Ilker Yilmaz - Academia.edu (original) (raw)

Papers by Ilker Yilmaz

Havacilik sektoru surekli olarak gelisme gostermektedir. Buna paralel olarak hava tasimaciliginda... more Havacilik sektoru surekli olarak gelisme gostermektedir. Buna paralel olarak hava tasimaciliginda onemli birartis soz konusudur. Hava trafigindeki artis ucak motorlarindan kaynaklanan kirletici emisyonlari artirmaktadir.Bu calismada, yolcu tasimaciligi ve ozel amaclar icin kullanilan farkli uretici firmalarin turbofan ve turbojetmotorlarindan kaynaklanan azotoksit (NOx), karbon monoksit (CO) ve yanmamis hidrokarbon (HC) emisyonlariincelenmistir. Calismada, Uluslararasi Sivil Havacilik Teskilati (ICAO) verileri kullanilarak motoremisyonlarinin yakit akisi ve motor guc orani ile degisimleri belirlenmistir. Ayrica, calismada Jet A yakiti ilebiodizel olarak Metil Butanol’un farkli oranlarda karistirilmasi ile elde edilen karisimli yakitin CF6-80C gazturbinli turbofan motor emisyonuna etkisi incelenmistir. NOx emisyonu calismada incelenen motorlar icin, yakitakis miktarinin artmasi ile arttigi belirlenmistir. CO ve HC emisyonlari ise; NOx emisyonunun tam tersinecalismada kullanilan motor...

International Journal of Hydrogen Energy, 2017

This paper aims to present modeling results of hydrogen/air combustion in a microcylindrical comb... more This paper aims to present modeling results of hydrogen/air combustion in a microcylindrical 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 NO x 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.

Open Engineering, 2018

In this study, the effect of swirl number, gas composition and CO2 dilution on combustion and emi... more 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.

Bu makalede; hava fazlalik katsayisinin yanma verimi ve emisyonlara etkisinin belirlenmesi amacla... more Bu makalede; hava fazlalik katsayisinin yanma verimi ve emisyonlara etkisinin belirlenmesi amaclanmistir. Iki farkli yakit, uc farkli sivi yakit kazaninda yakilmis ve duman kanalindan degisik radyal uzakliklarda kazan yanma verimleri ve emisyon davranislari deneysel olarak incelenmistir. Yapilan calismalar ile cok sayida deneysel veriler elde edilmistir. Hava fazlalik degeri arttikca NOX emisyonunun genellikle azaldigi, SO2 emisyonun fazla degismedigi gorulmustur. Hava fazlalik degeri arttikca CO emisyonunun ve isil verimin azaldigi gorulmustur. Ayrica SO2 emisyonunun yakittaki kukurt miktarina bagli olarak degistigi gorulmustur. The aim of study is to determine the effect of excess-air level on combustion efficiency and emissions. Two different fuel are burned in three various liquid fuel boiler. Combustion performance and emission behaviours are experimentally investigated at different radial distance from boiler-flue connection section. Wide range of experimental results have bee...

Fuel, 2021

Abstract The instability changes of oxygen-enriched fuel mixtures under acoustic enforcement in a... more Abstract The instability changes of oxygen-enriched fuel mixtures under acoustic enforcement in a premixed and swirl supported system were investigated in this study. Different amounts of hydrogen (0%, 10%, 20%) were added to methane used as fuel and oxygen enrichment process (21%, 24%, 26%) was applied in hydrogen-added fuel mixtures. The equivalence ratio was kept constant at 0.7 in experiments conducted under constant burner power and swirl support. Experiments showed that although oxygen enrichment up to 24% ratio increases stability by increasing the laminar flame speed, stability decreases when the oxygen content in the oxidizer was increased to 26%. As a result of increasing both hydrogen ratio in fuel mixture and oxygen enrichment, instabilities grow up with decreasing of Markstein length. In this situation, burning in combustion chamber did not continue under acoustic force. According to the emission values taken during combustion experiments, the addition of oxygen increased NOx emissions due to increased adiabatic temperature and sudden NOx formations, while contributing to the reduction of CO emissions. Although the addition of hydrogen reduces NOx emissions in case of combustion with air (%21 O2), it has increased the CO emissions from 2 ppm to 13 ppm because it triggers instabilities when combined with oxygen enrichment.

Combustion Science and Technology, 2020

Chemical composition of synthetic gas and concentration of its components depend on gasification ... more Chemical composition of synthetic gas and concentration of its components depend on gasification process and feedstock. Synthetic gas mainly consists of hydrogen (H 2) and carbon monoxide (CO), and may contain trace amounts of carbon dioxide (CO 2) and methane (CH 4). In this study, combustion and emission characteristics of H 2 /CO/CH 4 /CO 2 blending syngas mixtures with high H 2 /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%H 2-22.5%CO-5%CO 2-5%CH 4 mixture to acoustic forcing were also detected. During the experiments, CH 4 amount in tested gas mixtures varied between 5% and 20% by volume (at intervals of 5%), and H 2 /CO ratio and CO 2 concentration were kept constant at the values of 3 and 5%, respectively. As a consequence, mixtures of 67.5%H 2-22.5%CO-5%CO 2-5%CH 4 , 63.75%H 2-21.25%CO-5%CO 2-10%CH 4 , 60%H 2-20%CO-5%CO 2-15%CH 4 and 56.25%H 2-18.75%CO-05%CO 2-20%CH 4 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, CH 4 addition effects on combustion and emission characteristics of such mixtures were evaluated via utilizing axial and radial temperature, CO and O 2 profiles. Lastly, flame behavior of 67.5%H 2-22.5%CO-5%CO 2-5%CH 4 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 CH 4 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 environmentfriendly manner under such conditions.

Fuel, 2019

Abstract In this study, combustion and emission characteristics of output synthetic gas mixtures ... more Abstract 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.

Journal of the Energy Institute, 2019

In this study, effects of synthetic gas constituents on combustion and emission behavior of premi... more In this study, effects of synthetic gas constituents on combustion and emission behavior of premixed H 2 / CO/CO 2 /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/H 2 /CO with varying H 2 /CO ratios were tested and then each mixture was diluted with the same amount of CO 2 (20% by volume) to better represent synthetic gas. H 2 /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, CO 2 and NO x 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: H 2 /CO ratio slightly alters temperature distribution throughout combustor, while hydrogen reaction kinetics play the most significant role in synthetic gas combustion (1), CO 2 addition tremendously increases emissions of CO (2).

Journal of Energy Resources Technology, 2013

This paper presents the effect of swirl number on combustion characteristics such as temperature,... more This paper presents the effect of swirl number on combustion characteristics such as temperature, velocity, gas concentrations in a natural gas diffusion flame. Numerial simulations carried out using the commercial computational fluid dynamics (CFD) code, Fluent by choosing appropriate model parameters. The combustion reaction scheme in the flame region was modeled using eddy dissipation model with one step global reaction scheme. A standard k-ε turbulence model for turbulent closure and P-I radiation model for flame radiation inside the combustor is used in the numerical simulations. In order to investigate the swirling effect on the combustion characteristics, seven different swirl numbers including 0; 0.1; 0.2; 0.3; 0.4; 0.5; and 0.6 are used in the study. Numerical results are validated and compared with the published experimental and simulation results. A good consistency is found between the present results and those published measurement and simulation results in the availabl...

International Journal of Hydrogen Energy, 2005

In this paper, the numerical simulation of a turbulent non-premixed hydrogen (H 2) diffusion flam... more In this paper, the numerical simulation of a turbulent non-premixed hydrogen (H 2) diffusion flame has been performed in a model combustor. CFD studies using Fluent code were carried out changing fuel composition from pure hydrogen to natural gas (100% H 2 , 70% H 2 + 30% CH 4 , 10% H 2 + 90% CH 4 , and 100% CH 4). The model prediction studies have been extended to combustion air staging. Air 25% was staged and introduced through the two tangential inlets. The predictions are validated and compared against the experimental results obtained in this study and results from the literature. Turbulent diffusion flames are investigated numerically using a finite volume method for the solution of the conservation and reaction equations governing the problem. The standard kmodel is used for modelling of turbulent flow as the model was far enough for the turbulence phenomena in the combustor. The chemical combustion reactions are described by seven species and three steps. A NO x post-processor has been used for predicting NO x emissions from the combustor. The temperature and major pollutant concentration (CO and NO x) distributions are in good agreement with the experimental measurements. The overall flame temperature increases as hydrogen is added or decreases as methane is added to the fuel mixture. The addition of methane to hydrogen decreases the flame temperature and thus NO x emissions considerably. Air staging causes rich and lean combustion regions and thus lower NO x emissions through the combustor exit.

International Communications in Heat and Mass Transfer, 2008

In this study, temperature distributions from turbulent chemical reactive flow inside a model com... more In this study, temperature distributions from turbulent chemical reactive flow inside a model combustor have been presented for various mixtured hydrogen–methane fuels. The gas emissions were also obtained at the combustor exit. A platinum–platinum 13% rhodium thermocouple (R type) was used for measurement of axial and radial temperatures. The axial and radial temperature measurements were taken from six various distances and four distances, respectively. Experimental measurements were made at excess air ratios of 1.2 and 1.7, two various thermal powers including 40 and 60 kW and two various hydrogen–methane blending fuels (volumetrically 30% H2–70% CH4 and 70% H2–30% CH4). The results show that the temperature level increases, CO and CO2 emissions decrease when the hydrogen content is increased in mixtured fuel, hydrogen–methane mixtured fuels are successfully used without any important modification in natural gas burner.

Energy, 2017

In this study, effect of micro combustor geometry on combustion and emission behavior of premixed... more 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 NO x levels from combustor outlet with proposed geometric variations.

Energetika

In a combustion device, unsteady heat release causes acoustic energy to increase when acoustic da... more 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 variable 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 inte...

International Journal of Hydrogen Energy

Fuel

Abstract Main challenges for a fuel efficient micro scale combustion are rooted from size restric... more Abstract 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-e. 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.

International Journal of Hydrogen Energy

International Journal of Energy Research, 2012

This paper presents gas emissions from turbulent chemical flow inside a model combustor, for diff... more This paper presents gas emissions from turbulent chemical flow inside a model combustor, for different blending ratios of hydrogen-methane composite fuels. Gas emissions such as CO and O 2 from the combustion reaction were obtained using a gas analyzer. NOx emissions were measured with a NOx analyzer. The previously obtained flame temperature distributions were also presented. As the amount of hydrogen in the mixture increases, more hydrogen is involved in the combustion reaction, and more heat is released, and the higher temperature levels are resulted. The results have shown that the combustion efficiency increases and CO emission decreases when the hydrogen content is increased in blending fuel. It is also shown that the hydrogen-methane blending fuels are efficiently used without any important modification in the natural gas burner.

International Communications in Heat and Mass Transfer, 2012

A numerical study has been conducted to analyze the turbulent forced convection heat transfer for... more A numerical study has been conducted to analyze the turbulent forced convection heat transfer for double forward facing step flow with obstacles. Obstacles have rectangular cross-sectional area with different aspect ratio that is located before each step. The numerical solutions of continuity, momentum and energy equations were solved by using a commercial code which uses finite volume techniques. The effect of turbulence was modeled by using a k-ε model. The effects of step height, obstacle aspect ratio and Reynolds number on the flow and heat transfer are investigated. The obtained results show that the rate of heat transfer is enhanced as aspect ratio of obstacle increases and this trend is affected by the step height. Also the results verified that the pressure drop decreases as obstacle aspect ratio increases.

Energy Conversion and Management, 2012

Fossil-based fuels are commonly used in aircraft engines but they have a polluting effect and the... more Fossil-based fuels are commonly used in aircraft engines but they have a polluting effect and they cause a greenhouse effect for our world. This study reports a research about aircraft gas turbine engines which are fired by liquid hydrogen (LH 2) in terms of performance and environmental aspects. Also, the performance and emissions of LH 2 fueled engines are compared with those of kerosene fired aircraft engines. Same flights from Istanbul to London, and Paris to Kabul are examined to estimate the emission from a conventional aircraft as an application in aviation sector. It is shown that the amount of NO x , HC and CO emissions for traveling by a conventional aircraft for London is 78.36, 1.202 and 22.4 kg, while Paris is 71.55, 1.171 and 21.63 kg, and Kabul is 111.44, 1.36 and 26.11 kg, respectively. For the use of liquid hydrogen as a fuel, amount of gas emissions decreases for any destination like London, Paris and Kabul. Total HC and CO emissions are going to be nearly 0 kg because of lack of carbon in the fuel. Also NO x emission is lower because of wider flammability limit of LH 2. Results show that the aircraft engines with LH 2 have great potential for emissions reduction and engine performance parameters are a little better for LH 2 fuel. It is strongly emphasized that one of the most important advantages for the use of LH 2 is national independence for fuel supply. Oil cannot be extracted in every countries territory but LH 2 is producible for every country and this is so important for a countries freedom.

Havacilik sektoru surekli olarak gelisme gostermektedir. Buna paralel olarak hava tasimaciliginda... more Havacilik sektoru surekli olarak gelisme gostermektedir. Buna paralel olarak hava tasimaciliginda onemli birartis soz konusudur. Hava trafigindeki artis ucak motorlarindan kaynaklanan kirletici emisyonlari artirmaktadir.Bu calismada, yolcu tasimaciligi ve ozel amaclar icin kullanilan farkli uretici firmalarin turbofan ve turbojetmotorlarindan kaynaklanan azotoksit (NOx), karbon monoksit (CO) ve yanmamis hidrokarbon (HC) emisyonlariincelenmistir. Calismada, Uluslararasi Sivil Havacilik Teskilati (ICAO) verileri kullanilarak motoremisyonlarinin yakit akisi ve motor guc orani ile degisimleri belirlenmistir. Ayrica, calismada Jet A yakiti ilebiodizel olarak Metil Butanol’un farkli oranlarda karistirilmasi ile elde edilen karisimli yakitin CF6-80C gazturbinli turbofan motor emisyonuna etkisi incelenmistir. NOx emisyonu calismada incelenen motorlar icin, yakitakis miktarinin artmasi ile arttigi belirlenmistir. CO ve HC emisyonlari ise; NOx emisyonunun tam tersinecalismada kullanilan motor...

International Journal of Hydrogen Energy, 2017

This paper aims to present modeling results of hydrogen/air combustion in a microcylindrical comb... more This paper aims to present modeling results of hydrogen/air combustion in a microcylindrical 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 NO x 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.

Open Engineering, 2018

In this study, the effect of swirl number, gas composition and CO2 dilution on combustion and emi... more 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.

Bu makalede; hava fazlalik katsayisinin yanma verimi ve emisyonlara etkisinin belirlenmesi amacla... more Bu makalede; hava fazlalik katsayisinin yanma verimi ve emisyonlara etkisinin belirlenmesi amaclanmistir. Iki farkli yakit, uc farkli sivi yakit kazaninda yakilmis ve duman kanalindan degisik radyal uzakliklarda kazan yanma verimleri ve emisyon davranislari deneysel olarak incelenmistir. Yapilan calismalar ile cok sayida deneysel veriler elde edilmistir. Hava fazlalik degeri arttikca NOX emisyonunun genellikle azaldigi, SO2 emisyonun fazla degismedigi gorulmustur. Hava fazlalik degeri arttikca CO emisyonunun ve isil verimin azaldigi gorulmustur. Ayrica SO2 emisyonunun yakittaki kukurt miktarina bagli olarak degistigi gorulmustur. The aim of study is to determine the effect of excess-air level on combustion efficiency and emissions. Two different fuel are burned in three various liquid fuel boiler. Combustion performance and emission behaviours are experimentally investigated at different radial distance from boiler-flue connection section. Wide range of experimental results have bee...

Fuel, 2021

Abstract The instability changes of oxygen-enriched fuel mixtures under acoustic enforcement in a... more Abstract The instability changes of oxygen-enriched fuel mixtures under acoustic enforcement in a premixed and swirl supported system were investigated in this study. Different amounts of hydrogen (0%, 10%, 20%) were added to methane used as fuel and oxygen enrichment process (21%, 24%, 26%) was applied in hydrogen-added fuel mixtures. The equivalence ratio was kept constant at 0.7 in experiments conducted under constant burner power and swirl support. Experiments showed that although oxygen enrichment up to 24% ratio increases stability by increasing the laminar flame speed, stability decreases when the oxygen content in the oxidizer was increased to 26%. As a result of increasing both hydrogen ratio in fuel mixture and oxygen enrichment, instabilities grow up with decreasing of Markstein length. In this situation, burning in combustion chamber did not continue under acoustic force. According to the emission values taken during combustion experiments, the addition of oxygen increased NOx emissions due to increased adiabatic temperature and sudden NOx formations, while contributing to the reduction of CO emissions. Although the addition of hydrogen reduces NOx emissions in case of combustion with air (%21 O2), it has increased the CO emissions from 2 ppm to 13 ppm because it triggers instabilities when combined with oxygen enrichment.

Combustion Science and Technology, 2020

Chemical composition of synthetic gas and concentration of its components depend on gasification ... more Chemical composition of synthetic gas and concentration of its components depend on gasification process and feedstock. Synthetic gas mainly consists of hydrogen (H 2) and carbon monoxide (CO), and may contain trace amounts of carbon dioxide (CO 2) and methane (CH 4). In this study, combustion and emission characteristics of H 2 /CO/CH 4 /CO 2 blending syngas mixtures with high H 2 /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%H 2-22.5%CO-5%CO 2-5%CH 4 mixture to acoustic forcing were also detected. During the experiments, CH 4 amount in tested gas mixtures varied between 5% and 20% by volume (at intervals of 5%), and H 2 /CO ratio and CO 2 concentration were kept constant at the values of 3 and 5%, respectively. As a consequence, mixtures of 67.5%H 2-22.5%CO-5%CO 2-5%CH 4 , 63.75%H 2-21.25%CO-5%CO 2-10%CH 4 , 60%H 2-20%CO-5%CO 2-15%CH 4 and 56.25%H 2-18.75%CO-05%CO 2-20%CH 4 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, CH 4 addition effects on combustion and emission characteristics of such mixtures were evaluated via utilizing axial and radial temperature, CO and O 2 profiles. Lastly, flame behavior of 67.5%H 2-22.5%CO-5%CO 2-5%CH 4 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 CH 4 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 environmentfriendly manner under such conditions.

Fuel, 2019

Abstract In this study, combustion and emission characteristics of output synthetic gas mixtures ... more Abstract 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.

Journal of the Energy Institute, 2019

In this study, effects of synthetic gas constituents on combustion and emission behavior of premi... more In this study, effects of synthetic gas constituents on combustion and emission behavior of premixed H 2 / CO/CO 2 /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/H 2 /CO with varying H 2 /CO ratios were tested and then each mixture was diluted with the same amount of CO 2 (20% by volume) to better represent synthetic gas. H 2 /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, CO 2 and NO x 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: H 2 /CO ratio slightly alters temperature distribution throughout combustor, while hydrogen reaction kinetics play the most significant role in synthetic gas combustion (1), CO 2 addition tremendously increases emissions of CO (2).

Journal of Energy Resources Technology, 2013

This paper presents the effect of swirl number on combustion characteristics such as temperature,... more This paper presents the effect of swirl number on combustion characteristics such as temperature, velocity, gas concentrations in a natural gas diffusion flame. Numerial simulations carried out using the commercial computational fluid dynamics (CFD) code, Fluent by choosing appropriate model parameters. The combustion reaction scheme in the flame region was modeled using eddy dissipation model with one step global reaction scheme. A standard k-ε turbulence model for turbulent closure and P-I radiation model for flame radiation inside the combustor is used in the numerical simulations. In order to investigate the swirling effect on the combustion characteristics, seven different swirl numbers including 0; 0.1; 0.2; 0.3; 0.4; 0.5; and 0.6 are used in the study. Numerical results are validated and compared with the published experimental and simulation results. A good consistency is found between the present results and those published measurement and simulation results in the availabl...

International Journal of Hydrogen Energy, 2005

In this paper, the numerical simulation of a turbulent non-premixed hydrogen (H 2) diffusion flam... more In this paper, the numerical simulation of a turbulent non-premixed hydrogen (H 2) diffusion flame has been performed in a model combustor. CFD studies using Fluent code were carried out changing fuel composition from pure hydrogen to natural gas (100% H 2 , 70% H 2 + 30% CH 4 , 10% H 2 + 90% CH 4 , and 100% CH 4). The model prediction studies have been extended to combustion air staging. Air 25% was staged and introduced through the two tangential inlets. The predictions are validated and compared against the experimental results obtained in this study and results from the literature. Turbulent diffusion flames are investigated numerically using a finite volume method for the solution of the conservation and reaction equations governing the problem. The standard kmodel is used for modelling of turbulent flow as the model was far enough for the turbulence phenomena in the combustor. The chemical combustion reactions are described by seven species and three steps. A NO x post-processor has been used for predicting NO x emissions from the combustor. The temperature and major pollutant concentration (CO and NO x) distributions are in good agreement with the experimental measurements. The overall flame temperature increases as hydrogen is added or decreases as methane is added to the fuel mixture. The addition of methane to hydrogen decreases the flame temperature and thus NO x emissions considerably. Air staging causes rich and lean combustion regions and thus lower NO x emissions through the combustor exit.

International Communications in Heat and Mass Transfer, 2008

In this study, temperature distributions from turbulent chemical reactive flow inside a model com... more In this study, temperature distributions from turbulent chemical reactive flow inside a model combustor have been presented for various mixtured hydrogen–methane fuels. The gas emissions were also obtained at the combustor exit. A platinum–platinum 13% rhodium thermocouple (R type) was used for measurement of axial and radial temperatures. The axial and radial temperature measurements were taken from six various distances and four distances, respectively. Experimental measurements were made at excess air ratios of 1.2 and 1.7, two various thermal powers including 40 and 60 kW and two various hydrogen–methane blending fuels (volumetrically 30% H2–70% CH4 and 70% H2–30% CH4). The results show that the temperature level increases, CO and CO2 emissions decrease when the hydrogen content is increased in mixtured fuel, hydrogen–methane mixtured fuels are successfully used without any important modification in natural gas burner.

Energy, 2017

In this study, effect of micro combustor geometry on combustion and emission behavior of premixed... more 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 NO x levels from combustor outlet with proposed geometric variations.

Energetika

In a combustion device, unsteady heat release causes acoustic energy to increase when acoustic da... more 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 variable 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 inte...

International Journal of Hydrogen Energy

Fuel

Abstract Main challenges for a fuel efficient micro scale combustion are rooted from size restric... more Abstract 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-e. 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.

International Journal of Hydrogen Energy

International Journal of Energy Research, 2012

This paper presents gas emissions from turbulent chemical flow inside a model combustor, for diff... more This paper presents gas emissions from turbulent chemical flow inside a model combustor, for different blending ratios of hydrogen-methane composite fuels. Gas emissions such as CO and O 2 from the combustion reaction were obtained using a gas analyzer. NOx emissions were measured with a NOx analyzer. The previously obtained flame temperature distributions were also presented. As the amount of hydrogen in the mixture increases, more hydrogen is involved in the combustion reaction, and more heat is released, and the higher temperature levels are resulted. The results have shown that the combustion efficiency increases and CO emission decreases when the hydrogen content is increased in blending fuel. It is also shown that the hydrogen-methane blending fuels are efficiently used without any important modification in the natural gas burner.

International Communications in Heat and Mass Transfer, 2012

A numerical study has been conducted to analyze the turbulent forced convection heat transfer for... more A numerical study has been conducted to analyze the turbulent forced convection heat transfer for double forward facing step flow with obstacles. Obstacles have rectangular cross-sectional area with different aspect ratio that is located before each step. The numerical solutions of continuity, momentum and energy equations were solved by using a commercial code which uses finite volume techniques. The effect of turbulence was modeled by using a k-ε model. The effects of step height, obstacle aspect ratio and Reynolds number on the flow and heat transfer are investigated. The obtained results show that the rate of heat transfer is enhanced as aspect ratio of obstacle increases and this trend is affected by the step height. Also the results verified that the pressure drop decreases as obstacle aspect ratio increases.

Energy Conversion and Management, 2012

Fossil-based fuels are commonly used in aircraft engines but they have a polluting effect and the... more Fossil-based fuels are commonly used in aircraft engines but they have a polluting effect and they cause a greenhouse effect for our world. This study reports a research about aircraft gas turbine engines which are fired by liquid hydrogen (LH 2) in terms of performance and environmental aspects. Also, the performance and emissions of LH 2 fueled engines are compared with those of kerosene fired aircraft engines. Same flights from Istanbul to London, and Paris to Kabul are examined to estimate the emission from a conventional aircraft as an application in aviation sector. It is shown that the amount of NO x , HC and CO emissions for traveling by a conventional aircraft for London is 78.36, 1.202 and 22.4 kg, while Paris is 71.55, 1.171 and 21.63 kg, and Kabul is 111.44, 1.36 and 26.11 kg, respectively. For the use of liquid hydrogen as a fuel, amount of gas emissions decreases for any destination like London, Paris and Kabul. Total HC and CO emissions are going to be nearly 0 kg because of lack of carbon in the fuel. Also NO x emission is lower because of wider flammability limit of LH 2. Results show that the aircraft engines with LH 2 have great potential for emissions reduction and engine performance parameters are a little better for LH 2 fuel. It is strongly emphasized that one of the most important advantages for the use of LH 2 is national independence for fuel supply. Oil cannot be extracted in every countries territory but LH 2 is producible for every country and this is so important for a countries freedom.