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- ArticleYalnız künye2026Experimental and numerical thermo-hydraulic performance optimization of fin and tube heat exchanger using genetic algorithms
Tepe, Ahmet Ümit; Kuru, Muhammet Nasıf; Yilmaz, Harun
This study focuses on the multi-objective optimization of fin and tube heat exchangers to maximize the Thermal Performance Factor and minimize the Volume . A novel fin design is proposed and integrated onto the tube surfaces to enhance thermo-hydraulic performance. The numerical simulations were conducted using Computational Fluid Dynamics with the conjugate heat transfer method, while the optimization framework was established on modeFRONTIER using a Multi-Objective Genetic Algorithm (MOGA-II). The numerical model was validated against experimental data in this study and existing literature data. The optimization process investigated various fin parameters, (Dwing, Dring, αback,αfront and Gwing), alongside heat exchanger design parameters (ST and SL) and inlet velocity (Vinlet) including 0.3–10 m/s. A total of 1271 design points were evaluated, resulting in 998 feasible configurations and 24 distinct Pareto-optimal designs. The Pareto-optimal Design set yielded TPF values ranging from 1.09 to 1.66. The results highlight the typical trade-off between thermal performance and heat exchanger Volume . Higher TPF values generally correspond to larger volumes, with Design ID 1 achieving the maximum TPF (1.66) but also the largest volume. Conversely, designs with smaller volumes (Design IDs 22–24) exhibit lower TPF values (≈1.09–1.13). Even among designs with the same volume and inlet velocity, variations in fin geometry significantly affect thermal performance. Therefore, designs with higher TPF are preferable when thermal efficiency is the priority, while more compact designs are suitable when minimizing volume is the main goal.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2025Combustion and emission characteristics of laser-ignited pure methane in a rapid compression machine
Yilmaz, Harun; Schröder, Lukas; Hillenbrand, Thomas; Brüggemann, Dieter
In this study, effects of number of consecutive laser ignition pulses on combustion and particle emission characteristics of CH4/Air mixtures were investigated in a rapid compression machine (RCM) by using a passively Q-switched Nd:YAG laser ignitor. To that end, ignition kernel formation and flame evolution characteristics were analyzed with the instrumentality of a high-speed camera (Schlieren setup), while combustion and emission properties were examined by measuring pressure and particulate emissions, respectively. The variation of pressure was also recorded to calculate (with a MATLAB code) indicated work, indicated mean effective pressure and efficiency. Results of this study revealed the linear dependence of ignition possibility to the number of pulses. Ignition possibility increased with the increasing number of pulses. It was 72.72% at 1 pulse and became 92.10% at three pulses. However, number of pulses differently affected other measured or calculated parameters. Depending on the number of pulses, improvements and deteriorations were observed in performance metrics.
RDL Kalıcı Kaydıİncele - CorrectionAçık Erişim2025Correction to: Combustion and emission characteristics of laser-ignited pure methane in a rapid compression machine (Journal of the Brazilian Society of Mechanical Sciences and Engineering, (2025), 47, 2, (95), 10.1007/s40430-025-05415-1)
Yilmaz, Harun; Schröder, Lukas; Hillenbrand, Thomas; Brüggemann, Dieter
The article “Combustion and emission characteristics of laser-ignited pure methane in a rapid compression machine”, written by Harun Yilmaz, Lukas Schröder, Thomas Hillenbrand and Dieter Brüggemann was originally published under exclusive license to The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering 2025. As a result of the subsequent decision to publish the article under the open access model, the article’s copyright notice was changed on 08 May 2025 to © The Author(s) 2025 and the article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/. The original article has been corrected.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2023Laser and pre-chamber ignition, combustion and flame propagation characteristics of CH4/air mixtures in a constant volume combustion chamber
Yilmaz, Harun; Schröder, Lukas; Hillenbrand, Thomas; Brüggemann, Dieter
The most important stages determining the qualitative and quantitative characteristics of a combustion process are mixture preparation, ignition, combustion itself and pollutant emissions. Among these, the ignition phenomenon stands out in terms of ensuring a reliable operation under every working condition (which also affects subsequent stages). In this study, the influence of the properties and the type of the ignition source on combustion and flame propagation characteristics of methane/air mixtures were investigated by using a passively Q-switched Nd:YAG crystal laser and a pre-chamber ignitor in a constant volume combustion chamber. The number of consecutive pulses and the air-fuel-equivalence ratio are studied parameters. With the laser ignition system, it was possible to ignite fuel-air mixtures at very lean conditions. However, as flow conditions in the combustion chamber varied due to the protruding part of the pre-chamber ignitor, ignition possibility decreased and combustion metrics worsened. The number of pulses affected combustion parameters such as the ignition delay time, the combustion duration, the rate of pressure rise etc. in a non-monotonic manner. Deteriorations and improvements on such parameters were detected depending on the air–fuel-equivalence ratio λ.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2023Colorless distributed combustion characteristics of hydrogen/air mixtures in a micro combustor
Yilmaz, Harun; Karyeyen, Serhat; Tepe, Ahmet Ümit; Brüggemann, Dieter
Colorless distributed combustion technique enables less pollutants emissions for a fuel/oxidizer mixture to be combusted. In this study, colorless distributed combustion characteristics (CDC) of hydrogen/air mixtures were numerically investigated in a micro combustor to overcome the difficulties associated with micro combustion and to obtain a more uniform temperature profile on the outer wall. To that end, hydrogen/air combustion was simulated by using ANSYS/Fluent CFD code at a constant equivalence ratio (1.0) and thermal input (100 W) and different mixture inlet temperatures of 300 K, 600 K and 1000 K to seek colorless distributed combustion. CDC conditions were tried to be achieved by decreasing the oxygen concentration from 21 % to 9 % at an interval of 3 %. In conclusion, colorless distributed combustion conditions could be achieved at different O2 concentrations, irrespective of the mixture inlet temperature. At 300 and 600 K, such conditions did not make any positive contribution to the power output of the micro combustor. Nevertheless, at 1000 K and 9 % O2 concentration, all combustion and emission performance metrics were improved in a manner that could increase the power output of the micro power generator.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2023Effects of hydrogen addition on combustion and flame propagation characteristics of laser ignited methane/air mixtures
Yilmaz, Harun; Schröder, Lukas; Hillenbrand, Thomas; Brüggemann, Dieter
In this study, effects of hydrogen addition on combustion and flame propagation characteristics of methane/air mixtures were investigated in a constant volume combustion chamber. Tested gas mixtures are 100% CH4, 05% H2 – 95% CH4, 10% H2 – 90% CH4 and 15% H2 – 85% CH4, and such mixtures were ignited using a passively Q-switched Nd:YAG laser ignitor which has a pulse energy of 12.3 mJ, pulse duration of 2.4 ns and wave length of 1064 nm. A Schlieren setup coupled with a high-speed camera enabled evaluating flame propagation behavior, while pressure curve analysis provided necessary data for characterization of combustion properties. Additionally, lean flammability limits of gas mixtures were also determined at the test conditions. The unique properties of hydrogen (such as low density, high reactivity, high diffusivity etc) widened lean flammability limit. Rate of pressure rise and measured pressure values increased with hydrogen addition, regardless of the air-fuel equivalence ratio (λ). Lastly, hydrogen addition uniformly affected flame propagation characteristics and flame luminosity. Combustion process became more stable with hydrogen addition.
RDL Kalıcı Kaydıİncele - ArticleAçık Erişim2022Thermal–hydraulic performance of the circular-slice-shaped-winglet for tube bank heat exchanger
Tepe, Ahmet Ümit; Yilmaz, Harun
In this study, heat transfer performance of circular-slice-shaped-winglet (CSSW) for tube bank heat exchanger (TBHE) was numerically investigated. Circular-slice angle (α = 5°, 10° and 20°), layer gap (h/d = 0.08, 0.14, and 0.20) and winglet diameter (D/d = 1.60, 1.76 and 1.92) were analyzed as geometric parameters to obtain optimal design. Comprehensive numerical simulations were conducted under both laminar and turbulent flow (1100 ≤ Re ≤ 8500) conditions. Navier Stokes Equations were solved by using RNG k-ε turbulence model (with enhanced wall treatment). Colburn-j factor (j), friction factor (f), modified London area goodness factor (j/f1/3) and performance evaluation criterion (PEC) were investigated quantitatively. Flow characteristics were also analyzed to elucidate the underlying physics of the effects of CSSW on thermal-hydraulic performance for TBHE. Results were compared with the data related to bare tube heat exchanger, and showed that the highest modified London area goodness factor is 26.34% with α = 10°, h/d = 0.20 and D/d = 1.92 CSSW winglet design. Additionally, numerical calculations revealed that PEC increased to 1.356 with these CSSW design parameters, which corresponds to reduction of the required total heat transfer area by 36.60% compared to the bare tube heat exchanger for the same heat duty at a fixed pumping power.
RDL Kalıcı Kaydıİncele - 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 - ArticleAçık Erişim2019Numerical Investigation of Combustion and Emission Behavior of Shale Gas Mixtures in a Laboratory Scale Combustor
Yilmaz, Harun
In this study, effects of gas composition and swirl number on combustion and emission behavior of shale gas mixtures were numerically investigated in a laboratory scale combustor. For this purpose, a two-dimensional model of an experimentally tested premixed combustor was formed. In this model, methane/air combustion was simulated, and achieved results were compared with experimental data to validate applicability of the model. Numerical studies were performed using computational fluid dynamics software, ANSYS/Fluent. Tested shale gas mixtures are; 86% CH4 - 14% C2H6, 81% CH4 - 10% C2H6 - 9% N2 and 58% CH4 - 20% C2H6 - 12% C3H8 - 10% CO2. Combustion and emission behavior of the respective mixtures were determined by examining temperature and species (CO2 and NOx) distributions throughout the combustion chamber. Results of this study showed that %86 CH4- %14 C2H6 mixture is favorable in terms of combustion and emission performance; emissions of NOx are highly dependent on gas composition and swirl number, and axial temperature values and reaction rate are directly proportional to swirl number.
RDL Kalıcı Kaydıİncele - ArticleYalnız künye2019Investigation of combustion and emission performance of a micro combustor: Effects of bluff body insertion and oxygen enriched combustion conditions
Yilmaz, Harun
Major challenges for micro combustors are high heat losses and inappropriate residence time. In this study, it was aimed to eliminate these challenges via placing bluff bodies into the combustion zone and combusting fuel with oxygen enriched air. To this end, micro combustor models with different geometries were constructed and in these models, premixed H2/air combustion was simulated by using ANSYS/Fluent CFD code to investigate effects of bluff body shape, location and thickness, and low level O2 enhancement on performance determining parameters such as rate of conversion of fuel to useable heat, temperature uniformity, pollutant emissions etc. To further analyze effects of micro combustor geometry, a perforated plate was also placed into the combustion zone. Thermal performance of the micro combustor with perforated plate insertion in O2 enriched conditions was found to be highest in terms of increased reaction kinetics and heat transfer characteristics. The trade-offs of respective design are increased NOx emissions and slightly decreased temperature uniformity.
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.
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