Types Of Engines:
The engine is the most important component of a vehicle. It is known as the powerhouse of the automobile. It converts the chemical energy of the fuel into mechanical energy, which propels the vehicle. Most of the vehicles today are fitted with internal combustion engines.
The engines are classified into various types based on certain criteria. Some of those criteria are:
1. Mode of combustion
2. Fuel Used
3. Number of strokes
Types of Engines Based on Combustion:
1.) Internal Combustion Engines:
Internal combustion engines are those engines in which combustion takes place Inside the engine. example n case of gasoline or diesel engines, the products of combustion generated by the combustion of fuel and air within the cylinder form the working fluid.
2. External Combustion Engines:
External combustion engines are those in which combustion takes place out-side the engine.
These engines are huge in size and have very low efficiency. However, they produce lesser noise as compared to the IC engines. One major disadvantage with these engines is that they take a significant amount of time to start. An example of external combustion engines is the Steam Engine (Locomotive engine).
Types of Engines Based on Motion Of Piston:
1. Reciprocating Engines
These are the piston-cylinder type engines. These are very common and are used in almost all vehicles. They convert the chemical energy of fuel into mechanical energy by the reciprocating motion of their piston.
These engines have a very large number of moving parts and hence produce a lot of vibrations.
2. Rotary Engine
A rotary engine is also called Wankel engines. They consist of rotors instead of pistons. They are very compact and smooth. They do not have any reciprocating part, hence they are very stable.
They have three power strokes per cycle of the engine. They can rotate at very high speed and need very less number of components as compared to reciprocating engines.
But, the major drawbacks of these engines are their low efficiency and high pollution.
Types of Engines Based on Number of Strokes:
A two-stroke engine completes its power cycle in two piston strokes. The inlet and the compression of charge take place in the first stroke while the combustion and exhaust take place in the second. It is simple in design and produces more power per unit mass as compared to the four-stroke engine. However, it is less efficient and causes more pollution. In these engines, the engine oil has to be mixed with fuel for the lubrication of engine components. The burning of the engine oil further increases the pollution level.
2. Four-Stroke Engines
The four-stroke engines complete their power cycle in four strokes i.e.
Intake
Power
Exhaust
The crankshaft of the four-stroke has to complete two revolutions for each power cycle. They are more complex and produce less power per unit mass. However, they cause less pollution as compared to 2 stroke engines.
Types Of Engines Based On Type Of Fuel:
1. Petrol Engine
Petrol engines use Gasoline as fuel. These engines are also called Spark Ignition or SI engines. They require a spark plug to ignite the Air-Fuel mixture. These engines are generally smaller and less efficient as compared to petrol engines. However, petrol is a cleaner fuel as compared to diesel and produces a lesser amount of Nox on burning.
2. Diesel Engines
Diesel Engines are also known as Compression Ignition or CI engines. These engines do not need any spark plug for ignition. Diesel being less volatile can not form proper Air-Fuel mixture and also it has a lower ignition temperature. Hence, in CI engines, self-ignition occurs due to high temperature of compressed air. These engines can work on very high compression ratios and hence are more efficient than the petrol engines. Petrol engines on the other hand can not work on high compression ratios. They experience the problem of knocking and detonation on increasing their compression ratio.
3. Gas Engines
These engines are also spark-ignition engines. They use compressed natural gas (CNG) as fuel and require a spark plug for igniting the Air-Fuel mixture. They are efficient and less polluting than petrol engines. These engines have a higher rate of wear and tear as compared to petrol engines as the gaseous fuel can not cause the cooling of the combustion chamber. The petrol on other hands evaporates inside the combustion chamber and causes a cooling effect.
Cylinder Arrangements:
Two terms used in connection with cylinder arrangements must be defined first.
(i)Cylinder Row:
An arrangement of cylinders in which the centreline of the crankshaft journals is perpendicular to the plane containing the centrelines of the engine cylinders.
(ii)Cylinder Bank:
An arrangement of cylinders in which the centreline of the crankshaft journals is parallel to the plane containing the centrelines of the engine cylinders.
(iii)In-line Engine:
Inline or straight engines are those in which cylinders are arranged in straight lines. These engines are stable and simple in construction. The pistons of these engines are designed to move in tandem with each other such that the inertial forces are cancelled out. These forces are generated due to continuous change in momentum of the piston. Their crank throws are also designed in a way such that the connecting rods are connected at equal angles on the crankshaft. This helps in balancing out the forces generated due to the power transfer from the connecting rod to the crankshaft. One major disadvantage of these engines is their large size.
Single Cylinder Engine
Single Cylinder Engines have only one cylinder and piston arrangement. They are simple in construction and are used generally in motorcycles. The problem with single-cylinder engines is that they are not balanced and produce huge vibrations. The piston when changes its direction produces unbalanced inertial forces. Also, power transfer to the crankshaft is done only during the power stroke, and for the rest strokes engine runs on its own. This uneven power transfer makes these engines unstable. These engines need large balancing wights on their crankshaft to keep them stable.
Multi-Cylinder Engines
Multi-Cylinder Engines may have two or more than two cylinders. They are more balanced and smooth as compared to the Single Cylinder Engines. In multi cylinder engines, all the pistons move in different directions, this cancels outs the inertial forces produced by each other. Also, since all the cylinders have different firing order, the power supply to the crankshaft is uniformly done along with the whole engine cylinder.
‘V’ Engine :
In this engine there are two banks of cylinders (i.e., two inline engines) inclined at an angle to each other and with one crankshaft. Mostof the high powered automobiles use the 8 cylinder ‘V’ engine, four in-line on each side of the ‘V’. Engines with more than six cylinders generally employ this configuration.
Opposed Cylinder Engine :
This engine has two cylinder banks located in the same plane on opposite sides of the crankshaft. It can be visualized as two ‘ in-line’ arrangements 180 degrees apart. It is inherently a well balanced engine and has the advantages of a single crankshaft. This design is used in small aircrafts.
Opposed Piston Engine :
When a single cylinder houses two pistons,each of which driving a separate crankshaft, it is called an opposed piston engine. The movement of the pistons is synchronized by coupling the two crankshafts. Opposed piston arrangement, like opposed cylinder arrangement,and is inherently well balanced. Further, it has the advantage of requiring nocylinder head. By its inherent features, this engine usually functions on theprinciple of two-stroke engines.
Radial Engine :
Radial engine is one where more than two cylinders in each row are equally spaced around the crankshaft. The radial arrangement of cylinders is most commonly used in conventional air-cooled aircraft engines where 3, 5, 7 or 9 cylinders may be used in one bank and two to four banks of cylinders may be used. The odd number of cylinders is employed from the point of view of balancing. Pistons of all the cylinders are coupled to the same crankshaft. All the cylinders in these engines lie in one plane, hence they can be very easily cooled by air. These engines were used in aeroplanes for a long period of time.
‘X’ Type Engine :
This design is a variation of ‘V’ type. It has four banks of cylinders attached to a single crankshaft.
‘H’ Type Engine :
The ‘H’ type is essentially two ‘Opposed cylinder’ typeutilizing two separate but interconnected crankshafts.
‘U’ Type Engine :
The ‘U’ type is a variation of opposed piston arrangement.
Delta Type Engine :
The delta type is essentially a combination of three opposed piston engine with three crankshafts interlinked to one another.In general, automobile and general purpose engines utilize the ‘in-line’ and‘V’ type configuration or arrangement. The ‘radial’ engine was used widely in medium and large aircrafts till it was replaced by the gas turbine. Small aircrafts continue to use either the ‘opposed cylinder’ type or ‘in-line’ or ‘V’type engines. The ‘opposed piston’ type engine is widely used in large diesel installations. The ‘H’ and ‘X’ types do not presently find any application,except in some diesel installations. A variation of the ‘X’ type is referred to as the ‘pancake’ engine.
W- Type Engines:
W- Engines have three rows of cylinders placed in a way such that the arrangement forms a W shape. These engines are generally used in high power cars. The W configuration allows a very large number of cylinders to be stacked in a smaller space. Some common W- Engines are W-16 and W-18 engines.
Radial Engines:
Radial Engines have all their cylinders arranged radially along their crankshaft. They need a very small crankshaft as all of their pistons are connected at a common point. These engines are very stable due to their radial arrangement. All the cylinders in these engines lie in one plane, hence they can be very easily cooled by air. These engines were used in aeroplanes for a long period of time.
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