MECHANICAL FACULTY Eng. Adrian-Ioan Botean PhD THESIS abstract Research regarding mechanical and thermal loads in SI engine cylinder head Scientific advisor, Prof.dr.ing. Mihail HĂRDĂU Evaluation board: PRESIDENT: MEMBERS: - Prof.dr.ing. Liviu Vaida - prodean, Mechanical Faculty Technical University of Cluj-Napoca; -Prof.dr.ing. Mihail Hărdău scientific advisor, Technical University of Cluj-Napoca; -Prof.dr.ing. Ioan Curtu - reader, Transilvania University of Brasov ; -Prof.dr.ing. Dan Mihai Constantinescu - reader, Politechnic University of Bucuresti; - Prof.dr.ing. Nicolae Burnete - reader, Technical University of Cluj-Napoca. 17 November 2009
1.1 The purpose of the work The main purpose of the PhD topic is to establish the stresses and deformations state of the cylinder head from a spark ignition engine. The study is focused on the bridge area between the valves; area which is powerful stressed both from mechanical and thermal loadings. 1.2 Justifying the topic The theme is justified by the following considerations: - The absence of certain data referring to the stress and deformation states (mechanical and thermal stresses) of the bridge area between the inlet and exhaust valves from the spark ignition engines. - The great variety of factors that influence the behavior, put under charge, of the bridge area between the valves. - In the case of internal combustion engine appear both mechanical and thermal loadings (is a very important factor that limits the power developed by the engines with internal combustion). - As a result of the research analysis upon mechanical and thermal loadings of the internal combustion engines cylinder head, it can be concluded that the number of published studies is quite low and it does not contain results which to reflect complete information about the stress and deformation states, although researches involving mechanical, thermal and thermo mechanical requests studies are being made of a long time. - In order to improve the heat transfer to reduce the thermal stress of the combustion chamber and bridge area, there can be found a particularization of engine types, for numerical and experimental studies. - Most of the studies concerning this field refer to a particular type of engine, being few cases in which established relations in order to estimate the sizes characterizing thermal condition, have a larger field of activity. - The correlation of thermal stress regarding engine s parts cracking is little mentioned in specialized literature. 1.3 Content 1 st Chapter Introduction presents in a brief description the content of each chapter of the work. It is presented the theme of each chapter, the
way of solving the problems as well as observations and conclusions resulting from these studies. 2 nd Chapter entitled Considerations on the combustion engines cylinder head it is described the functioning role of the cylinder head (2.1. Functional conditions), the construction of the cylinder head individualized depending on the way of cooling the engine (2.2.1 The construction of cylinder head for engines cooled with air and 2.2.2 The construction of cylinder head for engines cooled with liquid). In these two subchapters there are mentioned the particularities of the combustion chambers, of the gas distribution channels, the way in which the inletting and exhaustion vales are placed, the placement of the fixing screws, the particularities of the cooling circuit, the constructive parameters especially regarding the thickness of the walls, the particularities of the seat valves, of the valve guide. A special attention is given to characteristics of the materials from which the cylinder head is made, to semiproducts used in the process of casting the cylinder head, all this being presented in a succession of images, the casting and the debate of the piece. Subchapter 2.3 contains a brief presentation of loading types the cylinder head has to face while functioning: mechanical and thermal loadings. As a consequence of these loadings there may appear cracks, especially in the bridge area between the valves. Repairing methods will be needed in those situations (subchapter 2.4. Repair of the cylinder head). Mainly, in case of a crack in the bridge area between the valves, the cylinder head can be repaired either through welding in Argon protected environment (MIG Metal Inert Gas) or through adding material in the crack area using a bolt, method illustrated in figure 2.26.a-y. Subchapter 2.5 presents a series of conclusions and observations referring to the functioning and the construction characteristics of the cylinder head but also the main study directions: analytical, numerical and experimental. 2 nd Chapter ends with a bibliographical list containing 35 studied works. 3 rd Chapter entitled Mechanical Loadings Study, treats the mechanical loadings to which the cylinder head is subjected while functioning. The study focuses on the mechanical loadings due to gas pressure inside the combustion chamber. In the first part 3.1 General considerations there is a brief presentation on the modes of operation of the engines with internal combustion (stabilized, non- stabilized, transitional). It also emphasizes the importance of knowing
the indicated diagram which represents a very good indicator of the loading level from a mechanical point of view. The mechanical loading study is based on the fact that the combustion chamber area represents a circular or rectangular plate loaded with pressure (pressure given through the burning of the fuel in the combustion chamber) in a transversal plane. (3.2.1. Approximate calculation model). The study was made both analytical and numerical, by using the finite element method. With the help of the simplified model it was established that the mechanical loadings of the fixing studs contraction and of the pressure from the combustion chamber, are negligible but the influence of the inlet and exhaust galleries, of the spark hole, must be taken into consideration. It must not be neglected the fact that the transversal section of the cylinder cover is not constant but variable because of the cooling circuit, of the inlet and exhaust galleries, of the combustion chamber etc. Subchapter 3.2.3 studies four configurations of the circular plate being used different methods of research: numerical and experimental analysis (digital image correlation method). The real model analysis appears in subchapter 3.3, where, according to different functioning phases of an functioning cycle (inletting, compression, combustion and exhaustion), the stress and deformation state from the bridge area between the valves is marked out. 3 rd Chapter ends with a bibliographical list containing 58 studied works. 4 rd Chapter studies the thermal loadings on the bridge area between the valves. There are presented: fundamental equations of thermo-elasticity for the general but also plain state of the stresses and deformations (subchapter 4.2 and 4.3), it is described the device and the formation conditions of thermal loadings (subchapter 4.3) but also the exploitation (functioning) defects of the cylinder head of the engines with spark ignition. Subchapter 4.5 contains the analytical model of calculating the thermal stresses of the bridge between two wholes with equal diameter of a circular plate, model made by C.A.M. van de Linden and overtaken by Irmler Ch. Numerical it is validated the analytical model and experimental are studied the 4 th configurations of the studied at the 3th chapter. The analysis of the real model (subchapter 4.6) can be made if it is well known: the manner of heat transfer towards the combustion chamber walls (subchapter 4.6.1), the heat transfer in the combustion chamber walls (subchapter 4.6.2), the heat transfer from the combustion chamber walls towards the cooling liquid (subchapter 4.6.3). The factors that influence the heat transfer must also be known: the functional factors, the constructive
factors and the influence of coal and salt deposits, the influence of the cooling regime, the influence of the excess air coefficient. The cylinder head is studied from a thermal loading point of view (4.6.6), appealing to the finite element method. 4 rd Chapter ends with a bibliographical list containing 89 studied works. 5 th Chapter Thermo mechanical loadings contains the superimposed effects of both mechanical and thermal loadings upon the cylinder head of 1.6 l Dacia engine. 5 th Chapter ends with a bibliographical list containing 4studied works. 6 th Chapter, entitled General conclusions and personal contributions, submits the main conclusions, as a result of analysis of stress and deformation states of the cylinder head of a spark ignition engine, mechanical (by the combustion chamber pressure) and thermal loaded (burning of the mixed fuel from the combustion chamber). It also presents the author s personal contributions at this study and not least the research directions which will be made in perspective. In the final part of the work it can be found a large bibliographical list, containing all studied works (219) from all chapters. The work contains a series of appendix describing: technical characteristics of 1.6 l Dacia engine (appendix 1), the determination of the elasticity modulus for aluminum alloy from which the plates studied in chapter 3 and 4 (appendix 2) are made, the method of digital correlation of the image (appendix 3), Spider 8 and CatmanEasy data acquisition system configuration (appendix 4), 1,6 l Dacia engine testing stand (appendix 5). The authors CV, the list of published works and also 3 representative works published at several scientific manifestations can also be found at the end of the work.