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Kıvılcım ateşlemeli doğal gazlı motorlarda hidrojen ilavesinin yanma karakteristiği ve performans üzerine etkisinin had yöntemi ile incelenmesi

Investigation of the effects of hydrogen addition on combustion characteristic and performance of a natural gas-fueled spark-ignition engine using the CFD method

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  1. Tez No: 985724
  2. Yazar: BARIŞ BİNGÜL
  3. Danışmanlar: DR. ÖĞR. ÜYESİ HİKMET ARSLAN
  4. Tez Türü: Yüksek Lisans
  5. Konular: Makine Mühendisliği, Otomotiv Mühendisliği, Mechanical Engineering, Automotive Engineering
  6. Anahtar Kelimeler: Emisyon, İçten yanmalı motorlar, Emission, Internal combustion engines
  7. Yıl: 2025
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Lisansüstü Eğitim Enstitüsü
  11. Ana Bilim Dalı: Makine Ana Bilim Dalı
  12. Bilim Dalı: Otomotiv Bilim Dalı
  13. Sayfa Sayısı: Belirtilmemiş.

Özet

Fosil yakıtların neden olduğu çevresel etkiler ve sıkılaşan emisyon standartları, içten yanmalı motorlarda alternatif yakıt arayışlarını hızlandırmıştır. Bu kapsamda karbon içermemesi, yüksek yanma hızı ve geniş tutuşma aralığı gibi özellikleriyle hidrojen, çevreci bir enerji taşıyıcısı olarak öne çıkmaktadır. Ancak hidrojenin düşük hacimsel enerji yoğunluğu ve yüksek yanma sıcaklığı gibi bazı dezavantajları, doğrudan yakıt olarak kullanımını sınırlamaktadır. Bu nedenle, doğal gaz-hidrojen karışımları hem teknik uygulanabilirlik hem de emisyon azaltımı açısından önemli bir alternatif oluşturmaktadır. Bu tez çalışmasında, İstanbul Teknik Üniversitesi Otomotiv Laboratuvarı'nda bulunan tek silindirli, buji ateşlemeli deney motorunun (Antor 3LD450) doğal gaz ile elde edilmiş deneysel verileri, ANSYS Forte yazılımı kullanılarak gerçekleştirilen üç boyutlu Hesaplamalı Akışkanlar Dinamiği (HAD) analizi ile doğrulanmıştır. Model doğrulamasının ardından, karışıma farklı oranlarda (%5, %10, %15 ve %20) hidrojen ilave edilerek yanma karakteristikleri, performans değerleri ve egzoz emisyonları üzerindeki etkiler sayısal olarak incelenmiştir. Modelleme sürecinde GRI-Mech 3.0 kimyasal kinetik mekanizması, standart k–ε türbülans modeli ve çözümün ağ yapısından bağımsızlığını sağlayan adaptif ağ stratejisi kullanılmıştır. Başlangıç ve sınır koşulları, Hüseyin Emre Doğan tarafından doğal gazla yürütülen deneysel çalışmadan alınan verilerle tanımlanmıştır. İlk olarak, deney koşullarındaki sabit ateşleme avansı değeri için simülasyonlar gerçekleştirilmiş, ardından farklı hidrojen oranları için ateşleme avansı optimizasyonu yapılmıştır. Bu optimizasyon sonucunda, motorun maksimum basınç noktası ve ısı açığa çıkış oranı dikkate alınarak yanma verimliliğini artıran en uygun ateşleme zamanlaması belirlenmiştir. Farklı hidrojen oranları için yapılan karşılaştırmalarda, hidrojen ilavesiyle birlikte yanma süresinin kısaldığı, maksimum basınç değerlerinin arttığı ve CO ile HC emisyonlarının belirgin biçimde azaldığı gözlemlenmiştir. Bununla birlikte, hidrojenin yüksek alev sıcaklığı nedeniyle NOx emisyonlarında artış eğilimi görülmüştür. Sonuç olarak, bu çalışma hidrojenin doğal gazla birlikte kullanılmasıyla daha temiz yanma, yüksek verim ve düşük karbonlu motor teknolojileri için önemli bir potansiyel sunduğunu göstermektedir. Çalışma, içten yanmalı motorlarda hidrojen entegrasyonuna yönelik gelecekteki deneysel ve sayısal araştırmalar için de bir temel oluşturmaktadır.

Özet (Çeviri)

The increasing global attention on climate change, environmental pollution, and the depletion of fossil fuel reserves has made it necessary to develop cleaner and more efficient energy systems. Internal combustion engines remain widely used in transportation, agriculture, power generation, and industrial applications due to their well-known technology, reliability, and available infrastructure. However, their negative impact on the environment, especially through harmful exhaust emissions such as CO, HC, and NOx, requires new approaches to fuel selection and combustion strategies. In recent years, stricter emission regulations have intensified the investigation of alternative fuels. Hydrogen has become one of the leading candidates due to its excellent combustion properties. It contains no carbon, which allows zero CO and HC formation, and it has high diffusivity, wide flammability limits, and a very high laminar flame speed. These features enable hydrogen to burn more completely and more rapidly compared to conventional hydrocarbon fuels. Despite these advantages, using hydrogen directly in spark-ignition engines presents several challenges. Its low volumetric energy density requires either large storage volumes or high-pressure tanks. Hydrogen also causes very high combustion temperatures, which tend to increase NOx emissions. Furthermore, if used at high fractions without the necessary engine modifications, hydrogen can cause backfiring, pre-ignition, and knocking. Because of these problems, many researchers have focused on hydrogen–natural gas mixtures as a practical and technically feasible intermediate solution. Natural gas is already widely used around the world, has a cleaner combustion profile compared to gasoline and diesel, and benefits from an established distribution infrastructure. Adding hydrogen to natural gas can improve the combustion process while avoiding the extreme challenges associated with 100% hydrogen fueling. This thesis focuses on the detailed numerical investigation of hydrogen-enriched natural gas combustion in a single-cylinder spark-ignition engine, the Antor 3LD450, located at the Istanbul Technical University Automotive Laboratory. The main purpose of the study is to explore how different hydrogen blending ratios influence combustion characteristics, engine performance parameters, and emission formation. The research was conducted using three-dimensional Computational Fluid Dynamics (CFD) simulations performed with ANSYS Forte 2023 R1, a specialized software for internal combustion engine modeling. To ensure the accuracy of the CFD predictions, the first phase of the study involved the validation of the numerical model using experimental data from pure natural gas operation. These experimental data, obtained by Dr. Hüseyin Emre Doğan, included cylinder pressure traces, heat release rates, and other performance indicators measured under controlled laboratory conditions. The validation process is crucial because it ensures that the CFD model can reliably replicate the real engine behavior before introducing hydrogen into the simulations. Good agreement between experimental and numerical results was achieved, which allowed the study to proceed to the hydrogen-enriched cases confidently. The chemical reaction mechanism used in the simulations was GRI-Mech 3.0, which contains detailed reaction pathways for methane and hydrogen oxidation. The mechanism includes hundreds of reactions and dozens of chemical species, making it appropriate for accurately modeling the combustion of natural gas–hydrogen mixtures. The standard k–ε turbulence model was selected for turbulence closure because of its robustness and compatibility with in-cylinder CFD simulations. Adaptive mesh refinement (AMR) was applied to ensure proper resolution of the flame front and the rapid chemical reactions occurring during combustion. AMR refines the mesh locally, reducing the computational requirements compared to uniformly fine meshes. The engine operating conditions, including intake air temperature, intake pressure, valve timings, engine speed, and spark timing, were taken directly from the experimental study to ensure consistency. All simulations were carried out at the same engine speed and load, enabling direct comparison between the baseline natural gas case and the hydrogen-enriched cases. Four hydrogen blending ratios—5%, 10%, 15%, and 20% by energy—were tested in the simulations to identify trends and evaluate the intensity of the effects. The second major part of the study involved spark advance optimization. Because hydrogen increases the combustion speed and can advance the location of peak pressure, the original ignition timing used for natural gas is not appropriate when hydrogen is added. If the ignition timing is too advanced, rapid pressure rise may lead to knocking and engine damage. If it is too retarded, engine efficiency decreases. Therefore, the ignition timing was varied for each hydrogen ratio, and the corresponding effects on in-cylinder pressure, heat release rate, combustion duration, thermal efficiency, and NOx formation were evaluated. This process allowed the determination of an optimal ignition timing for each mixture, ensuring maximum efficiency without causing abnormal combustion. The results of the study show that hydrogen addition significantly modifies the combustion behavior. The combustion duration decreases as the hydrogen fraction increases, due to hydrogen's high flame speed. The peak cylinder pressure increases and occurs earlier in the cycle, reflecting the faster and more intense combustion. These changes improve the thermal efficiency of the engine because more of the combustion occurs near top dead center, where the mechanical advantage is greatest. The numerical results also show that hydrogen addition improves flame propagation throughout the chamber and reduces cycle-by-cycle variability, which can be particularly beneficial in lean combustion conditions. Hydrogen also reduces CO and HC emissions, which are directly related to incomplete combustion. Since hydrogen does not contain carbon, CO and HC emissions naturally decrease when hydrogen replaces a portion of the natural gas. In addition, the enhanced flame propagation helps burn regions that normally remain unburned during natural gas operation, such as crevice areas. However, the results reveal a consistent increase in NOx emissions with higher hydrogen fractions. This is mainly due to the higher combustion temperatures generated by hydrogen. NOx formation is strongly temperature-dependent, and even small temperature increases can cause large changes in NOx production. Ignition timing optimization was shown to be an effective way to limit NOx emissions while still maintaining performance improvements. Slightly retarding the ignition timing for higher hydrogen ratios helps reduce the maximum temperature and therefore reduces NOx formation. An important finding of this study is that hydrogen blending ratios up to 20% by energy do not require any modifications to the engine's geometry or its cooling system. The engine remained stable throughout the simulation range, indicating that hydrogen-enriched natural gas can be used safely in existing spark-ignition engines. This makes the approach attractive for real-world applications, including public transportation, generator systems, and industrial engines that already use natural gas. In conclusion, this thesis demonstrates that hydrogen addition to natural gas has the potential to significantly improve combustion efficiency, reduce carbon-based emissions, and enhance the stability of spark-ignition engines. However, the increase in NOx emissions requires careful attention and appropriate ignition timing adjustment. The validated CFD model developed in this study can be used as a foundation for future numerical research involving alternative fuels, advanced ignition strategies, different hydrogen ratios, and various engine geometries. The results contribute to the global efforts to reduce emissions from internal combustion engines and support the transition toward cleaner and more sustainable energy systems.

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