The mechanical load of the main parts of Marine diesel engine parts

The mechanical load of the main parts comes from the gas force in the working cycle, the motion inertia force of the parts and the pretension force generated by the joints of the parts.

1. Gas force

In the working cycle, the total gas pressure Fg on the top surface of the piston (or the bottom of the cylinder head) is equal to the product of the gas pressure pg and the piston area F. The maximum value of Pg is called the maximum burst pressure Pmax.

Gas pressure Pg and total gas pressure Fg change periodically in the working cycle, and the frequency of change is proportional to the speed. The maximum value is when the highest explosion pressure Pmax occurs.

The cyclic change of air force will produce pulsating stress on the mechanical parts, which will cause the vibration of the diesel engine to appear as high frequency stress during the transmission process, and will make its material fatigue. The fatigue damage degree of diesel engine parts is proportional to the speed n, the maximum (burst) pressure value Pmax and the combustion pressure rise rate. The maximum (burst) pressure Pmax is usually used as the main indicator of the loading of diesel engines.

2. Motion inertia force

The piston assembly and the small end of the connecting rod will produce reciprocating inertia force when the variable speed reciprocating movement. When the big end of the connecting rod and the shank pin and shank turn around the center of the crankshaft, the centrifugal inertia force is generated. The two kinematic inertia forces increase with the square increase of the movement mass and speed. They also change periodically, which can also cause fatigue, and the unbalanced inertia force and moment of motion can also cause vibration of the machine.

3, the connection fastening pre-tightening force

The stress caused by the pretension force exerted by the connecting fasteners on the connected parts is called the installation stress. It is generally shown as static stress. Various mechanical loads cause deformation or even destruction of the parts, so it has a decisive impact on the performance and life of the diesel engine, and should be limited in management and maintenance.