Introduction of Cylinder Head

The role of the cylinder head is to seal the cylinder, and the piston together to form the combustion space, and withstand the high temperature and high-pressure gas. The cylinder head with gas force and fastening cylinder bolt is caused by the mechanical load, but also due to contact with high-temperature gas and bearing a high thermal load. In order to ensure a good seal of the cylinder, the cylinder head can neither be damaged nor deformed. For this reason, the cylinder head should have sufficient strength and rigidity.

Working Conditions

The role of the cylinder head is to seal the gas, form the combustion space together with the piston, and withstand high temperature and pressure gas. The cylinder head works as follows
The cylinder head is subjected to high temperature and high-pressure gas, bearing a large bolt preload force, resulting in large mechanical stress.
The cylinder head structure is complex, and the temperature field is seriously uneven, resulting in thermal stress, serious will cause cracks and overall deformation of the cylinder head

So the cylinder head design requirements are

Have enough rigidity and strength, and work deformation is small, to ensure sealing.
Reasonable arrangement of the combustion chamber, valve, and airway, to ensure the working performance of the engine.
Good workmanship, temperature field as uniform as possible, reduce thermal stress, avoid the thermal cracking phenomenon.

Cylinder Head Material

Cylinder heads are generally made of high-quality gray cast iron or alloy cast iron casting, gasoline engines for cars are mostly aluminum alloy cylinder heads. Aluminum alloy thermal conductivity is good, to improve the engine compression ratio. Second, casting performance is suitable for casting complex structures of the parts. But must pay attention to the aluminum alloy cylinder head cooling, and control the temperature of the bottom plane at 300 ℃ or less. Otherwise, the bottom plane overheating will produce plastic deformation and warpage.

Cylinder Head Structure

The cylinder head is a box-shaped part with a complex structure. It is machined with an intake and exhaust valve seat hole, valve guide hole, spark plug installation hole (gasoline engine), or fuel injector installation hole. The cylinder head is also cast in the water jacket, intake and exhaust channels, and combustion chamber or part of the combustion chamber. If the camshaft is installed in the cylinder head, the cylinder head is also machined with cam bearing holes or cam bearing seat and its lubrication channel.

There are many cylinder head types, water-cooled engine cylinder head has a whole, block type, and monoblock type three structural forms. In the multi-cylinder engine, all cylinders share a cylinder head, the cylinder head for the overall cylinder head; if every two cylinders is a cover or three cylinders a cover, the cylinder head for the block type cylinder head; if each cylinder is a cover, then the monoblock type cylinder head. Air-cooled engines are monoblock cylinder heads.

Cylinder Cracking

Winter temperature is low, the diesel engine cylinder head is prone to cracks and leaks. The main reasons for this are the following.

1, after the start, add cooling water. After the diesel engine starts, the temperature inside the engine rises immediately, if the cooling water is added at this time, the cylinder block and cylinder head cool sharply, and it will be cracked due to cold shrinkage.

2、After shutdown, no cooling water is put in. The water inside the machine freezes into ice, the volume increases, and cylinder block and cylinder head cracking occurs.

3, diesel engine running, cooling water is not enough, or the water tank open pot machine temperature is too high, suddenly add cooling water. Cylinder block and cylinder head overcooling shrinkage will also cause cracking.

4, diesel engine running for a long time, the temperature inside the machine is high, immediately after stopping to drain the high-temperature water. This will lead to high-temperature parts suddenly encountering cold air and cracking.

5, the use of a decompression machine stop, so that the high-temperature cylinder head suddenly encounters cold air and leads to cracking.

Prevention of Cylinder Block and Cylinder Head Cracking Method

Before you start the diesel engine, should first add warm water to the tank, In the harsh winter season fill the hot water 2 ~ 3 times, to be released in the valve out of the water about 30 ~ 50 ℃ when starting well.
When the diesel engine runs for a long time, it should wait for about half an hour after shutdown, and then put the cooling water when the machine temperature drops to 40~50℃. After releasing the water, it is best to use a thin wire to stab through the water release valve switch to prevent the sediment from blocking the water release valve.
A diesel engine running overheating serious water shortage should let the diesel engine low-speed idling for 10 ~ 15 minutes, and then slowly add cooling water.