Internal Combustion Engine. _I C Engine_

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Internal Combustion Engine. _I C Engine_ Powered By Docstoc
					Internal Combustion Engine.
         (I C Engine)




        Dept. of Mech & Mfg. Engg.   1
         Classification of I C Engines
• According to:
• (i) Nature of Thermodynamic Cycle :
  – 1. Otto cycle engine.
  – 2. Diesel cycle engine.
  – 3. Dual combustion cycle engine.
• (ii) Type of the Fuel- used :
  –   1. Petrol engine.
  –   2. Diesel engine.
  –   3. Gas engine.
  –   4. Bi-fuel Engine.
  –   5. Dual Fuel Engine

                     Dept. of Mech & Mfg. Engg.   2
       Classification of I C Engines
(iii) Number of Strokes :-
  –   1. 2 - stroke engine
  –   2. 4 - stroke engine
(iv) Method of Ignition:
  –   1. Spark ignition engine, [S.I. Engine].
  –   2. Compression ignition engine, [C.I. engine].
(v) Number of Cylinders
  –   1. Single cylinder engine.
  –   2. Multi-cylinder engine.



                    Dept. of Mech & Mfg. Engg.         3
           Classification of I C Engines
•       (vi) Position of the Cylinder:
    –     1. Horizontal engine
    –     2. Vertical engine
    –     3. V- engine.
    –     4. Radial engine.
•       (vii) Method of Cooling :
    –     1. Air cooled engine.
    –     2. Water cooled engine
•       (viii) Speed of the Engine :
    –     1. Low speed engine.
    –     2. Medium speed engine.
    –     3. High speed engine.


                          Dept. of Mech & Mfg. Engg.   4
I C Engine Parts




                   Dept. of Mech & Mfg. Engg.   5
I C Engine terms & Definition
                                                              Spark plug  




TDC (top dead center):                                              Valve


It is the top most position                                                  Clearance 
                                        TDC                                  volume 
   of the piston towards                               Bore


   head side of the cylinder
                                              Stroke




BDC (bottom dead center):               BDC


                                                                     Piston
The lowermost position of
 the piston towards the
 crank end side of the
 cylinder.
               Dept. of Mech & Mfg. Engg.                            6
Stroke:
 It is the linear distance
 traveled by the piston
 when it moves from one
 end of the cylinder to the
 other end
   Bore:
              It is the
           inside diameter
              of the
           cylinder.

                  Dept. of Mech & Mfg. Engg.   7
 Swept volume or
(Displacement volume)
It is the volume swept
through by the piston in
moving between TDC and
BDC


Clearance volume:
It is the volume contained
in the cylinder above the
top of the piston, when the
piston is at TDC.




                    Dept. of Mech & Mfg. Engg.   8
  Total volume = swept volume + clearance volume.
  Compression ratio: “r”
  It is the ratio of total cylinder volume to clearance
  volume.
  r = Total volume
       clearance volume

Value of “r” for,
petrol engine lies between 7 to 9
Diesel engine lies between 15 to 22




                    Dept. of Mech & Mfg. Engg.    9
  Working of 4-S Petrol engine
• The petrol engines work on the principle of
  “OTTO CYCLE”, also known as constant
  Volume cycle.
• The engines operating on this cycle use
  either petrol or other spirit fuels or the
  gases such as LPG / CNG as their fuels.




                Dept. of Mech & Mfg. Engg.   10
•   In a 4-Stroke petrol engine, the charge is
    admitted to the engine cylinder is a
    homogeneous mixture of petrol and air.


•   Depending on the load on the engine,
    the fuel and air is mixed in proper
    proportions and sent in to the cylinder by
    a popular device known as “carburetor”.



                Dept. of Mech & Mfg. Engg.   11
In a 4-stroke petrol engine there are four
    main events taking place, they are
1. Suction
2. Compression
3. Working or power or expansion, and
4. Exhaust

So in a cycle there are four events to take
   place, and each of this is performed
   during a single stroke of the piston

Since ignition in these engines is due to a spark,
    they are also called spark ignition engines .




                  Dept. of Mech & Mfg. Engg.    12
Dept. of Mech & Mfg. Engg.   13
1. INTAKE [Suction]: During the intake stroke, the
  piston moves down ward, drawing a fresh charge of
  vaporized fuel-air mixture, This operation is
  represented by the line AB on the P-V diagram.  
                  Pressure [P]
            TDC




           BDC
                                       A
                                                     B


                                                  Volume [V]



                     Dept. of Mech & Mfg. Engg.          14
2. Compression Stroke: During compression stroke, the piston
  moves from BDC to TDC, thus compressing air petrol mixture. Due to
  compression, the pressure and temperature are increased and is shown by
  the line BC on the P- V diagram. Just before the end of this stroke the spark
  - plug initiates a spark which ignites the mixture and combustion takes place
  at constant volume as shown by the line CD  
                         Pressure [P]       D
                TDC


                                            C



               BDC
                                              A
                                                                   B


                                                               Volume [V]



                            Dept. of Mech & Mfg. Engg.                 15
3. Working Stroke: The expansion of gases due to
  the heat of combustion exerts a pressure on the
  piston. Under this impulse, the piston moves from
  TDC to BDC and thus the work is obtained in this
  stroke as shown by the line DE
                Pressure [P]       D
          TDC


                                   C

                                                       E
         BDC
                                     A
                                                   B


                                                Volume [V]

                   Dept. of Mech & Mfg. Engg.          16
4. Exhaust Stroke: At the end of the power stroke, the exhaust valve is
   opened & greater part of the burnt gases escapes because of their
   own expansion. The drop in pressure at constant volume is
   represented by the line EB. During this stroke the piston moves from
   BDC to TDC and pushes the remaining gases to the atmosphere. This
   stroke is represented the line BA on the P-V diagram.


                       Pressure [P]       D
              TDC


                                          C

                                                                   E
             BDC
                                            A
                                                               B


                                                           Volume [V]

                          Dept. of Mech & Mfg. Engg.               17
       P V diagram for
SI Engine / Otto cycle engine
                         D




                     D



   TDC
                 C
            Pressure

                                                  E


                 A                                B


   BDC                         Volume
                         Theoretical Otto cycle




         Dept. of Mech & Mfg. Engg.                   18
Working of 4-S Diesel engine
 The basic construction of a four stroke
diesel engine is same as that of four stroke
petrol engine.
  Except that instead of a spark plug, a fuel
INJECTOR is mounted in its space.
 Fuel injector injects the fuel in to the
cylinder as a fine spray at very high
pressure

              Dept. of Mech & Mfg. Engg.   19
 In case of diesel engine, the air enters the inside
the cylinder during suction, and it will get
compressed during the compression stroke. (i.e..
charge is only air)
 At the end of the compression stroke the diesel is
injected in to the cylinder in the form of fine spray
 When this fine spray diesel comes in contact with
hot air in the cylinder, it auto ignites and results in
a combustion of injected diesel fuel.
 Since ignition in these engines is due to the
temperature of the compressed air, they are also
called compression ignition engines.

                 Dept. of Mech & Mfg. Engg.      20
Dept. of Mech & Mfg. Engg.   21
1. INTAKE [Suction]: During the intake
 stroke, the piston moves down ward,
 drawing a fresh charge [AIR]. This
 operation is represented by the line AB on
 the P-V diagram.  
              Pressure [P]
        TDC




                                 A
        BDC                                        B


                                                Volume [V]

                   Dept. of Mech & Mfg. Engg.          22
2. Compression Stroke: During compression
  stroke, the piston moves from BDC to TDC, thus
  compressing air. Due to compression, the
  pressure and temperature are increased and is
  shown by the line BC on the P- V diagram. Just
  before the end of this stroke, aDmetered quantity
                             C
  of Diesel is injected into the hot compressed air in
  the form of fine sprays by means of fuel injector.
                Pressure [P]
            starts burning at constant pressure
  The fuel TDC
  shown by the line CD.


                                A
          BDC                                     B


                                               Volume [V]

                  Dept. of Mech & Mfg. Engg.          23
3. Working Stroke: The expansion of gases
  due to the heat of combustion exerts a
  pressure on the piston. Under this impulse,
  the piston moves from TDC to BDC and
  thus the work is obtained in this stroke as
                          C
                             D

  shown by the line DE
             Pressure [P]
         TDC


                                                    E



                              A
        BDC                                     B


                                             Volume [V]

                Dept. of Mech & Mfg. Engg.              24
4. Exhaust Stroke: At the end of the power stroke,
  the exhaust valve is opened & greater part of the
  burnt gases escapes because of their own
  expansion. The drop in pressure at constant
  volume is represented by the line EB. During this
                                  D
  stroke the piston moves   Cfrom BDC to TDC and

  pushes the remaining gases to the atmosphere.
               Pressure [P]
  This stroke is represented the line BA on the P-V
           TDC

  diagram.
                                                      E



                                A
          BDC                                     B


                                               Volume [V]

                  Dept. of Mech & Mfg. Engg.              25
        P V diagram for
CI Engine / Diesel cycle engine
                        D




                 C               D



    TDC
             Pressure

                                                       E


                   A                                   B

                                     Volume
    BDC
                            Theoretical Diesel cycle




          Dept. of Mech & Mfg. Engg.                       26
    Comparison between Petrol & Diesel
                 Engine
         Petrol engine      Diesel engine
1   It works on Otto cycle. It works on diesel cycle.
2   Air and petrol are             Diesel is fed into the
    mixed in the                   cylinder by fuel injection
    carburetor before they         and is mixed with air
    enter into the cylinder.       inside the cylinder.
3   It compresses a                It compresses only air
    mixture of air and             and ignition is
    petrol and is ignited by       accomplished by the
    an electric spark.             heat of compression.
    (Spark Ignition)               (Compression Ignition)
                     Dept. of Mech & Mfg. Engg.          27
    Cylinder is fitted with a       Cylinder is fitted with a
4
    spark plug.                     fuel injector.
5   Less thermal efficiency More thermal efficiency
    and more fuel           and less fuel
    consumption.            consumption.
6   Compression ratio               Compression ratio
    ranges from 4:1to10:1           ranges from 12:1 to 22:1
7   Less initial cost and           More initial cost and less
    more running cost.              running cost.
8   Light weight and                Heavy and occupies
    occupies less space.            more space.

                     Dept. of Mech & Mfg. Engg.           28
                           Difficult to start in cold
     Easy to start even in
9                          weather and requires
     cold weather.
                           heater plugs.
                           They run for longer
     Requires frequent
10                         periods between
     overhauling.
                           overhauls.
     Fuel (petrol) is      Fuel (diesel) is cheaper
11   costlier and more     and less volatile.
     volatile.
     Used in light         Used in heavy duty
12
     vehicles like cars,   vehicles like tractors,
     motor cycle,          trucks, buses,
     scooters, etc.        locomotives, etc.
                   Dept. of Mech & Mfg. Engg.    29
  Working of the Two Stroke
           engine.
In a two stroke engine, a cycle is
completed by the two strokes of the piston.
Out of the four strokes, the two strokes
that are eliminated are, suction and
exhaust strokes.
However, the exhaust process is achieved
by the admission of charge which is
extremely compressed, which drives out
the burnt gases out and this process is
popularly called as SCAVENGING.

              Dept. of Mech & Mfg. Engg.   30
In case of the two stroke engines instead of
  valves, ports are used.
Ports in the cylinder liner, opened and closed by
  the piston motion itself




                  Dept. of Mech & Mfg. Engg.   31
Working of Two Stroke Petrol
          Engine




 First stroke                 First stroke

                Dept. of Mech & Mfg. Engg.   32
     Working of Two Stroke Petrol
               Engine
• First stroke (Downward) As
  soon as the charge is ignited,
  the hot gases force the piston
  to move downwards, rotating
  the crankshaft, thus doing the
  useful work. During this stroke
  the inlet port is covered by the
  piston and the new charge is
  compressed in the crank case
  as shown in the fig.

                     Dept. of Mech & Mfg. Engg.   33
• Further downward movement of the piston uncovers
  first the exhaust port and then the transfer port.
• The burnt gases escape through the exhaust port.

 • As soon as the transfer port opens,
   the compressed charge from the
   crankcase flows into the cylinder.
 • As the compressed charge enters
   into the cylinder, it pushes out the
   exhaust gases from the cylinder.
 • The process of removal of exhaust
   gases by the fresh incoming
   charge is known as scavenging.

                   Dept. of Mech & Mfg. Engg.   34
• Second stroke: (upward)
  Here the piston moves from
  BDC to TDC, during the
  process the exhaust port and
  transfer port are covered and
  the charge in the cylinder is
  compressed. Simultaneously,
  vacuum is created in the
  crankcase, and a new charge
  is drawn into the crankcase
  through the uncovered inlet
  port.

                  Dept. of Mech & Mfg. Engg.   35
• The compressed
  charge is ignited in the
  combustion chamber
  by a spark provided by
  the spark plug and the
  cycle of events is then
  repeated.




                    Dept. of Mech & Mfg. Engg.   36
Working of Two Stroke Diesel
           Engine




   First stroke                                Second stroke


                  Dept. of Mech & Mfg. Engg.                   37
• First stroke (Downward)
  Combustion starts once the
  diesel is injected in to the hot
  compressed air, the hot gases
  force the piston to move
  downwards, rotating the
  crankshaft, thus doing the
  useful work. During this stroke
  the inlet port is covered by the
  piston and the new charge [air]
  is compressed in the crank
  case as shown in the fig.

                    Dept. of Mech & Mfg. Engg.   38
• Further downward movement of the piston
  uncovers first the exhaust port and then the
  transfer port.
• The burnt gases escape through the exhaust port.
 • As soon as the transfer port opens,
   the compressed charge from the
   crankcase flows into the cylinder.
 • As the compressed charge enters
   into the cylinder, it pushes out the
   exhaust gases from the cylinder.
 • The process of removal of exhaust
   gases by the fresh incoming air is
   known as scavenging.
                   Dept. of Mech & Mfg. Engg.   39
• Second stroke: (upward)
  Here the piston moves from
  BDC to TDC, during the
  process the exhaust port
  and transfer port are
  covered and the fresh air in
  the cylinder is compressed.
  Simultaneously, vacuum is
  created in the crankcase,
  and a new charge [air] is
  drawn into the crankcase
  through the uncovered inlet
  port.

                  Dept. of Mech & Mfg. Engg.   40
• At the end of the compression diesel is injected
  to the compressed air which is at a temperature
  higher than the self ignition temperature of
  diesel. Hence, the injected diesel auto ignites
  when it comes in contact with hot air. And the
  cycle of events is then repeated.




                  Dept. of Mech & Mfg. Engg.   41
    Comparison between 4 - stroke &
          2 - stroke Engine
        4 – stroke engine              2 – stroke engine
1   One Working stroke for         One working stroke for
    every two revolution of        each revolution of the
    the Crank shaft                crank shaft
2   Turning moment on the          Turning moment on the
    crank shaft is not even,       crank shaft is more
    hence heavier flywheel         even, hence lighter
    is required                    flywheel is required
3   Less fuel consumption More fuel consumption.


                    Dept. of Mech & Mfg. Engg.       42
    More output due to full          Less output due to
4   fresh charge intake and          mixing of fresh charge
    full burnt gases exhaust.        with the burnt gases.
5   Higher thermal efficiency        Lower thermal
                                     efficiency
6   Engine design is                 Engine design is simple.
    complicated

7   Lesser rate of wear and          Greater rate of wear
    tear.                            and tear.
8   It has inlet and exhaust         It has inlet and exhaust
    valves                           ports
                    Dept. of Mech & Mfg. Engg.          43
                              For the same power, the
     Engine is heavy &
9                             engine is light and compact.
     bulky.

     It requires lesser       It requires greater cooling
10   cooling and              and lubrication. (consumes
     lubrication              more lubricating oil)
11   More initial cost        Less initial cost.
                        More running noise due to
12   Less running noise the sudden release of the
                        burnt gases.
     Used in cars,      Used in mopeds, motor
13   trucks, buses,     cycles, scooters, etc.
     tractors, etc.
                    Dept. of Mech & Mfg. Engg.      44
            Important definitions
 • Brake Power [B.P]: It is the power developed by
   the engine at the output shaft.



Where, N = Speed of the crank shaft in rpm.
T =Torque applied on the brake drum due to load “W”, (N-m)
R = Radius of the brake drum (m)


          T = W x R kg-m
           = 9.81 x W x R N-m

                    Dept. of Mech & Mfg. Engg.     45
• Indicated Power [I.P]: It is the power
  developed inside the IC engine cylinder



Where, n = No. of working cycles/ min.
                             ,

        n = N/2, for 4 stroke engine
         = N, for 2 stroke engine
        L = Stroke length (m), D = Bore diameter (m)
      Pm = Indicated mean effective pressure (N/m2)
        A = Area of the cylinder,
                   Dept. of Mech & Mfg. Engg.   46
• Frictional Power [F.P]: It is the difference between
  the indicated power and the brake power.
                 F.P = [I.P – B.P] kW

                              ,


• Mechanical Efficiency [ηmech ]: It is the ratio of the
  brake power and the indicated power.




                    Dept. of Mech & Mfg. Engg.    47
• Brake thermal Efficiency [ηbth ]: It is the ratio of
  the brake power to the heat supplied by the fuel.




• Indicated thermal Efficiency [ηith ]:
  It is the ratio of the indicated power to the heat
  supplied by the fuel.



  Where, mf = mass of the fuel supplied (kg/hr)
        CV = Calorific Value of the fuel (kJ/kg)
                     Dept. of Mech & Mfg. Engg.        48
               Working of a Simple Carburetor
• The petrol enters the float chamber through the needle valve,
  Purpose of needle valve is to maintain the constant level of
  petrol in the float chamber.

• When engine runs, the air is
  sucked through the venturi tube.
  As a result pressure at throat
  reduces (-) and the petrol issues
  out of the main jet located at the
  throat.
• Thus amount of petrol issuing
  from jet proportional to the
  velocity of air through the venturi
  tube.
                         Dept. of Mech & Mfg. Engg.      49
                Working of a Diesel pump
 • Plunger of the fuel pump is operated by the cam roller
   mechanism, which derives the power from the engine. El.
 • As plunger moves up, the fuel filled above the plunger is
   pressurized and pressurized fuel flow through the barrel.
• The outlet of from the fuel pump
  barrel is closed by a spring loaded
  delivery valve which opens only at
  prescribed pressure of the fuel.

• As the fuel pressure rises, the
  delivery valve and is forced out
  towards the injector.


                         Dept. of Mech & Mfg. Engg.      50
            Working of a Diesel injector
• Fuel under pressure from the
  pump, passes down through
  passages in the injector body
  to an annular space in the
  nozzle and lifts the needle
  valve against pressure of the
  spring
• As a result fuel is forced
  through the holes of injector
  under high pressure resulting
  in finely atomized spray.

                    Dept. of Mech & Mfg. Engg.   51

				
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