TURBOCHARGER

BY TURBOCHARGING AN ENGINE, THE FOLLOWING ADVANTAGES ARE OBTAINED:

• INCREASED POWER FOR AN ENGINE OF THE SAME SIZE OR REDUCTION IN SIZE FOR AN ENGINE WITH THE SAME POWER OUTPUT.
• REDUCED SPECIFIC FUEL OIL CONSUMPTION - MECHANICAL, THERMAL AND SCAVENGE EFFICIENCIES ARE IMPROVED DUE TO LESS CYLINDERS, GREATER AIR SUPPLY AND USE OF EXHAUST GASSES.
• THERMAL LOADING IS REDUCED DUE TO SHORTER MORE EFFICIENT BURNING PERIOD FOR THE FUEL LEADING TO LESS EXACTING CYLINDER CONDITIONS.

CONSTRUCTION DETAILS:-

• THE TURBOCHARGER CONSISTS OF A SINGLE STAGE IMPULSE TURBINE CONNECTED TO A CENTRIFUGAL IMPELLER VIA A SHAFT.

• THE TURBINE IS DRIVEN BY THE ENGINE EXHAUST GAS, WHICH ENTERS VIA THE GAS INLET CASING. THE GAS EXPANDS THROUGH A NOZZLE RING WHERE THE PRESSURE ENERGY OF THE GAS IS CONVERTED TO KINETIC ENERGY. THIS HIGH VELOCITY GAS IS DIRECTED ONTO THE TURBINE BLADES WHERE IT DRIVES THE TURBINE WHEEL, AND THUS THE COMPRESSOR AT HIGH SPEEDS (10 -15000 RPM). THE EXHAUST GAS THEN PASSES THROUGH THE OUTLET CASING TO THE EXHAUST UPTAKES.

      · ON THE AIR SIDE AIR IS DRAWN IN THROUGH   FILTERS, AND ENTERS THE     COMPRESSOR WHEEL AXIALLY WHERE IT IS ACCELERATED TO HIGH VELOCITY. THE AIR EXITS THE IMPELLER RADIALLY AND PASSES THROUGH A DIFFUSER, WHERE SOME OF THE KINETIC ENERGY GETS CONVERTED TO PRESSURE ENERGY. THE AIR PASSES TO THE VOLUTE CASING WHERE A FURTHER ENERGY CONVERSION TAKES PLACE. THE AIR IS COOLED BEFORE PASSING TO THE ENGINE INLET MANIFOLD OR SCAVENGE AIR RECEIVER.

     ·THE NOZZLE RING IS WHERE THE ENERGY IN THE EXHAUST GAS IS CONVERTED INTO KINETIC ENERGY. IT IS FABRICATED FROM A CREEP RESISTANT CHROMIUM NICKEL ALLOY, HEAT RESISTING MOLY-CHROME NICKEL STEEL OR A NIMONIC ALLOY WHICH WILL WITHSTAND THE HIGH TEMPERATURES AND BE RESISTANT TO CORROSION.

•  LABYRINTH SEALS OR GLANDS ARE FITTED TO THE SHAFT AND CASING TO PREVENT THE LEAKAGE OF EXHAUST GAS INTO THE TURBINE END BEARING, OR TO PREVENT OIL BEING DRAWN INTO THE COMPRESSOR.

      

     

• A LABYRINTH ARRANGEMENT IS ALSO FITTED TO THE BACK OF THE COMPRESSOR IMPELLER TO RESTRICT THE LEAKAGE OF AIR TO THE GAS SIDE

           

• DISCOLORING OF THE OIL ON A ROTOR FITTED WITH A ROLLER BEARING WILL ALSO INDICATE A FAILURE IN THE TURBINE END GLAND.

TURBOCHARGER TYPES

(A) AXIAL FLOW :-

•     SINGLE STAGE IMPULSE REACTION TURBINE IS USED.
•     TURBINE DRIVES A CENTRIFUGAL COMPRESSOR.
•     EXHAUST FLOW IN AND OUT OF TURBINE BLADE IS ALONG THE AXIS OF THE SHAFT.
•     MOST COMMONLY USED IN MARINE APPLICATION

(B) RADIAL FLOW

·         EXHAUST FLOW INTO THE TURBINE BLADE IS ALONG THE RADIAL DIRECTION.
·         OUTLET OF TURBINE IN ALONG THE AXIX OF ROTOR.
·         USED IN SMALL HIGH SPEED ENGINES.  

MATERIALS USED IN T/C

TURBINE WHEEL, NOZZLE RING, ROTOR SHAFT AND BLADES:

·  NICKEL-CHROME ALLOY (NI 75%, CO 18%, TI 3%, AL 2%, CR 2%)

TURBINE CASING:

• CAST IRON WITH CORROSION PREVENTIVE PLASTIC COATINGS IN CASE OF WATER COLED T/C.

COMPRESSOR IMPELLER, VOLUTE CASING, DIFFUSER, & INDUCER:

• ALUMINIUM ALLOY FOR LIGHT WEIGHT AND STRENGTH OR MORE EXPENSIVE TITANIUM 

TURBOCHARGER SURGING

·     WHEN THE DISCHARGE PRESSURE EXCEED THE PRESSURE BUILD UP IN THE DIFFUSER AND IMPELLER.

·     IT PRODUCES A BACK FLOW OF AIR FROM DISCHARGE TO SUCTION.

·     BACK FLOW FROM SCAVENGE AIR MANIFOLD TO THE T/C DIFFUSER.

·     CHARACTERISED BY NOISE AND VIBRATION.

RASONS FOR T/C SURGING

• ·     SCAVENGE SPACE FIRE
• ·         DIRTY NOZZLE AND BLADE
• ·         INDIVIDUAL CYLINDER MISFIRE
• ·         CHOCKED SCAVENGE/EXHAUST PORT
• ·         INCORRECT MATCHING OF T/C TO ENGINE
• ·         POOR SCAVENGING OR LEAKY EXHAUST VALVE
• ·         SUDDEN LOAD CHANGE BY BAD WEATHER
• ·         POOR POWER BALANCE

SURGING REMEDY AND ACTION

• REDUCE ENGINE SPEED

              -IT WILL REDUCE SCAVENGE AIR PRESSURE

              -HENCE LESS TENDENCY OF REVERSE FLOW