Fault Tree Analysis Method for Lubricating Oil Emulsification of Marine Air Compressor

The marine air compressor is mainly used for starting and controlling the main and auxiliary engines of the ship, and also for other auxiliary mechanical equipment (such as pressure water tank, whistle, etc.) that need compressed air. It is one of the important auxiliary equipments of the ship. A ship uses the WP270 air compressor as a single-acting two-stage compression air compressor. The differential piston can be used to compress the atmosphere to a maximum exhaust pressure of 3. OMPa. The air filtered by the wet muffler filter is combined by a class I. The suction part of the valve is sucked into the Class I cylinder, compressed to a certain pressure, discharged from the discharge part of the I-stage combination valve, enters the cylinder head cooled by water, and then cooled by a cooling tube with a spiral piece and flows into the crankcase. Within the buffer volume. The condensate accumulation generated after cooling is also in the separator as the penetrating window cover, and the air is passed through the air passage port through the stage cylinder, compressed to the exhaust pressure, discharged from the discharge portion of the stage combination valve, and cast in the cylinder. The air passage enters the suspended stage cooler for cooling, then cools and then gas-liquid separation, and finally the clean compressed air is sent to the cylinder (as shown).

The working principle of WP270 air compressor is found to be abnormal during the voyage of the air compressor. The specific phenomenon is: when the lubricant is drained to the test bottle, 300ml, the color of the oil is changed from the original brownish yellow. The turbid milk (white) yellow, after 2 hours of precipitation, found a weak oil boundary layer.

The good state of the oil is the key to the normal operation of the air compressor. The key reason for the emulsification is that excessive oil is mixed into the oil, and the water does not evaporate. After discovering the emulsification phenomenon of the lubricating oil, the maintenance personnel quickly disassembled the cooling water system, the breathing system, the sealed space and other parts of the No. 2 air compressor, and found that the equipment was operating normally. According to the data, it is judged that the sea air is humid and the temperature is high. After entering the air compressor screen, the water can not be filtered, enter the compression space, and dissolve into the lubricating oil of the air compressor; in addition, the compressed high temperature gas is After cooling, condensed water is formed, and part of the condensed water is dissolved in the lubricating oil. In order to ensure the smooth sailing of the ship, a replacement of the oil was adopted, and a plan for releasing the condensate once a week was made.

Air compressor oil emulsification refers to the emulsification phenomenon of the air compressor lubricating oil after a period of use, which affects the normal operation of the air compressor. In order to highlight the key points of fault analysis, the air compressor oil emulsification is mainly due to the oil entering. Water and other factors. When the air compressor oil emulsification failure occurs, it will affect the normal operation of the air compressor, resulting in economic decline, and serious air compressor damage. According to the work experience, the author summarizes and establishes the air compressor oil emulsion fault tree (for example). The fault tree is described as follows: Gonggong a air compressor oil is the key condition for the air compressor to work normally. If the oil is used before the quality If it is poor, it will directly lead to the phenomenon of oil emulsification.

The root cause of oil emulsification is that the gas in the cylinder contains moisture, and the water is mixed into the oil molecules under the action of the high-speed rotating crankshaft, resulting in excessive moisture content of the oil.

The humidity in the environment is too large, which means that the air content of the air compressor is large, due to natural or man-made reasons. The environment has an impact on any event in it, especially for oil parameters.

3.2.2 Compression mechanism The poor compression mechanism consists of piston, cylinder, combination valve, etc. The piston inhales or compresses air when reciprocating in the cylinder. When the compression mechanism is poorly sealed, the compression gas is lost on the other hand. Cause some water vapor to dissolve into the oil.

1 piston ring damage air compressor piston has a total of 7 piston rings, the main function is oil lubrication, sealing, when the air intake is not clean or the cylinder temperature is too high, the quality of the oil is poor, the thermal expansion gap at the opening is small, etc. When the piston ring is damaged, high-pressure compressed air with a high water vapor content is leaked into the oil in the oil sump.

1.1 The scraper ring damages the scraper ring to play the role of oil and oil lubrication. If the scraper ring is damaged, the cylinder liner will be poorly lubricated, which will cause the cylinder liner and compression ring to damage the ring, resulting in high high pressure compressed air leakage. In the oil in the oil pan.

1.2 Compression ring damage The compression ring acts to seal the high pressure gas. If the compression ring is damaged, the cylinder liner will be poorly sealed, resulting in high high pressure compressed air leaking into the oil in the oil sump.

2 Cylinder liner wear is serious. The cylinder liner is a relatively easy to damage component in the compression mechanism. It wears a lot on the technical information perpendicular to the axial direction of the air compressor. When the wear is large, high pressure compressed air will leak into the oil sump. In the oil.

It is normal to mix some water into the oil when the air compressor is working. If the air compressor works for a long time, the temperature inside the cylinder rises, the crankshaft continuously splashes the oil, the temperature of the oil rises, and the water evaporates into a gas, passing through the breathing port ( The internal venting hole is drained out, and the oil will not be emulsified when the air compressor is working. However, if the breathing port is blocked, the excess water mixed in the lubricating oil will not evaporate, and emulsification will occur at this time.

The gas in the cylinder contains moisture, and the moisture is mixed into the oil molecules under the action of the high-speed rotating crankshaft, thereby causing the water content of the oil to be too high. If the air compressor is working for a long time, the temperature inside the cylinder rises, the crankshaft continuously splashes the oil, the temperature of the oil rises, the water evaporates into a gas, and is discharged through the internal vent hole, and the oil does not appear to be emulsified during the operation of the air compressor. When the oil breathing port is blocked, the water vapor can not be excreted in time, and finally dissolved into the lubricating oil and emulsified.

There is always some moisture in the working environment. When the air humidity is high and the inlet filter has no drying function, the air with a large moisture content enters the working area, which will cause some water to mix into the oil, which will cause the oil to emulsifie.

The first-stage solenoid valve is connected to the oil-water separator to play the role of condensing and condensing water and discharging impurities. When the first-stage solenoid valve cannot be opened in time, the condensate cannot be discharged in time, and the high-pressure air contains excessive water. In the case of high temperature, it is converted into water vapor, flows into the secondary compression mechanism, and partially leaks into the oil sump, causing the oil to emulsifie.

3.2.4 Cooling fresh water system leakage failure The cooling system is composed of the water heaters of the 1st and 11th class coolers, cylinders and cylinder heads. The cooling water is used in the system to remove the heat generated by the compressed air and the friction part by the flow of water. If the cooling water system leaks, it will directly cause the cooling water to flow into the lubricating oil, which will cause the oil to emulsify, and the cooling water contains about 5% of the content of nitrite, which will cause serious corrosion to the body.

When there is a crack in the cylinder, the cooling water leaks when the cooling water passes, and enters the compression mechanism, the oil pan and the like, and the oil emulsification occurs when the cooling water enters the lubricating oil.

When there is a crack in the cylinder head, when the cooling water passes, the cooling water leaks and enters into the compression mechanism, the oil pan and the like, and the oil emulsification occurs when the cooling water enters the lubricating oil.

3.2.4.3 Leakage of the cylinder head waterway connection Leakage of the cylinder head waterway connection will also cause some water to directly enter the compression mechanism, some of which directly leak to the oil sump through the piston ring, and the other part is circulated in the form of water vapor. Oil sump.

When the primary cooler leaks, the cooling water directly enters the cooling chamber, and passes through the primary exhaust valve in the high-pressure air pipeline, flowing into the oil-water separator, the secondary compression space, and leaking into the lubricating oil, causing the oil to emulsifie. .

3.2.4.4.1 Sealing at the waterway joint is not good. When the water joint is poorly sealed, some cooling water will enter the cooling chamber, and finally enter the oil sump to cause oil emulsification.

3.2.4.4.2 Cracks in the cooling water pipe When the cooling water pipe in the cylinder breaks, the cooling water enters the cooling cavity and finally enters the oil pan to cause the oil to emulsifie.

When the oil reaches its service life, some components in the oil deteriorate, which in turn catalyzes the emulsification of the oil.

The air compressor is the key equipment for providing high-pressure air to all systems of the ship. Its working status is directly related to whether the ship can sail safely. The staff should use the air compressor correctly according to the requirements and maintain the air compressor. The oil emulsification phenomenon should be solved correctly in time.

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