Question # 79

What is the value of the maximum load that a diesel engine cylinder Cover and piston are subjected to? Give an example of the magnitude of this load in a slow-speed two-stroke diesel engine. Show how these loads are transmitted through the engine str

What is the value of the maximum load that a diesel engine cylinder Cover and piston are subjected to? Give an example of the magnitude of this load in a slow-speed two-stroke diesel engine. Show how these loads are transmitted through the engine structure.

By: Dimitros
on Oct. 1, 2016, 6:54 a.m.

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Answer(s):

The value of the maximum load on a cylinder cover and piston will be approximately the same, and will be the product of the area of the piston and the maximum gas pressure. In the case of the cover area it will be the projected area of the cylinder cover measured to the outer edge of the joint spigot. Ill some engines this may be considerably more than the piston area.
Example
Cylinder diameter = 980mm Maximum pressure = 78.5 bars (80 kg/cm2)
Maximum load * 0.7854 x 982 x 80/1000 tonnes = 600 tonnes approx
The load on the cylinder cover is transmitted into the cylinder beam through the cover studs. The load on the cylinder beam is passed down to the bedplate through the tie-bolts and transverses supporting the crankshaft main bearings. The upward direction of the forces on the cylinder cover is balanced by the downward forces on the piston, which are transmitted through the piston-rod, crosshead block, bearings, connecting-rod, crankshaft and crankshaft main bearings.
The system of parts may be likened to a square flat plate tied to a square frame below it by four long tie-bolts at the corners. If a round shaft is placed across the frame, bearing on the two sides, and a jack is inserted between the shaft and the plate, and loaded, we may say that the system of engine parts is
simulated. The load on the jack, which is simulating the firing load on the piston and transmission of the load to the shaft, produces tension in the tie- bolts, a bending moment on the shaft and a bending moment on the two sides of the frame supporting the shaft. The fiat plate at the top will also be subjected to a bending moment. The actual parts of an engine will be subjected to the same loads as the simulation rig. The engine tie-rods will be in tension and the trans- verses supporting the main bearings will be subjected to a bending moment. The cylinder beam will also be subjected to bending moments.
Note The gas load coming on to the cylinder cover studs will be calculated on the area to the outer edge of the spigot. The tension on the tie-bolts from gas load will be calculated on the area of the piston.
The stresses coming about from the bending moment on the shaft in the simulated rig will be additive to the other stresses set up during engine operation.
By: Dimitros
on Oct. 1, 2016, 6:54 a.m.

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