Analysis of Common Faults of Volvo Diesel Generator Sets Pistons

The piston is an indispensable part of the Volvo diesel generator set. The reciprocating motion in the cylinder transmits the force and completes the working cycle of the diesel engine; the piston, the cylinder head and the cylinder together form the combustion chamber, and the piston group acts as a seal to prevent the gas from penetrating into the crankcase, but also restricts the oil entering the combustion chamber. This paper studies and analyzes the common failures of pistons in diesel engines to make the pistons operate reasonably, efficiently and reliably.

1. Piston skirt wear

When the piston is working normally, its skirt and the piston pin seat hole form a vertical working surface. Due to the action of side pressure, it directly rubs with the cylinder wall, and the surface produces regular filamentous wear marks. In general, this wear does not affect the normal fit of the piston to the cylinder wall. When the piston is working, because it is equipped with a piston ring, its head is rarely in contact with the cylinder wall (the diameter of the head is generally smaller than that of the lower part, the difference is about 0.6-0.9mm), and the top is easy to expand because it is heated and the metal is also thicker. Although the skirt is in contact with the cylinder wall, its unit pressure is not large, and the lubrication conditions are good, so the wear is also small. Due to the side pressure generated when the piston and connecting rod are running at high speed, the piston will form radial wear. Therefore, the measure of the availability of the piston depends on the degree of increased clearance between the piston and the cylinder wall. As a result of the increase in the gap between the piston and the cylinder wall, the metal knocking sound (commonly known as the knocking of the cylinder) aggravates the wear of the piston and the cylinder wall, air leakage, poor start-up, unstable speed, decreased power, increased oil consumption, and exhaust gas blue smoke.

2. Piston ring groove wear

The piston ring of the Volvo diesel generator set moves in the ring groove, so that the piston ring groove is subject to maximum wear in the height direction, making it step-shaped or trapezoidal (large outside and small inside). The influence of the unit pressure and high temperature of the piston ring on the groove wall is the main cause of wear, and the wear speed of the ring groove depends to a large extent on the roughness of the piston ring plane and the structure of the piston. The side clearance and backlash of the piston ring increase, the oil channeling (fuel leaks into the oil basin), the pumping action increases (the oil participates in the combustion, and the exhaust emits blue smoke), the oil consumption increases, and the power and economy decrease.

3. Piston pin seat hole wear

The wear of the piston pin seat hole of Volvo diesel generator set is generally smaller than that of the piston ring groove, and the wear speed depends on the roughness of the piston pin seat hole and the fit of the piston pin and the pin seat hole. Due to the action of gas pressure and inertial force, the wear of the piston pin seat hole is not round, and the largest wear occurs in the direction perpendicular to the piston top (upper and lower of the piston pin seat hole). The fit of the pin hole is loose; the pin rattles; the pin jumps out and breaks the cylinder. In addition, the piston will also produce peripheral wall cracks and scratches and other faults. If the above damage is found, it cannot be used.

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