IT IS A METHOD OF OBTAINING MORE POWER WITHOUT INCREASING THE WEIGHT OF THE ENGINE. AIR IS ADMITTED AT HIGHER PRESSURE BUT THE POWER OF THE ENGINE INCREASES DUE TO THE LARGE MASS OF THE AIR THAT ENTERS DUE TO WHICH MORE FUEL CAN BE BURNT AND HENCE POWER OUTPUT WILL BE INCREASED.
SOMETIMES A QUESTION IS ASKED AS TO WHAT CONTROLS THE POWER OF THE ENGINE?
IN THIS CASE THE ANSWER WILL BE THE AMOUNT OF AIR PRESENT INSIDE THE CYLINDER DURING POWER STROKE WHEN BOTH THE VALVES ARE FULLY SHUT.
TURBOCHARGER BLADE CONSTRUCTI
TURBINE BLADES APPEAR TO BE TWISTED FROM ROOT TO THE TOP. THESE TWISTED BLADES HELP IN SMOOTH ENTRY TO THE BLADES AT ALL DIAMETER FROM ROOT TO THE TIP.
DAMPING LACE WIRE IS DISPENSED WITH FOR BETTER FLOW CHARACTERISTICS OF THE GAS OVER THE BLADES. IT ALSO PREVENTS VIBRATION.
INVERTED FIRE TREE SHAPED BLADE ROOT IS FITTED IN SIMILAR SHAPED GROOVES
BLADES ARE NOT PRESSED TIHT IN THE GRROVR AND SO THERE IS NO INITIAL STRESS IN METAL BUT IT BECOMES TIGHT AT WORKING TEMPERATURE AND REVOLUTION DUE TO HEAT EXPANSION AND CENTRIFUGAL EFFECT.
THE BLADES ARE LOCKED IN GROOVE TO RESIST SLIDING OUT BY AXIAL TRUST.
COMPRESSOR OF TURBOCHARGER:-
AIR IS DIRECTED THROUGH SILENSER AND GUIDEWAYS WITH SOUND ABSORBER ON THE HUB OF THE IMPELLOR WITHOUT SHOCK AND MINIMUM FRICTION. WHILE FLOWING THROUH THE IMPELLOR VANES THE FLOW IS GIVEN A RADIAL ACCELARATION AND CENTRIFUGAL FORCE DUE TO WHICH IT LEAVES THE IMPELLOR WITH A PRESSURE AND VELOCITY. THE DISPLACEMENT OF AIR CREATES A SUCTION INDUCING A CONTINOUS FLOW THROUGH THE SYSTEM.
THE PROCESS OF DIFFUSION STARTS WITHIN THE VANE SPACE OF THE DIFFUSER. THE KINETIC ENERGY OF THE FLUID (AIR)AT EXIT IS CONVERTED INTO A PRESSURE HEAD. FURTHER DIFFUSION TAKES PLACE WHEN THE FLOW IS PASSED THROUGH THE VOLUTE CASING OF GRADUAL INCREASING AREA.
TURBOCHARGER BEARING TYPES:-
- ROLLING CONTACT BEARING:-
A) FITTED AT THE OUTER ENDS OF THE ROTOR SHAFT FOR EASY ACCESSIBILITY.
B) BALL RACE FITTED AT COMPRESSOR END AS USED AS ANCHOR TO LOACTE SHAFT AXIALLY.
C) ROLLER BEARINGS ARE FITTED IN TURBINE SIDE WHICH ARE FREE TO SLIDE WITHIN THE BEARING HOUSING TO ACCOMODATE HEAT EXPANSION OF ROTOR RELATIVE TO CASING. BEARINGS ARE PROVIDED WITH LEAF TYPE SPRINGS ON THEIR OUTER SURFACE AND THUS COVERED OUTWARDLY WITH A RESILIENT MOUNTING.
ADVANTAGES:-
- ANTI FRICTION PROPERTY WHICH FACILITATES EASY STARTING AND ACCELERATION.
- CLEARANCE IS EXTREMELY SMALL AND HENCE IT MAINTAINS AN EXACT ALIGNMENT OF ROTOR SHAFT.
- CAN BE REMOVED WITHOUT DISMANTLING COMPRESSOR WHEEL AND ROTOR SHAFT.
- ANY IMBALANCE OF ROTOR SHAFT CAUSED BY CONTAMINATION IS ABSORBED BY DAMPING SPRING ASSEMBLY IN BEARING.
DISADVANTAGES:-
- TURBOCHARGER IS LONGER AND SUBJECT TO VIBRATION.
- GETS DAMAGED DUE TO BRINEELING.
2. SLEEVE TYPE BEARING:-
IT HAS A SINGLE SLEEVE BEARING AT THE CENTER WITH ADDITIONAL BEARING BUSH FOR FINER ALIGNMENT AND ADJUSTMENT OF TURBINE AND IMPELLOR CLEARENCE.
- COMPRESSOR SIDE :- AXIAL THRUST BEARING
THIS MAKES T/C COMPACT WITH LIGHTER ROTOR DUE TO SMALL INERTIA AND SHORTE DISTANCE BETWEEN THE BEARING. AND GIVE BETTER ACCESSIBILITY TO TURBINE AND COMPRESSOR.
THESE BEARINGS ARE LONGER IN LENGTH AND PROVIDE GREATER STABILITY TO HIGHER SPEED ROTOR SHAFT.
MAIN THRUST IS TAKEN BY SEALING AIR ACTING ON TURBINE DISC. THE AIR FLOW PAST LEAK OFF LAYBRINTH AT RATE DEPENDANT UPON CLEARANCE AS TURBOCHARGER LOAD INCREASES SO DOES AXIAL THRUST. THIS CAUSES ROTATING ELEMENT TO MOVE TOWARDS COMPRESSOR END AND CLEARANCE AT LEAK OFF LAYBRINTH DECREASES, AIR FLOW REDUCES, THRUST CHAMBER AIR PRESSURE ACTING ON TURBINE DISC INCREASES.