The cylinder liner forms a cylindrical space in which the piston reciprocates. The main reasons for manufacturing the liner separately from the cylinder block (jacket) in which it is located are as follows:
- The cylinder liner can be manufactured using a solid material to the cylinder block. While the cylinder block is built from a grey cast iron, the liner is manufactured from a cast iron alloyed with chromium, vanadium, and molybdenum. (Cast iron has graphite which is a lubricant. The alloying elements help improve the wear resistance and resist corrosion at high temperatures.)
- The cylinder liner wears with the use and therefore it needs to replace.
- At working temperature, the liner is way hotter than the jacket. The liner will expand more and is free to expand lengthwise and diametrically. If they are selected as a single piece, then unacceptable thermal stress would be set up, causing a fracture in the material.
- Low risk of defects. The more complex the selection, the more difficult to produce a homogeneous casting with low residual stress.
The Liner tends to get hot during engine operation as the heat energy from the burning fuel is transferred to the cylinder wall. So when the temperature is maintained within acceptable limits, then the liner remains cool.
The Cylinder liners from old low powered engines had a uniform wall thickness and the cooling was achieved by circulating cool water through a space formed between jacket and liner. The cool water space was sealed from the scavenge space using 'O' rings and a tell-tale passage between the 'O' rings led to the outside of the cylinder block to show a leakage.
To increase the power of the engine for a given number of cylinders, either the efficiency of the engine must be more or the fuel must burn more per cycle. To consume more fuel, the volume of the combustion space must be increased, and the mass of air for combustion must be increased. Because of the resulting high pressure in the cylinder from the high combustion of fuel, the liner must be made thicker at the top to accommodate the high hoop stresses, and prevent cracking of the material.
If the thickness of the material is raised to a certain level, then it stands to reason that the working surface of the liner is going to increase in temperature because the cooling water is now further away.
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Engines power machinery, from portable railways to weightlifting cranes, which is why it is necessary to equip the engines with proper devices that can prevent its undue wear and tear. Of all other supplementary equipment, cylinder liners are the simplest and most necessary protectors that have now become an essential part of engines.