Study of failures of reciprocating medium-speed diesel engines

Abstract

The article is focused upon the problems of reciprocating diesel engines. The main reason for the failure of cylinder-piston group (CPG) parts is insufficient strength, wear resistance, and resistance of the metal structure to vibration. There are studied the following periods of engine operation: running-in period; period of normal operation; period of intensive wear. In the burn-in period, the main cause of CPG failures is scuffing, when finger breaking or ring groove chipping take place. Sudden failures during normal operation occur due to the wear of the bushings to the limit size. In the third period of intensive wear the main cause of metal failures is the ultimate wear by cavitation erosion and breakage of the bushing collar. The block diagram of the CPG system with serial connection of elements is given. The rate of CPG failures is illustrated depending on the time of operation. It has been found that the failure rate during the running-in period due to scuffing is reduced because of stabilization of the structure, dimensions and mechanical properties of the piston at operating temperatures (300–350°C). The failure rate of the normal period of operation depends on the increase in the abrasive wear resistance of the metal of bushings, increased hardness, due to the replacement of gray cast iron with lamellar graphite by gray cast iron with vermicular graphite or by high-strength cast iron with spherical graphite inclusions. There are listed the positive and negative qualities of aluminum alloys in comparison with cast iron. Variants of damage to cylinder liners are considered in detail. The most dangerous defect in the bushing is the cracks in the upper liner collar, as a result of which about 40% of the cylinder bushings must be replaced. The formulas for calculating the actual wear rate of the CPG parts during the first (end of warranty periods), medium and major overhauls are given. The failure rate of the last period of operation (intensive wear) is reduced by reducing vibration in the CPG system, reducing the amplitude of forced vibrations and reducing the size of the thermal gap between the sleeve and the piston, increasing the rigidity of the sleeve. The rate of cavitation wear of modernized and conventional bushings is determined, the influence of the bushing stiffness on cracks under the shoulder and on cavitation wear up to the maximum permissible thickness is considered.