Research On Low-speed Marine Diesel Engine Crankshaft Strength

Diesel engine crankshaft, one of the most important and expensive parts and also hosting the most complicated boundary conditions, plays a significant role in translating the linear reciprocating motion of the piston group into rotary motion by the crank-connecting rod mechanism to make the diesel engine work normally. Gas pressure, inertia force, vibration,corrosion and many other factors make the crankshaft working conditions bad. In particular,the development of modern diesel engine design has more rigorous requirements on power density of diesel engine, which makes the crankshaft working conditions worse. It is proved that the diesel engine reliability and the life period largely depends on the strength and stiffness of the crankshaft. During the design phase, therefore, it is wise to put appropriate methods into accurate crankshaft strength analysis.Based on extensive research on related literature, the paper analyzes and compares various currently methods on crankshaft strength. In view of the enterprise product development requirements and work conditions, it gives priority to the finite element analysis software ANSYS, supplemented by 3-D model software Pro/Engineering, to carry out the research work. The paper calculates the crankshaft journal fillet safety factor according to the diesel engine crankshaft strength calculation specification recommended by International Association of Classification Societies, generates the 3D solid model by using Pro / Engineer in strict accordance with the 2-D crankshaft engineering drawings, then, imports the 3D entity model into ANSYS through the special connectivity module between ANSYS and Pro /Engineer,conducts static stress and a work cycle period of transient finite element analysis respectively, analyzes the influence of the crank arm structure and thickness?the main journal fillet radius?the crank pin fillet shape on the crankshaft stress distribution,and edits MATLAB procedure on the basis of cylinder pressure curves, in order to make the crank-connecting rod mechanism analysis accurate.The results calculated by the International Association of Classification Societies specification are 1.8906 and 1.3564 of the crank pin fillet and crank main journal fillet respectively. According to the static stress and transient stress finite element analysis, the paper gets the low-speed super-long stroke marine diesel engine crankshaft stress distribution when the crankshaft is at top dead center and other given time separately; according to the above finite element results, it calculates the crankshaft fatigue safety factor, 2.3111 and 2.2004 respectively. The results of the above three methods are meet the International Association of Classification Societies specification, i.e., the crankshaft strength and stiffness are sufficient. After comparing and analyzing the results, it shows that charpy type results are conservation caused by the simplify of the calculation process, while the finite element method (FEM) results are close to the experimental value because the FEM model and constraints are more in line with the real conditions. The above crankshaft strength analysis methods can provide guidance during the design phase. It is of great significance in marine diesel engine structure and performance optimization by offering a theoretical basis for further optimization design.