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İçten yanmalı motorlarda honlama açısının güç silindiri tribolojik performansı üzerine etkilerinin incelenmesi

The investigation of effect on engine honing angle on tribological performance at internal combustion engines power cylinder

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  1. Tez No: 467050
  2. Yazar: ONUR GEZER
  3. Danışmanlar: DOÇ. DR. ÖZGEN AKALIN
  4. Tez Türü: Yüksek Lisans
  5. Konular: Makine Mühendisliği, Mechanical Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 2017
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Makine Mühendisliği Ana Bilim Dalı
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 104

Özet

İçten yanmalı motorlar, 1800'lü yılların ikinci yarısında icatlarından sonra, gelişen teknik ile beraber taşıt tahrikinde kullanıma geçmiştir. İmalat teknolojisindeki ilerlemeler ile beraber kara yolu taşıtları orta-alt ekonomik sınıfları da kapsayacak şekilde kendisine pazar payı edinmiş ve günümüzün en çok kullanılan gereçlerinden biri haline gelmiştir. Bu durum da artan çevre kirliliği ve petrol rezervlerinin azalmasıyla sonuçlanmıştır.Artan çevre kirliliği sonucunda belli regülasyonlar devreye konmuştur. Bu durum ilgili alanda çalışan bilim insanları ve mühendisleri çeşitli araştırmalar yapmaya itmiş ve çeşitli stratejiler ile yakıt sarfiyatı ve emisyonlar belli değerlere indirgenmiştir. Günümüzde daha dar bir banda sıkışan emisyon değerleri ve yakıt tüketim değerleri sebebiyle yanmaya yapılan müdahalelerin haricinde motor konstrüksiyonu ve yüzey özelliklerine de müdahale edilmeye başlanmıştır. Bu çalışma kapsamında silindir yüzey tekstürü üzerinde karakteristik özellik olan ve tribolojik özellikler üzerinde önemli bir rol oynayan silindir honlama açıları değiştirilerek, bu durumun silindir yağ film kalınlığı, sürtünme kayıpları ve yağ sarfiyatı üzerindeki etkileri incelenmiştir. Çalışma kapsamında Reynolds denklemine, yüzey pürüzlülüklerinin etkisinin eklenmiş formu olan, Patir ve Cheng tarafından geliştirilen ortalama Reynolds denkleminden faydalanılmıştır. 15o, 30o, 45o ve 60o silindir honlama açıları için basınç farkından kaynaklanan akış faktörleri olan ϕx, ϕy değerleri ve pürüzlü yüzeyin pürüz hacimlerinin ek yağlayıcı taşımasından kaynaklanan, kesme kaynaklı akış faktörü olan ϕs değerleri elde edilmiştir. Daha sonra bu sonuçlar ''AVL-Excite'' programının ''Piston-Ring'' modülünde; kurulan matematiksel modelden elde edilen akış faktörleri, temel motor büyüklükleri ve termodinamik dataları gibi karakteristik çalışma özellikleri girilerek simüle edilmiştir. Yukarıda bahsedilen sürecin ardından motor simülasyon değerleri incelenmiştir. İnceleme silindir yağ film kalınlıkları, toplam segman-silindir sürtünme kuvveti, toplam sürtünme gücü, sürtünme kaynaklı ortalama efektif basınç düşüşü, mekanizmasına göre yağlayıcı sarfiyatı başlıklarını kapsamaktadır.

Özet (Çeviri)

Internal combustion engines came into use in vehicle drive through the advanced techniques following the inventions during the second half of the 1800s. Thanks to the improvements in the manufacturing technology, road vehicles have gained a market share including lower-middle economic classes, and have become the most commonly used instruments in today's world. This fact led to increasing environmental pollution and decreasing the oil reserves. Certain regulations were put into practice as a consequence of the increasing pollution. This prompted the scientists, and engineers working in the related field to do various researches, and thus fuel consumption and emissions have been reduced to a certain amount by means of several strategies. Apart from the interventions to combustion due to the emission values and fuel consumption currently restrained in a narrower band, there commenced some interventions to the engine construction, and surface as well. Within the scope of this study, engine honing cross-hatch angles, which have a characteristic and vital role on the surface texture of a cylinder, were changed to observe their impact on lubricant oil film thickness, friction loss, and lube oil consumption. Cylinder honing trace and honing angle exist as a natural result of the honing machining process method. Small volumes which comprise of during honing process function as a reservoir and transfer line for engine lubricating oil. The tribological properties of the honed surfaces differ according to the honing angle, peak and valley roughness values. Honing angle are generally between 40o-60o or 115o-140o ranges for conventional engines. 40o-60o range use more widely. 115o-140o range is preferred for helical slide honing. But sometimes we can be seen smaller honing cross-hatch values at race car engines. Friction force can be significantly reduced by manipulating with surface textures. The lowest oil film thickness which provided hydrodynamic lubrication regime, gives theoretically the lowest friction coefficient. Friction coefficient increases at higher or lower thickness than this point. Metal to metal contact will occur if oil film thickness will decrease. So friction coefficient increase and wear mechanisms take the action of oil film thickness decreasing. Especially concentrated wear at top dead centre limits the engine life. As a result, lubrication is getting worse and friction force increase gradually in consequence of increased amount of wear. The rings have larger wear effect than piston skirt in terms of contact frequency and contact mechanisms. The boundary lubrication regime at top and bottom dead centres is largely responsible for wear. On the other side, high combustion chamber temperatures, low film thickness and high acidic concentration are other wearing factors. At middle area of piston stroke hydrodynamic lubrication regime obtain, and wear at there are largely dependent on the presence of abrasive substances which is incorporated to engine lubrication oil. Piston-ring-cylinder system has a very important role in engine life and efficiency. The low cylinder liner roughness values decrease the engine lube oil affectivity. With getting thin lubricant oil film thickness wear mechanism actuates and friction force increases, because of metal to metal asperity contact. The higher surface roughness value improves the lubrication regime but it increases the friction forces. Increasing the surface roughness excessively cause an increase of friction force, wear and lube oil consumption. So both the spesific fuel consumption increasing as a result of the decrease in mechanical efficiency and increasing lube oil consumption and their emissions such as hydrocarbons, carbonmonoxide, carbondioxide and particulate matter. When examinig the tribological performance of the engine cylinder liners with considering only the surface roughness values can cause misleading results. Because, while honing the engine cylinder, it is generally necessary to mention three different processes and during the last process which is known as plateau honing, the valley roughness value don't change significantly, while peak roughness value show a considerable decrease. Thus, the risk of asperity contcat risk is reduced, reserve volumes are created during this moment and these volumes support the performance of lubricating oil. Another important parameter for the engine lubrication oil film is load carrying capacity at cylinder liner lubrication film. Because the load carrying capacity provide the stability of oil film. The smooth surfaces, that is, the surface which haven't significant surface roughness, is a too poor in point of load carrying capacity. The surface texture which is created by honing traces increases the load carrying capacity depending on the honing characteristic. Plateau honed surfaces have a significant effect on the load carrying capacity of cylinder lubrication oil film. It is known that the cylinder honing cross-hatch angle has a direct effect on the capacity, especially rings and cylinder liner interfeace. Considering that the rings roughness value is so low, the load carrying capacity is largely related with honing geometry on the cylinder liners. In this case the load carrying capacity grows as the of valley roughness depth to honing height ratio increases. If the honing cross-hatch angle is reduced to smaller value, the average friction coefficient of the cycle will decreases. On the other hand, engine honing cross-hatch angle has a direct effect on the oil consumption and the oil consumption decreases when the honing angle increases. In other words, as the honing angle decreases, the friction coefficient decreases and oil consumption increases. Because honing marks have a closer profile to the horizontal axis with decreasing cross-hatch angle and this situation create more resistance to the fluid flow of lubricatig oil. As a result of the increased inertia of the lubricating oil in this way, the lubrication oil film tends to increase film thickness. It is clear from this that changing the cross-hatch angle improves a feature while the other worsens. Hence, honing cross-hatch angle is stuck in a definite band, take into account of tribological performance. If we rule out helical slide honing which has been worked on recently, engine honing cross-hatch angle of conventional engines is between 45o and 55o. Textured surfaces are better for mechanical sealing than smooth surfaces. This also reduces the risk of delaceration of the lubricating oil film. In this way, the risk of metal to metal contact is reduced and friction force which causing by boundary lubrication and amount wear decreases. In this situation, gas leakage will be reduced to lower levels with increased sealing ability. As a result, the compression loseses will decrease, engine effective power incresae. So spesific fuel consumption and spesific emission levels decrease. In internal combustion engines, the oil consumption affect directly exhaust gas emissions and oil change duration. Therefore, oil consumption should be under control. Particulate matter emissions are one of the major emissions for conventional diesel engines and it have to be reduced. Particulate emissions which is produced by fuel, have been reduced via interfere to injection, combustion and improving combustion chamber air movements. In this case, the ratio of particulate matter emissions which is caused by lubricating oil is increase in total engine particulate emissions. In internal combustion engines, valves, turbocharging unit, cylinders, piston and rings are main source of lubricant oil consumption. Among them, piston-ringcylinder pack is the most important factor in oil consumption For this study, the Reynolds equation was used, which was developed by Patir and Cheng as a version including the impact of surface roughness. The shear flow factor of ϕs which come to mean roughness volume of the rough surface carrying additional lubricant, the pressure flow factors of ϕx, ϕy were obtained resulting from for the 15o, 30o, 45o, and 60o engine honing cross-hatch angles. Then these results were simulated by entering the study characteristics such as the flow factors obtained from the established mathematical model, the main engine sizes, and the thermodynamic data to the 'Piston-Ring' module of the 'AVL-Excite' program. The engine simulation values were analysed following the above-mentioned process. The analysis includes the cylinder lubricant oil film thickness, total segman-cylinder frictional force, total frictional loss power, frictional mean effective pressure decrease, and lubricant consumption by mechanism.

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