Introduction To Internal Combustion Engine

Engine:

A device used to convert one form of energy into useful work is called an Engine.

Heat Engine:

Engine which converts heat energy into useful mechanical work is called Heat Engine.

There are two types of Heat engine, namely:

1. Internal Heat Engine 
2. External Heat Engine 

1. Internal Heat Engine:

Engines in which combustion of fuel is done within the engine is called Internal Heat Engine.

2. External Heat Engine:

Engines in which combustion of fuel is done outside the engine is called External Heat Engine.

Main Components of Internal Heat Engine:

Main components of internal heat engines are described as follows:

1. Cylinder Block:

The main supporting structure of various components. The cylinder of a multi-cylinder engine are cast as a single unit called Cylinder Block.

2. Cylinder:

It is a cylindrical shape in which the piston make a reciprocating motion.

3. Piston:

It is a cylindrical components fitted into the cylinder forming the moving the boundary of the combustion chamber.

4. Combustion Chamber:

The space enclosed in the upper part of the cylinder between the cylinder head and the piston top during the combustion process is called Combustion Chamber.
In Cars:

In Planes:

5. Inlet Manifold:

The pipe which connects the intake system to the intake valve of the engine through which air or air-fuel mixture is drawn into the cylinder is called Inlet Manifold.

6. Exhaust Manifold:

The pipe which connects the exhaust system to the exhaust valve of the engine and through which combustion products escape into the atmosphere.

7. Inlet & Exhaust Valves:

Valves are commonly mushroom shaped poppet type. Valve through which air or air-fuel mixture comes into the cylinder is called Inlet Valve. Valve through which exhaust gases comes out of the cylinder is called Exhaust Valve.

8. Spark Plug:

It is a component used to initiate the combustion process in SI engines is called Spark Plug. It is located in the cylinder head.

The story of Spark Plug is:

9. Connecting Rod:

it connects the piston and crankshaft which transmits the gas force to the crankshaft. There are two ends of Connecting Rod, small end is connected to piston called Gudgeon Pin. The big end is connected to crankshaft is called Crank Pin.

10. Crankshaft:

It converts the reciprocating motion of the piston into useful rotary motion of the output shaft.

11. Piston Rings:

Rings fitted into the slots around the piston are called Piston Rings. There are three rings, upper two rings are compression rings which resist combustion gases goes through the spaces between the piston and cylinder walls and One is oil ring which resists oil flow.

12. Camshaft:

Device which controls the opening and closing of two valves is called Camshaft. The camshaft is driven by crankshaft by timing gears.

13. Cams:

The integral parts of the camshaft which open or close the piston by rocker arm of spring mechanisms.

There are different types of cam used which are:

14. Flywheel:

A wheel of rotating mass with a large moment of inertia connected to the crankshaft of the engine. It's purpose is to store engine and furnish a large angular momentum that keeps the engine operate.

15. Cooling Fins:

Metal fins on the outside of the cylinder and cylinder head of an air cooled engine.

16. Crankcase:

Part of engine block surrounding the rotating crankshaft.

 17. Fuel Injectors:

A nozzle which injects a pressurized fuel into the cylinder of engine is called Fuel Injector.

18. Glow Plug:

a small electrical resistance heater to start combustion in CI engines.

19. Head Gasket:

Gasket (made by metal and composite materials) which serves as a sealant between the engine block and head.

20. Starter:

Electric motor used to start an engine is called Starter.

Types of Internal Combustion Engine:

Types of Internal combustion engine are described ahead:

1. Cycle of Operation:

There are two types of ICE depending upon Cycle of Operation, namely:

1. Otto Cycle or Constant Volume Heat Addition.
2. Diesel Cycle or Constant Pressure Heat Addition.

2. Fuels:

Depending upon the vaporizing characteristics of fuel, engine are classified as:

1. Spark Ignition Engine   ⇔   Uses highly volatile liquids and gases for which air-fuel mixture can easily be produce. This engine use Spark Plug.
2. Compression Ignition Engine    ⇔   Uses low volatile liquids for which air-fuel mixture cannot be easily produce. This engine use Glow Plug.

3. Cylinder Arrangements:

a.       In- line engines: All cylinders are arranged linearly 

b.       V engines: Cylinders are in two banks inclined at an angle to each other and with one crank-shaft. 

c.        Radial engine: The radial engine is an engine with more than two cylinders in each row equally spaced around the crank shaft. Normally it is been used in air-crafts.

d.       Opposed cylinder: Banks located in the same plane on opposite sides of the crankshaft.

e.        Opposed piston engine: When a single cylinder houses two pistons, each of which drives a separate crank

4. Applications:

• Marine Engine   →   for propulsion of ships at sea
• Industrial Engine   →   for power generation on land
• Automotive Engine   →   for transport

5. Cooling:

• Water-Cooled Engines
• Air-Cooled Engines 

6. Ignition:

• Spark Ignition Engine (SI Engine)
• Compression Ignition Engine (CI Engine)

Working of 4-Stroke Engine:

1. Intake Stroke:

• The inlet valve is open and exhaust valve is close.
• Piston travels down the cylinder from TDC to BDC, drawing in a charge of air. In the case of a spark ignition engine the fuel is usually pre-mixed with the air.  

2. Compression Stroke:

•  Both valves are closed. 
• Piston travels up the cylinder from BDC to TDC. 
•  As the piston approaches TDC, ignition occurs.
• In the case of compression ignition engines, the fuel is injected towards the end of the compression stroke.

3. Power Stroke:

• Combustion propagates throughout the charge, raising the pressure and temperature, and forcing the piston down from TDC to BDC.  
• At the end of the power stroke the exhaust valve opens. 

4. Exhaust Stroke:

• The exhaust valve remains open.
•  Piston travels up the cylinder from BDC to TDC so the remaining gases are expelled.
• At the end of the exhaust stroke, when the exhaust valve closes some exhaust gas residuals will be left; these will dilute the next charge.

Working of 2-Stroke Engine:

The two-stroke cycle eliminates the separate induction and exhaust strokes. Cycle is explained below:

1. Compression Stroke:

• The piston travels up the cylinder, so compressing the trapped charge.
• Simultaneously the underside of the piston is drawing in a charge through a spring-loaded non-return inlet valve. 

     2. Power Stroke:

• The burning mixture raises the temperature and pressure as well which forces the piston to move.
• The downward motion of piston also compresses the charge in the crankcase called Crankcase Compression.
• As the piston approaches the end of its stroke, the exhaust port is uncovered.
• When the piston is at BDC, the transfer port is also uncovered and the compressed charge in the crankcase expands into the cylinder.
• Some of the remaining exhaust gases are displaced by the fresh charge because of the flow mechanism called Scavenging.
• As the piston travels up the cylinder, first the transfer port is closed by the piston and then the exhaust part is closed.

Basic Terminologies of Engine Cylinders:

A. Top Dead Center (TDC):

The point at which volume in the cylinder has minimum volume is called Top dead center.

B. Bottom Dead Center (BDC):

The point at which volume in the cylinder has maximum volume is called Bottom dead center.

C. Bore:

It is internal diameter of the piston.

D. Stroke:

It is the displacement of piston from top dead center to the bottom dead center.

E. Stroke to Bore Ratio:

By knowing the stroke to bore ratio one can know the type of engine whether it is a square or over-square or under-square .

d < 1 (under-square engine)

d = 1 (square engine)

d > 1 (over-square engine)

Over-square engine can operate at high speeds because of larger bore and shorter stroke.

F. Clearance Volume:

Minimum volume of the cylinder when the piston is at TDC is called Clearance Volume, Vc.

G. Displacement or Swept Volume:

Volume displaced by the piston as it travels through one stroke. Swept volume for one cylinder engine is given by:

H. Air-Fuel Ratio:

It is the ratio of mass of air to the mass of fuel.

I. Fuel-Air Ratio:

It is the ratio of mass of fuel to the mass of air.

J. Equivalence Ratio, 𝜙:

It is the ratio of actual fuel-air ratio to the stoichiometric fuel-air ratio.

K. Overhead Valve (OHV):

Valve mounted in head of an engine is called Overhead Valve.

L. Overhead Cam (OHC):

Cam mounted in engine head, giving more direct control of valves which are also mounted in engine head.

References:

• University notes + my knowledge.
• Videos from YouTube.
• Images from Google Images.
• Book: IC Engines by V Ganesan (4th Edition).
• Class Lectures.