Farklı yakıt karışımlarının ve çalışma parametrilerinin homojen dolgulu sıkıştırma ile ateşlemeli motor performansına etkileri

06.03.2018 tarihli ve 30352 sayılı Resmi Gazetede yayımlanan “Yükseköğretim Kanunu İle Bazı Kanun Ve Kanun Hükmünde Kararnamelerde Değişiklik Yapılması Hakkında Kanun” ile 18.06.2018 tarihli “Lisansüstü Tezlerin Elektronik Ortamda Toplanması, Düzenlenmesi ve Erişime Açılmasına İlişkin Yönerge” gereğince tam metin erişime açılmıştır.Günümüzde araçların az yakıt tüketmesi ve çevreye daha az zarar vermesi hem ülkeler hem de kullanıcılar için bir gereklilik haline gelmiştir. Bu nedenle bilim adamları yeni arayışlar içine girmişlerdir. Bilindiği üzere benzin motorları egzoz gazları emisyonu yönünden avantajlı iken dizel motorları da yakıt tüketimi bakımından avantajlıdır. Son dönemdeki yeni eğilim, silindirlere alınan dolgunun hazırlanmasında bu iki motorun karışım hazırlama işlemlerinin birleştirildiği homojen karışımlı sıkıştırma ile ateşlemeli (HKSA) motor uygulamasıdır. Homojen karışımlı sıkıştırma ile ateşlemeli motorlardaki yanma işlemi; ne buji ile ateşlemeli motorlardaki gibi alev cephesi şeklinde, ne de sıkıştırma ile ateşlemeli motorlardaki gibi difüzyon alevi şeklinde gerçekleşir. Bu yeni yanma teknolojisinde; yanma, yanma odasının her noktasında aynı anda başlamaktadır. Yanmanın bu şekilde gerçekleştirilmesi ile, NOx ve partikül madde (PM) emisyonlarında azalma elde edilirken, motor veriminde artışlar olmaktadır. Bu çalışmada klasik bir dizel motoru homojen karışım ile çalışacak şekilde modifiye edilmiştir. Homojen karışım temin edebilmek için literatürde mevcut olan üç yöntemden ikisi uygulanmıştır. Bunlar; test yakıtlarının silindir içerisine deney motorunun püskürtme avansı ve püskürtme basıncı değiştirilerek erken püskürtülmesi (erken direkt enjeksiyonlu HKSA yanma metodu) ve test yakıtının tasarlanan enjeksiyon sistemi ile emme manifolduna emme zamanında ( port yakıt enjeksiyonlu HKSA yanma metodu) püskürtülmesidir. Bu yöntemlerde; test yakıtı olarak, dizel yakıtıyla %5, %10 ve %20 oranlarında harmanlanmış benzin-etanol ve dizel yakıtı ile ön karışım oluşturacak şekilde %10, %20 ve %30 oranlarında benzin-etanol kullanılmıştır. Ayrıca üçüncü bir yöntem olarak da; ısıtılan emme havası içerisine emme zamanında, tasarlanan enjeksiyon sistemi aracılığı ile benzin püskürtülerek dizel motoru, tam homojen modda çalıştırılmıştır. Yapılan bu deneysel çalışmaların, motor performans parametrelerine etkisi, karşılaştırmalı olarak incelenmiştir. Çalışma sonucunda; mekanik ve ön karışım deneylerinde her iki yakıt karışımı, tam HKSA deneylerinde ise test yakıtı için motor gücü, döndürme momenti ve fren özgül yakıt tüketimi değerlerinde iyileşmeler gözlenmiştir.Nowadays reducing fuel consumption of the cars and exhaust gas emissions has become a necessity for both countries and users. Because of this the scientists have begun in new researches. It is well known that gasoline engines have advantages in terms of exhaust emission, but diesel engines have advantages in terms of fuel consumption. Today the new trend is that; during the preparation of the charge which is taken into the cylinder is the application of ignition engine which is homogenous charge compression that for those two combined engine mixture. Homogenous charge compression ignition (HCCI) combustion process occurs neither flame front as spark ignition engines, nor diffusion flame as compression ignition engines. In this new technology; combustion starts in every points of combustion chamber at the same moment. Since the realization of combustion in this way, engine performance will increase while NOx and particle matter (PM) emission decreases. In this study, a classical diesel engine has been modified to operate with homogenous charge. To obtain homogenous charge, two of the methods, which there are three in literature have been applied. These are; injection advance of test engine for test fuel into cylinder and to be injected early by changing injection impression (early direct injection HCCI combustion method) and to be injected of test fuel with planned injection system and suction stroke into suction manifold. (port fuel injection HCCI combustion method). In these methods, diesel fuel and 5, 10 and 20 % gasoline or ethanol blends and 10, 20 and 30 % gasoline or ethanol premixed and in-cylinder injected diesel fuel were used as test fuels. Besides, as a third method, diesel engine was operated fully on homogenous charge compression ignition mode by injection of gasoline by means of the designed injection system also intake air was heated by an electrical resistant. The effects of those experimental studies to the engine performance parameters were investigated as comparatively. At the end of the study, it was observed that engine power, torque and brake specific fuel consumption values have been improved in mechanical and premixed fuel experiments for both of test fuels (ethanol-diesel, gasoline-diesel) and in fully HCCI experiments for the test fuel of gasoline

A Different Flow Field Design Approach for Performance Improvement of a PEMFC

Flow fields influence the deployment of the reactant gases over the surface of catalyst layer and the removal of the produced water from the cell. An optimum flow field design should provide lowest energy loss, uniform mass distribution and minimize pressure drop between inlet and outlet of the gas stream. An even reactant distribution reduces the mass transport losses and thus allows higher power density. This study is focused on flow fields inspired by veins of the tree leaves, which have effective performance improvement by minimizing the pressure drop and even deploy reactant gases without water flooding. The branching of flow channels corresponds to the Murray's law, which is also applicable to plants. Additionally semi cylindrical obstacles were fabricated at the bottom of the daughter channels to increase the diffusion into the gas diffusion layer. Cylindrical obstacles were applied to reduce the concentration losses, especially at the high current densities. Cell performance and current density vs temperature distribution measurements show that the new innovative designs shows a better performance compared to standard serpentine design by 42.1% at 0.4 V operating voltage. Furthermore, homogenous current and temperature distributions and better water removal are achieved

Experimental investigation of methanol compression ignition in a high compression ratio HD engine using a Box-Behnken design

Methanol is an alternative fuel offering a lower well-to-wheel CO2 emission as well as a higher efficiency, given that the fuel is derived from biomass. In addition to reduced CO2, methanol does not emit soot particles when combusted which is a great advantage when attempting to reduce NOX levels due to the effectively non-existing NOX-soot trade-off. The engine setup used was a Scania D13 engine modified to run on one cylinder, utilizing a high compression piston with a rc of 27:1. This study analyzes the effects of four control parameters on gross indicated efficiency and the indicated specific emissions; CO, THC and NOX. The control parameters chosen in this work was common rail pressure (PRAIL), EGR, λ and CA50, running at 6 bar IMEPG and 1200 rpm. The effects of the control parameters on performance and emissions was analyzed using a surface response method of the Box-Behnken type. Predictive mathematical models were obtained from regression analysis performed on the responses from the experiments. The highest gross indicated efficiency achieved was ∼53%, when a high level of EGR was applied together with the combustion phasing set to its low level at CA50 = 6 CAD ATDC. The control parameters influencing the CO emissions are λ and the interaction between PRAIL and λ, while THC is only controlled by PRAIL and EGR. NOX emissions was, as expected, influenced mainly by EGR and λ, although PRAIL and CA50 also had minor effects. The effect of increased PRAIL, increased THC emissions which in its turn reduced the gross indicated efficiency. Throughout the experiment, THC concentration never decreased below ∼150 ppm due to utilization of high rc in combination with the volatility of methanol. It was also concluded that a rc = 27 is rather high if operation flexibility is required, especially at the higher load range