Denizaltılarda yakıt piline dayalı sevk sistemi uygulaması
Fuel cell based propulsion systems in submarines
Yazar: DİLŞAD KARATAŞ
Danışman: PROF. DR. KADİR SARIÖZ
İstanbul Teknik Üniversitesi / Fen Bilimleri Enstitüsü / Gemi ve Deniz Teknoloji Mühendisliği Ana Bilim Dalı / Deniz Teknolojisi Mühendisliği Bilim Dalı
Derece: Yüksek Lisans, 2019
Konu: Deniz Bilimleri = Marine Science ; Gemi Mühendisliği = Marine Engineering ; Savunma ve Savunma Teknolojileri = Defense and Defense Technologies

Özet:
Bu tez çalışmasında denizaltılarda kullanılmakta olan yakıt pili esaslı havadan bağımsız sevk sistemi incelenmiştir. Bu sistemin denizaltıların dalmış durumdaki seyir süresine, seyir sıasına ve periskop derinliğinde bataryaları şarj etmek için harcanan sürenin toplam seyir süresi oranı olan görünmezlik oranına (indiscretion rate) olan katkısı hesaplamalı olarak gösterilmiştir.
Öncelikle denizaltılarda kullanılan konvansiyonel, havadan bağımsız ve nükleer sevk sistemleri tanıtılmıştır. Konvansiyonel sevk sistemini oluşturan dizel makina, bataryalar, fırçasız tip doğru akım motoru çalışma prensipleri hakkında bilgi verilmiştir. Bağımsız sevk sistemleri başlığı altında kapalı çevrim dizel motoru, Stirling motoru, MESMA sistemi ve yakıt pili sistemleri tanıtılmıştır. Aynı çerçevede değişik Stirling motoru konfigürasyonları ile polimer elektrolit yakıt pili, fosforik asit yakıt pili, erimiş karbonatlı yakıt pili ve katı oksit yakıt pillerinin çalışma prensipleri sunulmuştur.
Konvansiyonel bir sevk sistemine göre yakıt piline dayalı sevk sisteminin performansını göstermek üzere yakıt pili sistemi ile donatılmış bir denizaltı için dalmış durumda gerekli şaft beygir gücü ve şnorkel seyrinde oluşan ek beygir gücü hesapları yapılmıştır. Batarya kapasitelerinin bulunması için TYPE 214, S1000 ve TYPE 212 denizaltılarının genel yerleşim planı ve kesit planlarından yararlanılmıştır. Batarya kuyusu hacmi olarak ölçülen ilk hacimden, batarya kuyusunun yanlarında ve altındaki tank hacimlerinin çıkarılmasının ardından kalan bölge yeni batarya kuyusu hacmi olarak ele alınmış ve bataryaların bu hacimde yaklaşık % 65'lik bir alan kapladığı bulunmuştur. Güç - akım grafiğinden akım verimine geçilerek hesaplara yakıt pillerinin değişik güç karşılama durumları için verimlerini veren bir denklem eklenmiştir. 
Bütün bu hesapların yapılabilmesi için MATLAB ortamında bir bilgisayar programı yazılmıştır. Problem çözümünde MATLAB'ın Optimizasyon modülündeki nonlineer programlama çözücüsü "fmincon" kullanılmıştır. Burada dikkat edilmesi gereken nokta denizaltının sınırlı yakıt pili kapasitesine sahip olmasıdır. Bu kapasite belli bir süratin üzerinde denizaltının sevki için tek başına yetersiz olacaktır. Bu yüzden optimizasyon problemi iki parçalı olmak üzere çözülmüştür. Düşük hızlarda sevk için gerekli gücü ve sistem-yaşam yükünü hem batarya hem de yakıt pili sabit bir şekilde paylaşacaktır ve hem bataryanın hem de yakıt pilinin aynı anda bitmesi beklenmektedir. Yüksek hızlarda şaft gücünün eksponansiyel olarak artması, bu artan güç karşısında yakıt pillerinin yetersiz kalması ile birlikte asıl yük bataryalara binecektir. Bu da aslında bataryaların yakıt pilinden çok önce tükenmesi anlamına gelmektedir. Bu şekilde yakıt pili kullanan denizaltılar için farklı ilerleme hızlarında sadece batarya ile sevk ve batarya ve yakıt pili ile beraber sevk durumlarında maksimum sevk süresi ve sıa hesabı yapılmıştır. Bu hesaplara ek olarak denizaltı görünmezlik oranı hesabı yapılmıştır.
Tez kapsamında sunulan hesaplamalar sonucunda konvansiyonel sevk sistemi ile karşılaştırıldığında yakıt piline dayalı havadan bağımsız sevk sisteminin dalmış durumdaki seyir süresini arttırması, dalmış durumdaki sıayı arttırması ve denizaltının görünmezlik oranını düşürmesi bakımından avantajlı olduğu açık bir şekilde gösterilmiştir.

Abstract:
From the beginnig of the first use in military, submarines became an important power source in navies. Starting with the Turtle submarine, which is used in American Independence War in late 1700's, importance of the submarines gradually increase with the increasing fire power and submerged sail time thanks to the developing technology and industry. Submarines, which sail with diesel engines on surface and sail with batteries submerged, which are first used by German Navy, play an important role in World War 1 by sinking many commercial and military vessels. 
With the start of World War 2 more advanced submarines took part in wars. In this period submarines still spend most of the time on surface. Because of that their hull forms are based on surface performance. Air independent walter engine, snorkel system, Rankine cycle motor which works with hydrogen peroxide are the studies performed by Germans to improve submerged sail time of submarines. The United States submarine force also become very effective against Japan forces. Unfortunately submarines were still surface vessels which only dive to attack using torpedoes. Their submerged speed while using batteries was still low.
At the end of the 1950's using nuclear power on submarines cause dramatic change in usage of submarines and their designs. By using nuclear power submarines can sail independently from surface. With this improvement their underwater performance had grown. Submarine's hull form changed to improve underwater performance. Weapons and sensors to be used underwater developed. However nuclear power isn't a technology that any country can reach because of it's high cost. As a consequence countries which don't use nuclear power started researching ways to improve their diesel electric submarines and consequently air independent propulsion consept came to exist.
Producing power without using oxygen in air is the basis of air indepent propulsion. For improving submerged duration of modern diesel electric submarines research like increasing of battery capacity and decreasing of submerged hotel load, is in progress. While achieving submerged duration of a couple of weeks with air independent propulsion systems, only contribution with degree of hours can be achieved using only batteries. 
Fuel cells directly convert the chemical energy of the reactants, afuel and an oxidant, into direct current electricity. Fuel cells will continue to operate for as long as the externally stored reactants are supplied. The fuel cell system includes the fuel cell stacks and control systems, the stored fuel and oxidant, storage vessels, associated pipework and reactant processing systems, and exhaust product handling system.
Commonly used reactants include air and oxygen as the oxidant and pure hydrogen or hydrogen derived from catalytically reformed hydrocarbons or cracked ammonia as the fuel. Hydrazine has been used in military fuel cells, and methanol has been used as a liquid fuel in the direct methanol fuel cell.
The fundamental components of the fuel cell are the porous gas diffusion electrodes, comprising the fuel electrode or anode and the oxidant electrode or cathode. These two reaction sites are seperated by an ion conducting electrolyte which can be either a liquid, a liquid immobilised on a porous substrate, or an ion conducting solid. The conductive electrodes are connected electrically through a load by ana external circuit. At the anode, oxidation of the incoming fuel produces electrons, which provide power in the external load, and then reduce the incoming oxidant at the cathode. A flow of ions through the electrolyte completes the circuit.
The most common fuel cell is the hydrogen/oxygen fuel cell, with either an acidic or an alkaline electrolyte. In ana acid electrolyte fuel cell, the conducting ions are protons produced at the anode, and water is the reaction product at the cathode. In an alkaline electrolyte fuel cell, hydroxide ions are produced at the cathode, and the water reaction product is produced at the anode.
In low temprature fuel cells, catalysts impregnated into porous gas diffusion electrodes are required to promote these reactions, whereas in high temprature fuel cells the kinetics are generally sufficiently fast that catalysts are not required.
Individual fuel cells connected in series form a fuel cell stack. The individual cells are connected by a ribbed bipolar plate that provides low electrical resistance between adjacent porous cathode and anode structures and also functions as a gas barrier between the fuel and oxidant streams in the adjacent cells.
By connecting a multiplicity of stacks it is possible to form a fuel cell of any desired voltage and current output. In low temprature fuel cells, the design must also facilitate removal of the water product from the stack to prevent flooding of the electrodes which may block the gas flow. 
In this thesis air independent propulsion systems based on fuel cell technology used in modern submarines are investigated. The performence of this system in terms of the submerged range, range and the indiscretion rate which is the ratio of the time needed to remain at periscope depth to recharge the batteries and the total operating time of submarine, is estimated by using computational procedures. 
First, the conventional propulsion system, air independent propulsion systems and the nuclear propulsion system used in modern submarines are described. Working principle of conventional propulsion system consisting of diesel engine, batteries and electrical motor is explained. Closed cycle diesel engines, Stirling engines, MESMA (Module d'Energie Sous-Marin Autonome) system and the fuel cell system are explained under air independent propulsion systems. Working principle of different configurations of Stirling engine and polymer electrolyte membrane fuel cells, molten carbonate fuel cells, phosphoric acid fuel cells and solid oxide fuel cells are also explained. 
In order to compare the performance of fuel cell based propulsion systems with that of conventional propulsion systems, submerged required power and additional power due to snorkeling are calculated for a typical submarine. Formulas for range calculations with batteries and with air independent propulsion systems are given. For calculating battery capacities of submarines general arrangement plans and section plans of TYPE 214, S1000 and TYPE 212 submarines are used. By subtracting volumes under and sides of battery room from overall volume of battery room section, the remaining volume is assumed to be used for the batteries. It is found that batteries take about % 65 of this new battery room volume. In order to estimate the efficiency of fuel cells under different power consumption rates current to efficiency graphs based on power to current data are generated. Indiscretion rate calculations are also presented.
For the performance predictions a MATLAB computer program is developed. To solve the nonlinear programming problem "fmincon" subroutine in MATLAB optimization module is used. The crucial point of the optimization problem is that the fuel cell power source capacity of a submarine is limited and not sufficient for propulsion beyond a certain speed. For this reason the problem is solved in two parts separated with an identified submerged speed. At lower speeds fuel cells and the batteries share both hotel load and propulsion load together so that they run out at the same time simultaneously. Since the required propulsion power exponentially increases with speed, at higher speeds the fuel cells become insufficient and the main propulsion power is provided by the batteries. For both cases, the maximum submerged range at any given speed for the conventional and the fuel cell based propulsion systems are estimated and compared. Furthermore indiscretion rate calculations for both systems are carried out. As a result of these calculations, submarine discharge rate graphs, range graphs and indiscretion rate graphs are developed and presented. 
The calculations presented in the thesis have clearly shown the advantages of fuel cell based air independent propulsion systems for increasing submerged range and endurance while decreasing indiscretion rate compared to the conventional propulsion systems.