共查询到20条相似文献,搜索用时 453 毫秒
1.
Lean premixed combustion is a well known method in gas turbine combustors that can reduce fuel consumption and decrease flame
temperature. In lean premixed flames, flame instabilities can occur because the combustion takes place near the lean flammable
limit. For the purpose of increasing flame stability, a small amount of hydrogen was added into a fuel, which has ultra low
lean flammable limit. The extinction stretch rate increased and total equivalence ratio at extinction decreased with hydrogen
addition; consequently, ultra lean premixed combustion was possible and flame stability could be achieved at low temperature
conditions. The NO x emission increased with hydrogen addition for the same stretch rate and equivalence ratio, but the extinction stretch rate
and lean flammability limit was enlarged. Consequently, NO x emission decreased with hydrogen addition in the near extinction conditions. Hydrogen addition could improve flame stability
and reduce NO x emission in ultra lean premixed combustion.
This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon
Dr. Eun-Seong Cho received his B.S. and M.S. degrees in Mechanical Engineering from Hanyang University, Korea, in 1996 and 1998, respectively.
He then received his Ph.D. degree from Seoul National University, Korea, in 2005. He was a principal engineer of KD Navien
research center and currently a research associate at Delft University of Technology, The Netherlands. His research interests
include eco-friendly clean combustion technology, new and renewable energy systems.
Prof. Suk Ho Chung received his B.S. degree from Seoul National University, Korea, in 1976 and Ph.D. degree in Mechanical Engineering from Northwestern
University, USA, in 1983. He is a Professor since 1984 in the School of Mechanical and Aerospace Engineering at Seoul National
University in Seoul, Korea. His research interests cover combustion fundamentals, pollutant formation, laser diagnostics,
and plasma-assisted combustion. 相似文献
2.
Diode laser sensor is conducted to measure the gas temperature in the liquid-gas 2-phase counter flow flame. C 10H 22 and city gas were used as liquid fuel and gas fuel, respectively. Two vibrational overtones of H 2O were selected and measurements were carried out in the spray flame region stabilized the above gaseous premixed flame. The
path-averaged temperature measurement using diode laser absorption method succeeded in the liquid fuel combustion environment
regardless of droplets of wide range diameter. The path-averaged temperature measured in the post flame of liquid-gas 2-phase
counter flow flame showed qualitative reliable results. The successful demonstration of time series temperature measurement
in the liquid-gas 2-phase counter flow flame gave us motivation of trying to establish the effective control system in practical
combustion system. These results demonstrated the ability of real-time feedback from combustor inside using the non-intrusive
measurement as well as the possibility of application to practical combustion system. Failure case due to influence of spray
flame was also discussed. 相似文献
3.
Because of the energy resource exhaustion, the aggravating environmental air pollution, the smoke phenomena and so on, the recent trends and targets in designing combustor are reduction of pollutant emissions and improvement of combustor efficiency. Therefore many combustion methods and emission control technologies have been proposed by many researchers through numerical and experimental analyses, One of the most available and effective combustion methods is the excess enthalpy combustion, so called, the superadiabatic combustion. In this study, the superadiabatic combustion with the reciprocating flow in a porous media has been investigated with the variation of equivalence ratio, flow velocity and reciprocating cycle time. In this system, the flow direction is reversed regularly by the solenoid valves. The results of this study show that the maximum gas temperature is remarkably higher than the theoretical adiabatic flame temperature and the emission characteristic is very excellent. The analyses reveal several attractive characteristics of the flame and the proposed idea is promising to burn mixtures of low heat content in a reciprocating type combustor. This combustor can be applied to the elimination of unburned compound, with more intensive and continuous study. 相似文献
4.
The objective of this paper is to characterize dynamic pressure traces measured at self-excited combustion instabilities occurring
in two combustion systems of different hardware. One system is a model lean premixed gas turbine combustor and the other a
fullscale bipropellant liquid rocket thrust chamber. It is commonly observed in both systems that low frequency waves at around
300Hz are first excited at the onset of combustion instabilities and after a short duration, the instability mode becomes
coupled to the resonant acoustic modes of the combustion chamber, the first longitudinal mode for the lean premixed combustor
and the first tangential mode for the rocket thrust chamber. Low frequency waves seem to get excited at first since flame
shows the higher heat release response on the lower frequency perturbations with the smaller phase differences between heat
release and pressure fluctuations. Nonlinear time series analysis of pressure traces reveals that even stable combustion might
have chaotic behavior with the positive maximum Lyapunov exponent. Also, pressure fluctuations under combustion instabilities
reach a limit cycle or quasi-periodic oscillations at the very similar run conditions, which manifest that a self-excited
high frequency instability has strong nonlinear characteristics. 相似文献
5.
Experimental investigations have been conducted to understand the combustion characteristics of a swirl-stabilized double-cone pre-mixed burner used for industrial gas turbines for power generation. NOx and CO emissions, extinction limit, combustion noise, pressure loss, and wall temperature distributions were measured for various operating conditions. Results show that NOx emissions are decreased with increasing air/fuel ratio or decreasing air load unless the air load is too small. CO emissions are also decreased with increasing air/fuel ratio, leading to a positive correlation between NOx and CO emissions. Flame extinction limit is reduced with increasing air flow rate as the flow residence time is reduced. Combustion noise has its peak amplitude at the frequencies of 150 or 300 Hz, which are considered to be the resonance frequencies of the longitudinal mode of the combustor. The noise level at the peak frequency is maximized when the flame is considered to be located near the burner exit. Pressure loss is decreased with the A/F ratio as the flame moves downstream out of the burner. 相似文献
6.
The effect of fuel concentration gradient on the propagation characteristics of tribrachial (or triple) flames has been investigated
experimentally in both two-dimensional and axisymmetric counterflows. The gradient at the stoichiometric location was controlled
by the equivalence ratios at the two nozzles; one of which is maintained rich, while the other lean. Results show that the
displacement speed of tribrachial flames in the two-dimensional counterflow decreases with fuel concentration gradient and
has much larger speed than the maximum speed predicted previously in two-dimensional mixing layers. From an analogy with premixed
flame propagation, this excessively large displacement speed can be attributed to the flame propagation with respect to burnt
gas. Corresponding maximum speed in the limit of small mixture fraction gradient was estimated and the curvefit of the experimental
data substantiates this limiting speed. As mixture fraction gradient approaches zero, a transition occurs, such that the propagation
speed of tribrachial flame approaches stoichiometric laminar burning velocity with respect to burnt gas. Similar results have
been obtained for tribrachial flames propagating in axisymmetric counterflow. 相似文献
7.
This paper describes the ignition and combustion characteristics of a gas turbine slinger combustor with rotating fuel injection
system. An ignition test was performed under various airflow, temperature and pressure conditions with fuel nozzle rotational
speed. From the test, there are two major factors influencing the ignition limits: the rotational speed of the fuel nozzle,
and the mass flow parameter. Better ignition capability could be attained through increasing the rotational speed and air
mass flow. From the spray visualization and drop size measurement, it was verified that there is a strong correlation between
ignition performance and drop size distribution. Also, we performed a combustion test to determine the effects of rotational
speed by measuring gas temperature and emission. The combustion efficiency was smoothly enhanced from 99% to 99.6% with increasing
rotational speed. The measured pattern factor was 15% and profile factor was 3%. 相似文献
8.
Flue gas recirculation (FGR) is widely adopted to control NO emission in combustion systems. Recirculated flue gas decreases
flame temperature and reaction rate, resulting in the decrease in thermal NO production. Recently, it has been demonstrated
that the recirculated flue gas in fuel stream, that is, the fuel induced recirculation (FIR), could enhance much improved
reduction in NO per unit mass of recirculated gas, as compared to conventional FGR in air. In the present study, the effect
of dilution methods in air and fuel sides on NO reduction has been investigated numerically by using N3 and CO2 as diluent
gases to simulate flue gases. Counterflow diffusion flames were studied in conjunction with the laminar flamelet model of
turbulent flames. Results showed that CO2 dilution was more effective in NO reduction because of large temperature drop due
to the larger specific heat of CO2 compared to N 2. Fuel dilution was more effective in reducing NO emission than air dilution when the same recirculation ratio of dilution
gas was used by the increase in the nozzle exit velocity, thereby the stretch rate, with dilution gas added to fuel side. 相似文献
9.
The characteristics of combustion oscillation of a silo-type 79.5 MW gas turbine combustor in commercial operation and its suppression have been investigated. The oscillation of the lean premixed
gas turbine combustor resulting from the combustion instability occurred at near full load operation. An FFT analysis of the
combustion dynamics showed that the dominant frequency of the oscillation would be that of the 1st longitudinal acoustic resonance
mode of the combustor. To suppress the combustion oscillation, a passive control technique for reducing the combustion instability
was employed; that is, the fuel to the combustor was redistributed by adjusting the operational schedule of one of six fuel
control valves, which would lead the increase of the local operational equivalence ratio near the central recirculation zone
of the combustor. By doing so, the oscillation was successfully reduced to the permissible level while the amount of NO x emission met proper regulatory level set by the local government. 相似文献
10.
This paper presents the effects of the temperature difference between gas and particle, different Lewis numbers, and heat
loss from the walls in the structure of premixed flames propagation in a combustible system containing uniformly distributed
volatile fuel particles in an oxidizing gas mixture. It is assumed that the fuel particles vaporize first to yield a gaseous
fuel, which is oxidized in a gas phase. The analysis is performed in the asymptotic limit, where the value of the characteristic
Zeldovich number is large. The structure of the flame is composed of a preheat zone, reaction zone, and convection zone. The
governing equations and required boundary conditions are applied in each zone, and an analytical method is used for solving
these equations. The obtained results illustrate the effects of the above parameters on the variations of the dimensionless
temperature, particle mass friction, flame temperature, and burning velocity for gas and particle. 相似文献
11.
Fundamental information about the ignition position and shape of a flame in highly preheated air combustion was obtained,
and the suitability of the suggested reduced kinetic mechanism that reflects the characteristics of the highly preheated air
combustion was demonstrated. Flame lift height and flame length with variations of premixed air temperature and oxygen concentration
were measured by CH* chemiluminescence intensity, and were computed with a reduced kinetic mechanism. Flame attached near
a fuel nozzle started to lift when preheated air temperature became close to auto-ignition temperature and/or oxygen concentration
reduced. The flame lift height increased but the flame length decreased with decreasing preheated air temperature and flame
length reversed after a minimum value. Calculated results showed good agreement with those of experiment within tolerable
error. Flame shape shifted from diffusion flame shape to partial premixed flame shape with increasing lift height and this
tendency was also observed in the computation results.
This paper was recommended for publication in revised form by Associate Editor Ohchae Kwon
Gyung-Min Choi studied the areas of combustion engineering, heat recirculating combustion, and solid fuel gasification, receiving his Ph.D.
degree in engineering from Osaka University in 2001. He served as a researcher at Japan Aerospace Exploration Agency and is
now an associate professor in the School of Mechanical Engineering at Pusan National University. 相似文献
12.
Chemical reactor networks (CRN) models were developed for lean premixed gas turbine combustor to predict the NOx emissions.
In this study, CRN models are constructed based on the computational fluid dynamics (CFD) for both non-pilot and pilot flame
cases. Predictions of NOx emissions in combustor with the developed models were made by using CHEMKIN code and full GRI 3.0
chemical kinetic mechanism in the CRN. The predicted results agree reasonably well with the experimental data obtained from
a simplified test combustor for the GE7FA gas turbine. The effects of overall equivalence ratio, swirl angle and pilot fuel
ratio on the NOx emissions were investigated. 相似文献
13.
Spray and combustion characteristics of a dump-type ram-combustor equipped with a V-gutter flame holder were experimentally
investigated. Spray penetrations with a change in airstream velocity, air stream temperature, and dynamic pressure ratio were
measured to clarify the spray characteristics of a liquid jet injected into the subsonic vitiated airstream, which maintains
a highly uniform velocity and temperature. An empirical equation was modified from Inamura’s equation to compensate for experimental
conditions. In the case of insufficient penetration, the flame in the ram-combustor was unstable, and vice versus in the case
of sufficient penetration. When the flame holder was not equipped, the temperature at the center of the ram-combustor had
a tendency to decrease due to the low penetration and insufficient mixing. Therefore, the temperature distribution was slanted
to the low wall of the ramcombustor. These trends gradually disappeared as the length of the combustor became longer and the
flame holder was equipped. Combustion efficiency increased when the length of the combustor was long and the flame holder
was equipped. Especially, the effect of the flame holder was more dominant than that of the combustor length in light of combustion
efficiency. 相似文献
14.
Numerical investigations on air staging and fuel staging were carried out with a newly designed coaxial cyclone combustor,
which uses the method of two stage coal combustion composed of pre-combustor and main combustor. The pre-combustor with a
high air/fuel ratio is designed to supply gas at high temperature to the main combustor. To avoid local high temperature region
in this process, secondary air is injected in the downstream. Together with the burned gas supplied from the pre-combustor
and the preheated air directly injected into main combustor, coals supplied through the main burner react rapidly at a low
air/fuel ratio. Strong swirling motion of cyclone combustor keeps the wall temperature high, which makes slagging combustion
possible. Alaska, US coal is used for calculations. Predictions were made for various coal flow rates in the main combustor
for fuel staging and for the various flow rate of secondary air in the pre-combustor for air staging. In-scattering angles
are also chosen as a variable to increase residence times of coal particles. Temperature fields and particle trajectories
for various conditions are described. Predicted temperature variations at the wall of the combustor are compared with corresponding
experimental data and show a similar trend. The in-scattering angle of 20° is recommended to increase the combustion efficiency
in the main chamber. 相似文献
15.
Large eddy simulation (LES) of turbulent premixed flame stabilized by the bluff body is developed by using sub-grid scale
combustion model based on the G-equation describing the flame front propagation. The basic idea of LES modeling is to evaluate the filtered-front speed,
which should be enhanced in the grid scale by the scale fluctuations. The dynamic sub-grid scale models newly introduced into
the G-equation are validated by the premixed combustion flow behind the triangle flame holder. The objective of this study is to
investigate the validity of the dynamic sub-grid G-equation model to a complex turbulent premixed combustion such as bluff body stabilized turbulent premixed flames for realistic
engineering application. A new turbulent flame speed model, introduced by the sub-grid turbulent diffusivity and the flame
thickness, is also proposed and is compared with the usual model using sub-grid turbulent intensity and with the experimental
data. The calculated results can predict the velocity and temperature of the combustion flow in good agreement with the experiment
data. 相似文献
16.
The understanding of the liquid fuel spray and flow field characteristics inside a combustor is crucial for designing a fuel efficient and low emission device.Characterisation of the flow field of a model gas turbine liquid swirl burner is performed by using a2-D particle imaging velocimetry(PIV)system.The flow field pattern of an axial flow burner with a fixed swirl intensity is compared under confined and unconfined conditions,i.e.,with and without the combustor wall.The effect of temperature on the main swirling air flow is investigated under open and non-reacting conditions.The result shows that axial and radial velocities increase as a result of decreased flow density and increased flow volume.The flow field of the main swirling flow with liquid fuel spray injection is compared to non-spray swirling flow.Introduction of liquid fuel spray changes the swirl air flow field at the burner outlet,where the radial velocity components increase for both open and confined environment.Under reacting condition,the enclosure generates a corner recirculation zone that intensifies the strength of radial velocity.The reverse flow and corner recirculation zone assists in stabilizing the flame by preheating the reactants.The flow field data can be used as validation target for swirl combustion modelling. 相似文献
17.
A new combustion concept, the so called RML, was investigated to validate its application as a gas turbine combustor for combustor outlet temperatures over 1973 K. The feasibility study of the RML combustor was conducted with zero dimensional combustion calculations. The emission characteristics of RQL, LEAN, EGR and RML combustors were compared. The calculation results showed that the RQL combustor has lower NOx emissions than the LEAN at high outlet temperature. NOx emissions of the RML combustor at equivalence ratio of the rich chamber of 2.0 can be reduced by 30 % compared with the EGR combustor, and lower than the RQL combustor at a combustor outlet temperature over 1973 K. However, the CO emissions of the RML combustor were higher than those of the LEAN and EGR combustors. Also, the possibility of applying the RML combustor to gas turbines was discussed considering residence time, equivalence ratio of the rich chamber and recirculation rate. Although further research to design and realize the proposed RML combustor is needed, this study verified that the RML concept can be successfully used in a gas turbine combustor. 相似文献
18.
Lean premixed combustion has been considered as one of the promising solutions for the reduction of NOx emissions from gas
turbines. However, unstable combustion of lean premixed flow becomes a real challenge on the way to design a reliable, highly
efficient dry low NOx gas turbine combustor. Contrary to a conventional diffusion type combustion system, characteristics
of premixed combustion significantly depend on a premixing degree of combusting flow. Combustion behavior in terms of stability
has been studied in a model gas turbine combustor burning natural gas and air. Incompleteness of premixing is identified as
significant perturbation source for inducing unstable combustion. Application of a simple convection time lag theory can only
predict instability modes but cannot determine whether instability occurs or not. Low frequency perturbations are observed
at the onset of instability and believed to initiate the coupling between heat release rate and pressure fluctuations. 相似文献
19.
The effects of pressure, temperature and equivalence ratio on soot formation in premixed propane-oxygen-inert gas combustion have been investigated over wide ranges of pressure (0.1 to 6 MPa), temperature (1200 to 2100 K) and equivalence ratio (1.5 to 2.7) in a specially designed disk-type constant-volume combustion chamber. To observe the soot formation under high pressure, premixtures are simultaneously ignited by eight spark plugs located on the circumference of chamber at 45 degree intervals. The eight converging flames compress the end gases to a high pressure. The soot volume fraction in the chamber center during the final stage of combustion at the highest pressure is measured by the in situ laser extinction technique and the burnt gas temperature during the same period by the two-color pyrometry method. The pressure and temperature during soot formation are varied by changing the initial charge pressure and by changing the volume fraction of inert gas in the premixture, respectively. It is found that the soot yield is dependent on the pressure, temperature and equivalence ratio, and the soot yield increases under the following conditions; (1) decreasing temperature and increasing equivalence ratio at constant pressure, (2) increasing pressure and decreasing temperature at constant equivalence ratio, (3) increasing equivalence ratio at constant temperature and pressure. 相似文献
20.
This paper addresses the characteristics of flame shapes and flame length in three types of coaxial air flames realizable
by varying coaxial air and/or fuel velocity. Forcing coaxial air into turbulent jet flames induces substantial changes in
flame shapes and NOx emissions through the complex flow interferences that exist within the mixing region. Mixing enhancement
driven by coaxial air results in flame volume decrease, and such a diminished flame volume finally reduces NOx emissions significantly
by decreasing NOx formation zone where a fuel/air mixture burns. It is found that mixing in the vicinity of high temperature
zone mainly results from the increase of diffusive flux than the convective flux, and that the increase of mass diffusion
is amplified as coaxial air is increased. Besides, it is reaffirmed that non-equilibrium chemistry including HO 2/H 2O 2 should be taken into account for NOx prediction and scaling analysis by comparing turbulent combustion models. In addition,
it is found that coaxial air can break down the self-similarity law of flames by changing mixing mechanism, and that EINOx
scaling parameters based on the self-similarity law of simple jet flames may not be eligible in coaxial air flames.
This paper was recommended for publication in revised form by Associate Editor Haecheon Choi
Hee-Jang Moon received his B.S. degree in Aeronautical Engineering from Inha University, Korea in 1986. He then received his M.S. and Doctoral
degrees from Universite de Rouen, France in 1988 and 1991, respectively. Dr. Moon is currently a Professor at the School of
Aerospace and Mechanical Engineering at Korea Aerospace University in Koyang, Korea. He serves on the Editorial Board of the
Korean Society of Propulsion Engineers. His research interests are in the area of turbulent combustion, hybrid rocket combustion
and nanofluids. 相似文献
|