New developed burner towards stable lean turbulent partially premixed flames (original) (raw)
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Experimental study of lean premixed turbulent combustion
The purpose of this experimental study is to identify the factors that give rise to combustion instability in case of lean premixed combustion. The studied experimental device is gas turbine combustor, where the flame is stabilized in the dump combustor with a swirling and bluff-body injector. This combustor is optically accessible. A parametrical study has been conducted in the way to provide information on the effect of the equivalence ratio, φ, while the mean inlet velocity remains constant. LDV and OH * chemiluminescence measurements were performed in the reacting flows for a 50° swirler and for different equivalence ratio conditions. LDV measurements show that two distinct recirculations zones appears in the resulting flow. One is formed in the corner due to the sudden-expansion, while the other one is due to the swirling motion of the incoming flow. In order to obtain the 2D mean reaction location, an Abel deconvolution algorithm is applied to the average of 200 OH* chemiluminescence images. It allows to enhance the following relationships: as the premixing becomes leaner, the flame takes different locations in the flow. For φ > 0.7, the flame is in a steady state, anchored near the bluff-body between the two recirculation zones. For 0.7 > φ > 0.65, an extension of reaction zone occurs in the corner recirculation zone and downstream near the quartz tube. For 0.65 > φ > 0.6, the flame becomes unsteady and an oscillation of the OH * emission intensity occurs with the same frequency as measured by dynamic pressure in the combustion chamber (≈16 Hz). For φ = 0.57, the flame becomes stable again without any reaction in the corner recirculation zone. When φ is more reduced (φ <0.57), the blow-out occurs. In order to characterize the unsteady state, CH * visualization is realized by triggering acquisition with the temporal signal of pressure. Results shows a periodic behavior of flame position and combustion intensity. The analysis of all results shows a coupling between the cyclic phenomenon of vortex shedding and fluctuations in gas supply inducing a cyclic equivalence ratio at the inlet.
Experimental investigation of flame instability in a premixed combustor
Fuel, 2019
In this study; effects of fuel composition, equivalence ratio and swirl number on flame behavior (dynamic and static) of premixed 100% CNG, CNG-H 2 , CNG-H 2-CO and CNG-H 2-CO 2-CO mixtures under externally altered acoustic conditions were experimentally investigated in a laboratory scale swirl stabilized combustor. During experiments, the amount of CNG in all gas mixtures tested was set as 20% and 40% by volume except for the CNG-H 2 mixture. Moreover, H 2 /CO ratios of CNG-H 2-CO mixtures were arranged to be able to provide low, medium or high heating value. To better represent synthetic gas, CNG-H 2-CO mixture was then diluted with the same amount of CO 2 , and mixtures of CNG-H 2-CO 2-CO with varying H 2 /CO ratios were achieved to evaluate effects of CO 2 dilution (in addition to flame behavior) on flame characteristics (i.e. performance metrics such as flame temperature and emissions). Acoustic field of the combustor was altered via side mounted loudspeakers to trigger combustion instabilities, and under these circumstances, flame behavior was evaluated by examining instantaneous flame images, pressure and luminous intensity profiles. Data obtained from pressure transducers and photodiodes was also utilized to detect whether dynamic instabilities, i.e. thermoacoustic instabilities, excite static instabilities such as blowout, flashback, and flame liftoff etc. or not. Results of this study showed that fuel composition, equivalence ratio and swirl intensity are determinant parameters on flame behavior. Two main inferences of this study are: swirl number has a monotonic impact on flame stability characteristics (1); under externally excited acoustic conditions, CO 2 presence in gas mixtures makes flames more resistant to dynamic instabilities (less axial and radial oscillations) and blowout but it increases flashback tendency (2).
Experimental Thermal and Fluid Science, 2010
Experiments were carried out on partially premixed turbulent flames stabilized in a conical burner. The investigated gaseous fuels are a mixture of CH 4 , CO, CO 2 , H 2 and N 2 , simulating typical products from gasification of biomass. The fuel and air were partially mixed in a co-centric tube. Flame stabilization behavior with and without the cone was investigated and significantly different stabilization characteristics were observed. Planar Laser induced fluorescence (LIF) of a tracer species, acetone, and OH radicals was carried out to characterize the flame structures. The data show that the flames with the cone are more stable than those without the cone. Without the cone the burner is a typical jet; the critical jet velocities for blowoff and liftoff of biomass derived gases are found to be much higher than that for methane/nitrogen mixture with the same heating values. With the cone, it was shown the stability of flames is not sensitive to the compositions of the fuels. From the PLIF images it was shown that in the conical burner, the flame is stabilized by the cone at nearly the same position for different fuels. The flame is believed to be controlled by the vorticity structure inside cone which depends on the cone angle and flow speed, and less sensitive to the fuel compositions.
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, 1998
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 NO x 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 possibly occur; this is associated with a risk of engine failure and higher NO x emissions.
Numerical Study of Turbulent Lean Premixed Methane-Air Flames
2016
Lean Premixed Combustion (LPC) is recently proposed in gas turbine combustors which have been operated traditionally in the non-premixed mode. In this method, fuel and air are mixed before entering the combustor. With LPC, the flame temperature is reduced due to the operating with excess air conditions. Thus, thermal NO x can be reduced to negligible levels at these lean conditions. On the other hand, the local and global flame extinction risks and therefore flame instabilities may arise because of operating at fuel-lean conditions near the lean flammability limit. In order to control such flames, both their chemical kinetics and flame propagation properties should be investigated in detail, mainly for various equivalence ratios. In this study, the numerical simulations based on experimental data obtained from the combustion chamber setup of the ICARE are performed. The experimental results concern turbulent premixed methane-air flames stabilized on a Bunsen type burner; they are obtained by LDA for the cold and hot flow velocity statistics and by laser induced Mie and Rayleigh scattering techniques for flame front statistics. The operating conditions in experiments are chosen to be close to the gas turbine combustor operating conditions. Numerical simulations are performed by using the Fluent ® software. Both the analysis of the flow and turbulence properties of the chamber by using the k-ε turbulence model and its variants and the premixed flame properties of the methane/air mixtures are investigated. The influence of the equivalence ratio on the flame properties is examined as well. It is observed that increase in equivalence ratio results in decrease in the flame length and the flame brush thickness. Similar tendencies are observed in the experiments. Flame front properties are examined with the combustion model provided by the Fluent ® software, namely Zimont premixed model, and y the well-known CFM turbulent premixed combustion model. Satisfactory results are obtained.
Measurements of premixed-flame turbulence generation and modification in a Taylor-Couette burner
Experimental Thermal and Fluid …, 2007
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Turbulent premixed flames of CNG, LPG, and H2 propagating past repeated obstacles
Experimental Thermal and Fluid Science, 2014
This paper presents a comparative study of turbulent premixed flames of three different fuels propagating past repeated solid obstacles. Compressed natural gas (CNG), liquefied petroleum gas (LPG), and hydrogen are employed separately at two different equivalence ratios. All three fuels are tested at an equivalence ration of 0.8 giving a good comparison between the cases. Three baffle plates and two obstacles with different blockage ratios are used in a range of configurations. In all tests, the mixture is initially at rest when ignited from a single point near the base of the chamber. Pressure-time traces as well as high-speed images of laser induced fluorescence from OH (HS-LIF-OH) are measured. The overpressure, pressure gradients, time to reach the peak pressure, location and speed of the flame front as well images of OH are compared for the three fuels. It is true for all fuels that the peak pressure and its rate of change can be increased by increasing the blockage ratio. For the same equivalence ratio of 0.8, the peak pressure and rate of change for hydrogen flames were about an order of magnitude higher than for LPG or CNG flames. For a given configuration of obstacles, the structure of hydrogen flames shows less distortion and wrinkling than for the other two hydrocarbon fuels at the same equivalence ratio. A good correlation seems to exist between the peak pressure, its rate of change and the time to reach the peak. The data forms a good platform for validating models of turbulent premixed combustion.
Combustion Science and Technology, 2018
Partially premixed combustion is characterized by mixture fraction inhomogeneity upstream of the reaction zone and occurs in many applied combustion systems. The temporal and spatial fluctuations of the mixture fraction have tremendous impact on the combustion characteristics, emission formation, and flame stability. In this study, turbulent partially premixed flames are experimentally studied in a slot burner configuration. The local temperature and gas composition is determined by means of one-dimensional, simultaneous detection of Rayleigh and Raman scattering. The statistics of the mixture fraction are utilized to characterize the impact of the Reynolds number, the global equivalence ratio, the progress of mixing within the flame, as well as the mixing length on the mixing field. Furthermore, these effects are evaluated by means of a regime diagram for partially premixed flames. In this study, it is shown that the increase of the mixing length results in a significantly more stable flame. The impact of the Reynolds number on flame stability is found to be minor.
Lean Premixed Combustion (LPC) is recently proposed in gas turbine combustors which have been operated traditionally in the non-premixed mode. In this method, fuel and air are mixed before entering the combustor. With LPC, the flame temperature is reduced due to the operating with excess air conditions. Thus, thermal NO x can be reduced to negligible levels at these lean conditions. On the other hand, the local and global flame extinction risks and therefore flame instabilities may arise because of operating at fuel-lean conditions near the lean flammability limit. In order to control such flames, both their chemical kinetics and flame propagation properties should be investigated in detail, mainly for various equivalence ratios. In this study, the numerical simulations based on experimental data obtained from the combustion chamber setup of the ICARE are performed. The experimental results concern turbulent premixed methane-air flames stabilized on a Bunsen type burner; they are ob...
Experimental Thermal and Fluid Science, 2018
Combustion of turbulent inhomogeneous mixtures of air and fuel is common in many practical systems providing improved stability for both gaseous and liquid fuels. Understanding the structure and stability of turbulent flames in this mode has been the aim of many research groups who employed special burner designs to control the fuel and air mixing process. In this work, a modified design inspired by the Wolfhard-Parker slot burner was developed for planar turbulent flames with inlet conditions that are overall lean yet either compositionally inhomogeneous or partially premixed. The new burner is referred as the Concentric Flow Slot Burner (CFSB). The stability characteristics and flame structure are investigated for methane and natural gas fuels using planar laser induced fluorescence of C 2 H x and high speed PLIF-OH. The effects of the jet equivalence ratio, the level of inhomogeneity, and the Reynolds number are investigated in this work. The data show that the flames with inhomogeneous mixture are more stable than fully premixed flames. Lean flames are stabilized in the CFSB burner. Stability is significantly improved by the use of a hollow truncated rectangular pyramid nozzle at the burner exit. The reaction zone structure varies significantly in the current burner from thin structures in rich flames to distributed with thick preheat zones in lean flames. The effect of the level of inhomogeneity on the reaction zone structure is presented and discussed. The new CFSB burner is able to generate a wide range of turbulent planar flames spanning the entire range from non-premixed to fully premixed flames. In addition, the high stability level of the burner allows for the study of highly turbulent flames of practical interest.