Gemi diesel motorlarında silindir modellemesi

Abstract

Bu tezde sunulmakta olan çalışma, Gemi Diesel Motorlarında Silindir Modellemesi ve bu modellemenin tek silindir için özelleştirilme sidir. Başlangıçta, konu ile ilgili olarak yapılmış olan kaynak araş tırması hakkıda kısaca bilgi verilmiş ve takiben Tek Boyutlu Zamana Bağlı Gaz Akımı Teorisi ve bazı diferansiyel denklem çözüm yöntemleri hakkında açıklamalar yapılmıştır. Tezde sunulmakta olan bilgisayar programında, silindir içindeki akımı çözerken Runge-Kutta Metodu, boru içindeki akım hesaplamaları için ise Mesh Metodu kullanılmıştır. Programa ve verilen datalara göre modellemesi yapılan diesel motor, borular vasıtasıyla, sonsuz büyüklük teki bir kontrol hacminden aldığı havayı ikinci bir sonsuz büyüklükteki kontrol hacmine egzoz alarak göndermektedir. Teze konu olarak seçilen motor, Bergen Diesel Fabrikasının KRG3 tipli diesel motorudur. Bu motora ait datalardan; emme valfı çapı, egzoz valfı çapı ve boru uzunluğu değerlerinden her biri beşer kere değiştirilerek, bilgisayar programının çalıştırılması sonucu elde edilen- çıktılardan (output) yararlanılarak bir çok eğri elde edilmiştir. Prog ramda, Runge-Kutta Metodu ile silindir içerisindeki başlıca değerler hesaplanırken krank açısı artımları araştırmacıların isteğine bırakılmış Dİup bu çalışmada beşer derecelik artım uygun bulunmuştur. Boru hesap ları esnasında ise krank açısı artımları programın kendi içinde hesap- latılmıştır. Tezin son bölümlerinde ise elde edilen eğriler hakkında yorumlar yapılarak, gelecekte benzer konuda yapılabilecek olan çalışmalar için öneriler verilmiştir.

The mark presented in this thesis is the modelling of the Cylinder with two pipes, which one of them is inlet and other one is exhaust, in Marine Diesel Engines. The system researched is taken from the engine called Bergen Diesel Engine, KRG3. The classical aproach 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 marine engine makes it essential for the engineer to he able to predict the behaviour of a proposed design through the utilisation of digital computers. CAD/CAM design and manufacture investigation programs and simulation models can be of great assistance to the engine designer and also the engine manufacturer whQ intends to carry out mass production, in case nf a good representation of the engine system. It is given that the power output from an engine depends upon the amount of fuel that can be usefully burnt inside the engine cylinder. The thesis has been starting with a brief summary as an opening part and, then a research related to the theoretical methods of solution of unsteady flow in pipe systems is presented. As a result of that research, it is decided to utilise the Method of Characteristics (Mesh Method ) far calculating pressures and temperatures at the different points of inlet and exhaust pipes, assuming the flow to be one-dimensional, and the flow at the pipes boundaries to be quasi-steady. The established theory of unsteady flow together with the boundary conditions has been utilised in the development of a general computer program developed in Fortran IU for the theoretical calculations of the fluid properties in the engine inlet systems and cylinders. The developed computer pragram, MODELLING, intends to simulate a Marine Diesel Engine which draws in its fresh charge from an infinite space and exhausts into a second infinite space by means of pipes. In the program, it is modelled that the cylinder and two pipes, which one of them is inlet and the other one is exhaust, and so, the flow in the pipes is tested. In this program, Runge-Hutta Method has been chosen to study the flow in the cylinder and Mesh Method has been chosen to study the flow in the pipes. In the program, during the calculation of the main thermody namics variables in the cylinder where the increments of the crank angle must be a constant value depending on the researchers' decisions. In this thesis, the increment of the crank angle has been selected 5 crank angle and the variables at each increment are read directly from the data file in the program. The thermody namics variables in the pipes have been calculated by means of the Mesh Method, as mentioned above. But during that calculations, the crank angle increment or time step is calculated in the program (in the sub-program CHAR). The fundamental equations for one - dimensional unsteady flow mentioned before, are as follows: 1. Continuity Equation &u u dE 1 33... 3S +. ( - - - + u - - ) * D 9x E dx 3 dt 2. Momentum Equation 3u 3u 1 3P + u + + F = D 9t ex s 9x 3. Energy Equation 3P dP aQ 30 (k-D.^.Cq + uF) = ( + u ) - a2 ( ^ + u -^ - ) 3 1 öx ât 3x The basic principle underlying the nozzle boundary conditions is that while the flow in the pipe connected to the nozzle is unsteady, the flow through the nozzle itself is quasi-steady. That means, at any instant of time, the flow through the nozzle is assumed to be the same as it would be under steady flow, with the same conditions of state and velocity at inlet and exhaust from the nozzle. In other words, quasi-steady flow through a nozzle is that the wave travel time is very short compared with the wave travel time of the pipe to which it is connected. Briefly the steady flow conditions through the nozzle are set up and arranged in a suitable form for inclusion on the characteris tics. There are many engineering situations which involve gas exchange between two or more vessels. In certain cases the volumes of some of the vessels change with time, such as cylinders of a multi-cylinder internal combustion engine, also the effects Df heat transfer from the vessel walls to the fluid inside may be important. XI In the case of non-homentropik flaw in the pipes, there are three characteristics : 7\, "j2> and c*.. Them's andŞ's are disturbance characteristics, and c*'s are path lines. The path lines are also characteristics. Mesh MethDd is a pratical method of performing a numerical solution to the characteristic problems. In the Mesh Method, the working section (the pipe) is divided into a number called, "meshes points", of rectangular parts having the same dimensions and the mesh length (Ax) is chosen constant. But its value depends on the length of the pipe. It is very important to choose the value, time step. In the thesis, it described that how to calculate the time step value after the choosing of mesh points. It is also important to choose the mesh points, if a big number is chosen, this leads to get better results, but it takes much time. Because of those reasons, it is important to determine the mesh length or the number of mesh points. The suitability equation is obtained by simutaneously solving the three equations; continuity equation, momentum equation and energy equation. The equation can be shown as follows. dP - a' dt dS dt - (k-D.g kf q + u = D In the Mesh Method, firstly the suitability equation is written by using the characteristics^, Ş and ex.. It can be shown that the increment in the value of ?\, £ and o< over a time step are given by the following equations (neglecting area change and heat transfer effects). d* JH* J±_ + J±_ and 2(k-1) (A+Ş>)2 " ID ca-^) ia-£j. zf l a - a.( - )2. k-1 1 + 2 ( - ) ^rP k-1 dz dz Using theseBequations and path line calculations, the variables at all mesh points, so thermodynamic variables, have been obtained. In the thesis, the main program, MODELLING, is terminated for different data, thirteen times. After each termination, according to the program, there are three files created. The files contain the main thermodynamics values of the cylinder and pipes. The data changes are done on the diameters of the inlet and exhaust pipes and their lengths. The program reads the pipe lengths from the data file at the same value. After all program termination using the other programs, written in Basic, some graphs are obtained by means of a graphic plotter (See Appendix B). xn A listing of the main computer program in Fortran IV used is given. Meanwhile, the descriptions of the programs and its subroutines are given in the section 5. The other programs in Basic used for drawing the graphs are also given. In the section 5, some brief descriptions exist. The data list of the main program are also presented in the Appendix A. The presentation of all the theoretical results are in graphical form and given in the Appendix B. The comparisons of the graphs are presented in detail in the section 6. The detailed conclusions are made at the end of the thesis and some suggestion are added for future works. The main thermodynamic variables in the cylinder can be calculated by other numerical methods and a comparision can be made on two or more numerical methods. The main computer program presented in this thesis intends to simulate a cylinder and two pipes of a diesel engines. In other works, this program can be developed by adding some conditions such as junction subroutine for a diesel engine that has multi-cylinder and cnmlex pipe system. A comparison can be made on total central processing unit (CPU) using time. The computing time with using Runge-Kutta Method and the computing time for calculations with one of the numerical solution methods can be compared. According to the results of this thesis; 1- The crank angle increment used for the calculations of the main thermodynamic variables in the cylinder is important to obtain better results and not to waste time. For this reasons, the optimum crank angle increment should be chosen. In this thesis the 5 - increment is chosen. 2- The variables obtained by means of the computer program MODELLING and the computer (IB1* Personal- Computer AT), and. are created at the end of the third cycle. 3- When the length of the inlet and exhaust pipes and especially the diameter of the inlet -pipe increased, the pressure value in the cylinder would also increase. k- When the length of the inlet and exhaust pipes and especially the diameter of the inlet pipe decreased, the total mass in the cylinder would increase.. 5- In the current environment conditions used in the computer program, MODELLING, it would be able to observe the back flow in the pipes from the graphical results. 6- During the increasing of the diameter of the inlet pipe, the maximum work value in the cylinder would increase but also the minimum work value in the cylinder would decreased. xm All the results presented in this thesis are theoretical. In the üther work (that can be done), an engine can be tested and the experimental results can be obtained from the test. So, a certain comment can be made comparing with the theoretical reaultsi and the experimental results.