Lazer Uyarmalı Floresan Tekniği İle Silindir Ve Segman Arası Yağ Film Kalınlığının Ölçülmesi

Abstract

Son yıllarda teknolojinin büyük bir hızla gelişmesi sonucu otomotiv sektöründeki rekabet de hızlı bir şekilde artmaya başlamıştır. Dünyada petrol ve türevi yakıtların rezervlerinin azalması ve dolayısıyla birim fiyatlarının artmasıyla başta otomotiv sektöründe olmak üzere tüm sektörlerde özgül enerji harcamasının azaltılmasına yönelik çok sayıda araştırma ve çalışmalar yapılmaktadır. Ekonomik kaygıların yanı sıra teknoloji ilerledikçe yürürlüğe giren katı egzoz emisyon standartları motor üreticilerini egzoz emisyonlarını azaltma konusunda zorlamaktadır. Otomotiv sektöründe enerji tüketimini azaltmaya yönelik çalışmalar ağırlık azaltma, sürtünmeleri azaltma ve ısıl verimi arttırma gibi başlıklar altında incelenmektedir. Motor kilometre ömrünün gittikçe arttığı günümüzde dinamik motor komponentlerinin yağlanması ömür açısından da oldukça büyük önem taşımaktadır. Yağlamanın iyileşmesi ile aşınmaların minimuma inmesini sağlanacak, bu da motor ömrünü uzatacaktır. Motordaki yağlama performansının geliştirilmesi; yakıt tüketimi, motor gücü, yağ tüketimi, motorun ömrü, verim ve egzos emisyonları üzerinde önemli iyileşmeler sağlamaktadır. Bu durum yatırımcı ve araştırmacıları silindir ve segman arasındaki yağ film kalınlığının ölçümü ve iyileştirilmesi konusu üzerinde araştırma yapmaya yöneltmiştir. Bu proje kapsamında içten yanmalı motorlarda yağ film kalınlığı ölçüm yöntemleri incelenmiş ve bu kapsamda ölçüm yöntemlerinden biri olan lazer uyarmalı floresan tekniği araştırılmıştır. İncelenen silindir-segman profili arasındaki yağ film kalınlığı, lazerle honlanmış silindir gömleği ile kalibre edilerek 1 motor çevrimi boyunca yağ film kalınlığının değişimi gözlemlenmiştir. Çalışma başlangıcında deney düzeneğini kurmak için gerekli ekipmanlar tedarik edilmeye çalışılmış ve akabinde deney düzeneği çalışır hale getirilmiştir. Kurulan deney düzeneğindeki lazeri Labview Programı üzerinden kontrol etmek için RS232 portu üzerinden haberleşme yapılarak, kontrol algoritması geliştirilmiştir. Lazerin piston-segman arasındaki floresan boyalı yağdan yansıyan ışınları fotomultiplikatörde (PMT) gerilim sinyallerine çevirilip National Instruments veri toplama kartı vasıtası ile toplanarak Labview Programında grafik haline getirilip kaydedilmiştir. Bu çalışma sonucunda, yanmanın olmadığı bir deney düzeneği üzerinde yağ film kalınlığı krank açısının fonksiyonu olarak lazer uyarmalı floresan tekniği ile ölçülmüştür. Kurulan deney düzeneği ile motordaki yağ film kalınlığının değişimi yorumlanarak buradaki tribolojik olaylara ışık tutmasına katkı sağlanmış ve farklı piston gömleği, segman ve yağ tiplerine göre çalışmaların yapılmasına olanak tanıdığından çalışmanın bundan sonraki tribolojik çalışmalara da rehberlik etmesi amaçlanmıştır.

In recent years, the rapid development of technology has led to a rapid increase in competition in the automotive sector. Unit prices increased in all sectors due to the reduction of oil and its derivative fuel reserves in the world, therefore especially in the automotive sector numerous researches are being carried out so as to reduction of specific energy consumption. Besides economic concerns, strict exhaust emission standards which apply because of technological progresses are forcing manufacturers to reduce engine exhaust emissions. Efforts to reduce energy consumption being examined as a title of weight reduction, friction reduction and improving thermal effiency in the automotive industry. Nowadays, getting increases the life of the engine mileage, lubrication of dynamic engine components is very important for engine life. As it is known, the total fuel energy cannot be taken as output energy from an internal combustion engine and there are several components of this power loss like heat, mechanical and pumping losses. The significant part of the total power loss is because of the piston ring and cylinder bore friction in a reciprocating engine. Oil film thickness is one of the effective element for reciprocating engines operation which is related to tribological performance. Wear is decreased by heal of lubrication which will extend the life of the engine. Improvement of lubrication performance ensures recruitment fuel consumption, engine power, oil consumption, engine life, efficiency, and exhaust emissions in engine. This lead investors and researchers to investigate the issue of measuring and improving the film thickness of the oil film between the cylinder and the ring. Numerous studies about elasto-hydrodynamic and hydrodynamic lubricant film thickness measurements eventually guided engine technology towards tribology reduction losses, via the formulation of new lubricants (additive technology, physical properties enhancement), a more controlled oil transport through the ring pack and the formulation of the proper lubricant film in the piston-liner interface. Piston rings of internal combustion engines are required to slide smoothly with great speed variation, including zero-speed, at high temperatures and loads, and to have small friction and wear even under severe conditions without a sufficient lubricating oil supply. The role of piston rings is also becoming more complex in line with the recent requirements for lower oil consumption and friction. The role of piston rings is also becoming more complex in line with the recent requirements for lower oil consumption and friction. The role of piston rings is also becoming more complex in line with the recent requirements for lower oil consumption and friction. The importance of piston rings is also increasing in terms of engine performance and durability. On the other hand, states of lubrication for individual piston rings have been steadily clarified, owing to efforts made by many researchers. However, further understanding and a more in-depth analysis of states of lubrication will be necessary in order to meet the requirements mentioned above which are becoming increasingly more complex and stringent. In particular, up to the present in order to measure oil film thickness between piston ring and cylinder surfaces of a variety of methods have been tried. These methods are electric, acoustic and optical method can be divided into three groups. In the electrical method , oil film thickness is measured between cylinder and piston ring by using resistance, inductance or capacitance. Piston ring must be electrically isolated at resistance method. DC current is applied between cylinder and piston ring, small voltage changing is measured by a bridge according to oil film thickness changing. Obtaining a signal proportional to the oil film thickness is difficult due to short circuit in the mixed regime, surface coating and to influence the electrical resistance of the tribofilm. Inductance method based on inductance changing according to located near object. In this method, AC voltage signal is applied to coil and object location is determined due to voltage phase delay. In the capacitence method, engine oil between cylinder and piston ring is carried insulating task and OFT is measured according to changing of capaticance value. Accurate results can be taken at fully hydrodynamic lubrication however in the mixed regime short circuit, cavitation and tribofilm cause to measurement diffuculties. Oil film thickness is calculated according to reflection ratio of ultrasonic signals on the OFT by using ultrasonic waves in the acoustic method . Oil viscosity also can be measured in this method. Measurement is difficult due to high calculated time, engine noise and need to sensitive instumentation. In the literature, there are only measurements made in the drifting engines. Results obtained from the combustion engine is not available. A new method has been developed for measuring the oil films on cylinder walls in engines that offers benefits in improved understanding of oil transport and oil consumption. A laser fluorescent diagnostic method was employed to measure lubricant film thickness on the cylinder wall/piston interface in engines. Laser induced florescence (LIF) technique which is a optical method, have been using for measuring oil film thickness (OFT) between cylinder and piston ring since1980’s. This technique gives more accurate results according to other methods but this method also has complicated measurement system and need to comprehensive study for calibration. A laser source which is canalized to a surface film and obtain more long wavelength with florescence glow. Photons that are collected only excitation bant by photomultiplier (PMT), reflected beam after passed a filter. The system output signal was calibrated using lubricant samples of known thickness, and by comparison of a known piston ring profile to measured lubricant film calibration. In this project, measuring methods of oil film thickness in internal combustion engine were investigated and laser induced florescence technique which is one of the measurement methods, was researched. The oil film thickness between the cylinder-piston ring profile was calibrated with the laser-honed cylinder in order to observe the oil film thickness changes for one engine cycle. The results were examined according to different temperature, engine speed and normal load due to compare the effect on each other. Research were showed that photobleaching could be significant problem in laser induced florescence (LIF) technique. The system which needed to be design, has continous fresh oil and be exposed to laser beam a very short period of time in order to prevent photobleaching. At the beginning of the experiment, necessary equipments were tried to supply and then experimental setup make functional. Controlling algoritm was developed in Labview for control the laser with RS232 port. Reflected beam from the florescence dye between the cylinder and piston ring which was converted voltage signals in PMT. Data were collected at National Instrument data acquisition card, subsequently data were recorded and graphed at Labview Program. As a result of this study, oil film thickness was measured as a function of crank angle at constanst temperature and normal load by LIF technique. Measuring of oil film thickness contribute to solve tribological issues and provide possible measurements with different piston liner, piston ring and oil types. Thereby it is instrumental in doing future tribological researches.