A. Cylinder, Cylinder Block
(1) Cylinder
A combustion chamber is made up of a cylinder, a cylinder head and a piston. A cylinder has a cylindrical shape and its inner surface is perfectly finished.
The piston slides up and down between top dead center and bottom dead center within the cylinder. The cylinder receives the most complicated forces in the entire engine because of the influence of the pressure and heat generated by the burnt gas.
Cylinder classification
Cylinders can be structurally classified into the following types:
1.In block cylinder : The cylinder and the cylinder block have singgle integrated structure
2.Liner type cylinder : The cylinder is inserted into separately manufactured cylinder block
(Dry liner type & Wet liner type )
In block cylinder type
The cylinder and the cylinder block are manufactured as a solid unit. Since no cylinder liner is used with an in-block cylinder, it has fewer parts than a liner type cylinder. For this reason, this type is suitable for mass production. Currently in-block cylinders are used most widely for gasoline engines with cast iron cylinder blocks.
The cylinder liner housing of the cylinder block is finished into a cylindrical diameter with a fitting tolerance from the finished dimensions of the cylinder. A separately manufactured cylinder liner is inserted into this. The cylinder liner is surrounded by the walls of cylinder block, so it never comes into direct contact with the engine cooling water.
The cylindrical part of the cylinder is made up entirely of the cylinder liner. The outer surface of the wet liner comes directly in contact with the cooling water.
For this reason, this type of cylinder liner can be cooled efficiently. Wet liners are easier to manufacture and assemble than dry liners.
The upper part of the cylinder liner has a flange which is used for positioning during assembly and which prevents water from leaking from the top. The lower part of the cylinder liner has a "rubber ring" to prevent water leakage. Ordinarily the liner thickness is 6 – 8% of the inner diameter of the liner.
(2) Cylinder Block
a) Cylinder block structure
A cylinder block has the following structural parts in addition to the cylinders that generate the power:
* Water jacket : The passage for the cooling water used to cool off the heat generated by the engine ( Not needed in an air-cooled engine).
* Oil gallery : Passage for oil sucked in by the oil pump.
* Crankshaft bearings : These hold the crankshaft by the bearings.
* Camshaft bearings : These hold the camshaft (Not needed for an overhead cam type cylinder block).
* Oil pan mountings, gear train mountings, etc,
The cylinder block must have enough strength to withstand the forces generated by the
explosions (combustion) within the engine and the inertia related to high speed rotation of the crankshaft. For this reason, the upper part of the cylinder block and the crankcase usually have a mono-block structure.
b) Cylinder and cylinder block materials
Cylinders must have the following properties because they are constantly exposed to the high temperature and high pressure generated by repeated combustion explosions:
a) They must have superior abrasion resistance in order to endure the reciprocating motion of the pistons.
b) They must have high melting temperature in order to withstand the hot burnt gas.
c) They must have high strength and hardness at high temperatures.
d) They must have large oil film retention strength.
Special cast iron is the most widely used material for cylinders at present. This is because cast iron has large abrasion resistance. Special cast iron contains phosphorus, nickel, chrome or molybdenum to achieve even higher abrasion resistance or copper to raise corrosion resistance.
(3) Cylinder Characteristics
a) Cylinder capacity
The highest piston position in a cylinder is called top dead center, while the lowest position is called bottom dead center. The distance that the piston moves between these two points is called the stroke and the capacity is called the cylinder capacity (displacement). This is the maximum volume of air that can be sucked in by the descent of the piston. The engine displacement of a multi cylinder engine is obtained by multiplying the cylinder capacity by the number of cylinders. It can be calculated by the following formula:
If the air taken into a cylinder is burnt without being compressed, not enough force will be generated to operate the engine. In order to obtain sufficient rotational power, the air must be compressed to some fraction of its original volume before it is burnt, causing explosive combustion.
Air is sucked in by the descent of the piston to bottom dead center, and the air is then compressed by the ascent of the piston to top dead center. The ratio of the volume after compression to the original volume is called
the compression ratio. The compression ratio
can be obtained by the following formula:
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