Yüksek devirli gemi diesel motorlarında farklı valf zamanlarının etkisi
Affect of different valve timing on the operation of high speed marine diesel engines
- Tez No: 39603
- Danışmanlar: PROF.DR. O. KAMİL SAĞ
- Tez Türü: Yüksek Lisans
- Konular: Gemi Mühendisliği, Marine Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1994
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 106
Özet
ÖZET Yapılan bu çalışma ile amaçlanan, çok silindirli, aşırı doldurmalı gemi diesel motorlarının emme ve egsoz manifoldları ile birlikte bir bütün olarak modelleyen ve listesi referans [1] 'de verilen bilgisayar programı yardımıyla farklı valf zamanlarının, özellikle 4 (2 emme ve 2 egsoz) veya daha fazla valflı motorlarda emme valflarının veya egsoz valflarının kendi aralarında farklı zamanlarda açıldığı ve kapandığı zaman, motorun işlevsel değerlerine (güç, basınç, sıcaklık, ortalama efektif basınç, yakıt tüketimi gibi) nasıl etkidiğini saptamaktır. Referans [1] 'de kullanılan programın dayandığı teorik temeller ise, diesel motorlarının emme ve egsoz manifoldlarında meydana gelen zamana bağlı gaz akımının, tek boyutlu ve gaz zerrecikleri arasında değişken antropiye sahip olarak dalgalar halinde ilerlediği düşüncesiyle, enerjinin korunumu, kütlenin korunumu ve momentumun korunumu ilkelerine dayanmaktadır. Modelleme sonucu ortaya çıkan lineer olmayan hiperbolik kısmi diferansiyel denklemler referans [1] 'de açık açık anlatılan karakteristikler metodu kullanılarak çözülmekte ve gereken sınır şartları Bölüm 5 'de belirtilmektedir. Sanayi uygulamalarına yönelik CAD araştırmalarında kullanılabilir nitelikte olduğu ispatlanan bu bilgisayar programı, emme ve egsoz valflarının birden fazla olduğu ve kendi aralarında farklı zamanlarda açıldığı veya kapandığı durumunda çalışmadığı için öncelikle bu nokta programda düzeltilmiş ve program daha üstün hale getirilerek sonuçların doğruluğu kontrol edilmiştir. 16 silindirli, 4 subaplı (2 emme ve 2 egsoz), direkt püskürtmeli, tek pistonlu, aşırı doldurmalı, emme ve egsoz manifoldlu gemi diesel motoru örnek alınarak Ek-A'da belirtilen 5 ayrı durum sistematik olarak incelenmiştir. Bölüm 7 'de tablolar ve Ek-A'da diyagramlar halinde verilen sonuçlar gözönüne alınarak ulaşılan netice tezin sonuçlar ve öneriler bölümünde açık bir şekilde belirtilmiştir. vıı
Özet (Çeviri)
AFFECT OF DIFFERENT VALVE TIMING ON THE OPERATION OF HIGH SPEED MARINE DIESEL ENGINES SUMMARY For years, internal combustion engines are known as the best power supply in industry and especially in transportation. For this reason, the importance extended to the design studies of modern marine diesel engines is increasing day by day and calling the researcher's attraction. For being able to design the most economical engine, the use of computer programms are gradually becoming attractive, because the prototype construction and experimental studies require high cost and long time in in the design of big marine diesel engines. That's why the design and production programms which are called CAD-CAM, help the researchers and engine manufacturers to a great extent in preparation of optimum design. In recent years, even the smallest progresses in the geometry of inlet and exhaust systems, cylinder valve timing, cylinder compressor and especially theoretical computations in turbocharge units are gainning importance. For this reason, has caused universities and resarch centers to concentrate their computerized modelling studies on these topics. The intent of this study is to determine how the different valve times affect the functional values of the engine (power, pressure, temperature, mean effective pressure, fuel oil consumption ) especially in the 4 ( 2 inlet and 2 exhaust ) or more valved engines when the inlet valves open anf close in different times between themselves. And the theoritical fundementals, which the programm used in reference [1] depend on, are based on the principles of conservation of energy, conservation of mass and conservation of momentum with the opinion that the gas flow which accurs time dependently in the inlet and exhaust manifolds of diesel engines, propagates in wave manner, one viiidimensionnally and possesing variable entropy between gas particles. The non-lineer hyperbolic partial differential equations which appear as a results of modelling, are solved by using the method of characteristics which is explained clearly in reference [1] and the necessary boundary conditions are stated in chapter 5. Because this computer programm which has been improved to have the quality of being usable in CAD research orient to industrial applications, does not work when the inlet and exhaust valves are more than one and thay open ang close at different times between themselves, at first this point in the program has been modified and the accuracy of the results has been checked out by making the program more superior. All these studies have been carried out by taking the marine diesel engine with 16 cylinders, 4 valves (2 inlet and 2 exhaust), direct injection, single piston, supercharged, inlet and exhaust manifolds, the configuration sheme of which is given in figure 1 Atachment-A. The name type and dimentions of the engine are kept secret pursuant to the agreement with the engine manufacturer. In this study 5 different conditions, the valve opennings of which are given as diagrams in figure 2, 3, 4, 5 and 6 Attachment-A, are investigated. Here the 1st condition is the original one and the inlet and exhaust valves are openning and closing at the same time between themselves. For each condition, taking the same input data except for the crank angles at which the valves are open and close, the program has been run recurrently. The change in pressure in the cylinder and inlet manifold according to crank angle, which is determined as a result of running the program, is demonstrated on a diagram for 1st, 2nd and 3 conditions and on another diagram for the 1st, 4th and 5th conditions for 4 strokes. The cylinder pressure distribution diagrams given in attachment-A are for the cylinder number 2, 4, 6 and 8. When we work at the cylinder pressure distribution diagrams and Table 7.1, it can be seen that in the 3rd and 4th conditions maximum cylinder pressure decreases by 1.5-2 bars approximately with respect to the 1st, 2nd and 5th conditons, and the highest maximum pressure occurs in the 1st and 5th conditions. In all these conditions, when approaching to the exhaust valves openning instant, it can be seen on the cylinder pressure distribution diagrams that the presure curves are gradually becomnig congruent. During the interval between the exhaust valves openning and inlet ixvalves openning, the cylinder pressure values in the 2nd, 3rd and 5th conditions are less than the ones in the 1st condition. But in the 4th condition the cylinder pressure are higher with respect to the 1st condition. During the interval between the inlet valves openning and exhaust valves closing (the overlap period when the valves are in conjunction), the cylinder pressures in the 3rd and 4th conditions reach up to higher values with respect to the other conditions. During the interval between the exhaust valves closing and inlet valves closing, it is seen on the diagrams that the cylinder pressures in the 4th condition are higher than the ones in the other conditions. When we look at Table 7.2, it can be seen that with respect to the 1st condition, specific fuel oil consumptions of the cylinders in the other conditions are approximately 1.5-2 g/kwh higher When we look at the values on Table 7.3 where the mean effective pressures of the cylinders are given, it can be seen taht with respect to the 1st condition the mean effective pressure decreases approximately 0.15-0.3 0 bar in other conditions, but in the 5th condition this value does not change considerably when compared with the 1st condition. It can also be obviously seen on Table 7.3, 7.4 and 7.2 that the decrease in the mean effective pressure causes the decrease in effective power of cylinders and consequently increase specific fuel oil consumption. The decrease in the mean effective powers of cylinders by approximately 0.85-2.10 kw with respect to the 1st condition can be seen on Table 7.4. This is caused by the decreas in the mean effective pressure of cylinders. It can be seen on Table 7.5 that the capacity of air sucked into the cylinders decrease in the other conditions approximately by % 1.5-6.0 in general with respect to the 1st condition. We can determine from Table 7.2, 7.4 and 7.5 that the decrease in the capacity of air sucked into the cylinder causes the fuel oil consumption increase and the power decrease. When we take into consideration the pressure distribution diagrams given for the inlet pipe end number 76, 92, 108 and 124 in Attachment -A, it is seen that the lowest pressure occurs in the 3rd condition and the highest one in the 5th. Theoretically, increase in pressure in the inlet pipe also increase the capacity of air sucked into the cylinder and provide a better comustion. xAfter the tables given in Chapter 7 and diagrams given in Attachment -A have been systematically interpreted, 6 main results stated below as items are concluded. i. Looking at the effective power and specific fuel oil consumption values of cylinders in the 1st and 2nd conditions on Table 7.4 and 7.2, it is concluded that earlier closing and opening of one of the exhaust valves with respect to the other (2 inlet valves open and close at the same time) causes the effective power decrease and causes the specific fuel oil consumption increase on the other hand. ii. It is concluded that the effective power of the engine increases and paralled to this the specific fuel oil consumption decreases when one of the exhaust valves opens and closes later than the other ( 2 inlet valves open and close at the same time ). We have come to this conclusion after looking at the values given in Table 7.4 and 7.2, and comparing the 3rd and 4th conditions together with the 1st condition. iii. When we compare the values given for the 1st and 3rd conditions in table 7.4 and 7.2 with eachother, we can come to the conclusion that effective power of the engine decreases and the specific fuel oil consumption increases if one of the inlet valves opens and closes earlier than the other ( 2 exhaust valves open and close at the same time ). iv. If one of the inlet valves opens and closes later than the other, in other words when we compare the 2nd and the 5th conditions together with the 1st condition in the respect of effective power and specific fuel oil consumption looking at Table 7.4 and 7.2, We come to the conclusion that effective power increases and the specific fuel oil consumption decreases. v. If one of the exhaust valves and one of the inlet valves open and close earlier with respect to the other ones, in other words, when we compare the 2nd and 3th conditions together with the 1st one observing Table 7.4 and 7.2 we can come to the conclusion that effective power of the engine decreases and the specific fuel oil cunsumpotion increases. vi. If one of the exhaust valves and one of the inlet valves open and close later than the others, it is concluded that effective power of the engine increases, specific fuel oil consumption of the engine decreases when the above conlusions are taken into consideration. xiIn order to determine more reliable and better results, it is advised to the researchers who are interested in this subject to carry out the same study, i. By increasing the interval between the inlet and exhaust valves' opening and closing later than the other between eachother. ii. For 6 ported (3 inlet and 3 exhaust), high revolution marine diesel engines with turbocharge unit. iii. For naturally ventilated marine diesel engines. XII
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