Abstract
In the cylinder cover of medium speed diesel engine, cracking often occurs between two adjacent valve ports on its fire side, and the major cause is considered to be thermal fatigue.
So the more exact estimation of thermal stress value is desired to establish the strength design method of the cylinder cover.
However, due to its complexity in construction, stress analysis examples are few.
In order to clarify the thermal stresses working on its fire side, a 4-valve double bottomed cylinder cover was subjected to two- and three-dimensional F.E.M stress analyses.
Through the investigations, the followings were clarified.
(i) By introducing the two-dimendisnal approximated model of the cylinder cover, the influences of the vertical wall, the middle wall and the outer side wall for the stresses working on the fire side of the cylinder cover and those of the positions of valve ports, are qualitatively calculated.
(ii) The largest thermal stress appears in the bridge area between the exhaust valve ports. This matter well explains the phenomena of cracking of the cylinder cover.
(iii) By taking consideration of restriction of the outer side wall, the thermal stress of the cylinder cover can be estimated through a simple equation using the arithmetic mean of the combustion surface TM and the correction factor K.
(iv) The propriety of the calculated thermal stress values were confirmed by the measurement of residual stresses on the fire side of the cylinder cover.
