Elements of Mechanical engineering (18ME15/25) a VTU syllabus topic.
Module 3: Internal Combustion engines introductions.

Internal Combustion Engines

•A heat engine is a device which transforms the chemical energy of a fuel into thermal energy and uses this energy to produce mechanical work

•It is classified into two types

  (a) External combustion engine

  (b) Internal combustion engine

(a)External combustion engine: An Engine in which combustion of fuel take place outside the engine cylinder is called external combustion engine. These engine generally called EC engines

Ex: Steam engines, steam turbines, closed cycle gas turbines

(b) Internal combustion engine: In this engine, the combustion of air and fuels take place inside the cylinder and are used as the direct motive force. These engine generally called as IC engines

Ex: petrol engines, diesel engines, gas engines.

Classification of IC engines

1)According to the type of fuel used.

a)Petrol engines: In this type of engines, the fuel used is petrol.

b)Diesel engines: In this type of engines, the fuel used is diesel.

c)Gas engines: In this type of engines, the gaseous fuels natural gas, biogas are used.

d)Bi-fuel engines: These engines use a mixture of two fuels.

2) According to the number of strokes per cycle.

a)4- stroke engines : in this type of engines, the working cycle is completed in four different strokes.

b)2- stroke engines : in this type of engines, the working cycle is completed in two different strokes.

3) According to the method of ignition

a)Spark ignition engines (S.I. engines) : In this type of engines, fuel is ignited by an electric spark generated by a spark plug.

b)Compression ignition engines (C.I. engines) : In this type of engines, the fuel gets ignited as it comes in contact with the hot compressed air. 

4) According to the cycle of combustion

a)Otto cycle engine : In this type of engines, combustion of fuel take place at constant volume.

b)Diesel cycle engines : In this type of engines, combustion of fuel takes place at constant pressure.

c)Duel combustion engines : In this type of engines, combustion of fuel first takes place at constant volume and then at constant  pressure.

5) According to the number of cylinders.

a)Single cylinder engines : This type of engines consist of only one cylinder.

b)Multi cylinder engines : This type of engines consist of 2,3,4,6 and 8 cylinders.

6) According to the arrangement of cylinders

a)Vertical Engine : In this type of engines, the cylinder is arranged in a vertical position.

b)Horizontal engine : In this type of engines, the cylinder is arranged in a horizontal position.

c)Inline engine : In this type of engines, cylinder are arranged in line.

d)Radial engine : in this type of engines, cylinders are arranged along the circumference of a circle.

e)V-Engine : In this type of engine, combination of two inline engines equally set an angle.

7) According to the method of cooling 

a)Air cooled engines : In this type of engine, the heated cylinder walls are cooled by continuous flow of air.

b)Water cooled engine : In this type of engine, water is used for cooling the heated cylinder walls.

c)Oil cooled engines : In this type of engine, oil is used for cooling the heated cylinder walls.

Principal parts of an I.C. engines

1) Cylinder

•It Is the cylindrical vessel in which the fuel is burnt and the power is developed. It is considered as heart of the engine. The primary functions of cylinder is

–To contain the working fluid under pressure and

–To guide the piston while reciprocating inside the cylinder.

2)Cylinder head

•The top end of the cylinder is closed by a removable cylinder head. The cylinder head consists of two valves ‘inlet valve’ and ‘exhaust valve’.

3)Piston

•It is a hallow cylindrical plunger reciprocating inside the engine cylinder. It transmits power developed by the combustion of the fuel to the crankshaft through connecting rod. It receives an impulse due to the expansion of gases during power stoke.

4)Piston rings

•The rings which are placed in the grooves cut towards top of the piston are called piston rings. There are two set of rings inserted into the groves. They are compressing rings and oil rings.

–Compression rings: The compression rings press hard with the cylinder walls forming a tight seal between the piston and the cylinder. This prevents escaping of the high pressure gases into the crankcase.

–Oil ring: The function of oil rings is to extract the lubricating oil form the cylinder walls and send it back to oil sump through the holes provided on the piston.

5)Connecting rod

•The connecting rod is a link that connects the piston and crankshaft. Its function is to convert the reciprocating motion of the piston into rotary motion of the crankshaft.

6)Crank

•The crank is a lever with one of its end connected to the connecting rod by  pin joint with other end connected rigidly to the crankshaft. The other end of the crank is connected to the crankshaft. The power required for any useful purpose is taken from the crankshaft

7)Crank case

It encloses the crankshaft and serves as a sump for the lubricating oil.

8)Valves

•The valves are control devices that allow the air/fuel to enter into the cylinder and also to discharge the burnt gases to atmosphere. There are two valves

–Inlet valve: It is the one through which fresh charge(air and fuel) enters into the cylinder.

–Exhaust valve: Through which the burnt gases are discharged out of the cylinder. These valves are actuated by means of cams.

9)Cams

•It is an element designed to control the movement of both the inlet and exhaust valves.

10)Flywheel

•It is a heavy mass of rotating wheel mounted on the crankshaft and is used as an energy storing device. The flywheel stores energy received during the power stroke and supplies the same during other strokes.

I.C. Engine Terminology

•Bore: The inside diameter of the cylinder is called bore.

•Top dead center(TDC): The extreme position of the piston near to the cylinder head is called ‘top dead center’ or ‘TDC’.

•Bottom dead center(BDC): The extreme position of the piston of the piston nearer to the crankshaft is called ‘bottom dead center’ or ‘BDC’.

•Stoke: It is the linear distance travelled by the piston from the TDC to BDC or BDC to TDC.

•Clearance volume(Vc): It is the volume above the top of the piston, when the piston is at the TDC.

Swept volume or stoke volume(Vs): It is the volume swept by the piston as the it moves from BDC to TDC or TDC to BDC.

•Compression ratio(Rc): The ratio of the total cylinder volume to the clearance volume is called compression ratio.

  Total cylinder volume = stroke volume(Vs) + Clearance volume(Vc)

Rc="Vs+Vc" /"Vc"

•Piston speed: The average speed of the piston is called ‘piston speed’.

–Piston speed = 2. L.N                      where L = Stroke length in m

                                                                 N =Speed of the engine in RPM