Yüksek devirli gemi diesel motorlarının analitik ve deneysel incelenmesi
An Analytical and exeperimental investigation of high speed marine diesel engines
- Tez No: 19363
- Danışmanlar: PROF.DR. OSMAN KAMİL SAĞ
- Tez Türü: Doktora
- Konular: Gemi Mühendisliği, Marine Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1991
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Belirtilmemiş.
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 258
Özet
ÖZET Sunulan çalışmada, çok silindirli, aşırı doldurmalı gemi diesel motorlarının manifoldları ile birlikte bütü nüyle modellenmesi, modellemeye uygun olarak bilgisayar programının geliştirilmesi, elde edilecek analitik sonuç ların deney sonuçları ile karşılaştırılması, böylece te ori ve bilgisayar programının hassasiyetinin araştırılarak, çalışmanın sanayi uygulamalarına yönelik CAD araştırmaların da kullanılabilirliğinin gösterilmesi amaçlanmaktadır. Teori, diesel motorlarının emme ve egzos manifoldların da meydana gelen zamana bağlı gaz akımının, tek boyutlu, za mana bağlı, gaz zerrecikleri arasında değişken antropiye sa hip olarak dalgalar halinde ilerlediği düşüncesine dayanmak ta olup, enerjinin korunumu, kütlenin korunumu ve momentumun korunumu aksiyomları ile model lenmektedir. Modelleme sonu cu elde edilen lineer olmayan hiperbolik kısmi diferansiyel denklemler, Karakteristikler Metodu kullanılarak çözülmek te, çözüm için gereken sınır koşulları ise Bölüm 5 'de anla tılan sınır koşulu teorilerinden yararlanılarak temin edil mektedir. Sözü edilen teoriye dayalı olarak geliştirilen bilgi sayar programı direkt püskürtmeli her çeşit diesel motoru nu ister tek silindirli ister çok silindirli olsun, emme ve egzos manifoldları ile birlikte, türboşarj ünitesine sa hip veya doğal havalandırmalı olarak bütünüyle modelleye- bilmektedir. Boyutları önceden seçilen yüksek devirli, 16 silindir li, tek pistonlu, direkt püskürtmeli, 4 subaplı, emme ve egzos manifoldlu, aşırı doldurmalı bir gemi diesel motoru örnek alınarak geliştirilen bilgisayar programı kullanıl mış, elde edilen analitik sonuçlar, deneyler yapılarak bulunan motor test sonuçları ile karşılaştırılmış, anali tik ve deneysel sonuçların birbirleriyle büyük uyum içeri sinde olduğu görülmüş, teorinin sağlıklılığı hakkında ve geliştirilen bilgisayar programının sanayide motorların ön dizayn, dizayn ve üretim safhalarındaki ileriye yönelik yenileştirme ve geliştirme çalışmalarında kullanılabileceği konusunda olumlu yargıya varılmıştır. Teorik ve deneysel sonuçlar Bölüm 7, 8 ve 9 'da detaylı olarak irdelenmiş olup, tezin son kısmında EK-B'de verilen diyagramlar ile Bölüm 7 'de verilen tablolar birlikte gözönüne alınarak, bilgisayar programının son haliyle sanayide kullanı labileceği anlaşılmıştır. viii
Özet (Çeviri)
AN ANALYTICAL AND EXPERIMENTAL INVESTIGATION OF HIGH SPEED MARINE DIESEL ENGINES SUMMARY Internal combustion engines date back to 1876 when Otto first developed the spark-ignition engine and 1892 when Diesel invented the compression-ignition engine. Since then these engines have continued to develop as our knowledge of engine processes has increased, as new technologies became available as demand for new types of engine arose, and as environmental constraints on engine use changed. Internal combustion engines and the industries that develop and manufacture them and support their use, now play a dominant role in the fields of power, propulsion, and energy. The last thirty years or so have seen an explosive growth in engine research and development as the issues of air pollution, fuel cost, and market competitiveness have become increasingly important. The classical approach to Marine Diesel Engine design in the form of manual theoretical calculations, prototype manufacture and testing can be extremely expensive in terms of time and money. The cost of developing the Modern Diesel Engine makes it essential for the engineers to be able to forecast the behaviour of a proposed design through the utilisation of digital computers. Thus, CAD and manifacture investigation programs and simulation models can be of great assistance to the engine designer and also the engine manufacturer who intends to carry out mass production, in case a good representation of the engine system. Engine performance analysis has increased at an accelerating rate over the last thirty years, since the application of the digital computer to the problem. The analysis of performance enables the research engineer to predict the power output of engines at the design stage ? it is now also possible to postulate models of the combustion process which are capable of predicting some of the emission levels from both diesel and petrol engines. The effect of inlet and exhaust manifolds on the power output, and emission levels, of engines can be calculated by applying techniques for solving the wave action in the manifold ; these can also be extended to study the effects of turbocharging the engine. IXThe essential elements involved in the prediction of turbocharged engine performance may be classified as: i) air flow modelling? ii) combustion and heat transfer in engine cylinders. These are brought together in iii) comprehensive engine simulation models. The work presented in this thesis, is concerned with the whole cycle modelling of the multi-cylinders turbocharged diesel engines and developing a general computer simulation programs for this purpose and matching the analytical results and theory with the experimental engine test results. The basical theory given in Part I, is based on the wave action techniques which involve the solution of the compressible gas flow equations and allow heterogeneous pressure levels to exist throughout the intake and exhaust manifolds. A solution is required for the non-linear hyperbolic partial differential equations which describe the passage of disturbances through a compressible medium. The equations are usually limited to one spatial dimension and are not capable of truly depicting two and three dimensional effects, e.g. junctions and diff users with separation. These wave action models are of paramount importance for the performance prediction of certain engine types, e.g. small two-stroke cycle petrol engines (in which manifold tuning is essential), multi -cylinder engines with long pipe runs, and multi-cylinder engines with interference between the cylinders. The technique can be usually applied to the initial design of any engine manifold system and will highlight both advantegeous and disadvantegeous resonances throughout the engine load and speed range; these can give rise to maldistribution of charge between engine cylinders, or a general reduction in the performance of the whole engine due to poor charging. Wave action methods can be applied to naturally aspirated and turbocharged engines. Models are also available for all internal combustion engine components: turbines, compressors, engine boundaries, carburettors, pulse converters, pipework junctions, etc. One dimensional time depended gas flow throughout the intake and exhaust manifolds of a marine diesel engine is successfully modellized by the non-homentropic gas flow theory. According to the theory, heat flux to the walls, friction factor in the pipes, variations of the cross sectional areas of the pipes, and entropy differentiation between the gas particles with respect to the time are assumed. Some pipe end thermodynamic characteristics like pressure, temperature, mass flow rate etc. at the end of the time step are determined by means of the boundary xconditions. Boundary conditions are generally classified in two groups like active boundary conditions and passive boundary conditions. Active boundary conditions are described as the reason of the time depended gas flow in control volume like cylinder, turbine, compressor etc. Passive boundary conditions are the factors absorbing and reflecting the waves inside of the pipes with many kinds of ways. Passive boundary conditions can be seperated into two groups. One of them is called as the middle of the system (Junctions) and the other one of them is called the end of the system (nozzles, valves etc.). Detailed descriptions and necessary formulas about the boundary conditions are given in Part 5. Developed computer simulation program moderated with the theory mentioned before is given in the appendix A. It is able to simulate every kind of marine diesel engines like single piston, opposite piston, 2 stroke or 4 stroke, turbocharged or naturally aspirated, motoring or whole cycled including the fuel injection and combustion process. Mainly outputs of the program are some cumulative values at the end of the cycle like specific fuel consumption, mean effective pressure, mass flow rates, power output, maximum combustion pressure, heat losses, thermal efficiency etc. Simulation program can also calculate some gas dynamic variables with respect to time like cylinder pressure, cylinder temperature etc, whenever they are needed at different measurement points on the inlet and exhaust manifolds. In order to compare the analytical results with the experimental engine test results, author had studied for six months at the test center of MTU Motoren-und Turbinen -Union Friedrichshafen GmbH, Germany, and he observed many kinds of engine whilst they had been testing. Analytical results and experimental test results are plotted together on same diagrams in appendix B. At the same time, some cumulative results and percentage error size between them are given by Table 1 and Table 2 in Part 7. According to the diagrams, calculated and measured manifold pressure variations along the four strokes are determined very close to each other. Both pressure curves show the same characteristics and same peak numbers. At the end of the comparison, it was noticed that the pressure curve variation characteristics and their values are nearly same with the experiment results. When inlet valves are open, the pipe pressure differences between the analytical and test results have an affect on the cylinder pressure and maximum combustion pressure. At the intake point of the inlet manifold, the pipe pressure has nearly smooth characteristic and it takes approximately a value of 2.9 bar. When the measurement point is changed from the cylinder B-l to B-8, then the calculated and measured pipe pressures are found a. s their curve characteristics xidrawed bigger amplitudes. Both curves showed the nearly same amplitudes and same variations at same crank angles. Differences between two curves can be neglected. Calculated and measured cylinder pressure fluctuations along the closed cycle (Compression and power strokes) are given in similar diagrams. Their curve characteristics are same and their values are close to eachother. The differences between the analytical and experimental results along the exhaust stroke can be seen in the diagrams. Significantly differences are found from the crank angle at which exhaust valves are opened to the crank aftgle at which exhaust valve lifting areas have their maximum value. Except for this region, the analytical and experimental results offer the same characteristics and different but nearly same values. Cylinder pressures along this region are calculated approximately 1.5-2.0 bar less than the measured value for each cylinder* The reason of this difference might be heat flux into the walls, flow coefficient of the valves or the sensitivities of the high pressure transducers, position at the cylinder head or the influence of temperature shock on the transducer. Because the exhaust valves are opened at the neighbourhood of 90 degree CA, and at this moment, cylinder pressure are much more higher than the exhaust manifold pressure, so there will be a turbulance inside of the cylinder. A high degree of measurement accuracy is mandatory in order to obtain true thermodynamic results from dynamic pressure measurement. Cylinder pressure is generally measured with piezo electric transducers. The degree of measurement accuracy, among other factors, is influenced by the characteristics of the selected pressure transducer, selection of the transducer position, calibration, determination of the true absolute pressures or determination of the cylinder volume to each corresponding cylinder pressure. Temperature shock effects are decisive criteria in determining the applicability of a transducer. Temperature shock is present during combustion when heat transfer of the transducer is rapidly increased thereby inducing deformation of transducer components» Consequently, special transducers, as shown in appendix B, figure 23, have been especially designed with temperature shock insensitivity in mind. Selection of the optimum transducer location is important, due to the fact that there exist local pressure differences within the cylinder. These are present especially when the piston is close to the cylinder head. Near TDC, squish effect gas motion takes place in and around the combustion bowlo In addition, pressure waves are created with the first combustion knock (see appendix B, figure 24). Pressure oscillation will also appear if the transducer.is not mounted flush to the cylinder head surface. The resulting oscillations have frequencies and amplitudes which are dependent on the volume enclosed between the transducer surface and the combustion chamber. Figure 25 in appendix B shows the heat release process calculated from measurement data with an improper transducer location. Other xiireason of this difference between the analytical and experimental results might be that the combustion in the combustion chamber was not finished after the exhaust valves are opened and a small amount of fuel is still burning. When the inlet valves are open, the difference between them decreased, and both curves come close to each other. Although two curves have different values whilst the inlet valves are opened, their differences are less than the differences in case of exhaust values are open. General characteristics of both curves are similar and their values close to each other. In the over lop period, cylinder pressures are calculated 0,3-0.9 bars less than the measured values. However, the cylinder pressure curves followed same characteristic at this region. Cumulative results and their error percentages ^are also given by Table 1 and Table 2 in Part 7. It can be seen that all values are very close to eachbther. If all diagrams and tables are appreciated together, one can say that one-dimensional, non-homentropic, gas flow theory gives satisfactory results and the developed computer simulation program can be used at pre design, design and manufacturing stages in the industry. xiii
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Gemi Mühendisliğiİstanbul Teknik ÜniversitesiGemi İnşaatı ve Gemi Makineleri Mühendisliği Ana Bilim Dalı
PROF. DR. OSMAN KAMİL SAĞ
