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- ArticleYalnız künye2022Combustion and emission characteristics of premixed biogas mixtures: An experimental study
Sivri, Ilker; Yilmaz, Harun; Cam, Omer; Yilmaz, Ilker
In this study, effects of fuel composition, swirl number and hydrogen addition on combustion and emission characteristics of various biogas mixtures were experimentally investigated. To this end, a laboratory scale combustor and a swirl stabilized premixed burner were designed and manufactured. Later on, this combusting apparatus was equipped with flow, control, safety and measurement tools, hence entire test system was constituted. Combustion and emission characteristics of tested biogas mixtures were determined by measuring temperature and species (CO2, CO, O2 and NO) distributions throughout the combustion chamber. Additionally, flame structures of tested biogas mixtures were evaluated by examining flame luminosity, visible flame length and flame thickness from instantaneous flame images. Results of this study showed that both radial and axial temperature distribution variations of tested biogas mixtures differently alter with hydrogen addition based on the gas composition. Although flame temperature increases with swirl number at burner outlet, it presents a non-monotonous dependence on swirl number outside the flame region because of the modified flow characteristics. This is also the case for emissions of CO2.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2021Flame and instability characteristics of high hydrogen content gas mixtures
Yilmaz, Harun; Yilmaz, Ilker
In this study, initially, 50%H2–25%CH4–25%CO2, 60%H2–20%CH4–20%CO2 and 70%H2–15%CH4–15%CO2 mixtures were combusted in a laboratory scale-swirl stabilized-premixed combustor so as to specify combustion and emission characteristics of respective gas mixtures. Later on, such mixture flames were exposed to acoustic perturbations at different frequencies between the values of 65–205 Hz and under these conditions, flame response was evaluated. The acoustic perturbations were intentionally created by loudspeakers located in side arms of the T-shaped combustor. Two openings on the combustor walls, and photodiodes and pressure sensors assembled in the experimental apparatus enabled interpreting flame response. During experiments, inlet parameters (such as thermal power – 4 kW, equivalence ratio – 0.5, mixture temperature, etc.) and geometric swirl number (1.2) were kept constant, and tested flames were acoustically forced for 30 s at each frequency step. Results showed that thermal Zeldovich mechanism doesn't dominate NOx formation for tested flames, and 50%H2–25%CH4–25%CO2 mixture emits nearly thirty times of magnitude of higher NO than 70%H2–15%CH4–15%CO2 mixture. Besides, the onset of flame instabilities depending on the forcing frequency isn't controlled by gas composition. However, flame and combustion chamber acoustics weakly couple, hence pressure and heat release rate oscillations weaken as hydrogen amount in gas mixture increases.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2021Swirler geometry effects (Dh /do ratio) on synthetic gas flames: Part 1: Combustion and emission characteristics; [Suktuvo geometrijos (Dh /do ) poveikis sintetinių dujų liepsnoms. 1 dalis: degimo ir emisijų charakteristikos]
Yilmaz, Harun; Cam, Omer; Yilmaz, Ilker
Swirling flows increase combustion performance via favour-ing flame stability, pollutant emissions, and combustion in-tensity. The strength of a swirling flow is characterized by a parameter known as swirl number, which is highly related to the dh /do ratio. In this study, effects of the swirler dh /do ratio on combustion and emission characteristics of the synthetic gas flames of premixed 20%CNG/30%H2 /30%CO/20%CO2 mix-ture were experimentally investigated in a laboratory-scale swirl stabilized combustor. For this purpose, twelve different swirl generators were designed and manufactured. dh /do ratios of these swirlers were set as 0.30 and 0.50, and the geometric swirl number was varied between the values of 0.4 and 1.4 (at 0.2 intervals). All experiments were conducted at a fuel-lean equivalence ratio (ϕ = 0.6), room temperature, and local at-mospheric conditions of the city of Kayseri, Turkey. A data logger was utilized to plot axial and radial temperatures and NOx, CO, and CO2 profiles, which were exploited to assess combustion and emission performance. Results showed that the dh /do ratio had a non-monotonic effect on the behaviour of combustion and emission of the tested synthetic gas mix-ture. Depending on the swirl number, increments and dec-rements were observed in temperature and emission values. ENERGETIKA. 2021. T. 67. Nr. 1–2. P. 48–54
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2021Experimental Investigation of Flame Characteristics of H2/CO/CH4/CO2 Synthetic Gas Mixtures
Yilmaz, Harun; Cam, Omer; Yilmaz, Ilker
Chemical composition of synthetic gas and concentration of its components depend on gasification process and feedstock. Synthetic gas mainly consists of hydrogen (H2) and carbon monoxide (CO), and may contain trace amounts of carbon dioxide (CO2) and methane (CH4). In this study, combustion and emission characteristics of H2/CO/CH4/CO2 blending syngas mixtures with high H2/CO ratio were experimentally investigated in a swirl-stabilized premixed combustor. Furthermore, stable operating ranges (flashback and blowout equivalence ratios) of such mixtures and flame response of 67.5%H2-22.5%CO-5%CO2-5%CH4 mixture to acoustic forcing were also detected. During the experiments, CH4 amount in tested gas mixtures varied between 5% and 20% by volume (at intervals of 5%), and H2/CO ratio and CO2 concentration were kept constant at the values of 3 and 5%, respectively. As a consequence, mixtures of 67.5%H2-22.5%CO-5%CO2-5%CH4, 63.75%H2-21.25%CO-5%CO2-10%CH4, 60%H2-20%CO-5%CO2-15%CH4 and 56.25%H2-18.75%CO-05%CO2-20%CH4 were derived and tested under the same boundary and physical conditions. All experiments were conducted at 0.4 equivalence ratio (Φ) and 0.2 geometric swirl number (SN). Preliminarily, stable operating ranges of respective gas mixtures were determined to find an equivalence ratio at which all gas mixtures could be tested without causing any flame instability and then, CH4 addition effects on combustion and emission characteristics of such mixtures were evaluated via utilizing axial and radial temperature, CO and O2 profiles. Lastly, flame behavior of 67.5%H2-22.5%CO-5%CO2-5%CH4 mixture was evaluated under externally modified acoustic conditions. Acoustic field in the combustor was mechanically altered by using side-mounted loudspeakers in the frequency range of 30–200 Hz. To identify flame instabilities and to evaluate the degree of coupling between heat release and pressure oscillations, pressure sensors and photodiodes installed on combustion chamber and burner were utilized. Results of this study showed that CH4 addition to synthetic gas mixtures improves rich flammability limits, and increases flame temperature, flame height and emissions. Under externally modified acoustic conditions, flame behavior slightly alters (flashback and blowout does not occur). Additionally, pollutant emissions improve in an environment-friendly manner under such conditions.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2021Swirler geometry effects (Dh/do ratio) on synthetic gas flames. part 2: Dynamic flame behaviour at externally altered acoustic conditions; [Suktuvo geometrijos (Dh/do ) poveikis sintetinių dujų liepsnoms. 2 dalis: dinaminė liepsnos elgsena veikiant išorėje pakeistomis akustinėmis sąlygomis]
Yilmaz, Harun; Cam, Omer; Yilmaz, Ilker
In a combustion device, unsteady heat release causes acoustic energy to increase when acoustic damping (energy loss) is not that effective, and, as a result, thermo-acoustic flame instabilities occur. In this study, effects of the swirler dh/do ratio (at different swirl numbers) on dynamic flame behaviour of the premixed 20%CNG/30%H2/30%CO/20%CO2 mixture under externally altered acoustic boundary conditions and stability limits (flashback and blowout equivalence ratios) of such mixture were investigated in a laboratory-scale var-iable geometric swirl number combustor. Therefore, swirl generators with different dh/do ratios (0.3 and 0.5) and geometric swirl numbers (0.4, 0.6, 0.8, 1.0 1.2 and 1.4) were designed and manufactured. Acoustic boundary conditions in the combustion chamber were altered using loudspeakers, and flame response to these conditions was perceived using photodiodes and pressure sensors. Dynamic flame behaviour of respective mixture was evaluated using luminous intensity and pressure profiles. Results showed that the dh/do ratio has a minor impact on dynamic flame behaviour.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2020Experimental investigation of flame instability in a premixed combustor
Yilmaz, Harun; Cam, Omer; Yilmaz, Ilker
In this study; effects of fuel composition, equivalence ratio and swirl number on flame behavior (dynamic and static) of premixed 100% CNG, CNG-H2, CNG-H2-CO and CNG-H2-CO2-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-H2 mixture. Moreover, H2/CO ratios of CNG-H2-CO mixtures were arranged to be able to provide low, medium or high heating value. To better represent synthetic gas, CNG-H2-CO mixture was then diluted with the same amount of CO2, and mixtures of CNG-H2-CO2-CO with varying H2/CO ratios were achieved to evaluate effects of CO2 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, CO2 presence in gas mixtures makes flames more resistant to dynamic instabilities (less axial and radial oscillations) and blowout but it increases flashback tendency (2).
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2020A comparison study on combustion and emission characteristics of actual synthetic gas mixtures
Yilmaz, Harun; Cam, Omer; Yilmaz, Ilker
In this study, combustion and emission characteristics of output synthetic gas mixtures of two different power stations, namely Schwarze Pumpe and Fife, were investigated in a swirl stabilized combustor. For this purpose, an experimental test rig which is equipped with a premixed burner that can combust synthetic gases in a wide gas composition range was built and utilized. Tested synthetic gas mixtures are 61.9%H2-26.2%CO-6.9%CH4-5.0%CO2 (Schwarze Pumpe - H2/CO: 2.36) and 34.4%H2-55.4%CO-5.1%CH4-5.1%CO2 (Fife - H2/CO: 0.62). Actually, these gas mixtures contain slight amount of N2 and Ar. Therefore, right amount of CO2 was added to each mixture to represent these inert constituents. The comparison of combustion behavior of respective synthetic gas mixtures was conducted via examining axial and radial temperature values throughout the combustor. Besides, emission behavior was interpreted by analyzing measured CO, CO2 and NO values at combustor chimney. Results of this study showed that 61.9%H2-26.2%CO-6.9%CH4-5.0%CO2 mixture performs better in respective combustor with regard to temperature distribution, and emitted CO and NO levels.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2019Effects of synthetic gas constituents on combustion and emission behavior of premixed H2/CO/CO2/CNG mixture flames
Yilmaz, Harun; Yilmaz, Ilker
In this study, effects of synthetic gas constituents on combustion and emission behavior of premixed H2/CO/CO2/CNG blending synthetic gas flames were experimentally investigated in a swirl stabilized laboratory scale combustor. Effects of these constituents on flashback and blowout equivalence ratios of respective mixtures were also determined. Firstly, mixtures of CNG/H2/CO with varying H2/CO ratios were tested and then each mixture was diluted with the same amount of CO2 (20% by volume) to better represent synthetic gas. H2/CO ratios of tested gas mixtures were so adjusted that heating value of each gas mixture was low, moderate or high. Combustion behavior of such mixtures was evaluated with respect to measured axial and radial temperature values. Moreover, emission behavior was analyzed by means of emitted CO, CO2 and NOx levels. Flame temperature measurements were conducted with B and K type thermocouples. Emission measurements were performed with a flue gas analyzer, which was equipped with a ceramic coated probe, as well. Results of this study revealed the great impact of gas composition on combustion and emission behavior of studied flames. Two main findings are: H2/CO ratio slightly alters temperature distribution throughout combustor, while hydrogen reaction kinetics play the most significant role in synthetic gas combustion (1), CO2 addition tremendously increases emissions of CO (2).
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2019Combustion and emission characteristics of premixed CNG/H2/CO/CO2 blending synthetic gas flames in a combustor with variable geometric swirl number
Yilmaz, Harun; Yilmaz, Ilker
This paper presents the results of experimental studies conducted on premixed CNG/H2/CO/CO2 blending synthetic gas flames in a laboratory scale combustor, with particular emphasis on effects of swirl number (from 0.2 to 1.6, at intervals of 0.2) and equivalence ratio (0.6, 0.8 and 1.0) on combustion and emission characteristics of such mixtures. Furthermore, effects of swirl number on lean blowout and flashback limits of studied mixtures were also investigated. Irrespective of the swirl number and equivalence ratio, H2/CO ratios of tested gas mixtures were kept constant (1.0), and mixtures of H2/CO/CNG/CO2 which were diluted with different amount of CO2 (0–20%, at intervals of 5%) were derived. Considering broadest operating range, mixture of 20%CNG/30%H2/30%CO/20%CO2 was determined as base fuel to be tested. Combustion and emission behavior of tested gas mixtures were assessed by examining axial and radial temperature, NOx, CO and CO2 distributions. Besides, swirl number and equivalence ratio effects on flame structure were evaluated by investigating instantaneous flame images (with the same focal length and exposure time). Results of this study showed that effects of swirl number on flame characteristics (temperature and pollutant emission distributions) is not monotonous, and equivalence ratio dependent flame behavior alters differently at different swirl numbers.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2018An experimental study on premixed CNG/H2/CO2 mixture flames
Yilmaz, Ilker; Yilmaz, Harun; Cam, Omer
In this study, the effect of swirl number, gas composition and CO2 dilution on combustion and emission behaviour of CNG/H2/CO2 gas mixtures was experimentally investigated in a laboratory scale combustor. Irrespective of the gas composition, thermal power of the combustor was kept constant (5 kW). All experiments were conducted at or near stoichiometric and the local atmospheric conditions of the city of Kayseri, Turkey. During experiments, swirl number was varied and the combustion performance of this combustor was analysed by means of centreline temperature distributions. On the other hand, emission behaviour was examined with respect to emitted CO, CO2 and NOx levels. Dynamic flame behaviour was also evaluated by analysing instantaneous flame images. Results of this study revealed the great impact of swirl number and gas composition on combustion and emission behaviour of studied flames.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2018Combustion characteristics of premixed hydrogen/air flames in a geometrically modified micro combustor
Yilmaz, Ilker; Yilmaz, Harun; Cam, Omer; Ilbas, Mustafa
Main challenges for a fuel efficient micro scale combustion are rooted from size restriction of micro combustors which results with inappropriate residence time of fuel/air mixture and intensified heat losses due to relatively high surface to volume ratio of such devices. One way of increasing energy output of micro combustors is to optimize its geometry by considering simplicity and easy manufacturability. In this study, effect of combustor geometric properties on combustion behavior of premixed hydrogen/air mixtures was numerically investigated. For this purpose, an experimentally tested micro combustor's geometric properties were modified by establishing a backward facing step which is varying distance from combustor inlet and has varying step height, and adding opposing cavities which are varying distance from combustor inlet and have constant length to depth ratio into the flow area. Modeling and simulation studies were performed using ANSYS Design Modeler and Fluent programs, respectively. Combustion behavior was analyzed by means of centerline and outer wall temperature distributions, amount of heat transferred through combustor wall, conversion ratio of input chemical energy to utilizable heat, and species distributions. Turbulence model used in this study is Renormalization Group (RNG) k-ε. Multistep combustion reaction scheme with 9 species and 19 steps was simulated using Eddy Dissipation Concept model (EDC). Results showed that backward facing step in the flame region alters reaction zone distribution, flame length and shape, and consequently temperature value and distribution throughout the combustor. Lastly cavity was found to slightly increase peak temperature value.
RDL Kalıcı Kaydıİncele - Book ChapterYalnız künye2018Investigation of an optimal operating condition for a micro combustor regarding basic thermophotovoltaic system requirements
Yilmaz, Harun; Cam, Omer; Yilmaz, Ilker; Nizetic, S; Papadopoulos, A
In this study, effects of equivalence ratio and thermal power on combustion and emission behaviour of premixed hydrogen air mixtures were numerically investigated by constructing 3D micro combustor models. Combustion behaviour was analysed by examining combustor outer wall and centreline temperature profiles, and convective and radiative heat transfer quantities. Besides, emission behaviour was analysed in terms of centreline NOx profiles and NOx amounts emanated from exhaust of the micro combustor. Regarding these, optimal operating condition with respect to combustion performance and pollutant emissions was investigated by varying thermal power and equivalence ratio. Turbulence model used in this study is RNG k-ε (Yilmaz et al. Int J Hydrog Energy 42:25744–25755, 2017). Multistep combustion reaction process with 9 species and 19 steps was simulated using Eddy dissipation concept model. Data obtained from this study was validated against published experimental data (Tang et al. Int J Hydrog Energy 40:2396–2403, 2015). Results showed that optimal operating condition can be gained at 0.8 equivalence ratio and 1200 ml/min hydrogen flux.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2017Effect of different turbulence models on combustion and emission characteristics of hydrogen/air flames
Yilmaz, Harun; Cam, Omer; Tangoz, Selim; Yilmaz, Ilker
This paper aims to present modeling results of hydrogen/air combustion in a micro-cylindrical combustor. Modeling studies were carried out with different turbulence models to evaluate performance of these models in micro combustion simulations by using a commercially available computational fluid dynamics code. Turbulence models implemented in this study are Standard k-ε, Renormalization Group k-ε, Realizable k-ε, and Reynolds Stress Transport. A three-dimensional micro combustor model was built to investigate impact of various turbulence models on combustion and emission behavior of studied hydrogen/air flames. Performance evaluation of these models was executed by examining combustor outer wall temperature distribution; combustor centerline temperature, velocity, pressure, species and NOx profiles. Combustion reaction scheme with 9 species and 19 steps was modeled using Eddy Dissipation Concept model. Results obtained from this study were validated with published experimental data. Numerical results showed that two equation turbulence models give consistent simulation results with published experimental data by means of trend and value. Renormalization Group k-ε model was found to give consistent simulation results with experimental data, whereas Reynolds Stress Model was failed to predict detailed features of combustion process.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2017Effect of micro combustor geometry on combustion and emission behavior of premixed hydrogen/air flames
Yilmaz, Harun; Cam, Omer; Yilmaz, Ilker
In this study, effect of micro combustor geometry on combustion and emission behavior of premixed hydrogen/air mixtures is numerically investigated. An experimentally tested micro combustor geometry is varied by establishing a cavity or a backward facing step or micro channels inside the combustor. Considering effect of combustor geometry on the amount of heat transferred through wall based on outer wall and combustor centerline temperature distributions, combustion behavior is analyzed. Emission behavior is examined by means of mixing conditions, combustion efficiency and maximum temperature value which are highly bound to geometric properties of a micro combustor. Turbulence model used in this study is Renormalization Group k-ε. For turbulence chemistry interaction, Eddy Dissipation Concept model is used. Multistep combustion reaction scheme includes 9 species and 19 steps. Numerical results obtained from this study are validated with published experimental data. Results of this study revealed that combustion in such combustors can be improved by means of quality of mixing process, residence time, combustor centerline and outer wall temperature distributions, conversion rate of input chemical energy to utilizable heat and emanated NOx levels from combustor outlet with proposed geometric variations.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2017A numerical study on combustion and emission characteristics of premixed hydrogen air flames
Cam, Omer; Yilmaz, Harun; Tangoz, Selim; Yilmaz, Ilker
Main challenges for micro power generators that utilize combustion process for energy production are inadequate residence time, destructive radical wall interactions and intensified heat loss which are mainly rooted from size limitation of such devices. To achieve high and uniform energy output, and bring in a solution to these challenges in an environment friendly manner without any kind of fundamental modification, effect of equivalence ratio on combustion and emission behavior of premixed hydrogen/air flames is numerically investigated in this study. For this purpose, an experimentally tested micro cylindrical combustor model is constructed and premixed hydrogen/air combustion in this model is simulated by varying equivalence ratio between 0.5 and 1.2 to find an optimal equivalence ratio with respect to drawbacks of micro power generators. Combustion and turbulence models implemented in this study are Eddy Dissipation Concept and Standard k-ε models, respectively. A detailed hydrogen/air reaction mechanism which consists of 9 species and 19 steps is employed to accurately gain insight into combustion process. Simulation results show that as the equivalence ratio decreases; centerline temperature distribution gets a lower value and the place where chemical reactions take place moves downstream. The most uniform temperature distribution is achieved between 0.8 and 1.0 equivalence ratios. The highest NOx formation is at 0.9 equivalence ratio and its mass fraction decreases sharply when the equivalence ratio reduces from 0.9 to 0.5.
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