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The Construction and Operation of Marine Diesel Engines

The Two Stroke Crosshead Diesel Engine Cylinder Liner

 

The cylinder liner forms the cylindrical space in which the piston reciprocates. The reasons for manufacturing the liner separately from the cylinder block (jacket) in which it is located are as follows;

  • The liner can be manufactured using a superior material to the cylinder block. While the cylinder block is made from a grey cast iron, the liner is manufactured from a cast iron alloyed with chromium, vanadium and molybdenum. (cast iron contains graphite, a lubricant. The alloying elements help resist corrosion and improve the wear resistance at high temperatures.)

  • The cylinder liner will wear with use, and therefore may have to be replaced. The cylinder jacket lasts the life of the engine.

  • At working temperature, the liner is a lot hotter than the jacket. The liner will expand more and is free to expand diametrically and lengthwise. If they were cast as one piece, then unacceptable thermal stresses would be set up, causing fracture of the material.

  • Less risk of defects. The more complex the casting, the more difficult to produce a homogenous casting with low residual stresses.

The Liner will get tend to get very hot during engine operation as the heat energy from the burning fuel is transferred to the cylinder wall. So that the temperature can be kept within acceptable limits the liner is cooled.

Cylinder liners from older lower powered engines had a uniform wall thickness and the cooling was achieved by circulating cooling water through a space formed between liner and jacket. The cooling water space was sealed from the scavenge space using 'O' rings and a telltale 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 increased or more fuel must be burnt per cycle. To burn 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 higher pressures in the cylinder from the combustion of this greater mass of fuel, and the larger diameters, the liner must be made thicker at the top to accommodate the higher hoop stresses, and prevent cracking of the material. 

marinediesels.co.uk deals with the construction, operation, running and maintenance of large slow speed two stroke crosshead diesel engines and medium speed four stroke trunk piston diesel engines, as found in the majority of ocean going merchant vessels. Learn about problems which can be encountered such as scavenge fires and crankcase explosions, and how to prevent them. Discover how the engine is built from bedplate, frames, entablature and tie bolts. Learn the operation of the 4 and 2 stroke diesel cycles, the difference between trunk piston and crosshead engines, the purpose of the component parts of the running gear of crankshaft, con rod, crosshead, liner, and piston. Find out how the Mean Indicated Power is calculated using the Mean Indicated Pressure, discover how the air start system operates and how Turbocharging, scavenging,  fuel injection timing and VIT  (Variable Injection Timing) works.

 

This is a cut down version of the main marinediesels website which is accessible here. The main website contains all this information with graphics, drawings and photos.