Diesel generator gas distribution mechanism and intake and exhaust system - diesel engine maintenance training diesel engine...

Diesel generator valve distribution system and intake and exhaust system - diesel generator maintenance training diesel engine -p32-p34 Section 3 gas distribution mechanism and intake and exhaust system

The diesel generator valve train is the control mechanism for the intake and exhaust of the diesel engine. It controls the opening and closing of the intake and exhaust valves in accordance with the working order of each cylinder of the diesel engine to ensure that enough fresh air enters the cylinder within the specified time, and exhausts the burned exhaust gas from the cylinder as thoroughly as possible. discharge.

The lubrication conditions of the moving parts of the diesel generator valve mechanism are poor, and parts wear is easily caused during use. When the wear is exacerbated, the working conditions of the gas distribution mechanism are changed, resulting in a decrease in the power of the diesel engine, an increase in fuel consumption, and other malfunctions. The purpose of repairing the gas distribution mechanism is to restore the original mechanical properties of the parts of the gas distribution mechanism, ensure that the valve is opened and closed on time, and the operation is stable and free of noise. The diesel engine has high-power output and normal operation with low fuel consumption.

At present, the most commonly used four-stroke engine is the valve-type valve mechanism. Valve-type valve mechanism is divided into side-mounted and top-mounted two types. The intake valve and exhaust valve of the side-mounted valve train are located on the same side of the cylinder block. The camshaft is used to push the tappet and the push rod to control the opening and closing of the valve. Side-mounted valve trains are generally suitable for single-cylinder gasoline engines. The overhead valve mechanism is most widely used in diesel engines. It is mainly composed of valve components, valve transmission components, intake and exhaust systems, and booster systems.

Valve assembly

The diesel generator valve assembly is mainly used to seal the intake and exhaust passages of the diesel engine and ensure the normal air exchange of the machine. Its main components include valves, valve springs, valve guides, valve seats, and locking devices. The lubricating and cooling conditions of the valve assembly in the entire diesel engine are extremely poor, and are affected by the impact of alternating cutting and high temperature, corrosion, etc., so this part is prone to failure. After the valve assembly is damaged, many fault phenomena occur in the diesel engine, such as increased fuel consumption, reduced power, difficulty in starting, and abnormal smoke exhaust.

(1) Valve

Diesel generator valves are divided into intake valves and exhaust valves. The physical shape of the valves is shown in Figure 2-32 and Figure 2-33. The cylinders of the diesel engine are properly ventilated.

The temperature of the intake and exhaust valves is quite different. When the diesel engine is operating at full load, the intake valve temperature is generally around 350°C and the exhaust valve temperature is up to 800°C. The materials they choose are different when they are manufactured. The intake valve section is made of chrome alloy steel. The exhaust valve is generally made of yttrium-chromium alloy steel with high temperature resistance and strong corrosion resistance. In order to increase the amount of intake air in the combustion chamber, the head of the intake valve is made larger than the exhaust valve. The taper angle of the sealing cone is also different. The angle of the exhaust valve is generally 45. The bevel. Due to the poor lubrication and cooling conditions of the valve, combined with the continuous impact of long-term exposure to alternating loads, the valve is more likely to fail.

Faults that are prone to valve failure include severe wear, burnout, and breakage. The most vulnerable part of the valve is the valve cone. The causes of wear and tear are caused by the long-term continuous impact of the alternating load on the valve and the excessive carbon deposition caused by diesel incomplete combustion in the combustion chamber. Valve burnout generally occurs in the exhaust valve. When the high-temperature exhaust gas in the combustion chamber is pulled out from the conical surface of the exhaust valve, it is easy to cause a burnout failure at the valve head. Valve breakage is generally caused by stuck valves or incorrectly installed valves (forged springs that have been forgotten for assembly, or poor spring-loaded enclosures, and incorrectly installed valve-locking clamps).

The following methods can be used to check diesel generator valve failures:

1 experience method. To determine whether the valve is faulty requires three conditions: the diesel engine is unstable during operation: the exhaust pipe has a sudden, sudden sound; the exhaust smoke is abnormal (smoke or blue marriage). When the diesel engine has these three conditions, a single-cylinder breaking method is used to determine the failed cylinder. The method is: disconnect the high-pressure tubing of each cylinder, observe the change of the working state of each cylinder before and after the disconnection of the high-pressure tubing. If the high-pressure tubing of a cylinder is disconnected, the black martial phenomenon disappears or weakens, indicating that the cylinder has malfunction. If the high-pressure fuel line of a cylinder is disconnected, the black smoke or blue smoke does not disappear, indicating that the cylinder has not failed. If no faulty cylinders are found after disconnecting the high-pressure oil pump tubings, the common faults that are prone to occur in the diesel engine should be analyzed.

2 instrument measurement. The diesel engine generally uses a threaded port type cylinder pressure gauge. When it is used, screw the cylinder pressure gauge thread into the injector seat hole (as shown in Figure 2-34), then use the starter to drive the crankshaft to rotate 4-6s. The engine speed is maintained at around 300r/mh. The pressure value indicated by the cylinder pressure gauge at this time is the compression force of the cylinder under test. Write down the measured value, then add a small amount of oil to the cylinder and turn the diesel engine. If the measured pressure value is significantly different from the normal value, it indicates that the valve in the cylinder under test is faulty.

3 Use observation method and experience method to judge whether valve breakage occurred. After removing the valve chamber cover, check it or use a flat-blade screwdriver to pull the diesel flywheel, as shown in Figure 2-35. If there is stuck phenomenon or the flywheel cannot be toggled, the meaning is that if the valve falls into the cylinder, the positioning key between the A-axis of the high-pressure oil pump assembly and the speed-adjusting gear is damaged, or the internal gear of the front gear box is engaged.

The diesel generator set valve is a wearing part. When the valve is severely burned or broken, it is generally necessary to replace the new model. If there is too little carbon deposit, pitting, or rust on the cone surface, use a valve grinder or hand grinding to achieve the effect of valve seal combustion chamber.

The method of manually grinding the valve is shown in Figure 2-36. When manual grinding, the method of valve reciprocating the manual grinding valve on the valve seat is shown in Figure 2-36. When grinding manually, the valve should rotate back and forth on the valve seat and change its position frequently. The position should not be changed 15 times each time. , so as not to wear ring marks. During the first pass of grinding, apply a thicker grindstone on the valve cone surface. When a scratch-free contact zone is worn between the valve cone and the valve seat, remove the coarse grout and replace it with a thread. Abrasive mortar continues to grind. Until the grey matt ring appears between the valve cone and the valve seat, the diesel oil is applied to remove the sand paste attached to the valve cone and the seat, and the seal is checked until the requirement is met.

(2) Valve guide

The physical appearance of the diesel generator valve guide is shown in Figure 2-37. The valve guide serves Guimeng’s valves and ensures that the head of the valve hardly falls on the seat of the valve, and it also transmits part of the heat of the valve. Valve guides are generally cast from cast iron. Because they work under conditions of high temperature and poor lubrication conditions, the parts are prone to wear.

To be continued...