İHA uygulamalarına uygun atmosferde çalışan bir Wankel motorunun performansının analizi ve iyileştirilmesi
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Dosyalar
Tarih
2022
Yazarlar
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Yayıncı
Bursa Teknik Üniversitesi, Lisansüstü Eğitim Enstitüsü
Erişim Hakkı
info:eu-repo/semantics/openAccess
Özet
Oldukça yüksek güç üretimini küçük motor hacminden elde etmeye imkân sağlayan döner pistonlu motorlar (Wankel motorları), düşük titreşime sahip olmaları, hafiflikleri, kompakt yapıları, güç/ağırlık oranının yüksek olması, daha yüksek volumetrik verim ve vuruntuya daha az bağımlılık gibi pek çok avantajlara sahiptir. Bu özelliklerinden dolayı denizcilik endüstrisinden hafif hava aracı endüstrisine kadar pek çok uygulama alanında tercih edilmektedirler. Bu motorların özellikle, güç/ağırlık ve güç/boyut oranı yüksek tahrik sistemlerinin kaçınılmaz olduğu İHA'larda kullanımı oldukça avantajlı ve yaygındır, yapılacak iyileştirmeler ile kullanım avantajları daha da arttırılabilir. Son dönemde ülkemizde yapılan yerli üretim çalışmaları kapsamında özellikle savunma sanayi tarafından İHA'larda kullanılmak üzere güç yoğunluğundan dolayı Wankel motoru üretimi arzu edilmektedir. Fakat bu konuda daha önce bir üretim girişimi, dolayısıyla bilgi birikimi ve üretim alt yapısı olmadığından şu ana dek yerli Wankel motoru üretimi gerçekleşmemiştir. Bu ihtiyacı giderme yolunda bir adım olmak üzere bu tez çalışmasının yapılmasına karar verilmiştir. Bu kapsamda, öncelikle TSK envanterinde İHA'larda kullanıma uygun olarak bulunan ve Vestel Savunma Sanayi'nden (LENTATEK) temin edilen Wankel motorunun üç boyutlu tarama teknolojisi ile ölçümleri alınarak bilgisayar destekli tasarım (BDT) modeli oluşturulmuştur. Ardından sırasıyla sıfır boyutlu, 1 boyutlu ve 3 boyutlu olarak Wankel motoru modellemesi gerçekleştirilmiştir. Bu aşamadaki hedef, 3B hesaplamalı akışkanlar dinamiği (HAD) simülasyonları sonucunda Wankel motorunun farklı irtifa koşullarında performansı, yanma karakterstikleri ve emisyonları konusunda bilgi sahibi olmaktır. Wankel motorunun yüzey/hacim oranı konvasiyonel pistonlu motorlara göre çok daha yüksektir. Dolayısıyla Wankel motorunun irtifa artışıyla birlikte ateşlememe sorunlarının olması kuvvetle muhtemeldir. Eğer Wankel motorunun yüksek irtifalardaki performansı, yanma karakterstikleri bilinebilirse ateşlememe sorununu bertaraf edilmesi konusunda tedbirler alınabilir. Gerçekleştirilen analizler ile bu tip muhtemel problemlerin görülebilmesi ve ona göre tedbir alınması mümkündür. Ayrıca artan irtifa ile birlikte ortam havasının sıcaklığı, basıncı ve yoğunluğu düşeceği için yanma odası içerisine alınan karışım özellikleri de değişmektedir. Bu sebeple hava fazlalık katsayısının değişiminin Wankel motor performansı üzerindeki etkilerinin incelenmesinde de fayda vardır. Bu çalışmada ele alınan bir diğer konu da budur. Wankel motorunda irtifa artışı ve hava yakıt oranı değişiminin referans Wankel motorunun performansı, yanma karakteristikleri ve emisyonları üzerine etkileri tespit edildikten sonra günümüzdeki Wankel motor performansını artırmaya yönelik en popüler metotlardan olan yakıta hidrojen zenginleştirme stratejisi uygulanmıştır. Gerçekleştirilen simülasyon sonuçları hidrojen zenginleştirme yaklaşımının Wankel motorların performansı üzerinde oldukça olumlu bir etkisi olduğunu göstermiştir. Benzinli 4 zamanlı referans Wankel motoruna %5 ve %10 oranlarında hidrojen katkısı yapıldığında, Wankel motorunun saf benzinle çalışma durumuna kıyasla ortalama efektif basıncında sırasıyla %8.18 ve %9.68, indike tork değerinde sırasıyla %6.15 ve %7.99 artış gözlemlenirken özgül yakıt sarfiyatı değerinde azalma olmuştur. Ayrıca uygulanan hidrojen zenginleştirme yöntemi sonucu hidrokarbon (HC) ve karbonmonoksit (CO) emisyonlarında da azalma olmuştur. Bununla birlikte hidrojen zenginleştirme stratejisi uygulanmış referans motorda saf benzinle çalışma durumuna göre daha sıcak çalışma şartları oluştuğu için Azotoksit (NOx) emisyonlarında ise artış gözlemlenmiştir. Bu tez çalışmasında İHA'larda kullanılan bir Wankel motoru için elde edilen numerik bulguların, hem geometrik hem de yakıt içeriği itibariyle Wankel motor konusunda üretim çalışmalarına katkı sağlaması beklenmektedir. Bunun yanısara, özellikle Wankel motorunun hidrojen katkısı ile prototip üretimi konusunda firmalarla görüşmeler gerçekleştirilmiş ve tez sonrası devam projesi olarak prototip üretimi konusunda adımlar atılmıştır.
Rotary piston engines (Wankel engines), which allow very high power generation from a small engine volume, have many advantages such as low vibration, light weight, compact structure, high power/weight ratio, higher volumetric efficiency and less dependence on knocking. Due to these characteristics, they are preferred in many application areas from the maritime industry to the light aircraft industry. The use of these engines is especially advantageous and common in UAVs where propulsion systems with high power/weight and power/size ratios are inevitable. With the further improvements to be made, the usage advantages can be increased even more. Within the scope of the recent domestic production studies carried out in our country, Wankel engine production is desired due to its power density, especially by the defence industry to be used in UAVs. However, no attempt has been made in this issue yet, since there was no production experiment and knowledge in the past. It was decided to carry out this thesis as a step towards meeting this need. In this context, a computer-aided design (CAD) model of the Wankel engine suitable for the UAVs in the TAF inventory, procured from Vestel Defence Industry (LENTATEK), was created by taking measurements with three-dimensional scanning technology. Then, Wankel engine modeling was carried out as zero-dimensional, 1-dimensional and 3-dimensional, respectively. The goal at this stage is to have information about the performance, combustion characteristics and emissions of the Wankel engine at different altitude conditions as a result of 3D computational fluid dynamics (HAD) simulations. The surface/volume ratio of the Wankel engine is much higher than that of the conventional piston engines. Therefore, it is highly likely that the Wankel engine will have misfire problems with increasing altitude. If the performance and combustion characteristics of the Wankel engine at high altitudes are known, measures can be taken to eliminate the misfire problem. Thanks to the analyses made, it is possible to see such potential problems and take precautions accordingly. In addition, since temperature, pressure and density of the ambient air decreases as the altitude increases, the mixture properties in the combustion chamber also change. For this reason, it is useful to examine the effects of excess air coefficient variations on Wankel engine performance. This is another issue addressed in this study. After determining the effects of altitude increase and air-fuel ratio variations on Wankel engine performance, combustion characteristics and emissions, hydrogen enrichment strategy was applied to the fuel, which is one of the most popular methods to increase Wankel engine performance. The simulation results showed that the hydrogen enrichment approach has a very positive effect on the performance of Wankel engines. When a certain amount of hydrogen was added to the gasoline 4-stroke reference Wankel engine, a significant increase was observed in performance characteristics such as average effective pressure, indicated power, and torque compared to the neat gasoline fuelled Wankel engine, while a decrease in the specific fuel consumption value was observed. In addition, there was a decrease in hydrocarbon (HC) and carbon monoxide (CO) emissions due to the hydrogen enrichment method applied. On the other hand, an increase in Nitrous Oxide (NOx) emissions was observed as warmer operating conditions occur in the reference engine in which the hydrogen enrichment strategy was applied according to the working condition with neat gasoline. It is expected that the simulation findings obtained from this thesis study will contribute to the production studies on the Wankel engine in terms of both geometric and fuel content. In addition to this, negotiations were held with companies on the production of prototypes, especially with the hydrogen contribution of the Wankel engine, and steps were taken in the production of prototypes as a follow-up project after the thesis.
Rotary piston engines (Wankel engines), which allow very high power generation from a small engine volume, have many advantages such as low vibration, light weight, compact structure, high power/weight ratio, higher volumetric efficiency and less dependence on knocking. Due to these characteristics, they are preferred in many application areas from the maritime industry to the light aircraft industry. The use of these engines is especially advantageous and common in UAVs where propulsion systems with high power/weight and power/size ratios are inevitable. With the further improvements to be made, the usage advantages can be increased even more. Within the scope of the recent domestic production studies carried out in our country, Wankel engine production is desired due to its power density, especially by the defence industry to be used in UAVs. However, no attempt has been made in this issue yet, since there was no production experiment and knowledge in the past. It was decided to carry out this thesis as a step towards meeting this need. In this context, a computer-aided design (CAD) model of the Wankel engine suitable for the UAVs in the TAF inventory, procured from Vestel Defence Industry (LENTATEK), was created by taking measurements with three-dimensional scanning technology. Then, Wankel engine modeling was carried out as zero-dimensional, 1-dimensional and 3-dimensional, respectively. The goal at this stage is to have information about the performance, combustion characteristics and emissions of the Wankel engine at different altitude conditions as a result of 3D computational fluid dynamics (HAD) simulations. The surface/volume ratio of the Wankel engine is much higher than that of the conventional piston engines. Therefore, it is highly likely that the Wankel engine will have misfire problems with increasing altitude. If the performance and combustion characteristics of the Wankel engine at high altitudes are known, measures can be taken to eliminate the misfire problem. Thanks to the analyses made, it is possible to see such potential problems and take precautions accordingly. In addition, since temperature, pressure and density of the ambient air decreases as the altitude increases, the mixture properties in the combustion chamber also change. For this reason, it is useful to examine the effects of excess air coefficient variations on Wankel engine performance. This is another issue addressed in this study. After determining the effects of altitude increase and air-fuel ratio variations on Wankel engine performance, combustion characteristics and emissions, hydrogen enrichment strategy was applied to the fuel, which is one of the most popular methods to increase Wankel engine performance. The simulation results showed that the hydrogen enrichment approach has a very positive effect on the performance of Wankel engines. When a certain amount of hydrogen was added to the gasoline 4-stroke reference Wankel engine, a significant increase was observed in performance characteristics such as average effective pressure, indicated power, and torque compared to the neat gasoline fuelled Wankel engine, while a decrease in the specific fuel consumption value was observed. In addition, there was a decrease in hydrocarbon (HC) and carbon monoxide (CO) emissions due to the hydrogen enrichment method applied. On the other hand, an increase in Nitrous Oxide (NOx) emissions was observed as warmer operating conditions occur in the reference engine in which the hydrogen enrichment strategy was applied according to the working condition with neat gasoline. It is expected that the simulation findings obtained from this thesis study will contribute to the production studies on the Wankel engine in terms of both geometric and fuel content. In addition to this, negotiations were held with companies on the production of prototypes, especially with the hydrogen contribution of the Wankel engine, and steps were taken in the production of prototypes as a follow-up project after the thesis.
Açıklama
Anahtar Kelimeler
Makine Mühendisliği, Mechanical Engineering
