Internal Combustion Engine

Internal combustion engine is an engine; it converts the chemical form of energy into the thermal form to produce mechanical output. In this process the combustion takes place inside the engine. In this engine, only exorbitant liquids and gaseous fuels are used for the process.

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Principles of operations:

In the combustion chamber air fuel mixture is ignited by a spark plug, in the spark ignition engine and by compression in the compression ignition engine. Inside the cylinder, due to ignition process high amount of pressure and heat are produced. This piston it induces the reciprocating motion. The piston includes reciprocating motion. The piston power must be transmitted to the crankshaft which undertakes the rotary motion. The developed rotary motion must be transmitted to the vehicle wheels, through the transmission system to produce propulsion in the vehicle.

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Internal combustion engine

Types of Internal Combustion Engines

Based on the standards, the internal combustion engine is divided into several types. They are

  • Based on the type of cycle
  • Based on the number of strokes per cycle
  • Based on the fuel used
  • Based on the type of ignition
  • Based on the cylinders
  • Based on the position of the cylinder
  • Based on the arrangement of valves
  • Based on the lubrication system
  • Based on the cooling system used
  • Based on the pressure boost given to the air fuel mixture (inlet air)
  • Based on the applications
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Based on the type of cycle

Based on the type of the cycle it is divided into three types they are:

  1. Diesel Cycle Engine
  2. Dual Cycle Engine
  3. Otto Cycle Engine

Based on the number of strokes per cycle

Based on the number of strokes per cycle it is divided into two types they are:

  1. Two stroke engine
  2. Four stroke Engine

Based on the fuel used

Based on the fuel used it is divided into two types they are:

  1. Petrol Engine
  2. Diesel Engine

Based on the type of ignition

Based on the type of ignition it is divided into two types they are:

  1. Spark ignition engine
  2. Compression ignition Engine

Based on the cylinders

Based on the cylinders it is divided into two types they are:

  1. Single cylinder Engine
  2. Multi Cylinder Engine

The multi cylinder Engine can be divided into seven types they are:

  1. Twin cylinder Engine
  2. 3 cylinder Engine
  3. 4 Cylinder Engine
  4. 6 Cylinder Engine
  5. 8 cylinder Engine
  6. 12 Cylinder Engine
  7. 16 Cylinder Engine

Based on the position of the cylinder

Based on the position of the cylinder it can be divided into eight types they are:

  1. Horizontal Engine
  2. Vertical Engine
  3. Radial Engine
  4. V Engine
  5. W Engine
  6. Opposed Cylinder Engine
  7. Opposed Piston engine
  8. Inline Engine

Based on the arrangement of valves

Based on the arrangement of valves it can be divided into four types they are:

  1. I head engine
  2. L head engine
  3. T head engine
  4. F head engine

Based on the lubrication system

Based on the lubrication system it can be divided into two types they are:

  1. Dry lubrication system
  2. Wet lubrication system

Based on the cooling system used

Based on the cooling system used it can be divided into two types they are:

  1. Air cooled Engine
  2. Water cooled engine

Based on the pressure boost given to the air fuel mixture (inlet air)

Based on the pressure boost given to the inlet, they are divided into four types they are:

  1. naturally aspired Engine
  2. Super charged Engine
  3. Turbo engine
  4. Crankcase compressed Engine

Based on the applications

Based on the applications they are divided into five types they are

  1. Aircraft Engine
  2. Automobile
  3. Locomotive Engine
  4. Marine Engine
  5. Stationary Engine

Different parts of an IC Engine:

In the internal combustion system the four stroke engine consists of connecting rod, crankshaft, camshafts and valves. Later considering the two stroke engine, it consists of fuel inlet and exhaust outlet in the place of valve system.

Common parts for the four and two stroke engines are: Cylinder, spark plug (for each cylinder), piston, crank pin and carburetor.

Piston:

Piston is located in a cylinder, which is the main component in the reciprocating engines. The piston is made up air tight by using the piston rings. In the cylinder the piston is used to transfer the force from the crank shaft to connecting rod.

In case of two stroke engine the piston must act as a valve and it must be used for covering and uncovering of the ports in the cylinder wall.

Piston is made up using the Al alloys

Cylinder:

Cylinder is the outer case of the engine; all the process must take place inside the cylinder only. Present days the cylinder must be made up of Al alloys.

Valves:

In the four stroke internal combustion engine, the valves are used to control the entry of the air and fuel into the combustion chamber.

In case of two stroke internal combustion engine, ports are used in the cylinder bore which was covered and uncovered by the piston, so there is a difference in the exhaust valve.

Piston Engine valve:

In the piston engine, the inlet valve is used for the intake of the fuel and air, later the outlet valve is used to escape the gases outside. The valves are opened once during the cyclic process.

Control valves:

The control valves are used to open and close the values for the intake of the fuel and air mixture, and then it leaves an outlet access for the exhaust of the gases. So they are used to adjust the flow rate and control the power or speed of the engine.

Exhaust System:

From the engine the internal combustion process, successfully manages the exhaust of the cooled combustion gas. The exhaust system consists of special devices that are used to control various pollutions like the noise pollution and chemical pollution. The exhaust system must be regularly tuned to improve the combustion system by emptying it.

Cooling system:

During combustion, heat is generated in high amount from which some amount of heat is transferred to the engine walls. If the temperature exceeds, then it leads to the failure of the engine bodies or otherwise the engine physically fails. Due to the impure lubricants they may be lead to the formation of the sludge in the engine. Basically cooling system work with the help of the air or liquid cooling and in some cases radiative cooling is used by the hit engines.

Propelling nozzle:

For jet engines propelling nozzle is present in the internal combustion engine. This takes the high pressure, high temperature exhaust that expands and later cooled. The exhaust nozzle moving out, leaves at greater speed and delivers thrust, as well as compresses the flow from the engine and raising the pressure in the rest of the engine, giving greater thrust for the exhaust mass that exits.

 Crank shaft:

A crank shaft is a mechanical part and it is able to perform a conversion between the rotational motion and reciprocating motion. In reciprocating engine the piston is used to translate the reciprocation motion into the rotational motion. In the reciprocating compressor it’s vice versa (rotational motion is converted into the reciprocating motion). For the conversation of the two motions, crankpins are attached to the crank shaft where the bearing surfaces axis is offset from the crank. Here, to the cylinder big end of the connecting rod is attached.

Flywheels:

Fly wheel is attached to the crank. It looks like a wheel or disk used for forming an inertial mass, which stores a rotational energy. Without single cylinder in the engine the flywheel is necessary to carry the energy from the power stroke followed by compression stroke. Mainly flywheels are arranged in the reciprocating engine to delivery smooth power for every rotation of the crank. In many of the automotive engines the gear rings are mounted on the starter. The rotational inertia of flywheel is used to improve the smoothness during the idle cases. The flywheel allows slower minimum unloaded speed. In most of the cases many engines use the neutral balancing fly wheel. Fly wheel is also used as mounting for the torque or clutch converter in many automotive applications.

Starter system:

To get into the operations each and every internal combustion engine requires some forms. Starter motor is used by the piston engine, it is powered by same battery and the remaining is run with the help of the electric system. Compressed air motor is used to run the gas turbines and the heavy jet engines that is regulate to one of the drive shaft of the engine. From the other engine, compressed air is supplied to the aircrafts.

Heat shielding system:

The heat shielding system can work with the combination of exhaust system and cooling system. To prevent the damage of the engine heat shielding is provided to avoid the damage of the heat sensitive components. To reduce the convection and thermal radiation steel heat shielding is used in the old cars. Now days, the cars are released with the aluminium heat shielding as it has having lower density. In heavy duty vehicles ceramic heat shielding is used to withstand at the time of high temperatures and also to formulate reduction in the heat transfer.

Lubrication system:

Lubrication system was required in the internal combustion system for the operation of the slide moving parts smoothly. Lack of the lubrication results in contact issues between the metals and also affects the rapid wear and heat generation in the parts. For these different types of lubrication systems are used.

Control systems:

To start or shut down the engine requires two or more control systems. The control parameters are speed, power, torque, combustion temperature, pollution and mainly efficiency.

Bearings:

Bearing is a mechanical element which acts as a supporting device. To minimize the power loss it provides relative movement to another element. The rotating components are equipped with the sleeve type bearings.

Thermodynamics law for Internal Combustion Engine:

Enthalpy of a system is the total energy present in the system because of its properties. Thermodynamically enthalpy must be expressed in H=U+PV

H= mC_vT+mRT

H= mC_vT+m(C_p-C_v)T

H= mC_pT

Then the equation must be changed to  dH= mC_pdT

The above equation can be applicable only for gases, not for the vapors.

Working of 4 stroke Engine

Top dead center of a piston is the nearest position to the valves. Bottom dead center is the opposite direction of the piston. The process can be done when the piston moves from the top dead center to the bottom dead center. At nearest constant speeds the crank shaft must rotate when the engine that is in operation.

Suction:

This is also known as the intake or induction. On the valve stem when the cam lobe is pressed down, that results in intake valves which are open. When the piston is moving downwards then the volume present in the combustion chamber is increased. It allows the air fuel mixture into the SI engine and air mixture in to the CI engine. The air mixture or air fuel mixture is known as charge.

Compression:

In this case of compression the piston must move from downwards to upwards, in this case the two valves are in closed state. Due to the movement of the piston the volume in the cylinder is reduced, it reaches to the minimum stage where the piston is at top dead center. The temperature, pressure and density must be increased due to the movement of the piston which is upwards. When the piston reaches the top dead center then ignition is to be started. In case of CI engine the fuel injector injects the fuel quickly into the combustion chamber as a spray, due to high temperature the fuel must be ignites. In case of the SI engine the spark plug collects the high voltage pulse that produces the spark.

Power stroke:

In the power stroke second cycle is started. In this the piston will close the top dead center then the compressed air fuel mixture can be ignited in the engine by using a spark plug. It results that the pressure from the combustion of the compressed air fuel mixture powers the piston back towards the bottom dead center.

Exhaust:

During the stroke the piston returns to the top dead center through the exhaust valve which is open. So it emits the spent air fuel mixture through the exhaust valve.

2 Stroke Engine:

For every crank shaft revolution the piston completes the cycle. In the 2 stroke engine the process is intake, compression, power stroke, exhaust and is completed in 2 strokes.

The piston must be at the bottom dead center. The transfer port is open at both the ends, the compressed air fuel mixture is below the piston and it rises from top through the transfer port. A projection is introduced on the top of the piston.

The fresh air fuel mixture is directed towards the exhaust port, which collides with the projection and is directed towards the top. This projection on the piston is known as crown. As the fresh air fuel mixture rises to the top then it pushes out the left over expanded gases through the exhaust port. This process is known as scavenging.

When the space above the piston is filled with the air fuel mixtures then the piston moves up from the body dead center. Above the piston the compression takes place from the fresh air fuel mixture. When the piston has completed 30% of the compression stroke, then the inlet port is open to the space below the piston. For further upwards motion of the piston, in the space below the piston fresh fuel air mixture is filled into the cylinder.

At the end of the compression stroke the piston is at the top dead center. Current is supplied to the spark plug and heat addition takes place at the constant volume.

At the end, due to heat addition the strong and hot gases push the piston downwards, at such instance useful power is obtained. When the piston has completed 70% of the downward stroke then the inlet port needs to be closed. Further downward motion of the piston compresses the fresh air fuel mixture of the next cycle partially.

When the piston has completed about 90% of the power stroke, then the exhaust port opens a major portion of the expanded gases that leaves the cylinder through expansion or power stroke. The piston reaches bottom dead center; later the operations there after are repeated.

 Calculation of power:

Calculation of volume:

Two stroke Engine:

One suction stroke  \to  volume of the air taken in V_s

For N rotation volume of air taken in =  V_s \times N

Four stroke Engine:

One suction stroke  \to  volume of the air taken in V_s

Average = volume of the air / rotation =\frac{V_s }{2}

For N rotations the volume of the air taken in =  \frac{V_s }{2} \times N=V_s \times \frac N 2

Mechanical Efficiency:

Mechanical Efficiency it used to measures the effectiveness of the machine, in transforming the power and the energy that is an input to the device into the output forces plus the movement. Efficiency is defined as the ratio of break work done to the indicated work done of an engine.

\eta_m=\frac{break \:\:\:work \:\:\:done}{indicated \:\:\: work \:\:\: done}

\eta_m=\frac{bmep \times V_s}{imep \times V_s}

\eta_m=\frac{bmep }{imep}

Calculation for break work done:

Break work done = F_b \times 2 \pi r_b \times N

If N is the rotation per minute then the equation must be

BWD/sec=F_b \times 2 \pi r_b \times \frac N {60}

Heat added:

HA/kg fuel = calorific value

HA/sec = calorific value mf/sec

Heat added

Thermal efficiency:

Thermal efficiency is defined as the ratio of the work done to heat addition.

\eta _{Thermal}=\frac{Work \:\:\: done}{Heat \:\:\: addition}

Break thermal efficiency:

Break thermal efficiency is defined as the ratio of the break work done to heat addition.

\eta _{B_{th}}=BWA/HA

Indicated thermal efficiency:

Indicated thermal efficiency is defined as the ratio of the break work done to heat addition

\eta _{I_{th}} = IWB/HA

Specific fuel consumption:

Specific fuel consumption is defined as the ratio of the mass fuel used by an engine to power.

SFC= \frac{mf/hr}{power(kw)}

Break specific fuel consumption:

Break specific fuel consumption is defined as the ratio of the mass fuel used by the engine to the break power.

BSFC= \frac{mf/hr}{Break \:\:\:\: power(kw)}

Indicated specific fuel consumption:

Indicated specific fuel consumption is defined as the ratio of the mass fuel used by the engine to indicated power.

ISFC= \frac{mf/hr}{Indicated \:\:\:\: power(kw)}

Power:

Power is defined as the work done; it is amount of energy consumed per unit time.

Power = work done/ time

Break power:

BP= BWD/sec

IP = IWB/sec

Average Piston speed:

Average piston speed = 2LN

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