Premixed ◽  
No Emissions

Most of the modern combustor’s designs use staged concepts for reducing thermal NO emissions. Usually, a combustion process takes place inside the main zone, which uses very lean premixed fuel/air mixtures. A diffusion pilot zone supports combustion process inside a lean main zone. Thermal NO formation process takes place predominantly inside hot diffusion flame. So, operation modes of pilot and main zones must be arranged to provide low NO emissions of pilot zone and maintain flame stability inside the main zone simultaneously. In this paper a concept of new turbulent model combustion model is presented. This model allows to model diffusion and premixed flames and takes into account various physical processes, which lead to flame destabilization. The model uses an equation for reaction progress variable. In the frameworks of considered approach this equation has three source terms. These terms are responsible for different conditions of combustion process: diffusion flames, premixed flames and distributed reaction zones. A proposed model was widely validated for different types of combustion chambers such as: 1) Bluff-body flameholder (lean premixed combustion: modeling of lean blow out); 2) Conventional diffusion regime of combustion chamber of gas turbine engine (modeling of flame stabilization and NO emissions); 3) Combined combustion regime of combustion chamber: burning process is inside pilot diffusion and main premixed zones (NO emissions and lean blow out limits for several operational modes). These tests had shown a good agreement of experimentally obtained data with results of simulations.

scholarly journals RESEARCH OF LOW FREQUENCY GAS PRESSURE OSCILLATIONS IN DUST SYSTEMS OF POWER PLANTS USING PROGRAM PROVISION

Akustika ◽  
2019 ◽  
Vol 34 ◽  
pp. 123-126
Author(s):  
Andrey Vasilyev
Keyword(s):  
Power Plants ◽  
Negative Impact ◽  
Mechanical Systems ◽  
Low Frequency ◽  
Gas Pressure ◽  
Frequency Noise ◽  
Pressure Oscillations ◽  
Noise And Vibration ◽  
Low Frequency Oscillations ◽  
Duct Systems

Vibration and related with it mechanical noise of power plants and joining mechanical systems are the factors negatively impacted not only to the health of workers, but also to the durability, reliability, productivity and other parameters of power plants. Significant input into generation of vibration and of low frequency noise are bringing pressure oscillations in ducts. Some approaches and results of program provision development for calculation of low frequency gas pressure oscillations in ducts of power plants are described. Results of program provision approbation are presented. Using of suggested program provision may be useful for calculation and design of duct systems of power plants and allows increase the efficiency of low frequency oscillations reduction in ducts of power plants systems and noise and vibration negative impact.

Dynamics of Non-Premixed Bluff Body-Stabilized Flames in Heated Air Flow

2010 ◽  
Author(s):  
Caleb Cross ◽  
Aimee Fricker ◽  
Dmitriy Shcherbik ◽  
Eugene Lubarsky ◽  
Ben T. Zinn ◽  
...  
Keyword(s):  
Heat Release ◽  
Vortex Shedding ◽  
High Speed ◽  
Bluff Body ◽  
Combustion Process ◽  
Flame Stabilization ◽  
Inlet Temperature ◽  
Fuel Injectors ◽  
Flame Holder ◽  
Process Heat

This paper describes a study of the fundamental flame dynamic processes that control bluff body-stabilized combustion of liquid fuel with low dilatation. Specifically, flame oscillations due to asymmetric vortex shedding downstream of a bluff body (i.e., the Be´nard/von-Ka´rma´n vortex street) were characterized in an effort to identify the fundamental processes that most affect the intensity of these oscillations. For this purpose, the spatial and temporal distributions of the combustion process heat release were characterized over a range of inlet velocities, temperatures, and overall fuel-air ratios in a single flame holder combustion channel with full optical access to the flame. A stream of hot preheated air was supplied to the bluff body using a preburner, and Jet-A fuel was injected across the heated gas stream from discrete fuel injectors integrated within the bluff body. The relative amplitudes, frequencies, and phase of the sinusoidal flame oscillations were characterized by Fourier analysis of high-speed movies of the flame. The amplitudes of the flame oscillations were generally found to increase with global equivalence ratio, reaching a maximum just before rich blowout. Comparison of the flame dynamics to the time-averaged spatial heat release distribution revealed that the intensity of the vortex shedding decreased as a larger fraction of the combustion process heat release occurred in the shear layers surrounding the recirculation zone of the bluff body. Furthermore, a complete transition of the vortex shedding and consequent flame stabilization from asymmetric to symmetric modes was clearly observed when the inlet temperature was reduced from 850°C to 400°C (and hence, significantly increasing the flame dilatation ratio from Tb/Tu ∼ 2.3 to 3.7).

Control of Combustion Driven Oscillations by Equivalence Ratio Modulations

1999 ◽  
Author(s):  
Christian Oliver Paschereit ◽  
Ephraim Gutmark ◽  
Wolfgang Weisenstein
Keyword(s):  
Control System ◽  
Heat Release ◽  
Fuel Injection ◽  
Combustion Instability ◽  
Combustion Process ◽  
Sudden Expansion ◽  
Pressure Oscillations ◽  
Reduced Pressure ◽  
Axisymmetric Mode ◽  
Recirculating Flow

Unstable thermoacoustic modes were investigated and controlled in an experimental low-emission swirl stabilized combustor, in which the acoustic boundary conditions were modified to obtain combustion instability. Several axisymmetric and helical unstable modes were identified for fully premixed conditions. The combustion structure associated with the different unstable modes was visualized by phase locked images of OH chemiluminescence. The axisymmetric mode showed large variation of the heat release during one cycle, while the helical mode showed variation in the radial location of maximal heat release. The helical and axisymmetric unstable modes were associated with flow instabilities related to the recirculating flow in the wakelike legion on the combustor axis and shear layer instabilities at the sudden expansion (dump plane), respectively. A closed loop active control system was employed to suppress the thermoacoustic pressure oscillations and to reduce undesired emissions of pollutants during premixed combustion. Microphone and OH emission detection sensors were utilized to monitor the combustion process and provide input to the control system. High frequency valves were employed to modulate the fuel injection. The specific design of the investigated experimental burner allowed testing the effect of different modulated fuel injection concepts on the different combustion instability modes. Symmetric and antisymmetric fuel injection schemes were tested. Suppression levels of up to 12 dB in the pressure oscillations were observed. In some cases a concomitant reductions of NOx and CO emissions were obtained, however, in other instances increased emissions were recorded at reduced pressure oscillations. The effect of the various pulsed fuel injection methods on the combustion structure was investigated.

Real-Coded Genetic Algorithm for Robust Design of UPFC Supplementary Damping Controller

2012 ◽  
pp. 283-288
Author(s):  
S. C. Swain ◽  
S. Mohapatra ◽  
S. Panda ◽  
S. R. Nayak
Keyword(s):  
Genetic Algorithm ◽  
Phase Angle ◽  
Single Machine ◽  
Low Frequency ◽  
Low Frequency Oscillations ◽  
Damping Controllers ◽  
Real Coded Genetic Algorithm ◽  
Simulation Results ◽  
Single Machine Infinite Bus ◽  
Damping Controller

In this paper RCGA is used in Designing UPFC based supplementary damping controllers for damping low frequency oscillations in a single machine infinite bus power system. The detail investigations have been carried out considering the four alternatives UPFC based damping controller namely modulating index of series inverter (MB),modulating index of shunt inverter (ME),phase angle of series inverter (∂B) & phase angle of shunt inverter (∂E).RCGA is employed to optimize damping controller parameters. Simulation results are presented & compared with a conventional method of tuning the damping controller parameters to show effective of the proposed design approach.

scholarly journals The Effect of RME-1-Butanol Blends on Combustion, Performance and Emission of a Direct Injection Diesel Engine

Energies ◽  
2021 ◽  
Vol 14 (10) ◽  
pp. 2941
Author(s):  
Wojciech Tutak ◽  
Arkadiusz Jamrozik ◽  
Karol Grab-Rogaliński
Keyword(s):  
Diesel Engine ◽  
Heat Release ◽  
Direct Injection ◽  
Specific Energy Consumption ◽  
Combustion Process ◽  
Constant Load ◽  
Combustion Stability ◽  
Performance And Emission ◽  
Energy Share ◽  
The Stability

The main objective of this study was assessment of the performance, emissions and combustion characteristics of a diesel engine using RME–1-butanol blends. In assessing the combustion process, great importance was placed on evaluating the stability of this process. Not only were the typical COVIMEP indicators assessed, but also the non-burnability of the characteristic combustion stages: ignition delay, time of 50% heat release and the end of combustion. The evaluation of the combustion process based on the analysis of heat release. The tests carried out on a 1-cylinder diesel engine operating at a constant load. Research and evaluation of the combustion process of a mixture of RME and 1-butanol carried out for the entire range of shares of both fuels up to 90% of 1-butanol energetic fraction. The participation of butanol in combustion process with RME increased the in-cylinder peak pressure and the heat release rate. With the increase in the share of butanol there was noted a decrease in specific energy consumption and an increase in engine efficiency. The share of butanol improved the combustion stability. There was also an increase in NOx emissions and decrease in CO and soot emissions. The engine can be power by blend up to 80% energy share of butanol.

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