ENGINE AND ITS TYPES
ENGINE
IS A MACHINE WHICH CONVERTS ONE FORM OF ENERGY TO ANOTHER .
INTERNAL COMBUSTION ENGINE
IN
THIS TYPE OF ENGINE COMBUSTION TAKES PLACE INSIDE THE CYLIDER
EXAMPLE
– PISTON ENGINE
EXTERNAL COMBUSTION ENGINE
IN
THIS TYPE OF ENGINE COMBUSTION TAKES PLACE OUTSIDE THE CYLINDER
EXAMPLE
– STEAM ENGINE
FOUR STROKE ENGINE
MOST
OF THE AIRCRAFTS OPERATE ON THE FOUR STROKE ENGINE PRINCIPLE . THIS IS ALSO
CALLED THE OH CYCLE , BEING THE
NAME OF THE INVENTER OF THE FIRST OH CYCLE ENGINE . THE ENGINE COMPRISES OF TWO
REVOLUTIONS OF THE RANK – SHAFT & CAONTAINS TWO UPWARD & TWO DOWNWARD
MOVEMENTS OF THE PISTON . THE CYCLE OF ROTATION IS COMMENCED BY ROTATING THE
RANK SHAFT EXTERNALLY UNTIL THE FIRST POWER STROKE OCCURS . THE MOVING PARTS
GAIN SUFFICIENT MOMENTUM FROM THEPOWER DEVELOPED TO COMPLETE THE CYCLE &
KEEP THE RANK – SHAFT TURNING UNTIL THE NEXT POWER STROKE OF FUEL IGNITION ARE
SUPPLIED TO THE ENGINE , IT
CONTINUES TO RUN .THE SEQUENCE OF OPERATION IS AS FOLLOWS :
1)
INDUCTION
STROKE -
THE INLET VALVE OPENS , THE PISTION MOVS FROM TDC TO BDC & AIR
FUEL MIXTURE IS DRAWN INTO THE CYLINDER.
2)
COMPRESSION
STROKE – THE
INLET VALVE CLOSES , THE PISTON MOVES FROM BDC TO TDC ,
COMPRESSING THE MIXTURE IN THE COMBUSTION CHAMBER.
3)
POWER
STROKE – WHEN AIR FUEL MIXTURE IS COMPRESSED TO THE
CHAMBER , A SPARK IS PRODUCED BY THE SPARK PLUG FITTED IN THE HEAD OF THE ENGINE
. THE IGNITION OF FUEL CAUSES A HIGH GAS PRESSURE IN THE CHAMBER . AS BOTH THE
VALVES ARE KEPT CLOSE THE INCREASED GAS PRESSURE FORCES THE PISTONDOWN IN THE
CYLINDER.
4)
EXHAUST
STROKE – THE
EXHAUST VALVE OPENS , THE PISTON MOVES FROM BDC TO TDC EXPELLING
ALL THE BURNT GASES . THIS STROKE COMPLETES ONE CYCLE OF OPERATION .
ADVANTAGES
OF 4 STROKE ENGINE
1)
ECONOMY
OF FUEL .
2)
LOWER
GRADE FUEL CAN BE USED , WHICH IS CHEPER & LESS VOLATILE .
3)
MINIMUM
FIRE RISK .
4)
HIGH
POWER OUTPUTS ARE POSSIBLE EVEN
WITH SINGLE CYLINDER ENGINE.
1)
HEAVY
WEIGHT .
2)
LARGE
DIMENSIONS TO INCREASE GREATER FRONTAL
AREA.
1)
LOW
WEIGTH FOR HORSE POWER DEVELOP AS EVERY DOWNWARD MOVEMENT OF THE PISTON IS A
POWER STROKE .
2)
ESY TO
START
3)
LESS
FRONTAL AREA
1)
FUEL
CONSUMPTION IS MORE THAN 4 STROKE ENERGY .
2)
WASTAGE
OF FUEL DUE TO MIXING WITH EXHAUST
GASES .
3)
EXCESSIVE
CONSUMPTION OF OIL BECAUSE THE CRANK CASE IS USED FOR COMPRESSING THE INCOMING
FUEL