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					Technical Training
Engine Principles of Operation
Four Events Explained
 Four   distinct events take place:

        Air and fuel are mixed and drawn into the engine

        The air-fuel mix is compressed to create as much
         energy as possible

        The compressed air-fuel mix is ignited and the
         combustion gases expand

        The left over gases of combustion are pushed out of the
         engine
Four-Strokes Explained

 We   usually speak of the four events as:
         Intake
         Compression
         Power
         Exhaust


 We   usually talk of these events in the above order

 You   may see them explained using other terms, such as:
        Induction, Compression, Expansion, Exhaust
Four-Stroke
Components




              Valve Train
Intake Stroke

  Key:
                     Air-Fuel Mix
  1.Spark Plug       Being Drawn In
  2. Inlet Port
  3. Intake Valve
  4. Piston
  5. Crankshaft
  6. Combustion
  Chamber
  7. Exhaust valve
  8. Exhaust Port
Compression Stroke

  Key:
  1.Spark Plug
  2. Inlet Port      Air-Fuel Mix
                     Being
  3. Intake Valve
                     Compressed
  4. Piston
  5. Crankshaft
  6. Combustion
  Chamber
  7. Exhaust valve
  8. Exhaust Port
Power Stroke
 Key:
 1.Spark Plug
 2. Inlet Port
                    Yellow: Spark
 3. Intake Valve
                           Air-Fuel
 4. Piston
                           Mix Is
 5. Crankshaft             Ignited
 6. Combustion
 Chamber
 7. Exhaust valve
 8. Exhaust Port
Exhaust Stroke

Key:
1.Spark Plug
2. Inlet Port
                   Exhaust Gases
                   Being Pushed
3. Intake Valve    Out
4. Piston
5. Crankshaft
6. Combustion
Chamber
7. Exhaust valve
8. Exhaust Port
Four Events in Order



 Intake      Compression         Power           Exhaust




          Two Full Rotations of the Crankshaft
Two-Strokes Explained

In a two-stroke design, the
four events of intake,
compression, power, and
exhaust, are actually
overlapped and combined,
so that a power stroke takes
place on every revolution of
the crankshaft
Two-Stroke Engine Components




           What’s Missing?
Two-Stroke Design
             Piston Port Design

                                  Cylinder        Carburetor

Carburetor


Cylinder




                                        Reed Valve Design
Intake and Compression
 Stroke
Key:
                      Compression
1. Combustion Chamber and Ignition of
2. Piston             Air-Fuel Mix
3. Exhaust Port
4. Inlet Port       Yellow: Spark
5. Crankcase
6. Crankshaft         Air-Fuel Mix
7. Transfer Port      Being Drawn
                      Into Crankcase
8. Spark Plug
Power and Exhaust Stroke

 Key:
 1. Combustion Chamber
 2. Piston
                    Power Stroke
 3. Exhaust Port
                    and Exhaust
 4. Inlet Port      Gases Pushed
 5. Crankcase       Out
 6. Crankshaft           Air-Fuel Mix
 7. Transfer Port        Transfer to
 8. Spark Plug           Combustion
                         Chamber
Comparison of
Two-Stroke and Four-Stroke
     Power Stroke on Every
    Revolution of Crankshaft

Power Stroke on Every Other
    Revolution of Crankshaft
Torque
 Two-Stroke Turns
Crankshaft for Short
 Duration, TDC to
Top of Exhaust Port




Four-Stroke Turns
 Crankshaft For
 Long Duration,
  TDC to BDC
Scavenge Loss




                Unburned Fuel
                 Escapes Out
                  the Open
                 Exhaust Port
Port Design



              2 Transfer Ports   4 Transfer Ports
Applications of Small Hand Held Engines
Summary
 Four-stroke    engines have good efficiency and low emissions
 Four-stroke    engine design has distinct events occurring in order:
     Intake
     Compression
     Power
     Exhaust
 Two-stroke    engines have a high power to weight ratio
 Two-stroke    engine design has the events overlapped and
 combined:
     Intake/ Compression
     Power/Exhaust
 Both designs have strengths and weaknesses
 New designs are being developed and introduced

				
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posted:9/13/2012
language:English
pages:20