Classification Of Engines


Classification of Engines
GIF Credits : Imgur
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 in to various types based on certain criteria. Some of those criterias are:
1. Mode of combustion
2. Fuel Used
3. Number of strokes
4. Number of cylinders
5. Arrangement of cylinders 
6. Type of cooling etc.


There are numerous other criterias and hence, there are huge variety of engines available. All those engines have different properties. The selection of engine for a particular work is done depending upon its properties. In this post, we will look at some of the classifications of the engines to  develop our understanding about the engines.


    Classification of Engines Based on Combustion

    1. Internal Combustion Engine

    Internal combustion or IC engines have their combustion chamber inside them. The energy produced by burning of fuel is supplied directly to their prime mover i.e. piston. These engines are compact and have better efficiency than the external combustion engines. Almost all the automobiles today use internal combustion engines.

    2. External Combustion Engines

    Classification of Engines Based On combustion
    A Steam Engine Locomotive
    External combustion engines have their combustion chamber away from their prime mover. They need a working fluid which is heated in their combustion chamber and is  used to run their prime mover. These engines are huge in size and have very low efficient. 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 Steam Engine.


    Classification 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 the vehicles. They convert the chemical energy of fuel into mechanical energy by the reciprocating motion of their piston. These engines have very large number of moving parts and hence produce a lot of vibrations. However, they are very efficient and reliable.

    2. Rotary Engine

    Classification of Engines Based On motion of prime mover

    Rotary engine are 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 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.

    Classification of Engines Based on Number of Strokes

    1. Two Stroke Engine

    Classification 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 takes place in first stroke while the combustion and exhaust takes 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 polution. 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


    Classification of Engines Based On number of strokes

    The four stroke engines complete their power cycle in four strokes i.e.

    • Intake 
    • Compression
    • 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.

    Classification 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 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 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 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 other hand can not work on high compression ratios. They experience 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 the petrol engines. These engines have higher rate of wear and tear as compared to petrol engines as the gaseous fuel can not cause the cooling of combustion chamber. The petrol on other hands evaporates inside combustion chamber and causes cooling effect.


    Classification Of Engines Based on Number of Cylinders

     1. Single Cylinder Engine

    Classification of Engines Based On number of cylinders

    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.

    2. Multi Cylinder Engines

    Classification of Engines Based On number of cylinders

    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 multicylinder engines, all the pistons move in different directions, this  cancel outs the inertial forces produced by each other. Also, since all the cylinders have different firing order, the power supply to the crank shaft is uniformly done along the whole engine cylinder.

    Classification of Engines Based On Arrangement Of Cylinders

    1. Inline Engines

    Classification of Engines Based On Arrangement Of Cylinders
    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 enertial 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 crank shaft. This helps in balancing out the forces generated due the the power transfer from the connecting rod to the crank shaft. One major disadvantage of these engines is their large size.

    2. V- Engines

    Classification of Engines Based On Arrangement Of Cylinders

    V-Engines haves two rows of cylinders arranged at angle of 60 or 90 degrees. These engines are compact and occupy lesser space as compared to Inline Engines. They are so compact that even a V-6 engine occupies lesser space as compared to Inline-4 engine. But a major problem with V-Engines is their complex design. They need two sets of cylinder heads, exhaust manifolds, camshafts etc.  They are also not as stable as Inline engines since the V arrangement can not cancel out all the enertial forces generated during their operation.

    3. W- Engines

    Classification of 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 very large number of cylinders to be stacked in a smaller space. Some common W- Engines are W-16 and W-18 engines.

    4.Horizontaly Opposite Or Boxer Engines


    Classification of Engines Based On Arrangement Of Cylinders
    Pic Credits : Subaru Global

    Boxer engines consist of two rows of cylinders arranged completely opposite to each other. This configuration completely cancel out the inertial forces generated due to motion of  the pistons. The centre of mass of these engines is also lower as compared to other engines. They produces very less vibrations and also improve the stability of the vehicle.  The problem with these engines is their huge width and complexity.

    5. Radial Engines

    Classification of Engines Based On Arrangement Of Cylinders, aeroplane engine

    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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