Sentetik gaz yanma karakteristiğinin incelenmesi
Investigation of combustion characteristics of syntetic gas
- Tez No: 938460
- Danışmanlar: PROF. DR. YAKUP ERHAN BÖKE
- Tez Türü: Doktora
- Konular: Enerji, Makine Mühendisliği, Energy, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 2025
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Lisansüstü Eğitim Enstitüsü
- Ana Bilim Dalı: Makine Mühendisliği Ana Bilim Dalı
- Bilim Dalı: Makine Mühendisliği Bilim Dalı
- Sayfa Sayısı: 117
Özet
Teknolojik ilerleme için ihtiyaç duyulan enerji halen çoğunlukla termodinamiğin en önemli konularından biri olan hidrokarbon yanmasından elde edilmektedir. Hidrokarbon yanmasında alevin kararlılığı hem brülör geometrisinin tasarımını hem de yanmanın enerji verimliliğini etkileyen bir parametredir. Kararlı bir alev oluşturmak için literatürde kullanılan çeşitli yöntemler vardır. Bu yöntemlerden biri olan girdaplı akış, brülörlerde yanma performansını artıran ve birçok mühendislik uygulamasında kullanılan bir tekniktir. Bu çalışmada girdaplı akışa sahip bir yakıcı tasarımı yapılması amaçlanmıştır. Bu amaçla yürütülen tez çalışması, doğrulama çalışması ve yakıcı tasarımı şeklinde iki temel adım ve bunların alt adımları olarak sunulmuştur. Doğrulama adımında, Sydney girdaplı alevlerinden SM1 alevi sayısal olarak analiz edilmiştir. İlk aşamada, iki denklemli Re-Normalisation Group (RNG) k-ε ve Shear Stress Transport (SST) k-ω türbülans modelleri ile akış ve GRI 3.0 reaksiyon mekanizması ile CH4 yanmasının kimyasal reaksiyonları modellenmiş ve literatürdeki elde edilen deneysel sonuçlarla karşılaştırılmıştır. Doğrulama çalışmasının ikinci aşamasında, deneysel sonuçları en iyi tahmin eden Shear Stress Transport k-ω türbülans modelinin sayısal sonuçları, Büyük Eddy Simülasyonu (LES) türbülans modeli kullanılarak SM1 alevi için literatürde yer alan bir sayısal analizin sonuçları ile karşılaştırılmıştır. Bu iki türbülans modelinin deneysel verileri tahmin etme düzeyleri ve akış bölgesindeki davranışları incelenmiştir. Karşılaştırma sonucunda Sydney girdap alev ailesinin kararlı alevleri için Shear Stress Transport k-ω türbülans modelinin kullanılmasının yeterli olduğu görülmüştür. Yakıcı geometrisi tasarımında da Shear Stress Transport k-ω türbülans modeli kullanılmasına karar verilmiştir. Yakıcı tasarımı iki alt aşamada değerlendirilmiştir. Birinci aşamada, doğrulama adımında incelenen SM1 alevinin geometrisi temel alınmıştır. Alev, ekivalans oranı ve hava fazlalık katsayısı açısından incelenmiştir. Kararlılığını etkileyen parametreler değerlendirilmiştir. Daha sonra endüstriyel yakıcılarda kullanılan yakıcıların güç, yakıt ve hava jet hızları ve hava fazlalık katsayısı gibi değişkenleri göz önüne alınmıştır. Bu yakıcılardaki hızların ve hava fazlalık katsayılarının SM1 alevine göre oldukça düşük oldukları gözlemlenmiştir. Düşük hava hızları ve makul hava fazlalık katsayısı ile yakıcı geometrisinin nasıl davrandığı incelenmiştir. Elde edilen sonuçlar yakıcının endüstriyel şartlarda kararlı bir alev oluşturmadığını göstermiştir. İnceleme esnasında hızların ve hava fazlalık katsayısının etkileri hakkında da bilgi birikimi oluşturulmuştur. Analizlerin sonucunda, yakıtın yakıcı yüzeyine yayılmasını sağlayacak geometrik bir çözüm gerekliliği görülmüştür. Yakıcı tasarımının ikinci aşamasında, konik bir geometrik engelin yakıt jeti önüne konulmasının etkileri incelenmiştir. Geometrik engel değerlendirilirken, engelin büyüklüğü ve yakıt girişini olan uzaklığı için farklı değerler kullanılarak parametrik bir çalışma yapılmıştır. Geometrik şeklin yakıtı yakıcı üzerinde yaymasını sağlamak ve bu esnada yakıt jetinin akış ayrılması sonucu akış alanını kesmesini engellemek karşılaşılan en büyük zorluk olmuştur. Bu zorlukları aşmak için geometrik engele eklemeler yapılmış ve sonuç geometrisi oluşturulmuştur. Yapılan uzun analizlerin sonucunda çalışmada kullanılan farklı gaz bileşimleri için kararlı alev oluşmasını sağlayan bir engel geometrisi elde edilmiş ve yapılan yakıcı tasarımı olarak sunulmuştur.
Özet (Çeviri)
Energy required for technological advancement is still predominantly derived from the combustion of hydrocarbons, one of the most critical topics in thermodynamics. In hydrocarbon combustion, flame stability is a parameter that affects both the design of burner geometry and the energy efficiency of combustion. Various methods have been employed in the literature to establish a stable flame. One such method is swirling flow, a technique that enhances combustion performance in burners and is widely used in many engineering applications. This study aims to design a burner with swirling flow. The thesis work conducted for this purpose is presented in two main steps, namely verification and burner design, along with their substeps. In the verification step, the SM1 flame of the Sydney swirl flames was numerically analyzed. The Sydney swirl flame series comprises eight flames. Researchers have conducted parametric studies on these flames by varying fuel jet velocities and using different fuels. All results of these studies are available in the literature. Due to these features, the SM1 flame was chosen for use in this study. The characteristics of the SM1 flame were examined, and information about its experimental model was obtained from relevant sources in the literature. Additionally, other studies related to this flame were reviewed to accumulate a substantial body of knowledge. In the first stage of the verification study, the hexahedral mesh structure of the burner geometry was created using ANSYS Fluent software. In the generated mesh structure, the two-equation Re-Normalization Group (RNG) k−ε and Shear Stress Transport (SST) k−ω turbulence models were employed to solve the flow field. Since the combustion is non-premixed, the non-premixed steady diffusion flamelet model was used to model the combustion. In this model, the GRI 3.0 reaction mechanism was selected. The SIMPLE algorithm was employed for the solution, with PRESTO! for pressure solution, QUICK for momentum solution, and second-order upwind options for other variables. The results obtained with both turbulence models were compared with experimental data. It was observed that the SST k−ωk-\omegak−ω turbulence model yielded results more consistent with experimental data. Therefore, it was decided to proceed with the SST k−ω turbulence model for the solution. In the second stage of the validation study, the results of another study from the literature, in which the SM1 flame was validated, were compared with the validation conducted in this research. In the literature study, the turbulence model used was LES (Large Eddy Simulation), and the combustion was modeled using the non-premixed steady diffusion flamelet model. Both analyses were examined by taking the experimental model as a reference. The review revealed that, in certain regions on the bluff body, the LES turbulence model calculated velocities more accurately; however, the differences were not significant. In terms of temperature and species, both analyses produced similar results and were consistent with the experimental model. For these types of flow fields, it was concluded that the two-equation turbulence model is sufficient instead of the LES turbulence model, which is significantly more computationally expensive in terms of core hours. With this, the validation study was completed, and the burner design phase was initiated. The burner design was evaluated in two sub-stages. In the first stage, the geometry of the SM1 flame, which was analyzed in the validation study, was used as a basis. The SM1 flame was examined in terms of equivalence ratio and excess air coefficient. Parameters influencing the stability of the SM1 flame were identified through the studies of the researchers who conducted the experiments. One of the most critical factors for flame stability in the SM1 flame is the axial air velocity entering the flow field. This velocity needs to be high. However, in industrial burners, such high air velocities and excess air coefficients are not typically employed. Based on this information, the performance of the existing SM1 burner was investigated under low velocities and different gas compositions. The burner to be designed was required to combust synthetic gas. Therefore, the gas compositions were first determined, and three different compositions were created. The burner power was set at 10 kW. To achieve this power, the jet velocity of the fuel was set at approximately 10 m/s for all gas compositions. To meet these conditions, the fuel inlet diameter in the SM1 burner geometry was adjusted to 10 mm. Finally, the excess air coefficient was set to 1.5. Despite these adjustments, the analysis of the resulting burner did not yield a stable flame. The low axial air velocity, identified as one of the most critical parameters influencing flame stability in the SM1 burner, was the cause of this outcome. To better understand the situation, an analysis with a high swirl number was conducted. The results were more favorable, and flame stability improved. However, since this was not the desired approach, the solution was not accepted. In the modified burner, the excess air coefficient was increased to 10, similar to the SM1 burner. Under these conditions, a stable flame was achieved. The analysis demonstrated that, despite the variations in gas composition and fuel jet velocity, the high axial air velocity associated with the high excess air coefficient was a significant parameter for flame stability. The findings obtained in the first stage of the design process revealed that the flame stability in the evaluated burner was significantly influenced by an excessive amount of combustion air. The SM1 burner imparts aerodynamic swirl to the air. Accordingly, the tangential air velocity is obtained by multiplying the axial air velocity by the swirl coefficient. High axial air velocity results in high tangential air velocity, which facilitates the substantial spreading of the fuel over the bluff-body. At low axial air velocities, this effect diminishes, and the fuel cannot spread sufficiently over the bluff-body. Additionally, the recirculation zone, which is a characteristic feature of such burners, cannot form on the bluff-body due to the low tangential velocity. To achieve a stable flame in the burner described above, the fuel must spread over the bluff-body. The design phase focused on addressing this issue. In the second stage of the burner design, based on the findings from the first stage, a method to distribute the fuel over the bluff-body was investigated. It was concluded that the most feasible approach was to introduce an obstacle into the flow field. This geometric obstacle needed to avoid disrupting the flow, distribute the fuel over the bluff-body, and support the formation of the lower recirculation zone. For this purpose, a geometric structure with a conical top was studied. The conical structure was positioned along the axis of the fuel jet. Due to its conical design, the geometric structure facilitated both the conical distribution of the fuel jet over the bluff-body and minimal resistance to the flow. During the evaluation of the geometric obstacle, a parametric study was conducted using different values for the size of the obstacle and its distance from the fuel inlet. The greatest challenges involved ensuring that the geometric structure distributed the fuel over the burner and prevented the flow field from being disrupted by the separation of the fuel jet. These challenges were addressed by modifying the dimensions of the geometric structure and adding a cylindrical piece to the base of the conical structure. The axial length of the structure also influenced the flame shape depending on its placement. In such flames, the characteristic recirculation zone narrows further downstream, forming a neck region. The axial length of the geometric obstacle, combined with its placement distance from the fuel inlet, should not extend into this neck region. Analyses conducted for various axial distances helped identify the problems caused by this configuration and assisted in determining the optimal axial placement. The study concluded that the best results were obtained with a conical piece aligned coaxially with the fuel inlet, positioned 6 mm downstream from the inlet, with a base diameter of 18 mm and a height of 12 mm. Additionally, a cylindrical piece with a diameter of 18 mm and a height of 4 mm, attached to the base of the conical piece, was found to yield the most effective results. Analyses were performed using three different gas compositions, and the results are presented within the scope of this thesis.
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