CHARGE AIR SYSTEM &

TURBO SUPERCHARGER

P.KumarLECT(D)

Requirement of Air Charging System

• Diesel engine produces Mechanical energy by converting Heat energy derived from burning of fuel inside the cylinder .ie for efficient burning of fuel oil.

FACTORS AFFECTING POWERHumidity- Water vapour in the air takes

the place of oxygen molecules. The molecular weight of water vapor is less than oxygen; as a result moist air is less dense than dry air. Less dense air means decreased performance.

Temperature- temperature affects air density which affects performance: T↑, d↓, P↓

Mixture- fuel: air ratio

SUPERCHARGINGSupercharging is the process of supplying the

intake air to the engine cylinder at a pressure greater than the pressure of the surrounding atmosphere .This is done by blower or compressor.

BENEFITS--PRODUCES 50%OR MORE POWER THAN A NATURALLY ASPIRATED FOR THE SAME BORE AND STROKE DIMENSION.THE POWER TO WEIGHT RATIO IS MUCH MORE IN THIS CASE.

CHARGING OF AIR DURING SUCTION STROKE CAUSES BETTER SCAVANGING

BETTER COOLING OF COMPONENTS i.e.piston,liners,cyl.head. DUE TO COOL AIR CHARGED INTO CYLINDER AND SAVE THEM FAILURE DUE TO THERMAL STRESS.BETTER IGNITION DUE TO HIGHER TEMP DEVELOPED BY CYLINDER.BETTER FUEL EFFICIENCY DUE TO COMPLETE COMBUSTION OF FUEL BY ENSURING AVAILABILITY OF MATCHING QUANTITY OF AIR/ O2.

COMPARISON OF SUPERCHARGED AND NATURALLY ASPIRATED AIR STANDARD DUAL-COMBUSTION CYCLES HAVING THE SAME

COMPRESSION RATIO

AMBIENT

BDCTDC

NATURALLY ASPIRATED

1

2

3 4

5 BOOST

SUPERCHARGED2’

3’ 4’

5’

1’

METHOD OF SUPERCHARGING• Different methods of

supercharging in diesel engines are adopted. They are reciprocating type air compressor, centrifugal blowers run by the exhaust gas driven turbine. The most efficient & economical methods of supercharging is by centrifugal blowers run by the exhaust gas driven turbine

C O M P R E S S O R(C O N V E N T IO N A L M E C H A N IC A LLY D R IV E N S U P E R C H A R G E R

T U R B O S U P E R C H A R G E R(U T IL IZ IN G E X H A U S T G A S E S T O D R IV E A C O M P R E S S O R )

S U P E R C H A R G IN G

POWER

INLET MANIFOLDAMBIENTAIR

EXHAUSTOUTLET

TURBINE

COMPRESSOR

EXHAUST MANIFOLD

POWERINLET MANIFOLD

CHAINORGEARDRIVE

EXHAUST OUTLET

COMPRESSOR

AMBIENTAIR

CHARGE AIR/ TURBO SUPERCHARGING SYSTEM

IMPORTANT SCHEDULE ACTIVITIES• insp of leakages and tell tale hole checking of A/Cooler: T-20•Changing of Turbo Filter Element: T-60/ 80• Turbo overhauling: M-12, 24, 48 (depending of type of turbo)

Working Principle Of Turbo Supercharger

The exhaust gas from all the cylinders accumulate in the common exhaust manifold at the end of which, turbo-supercharger is fitted. The gas under pressure enters the turbo-supercharger and passes through the fixed nozzle ring. Then it is directed on the turbine blades at increased pressure and at the most suitable angle to achieve rotary motion of the turbine at maximum efficiency.

After rotating the turbine, the exhaust gas goes out to the atmosphere through the exhaust chimney. The turbine has a centrifugal blower mounted at the other end of the same shaft and the rotation of the turbine drives the blower at the same speed. The blower connected to the atmosphere through a set of oil bath filters, sucks air from atmosphere.

The air then passes through the diffuser inside the turbo-supercharger, where the velocity is diffused to increase the pressure of air before it is delivered from the turbo-supercharger.. But due to compression heat develops, the density of air decreases. Then it passes through after cooler where cooling water of lower temperature is circulated through the tubes and around the tubes air passes.

The heat in the air is thus transferred to the cooling water and air regains its lost density. From the after cooler air goes to a common inlet manifold connected to each cylinder head. The maximum rotational speed of the turbine is 18000 rpm for the 720A model Turbo supercharger and creates 1.8 kg/cm2 air pressure in air manifold of diesel engine.

Main Components Of TSC• Gas Inlet Casing : It is made of CH20 stainless steel

which is highly heat resistant. The function of this casing is to take hot gases from the exhaust manifold & pass them through the nozzle ring.

• Turbine Casing : It is made of alloy CI or fabricated. It is fitted in between inlet & intermediate casing. This casing is water cooled.

• Intermediate Casing : It is made of alloy CI or fabricated like turbine casing. It is placed between turbine & intermediate casing. This casing is also water cooled. It separates exhaust & air side.

• Blower Housing Assembly : Air enters through the blower inlet axially & discharge radially the vane diffuser. The vane diffuser is a aluminum casting.

• Rotor Assembly : It contains rotor shaft, rotor blade, inducer etc. It is dynamically balanced component, as it has a very high rotational speed.

Comparison Between Air Compressor & Centrifugal blowers

Sl No. Air Compressor Centrifugal Blowers

01. Large Size Small Size

02. Requires More Power Requires Less Power

03. Does Not Maintain Proper Air – Fuel Ratio

Maintains Proper Air – Fuel Ratio

04. Less Efficient More Efficient

Turbo Run – Down Test

• This test is done to check the performance of turbo supercharger.

• Procedure for Turbo Run – Down Test• The engine is started at 8th notch for some

time and then at 4th notch ensuring water temperature should be 60°C.

• Engine is then shut down through the over speed trip mechanism.

• When the rotation of the crank shaft stops, the free running time of the turbine is watched through the chimney exhaust gas/torch light and recorded by a stop watch.

• The minimum tine allowed for free running is 90 sec and maximum 180 sec.

• If time is less than 90 sec, bearing of turbo supercharger is jammed. Fail the loco.

• If time is more than 180 sec, turbine is moving freely. Check towards compressor side.

TYPE OF TURBO SUPERCHARGERS

SL NO. TYPE OF TSC

RPM TRD THROTTLE POSITION FOR TRD CHECKING

FITTED IN LOCOMOTIVE

OVH DONE AFTER

1 ABB 28000 40-85 SEC 4TH WDM2,WDG3A, 18 MONTHS

2 NAPIER 28000 40-85 SEC 4TH WDM2,WDG3A, 03 YEARS

3 GE 28000-30000 90-120 SEC 4TH WDM3A,WDG3A, 06 YEARS

4 HYSPANO SUIZA

27000 90-180 SEC 4TH WDM3A,WDG3A 06 YEARS

5 720 A 18000 90-120 SEC 4TH WDM2 06 MONTHS

COMPARISON OF DIFFERENT MODELS OF TSC

Time Period 1960-90 1990-95 1995-2000 2001

Technology wise classification of TSC

Conventional High Efficiency Twin Discharge New Generation

Turbo models used by RDSO

ALCO 720A Napier NA-295ABB VTC304

GE 7S 1716 HS5800 NGT ABB TPR61

Overall Efficiency

50% 62% 64% 70%

SFC gm/BHP/Hr 168 156 154 151

Exhaust gas temp

600 Degree C 580 500 500

Frequency of Maintenance

6 months 2-3 Years 6 Years 3-6 Years

HIGH EFFICIENCY TSC (SINGLE DISCHARGE)

NAPIER ABB VTC304

TWIN DISCHARGE TURBOCHARGER

ABB VTC-304 TD GE 7S 1716

NEW GENERATION TURBOCHARGERS

ABB TPR61 HS5800 NGT

SALIENT FEATURES• EFFICIENCIES

• TURBINE 87.2%• COMPRESSOR 81.5%

• TEMP. FOR WHICH CRITICAL COMPONENTS ARE DESIGNED– COMPRESSOR STAGE--AIR TEMP UPTO 190.6OC– TURBINE STAGE

----GAS TEMP. UPTO 593.3OC ON INLET SIDE----GAS TEMP. UPTO 482.2OC ON OUTLET SIDE

CAUSES OF LOW BOOSTER AIR PRESSURE/LOW HAULING POWER

• LOW F/OIL PRESSURE.• FIP OR NOZZLE DEFECTIVE.• GOVERNOR MALFUNCTIONING.• TSC DEFECTIVE.• WHEEL SLIP OCCURING.• DEFECTS IN EXITATION SYSTEM.• DEFECTIVE AFTER COOLER.• BOOSTER AIR LEAKAGE FROM AIR ELBOW JOINTS.• EXHAUST GAS LEAKAGE FROM MANIFOLD(BELLOWS

CONNECTOR CRACK).