All About Turbocharger

ALL ABOUT TURBOCHARGER

1. Construction of exhaust gas Turbocharger:

    Exhaust gas turbocharger consists of a single-stage centrifugal blower and turbine which are built together as one unit.

    The exhaust gas from the engine flows through the water-cooled gas inlet casing, expands in the nozzle ring, transfers its energy to the blades of the turbine rotor and passes through the cooled gas out-casing and the exhaust duct into the atmosphere. 

    The air required for the engine reaches the guide wheel and the impeller after passing through the combined air suction filter and silencer. It then leaves the diffuser and pressure connection pipe of the air outlet casing.

    The partition wall completely separates the air and gas chamber. Sealing air for the labyrinth seal of the turbine rotor is taken through the duct from the blower. This prevents exhaust gas from entering the balance duct and the bearing housing.

    The rotor shaft is supported by a double ball bearing on the blower side and by a single ball bearing on the turbine side. The ball bearing on the turbine side allows the shaft to expand freely in the axial direction. Both the bearing is flexibly supported by means of damping spring. The passages balance the pressure in the bearing housing and prevent any loss of oil.

    Bearing covers are provided with a oil filling plug, oil drain plug, and oil level glass.

    The core holes which serve as cooling water inlet and outlet connection at the gas casing is provided with baffles to protect the casing against corroding and eroding action of the incoming jet of water.

    The core hole of the turbine casing is provided with anti-corrosive plugs in case of using seawater.

    Care should be taken to ensure good water flow through the charge air-cooler which is required for high super-charging.

    The air inlet and suction side must be fitted with a filter for protection against solid matters, dust and foreign substances.

2. Speed of Turbocharger:

    The speed of the turbocharger depends entirely upon the load on the Engine and its operation, since the charger works without any mechanical control.

    Note: Additional method of measuring the speed (R.P.M) is to connect a special electric tachometer to the bearing cover at blower side.

3. Suction and exhaust manifolds of the turbocharger:

The gas and air manifolds should never be connected rigidly to the charger. Because of the thermal expansion occurring due to heat, expansion-bellow should be used.

 4. Lubricating oil and temperature of turbocharger:

    Recommend the use of a good quality mineral turbine oil. The temperature is related to the turbine speed, suction air temperature for the blower side, and cooling water temperature for the turbine side. The maximum lub-oil temperature permissible is 120°C (248°F).

5. Before taking into service of turbocharger:

    Remove lub-oil filling plug and all drain plugs, check whether any rainwater of condensation has collected in the gas outlet-casing; if necessary, to clean carefully. All plugs to be replaced and fill both the reservoirs with clean and recommended lubricating oil up to the limit mark.

6. During the first taking into service of turbocharger:

    (i) Turn over the engine for a short time with the starter & ensure by listening through a metal rod whether the turbocharger rotates quietly or silently and freely.

    (ii) Turn over the engine for the short time, after that again check [item No. (i)]. As soon as engine has started check all gas, air and cooling water lines for leaks.

    (iii)(a) Check turbocharger speed (R.P.M

          (b) Turbocharging pressure.

          (c) Temperature before entering after leaving the turbine (cooling water a exhaust gas).

          (d) Cooling water temperature of the air cooler.

    (iv) The temperature rise of the cooling water in each of the gas inlet and outlet casing, gives an approximate idea of the flow. The difference of temperature is set to 8°C to 12°C (14°F to 22°F) with full load, by using restrictors in the water outlet connection.

        (a) The cooling water inlet temperature should be within 50°C to 70°C (122°F to 158°F) for marine engine but not more than 80°C (176°F). For land engine cooling water inlet temperature should be 50°C.

        (b) Cooling water outlet temperature should be approx. 10°C (18°F) under the boiling point.

7. Taking a turbocharger into service which was preserved.

     (a) Remove wooden blanking covers and clean the turbocharger externally.

    (b) Remove the bearing flanges from the bearing housing, clean carefully the oil reservoirs.

    (c) Replace bearing cover and fill with clean recommended lubricating oil up to the limit mark.

8. The following data should be recorded for a running turbocharger.

    (a) Output of the Engine. 

    (b) Speed (R.P.M) of the engine. 

    (c) Air inlet temperature.

    (d) Pressure loss in the air filter (if manometer is fitted).

    (e) Charge air pressure.

    (f) Air temperature after the blower and also after the air cooler (if fitted).

    (g) Inlet temperature of the cooling water to the air cooler.

    (h) Inlet temperature of the cooling water from the turbine casing.

    (i) Outlet temperature of the cooling water from the turbine casing.

    (j) Exhaust gas temperature after the cylinder.

    (k) Exhaust gas temperature before and after the turbine.

    (l) Turbocharger speed (R.P.M) by the tachometer at full load.

9. The following should be checked and cleaned periodically.

    (a) Air Filter.

    (b) Check the air pressure loss (if the manometer is installed on the filter).

    (c) Anti-corrosion zinc to be checked; if necessary, to be replaced.

    (d) Lubricating oil should be renewed every 500 hours running where possible, but not longer 1,000 hours running.

    (e) If any unusual wear, damage, heat, expansion and noise should occur to he bearing unit, replace it immediately.

    (f) The cooling water spaces of the turbine casing should be checked if necessary.

    (g) drain accumulated moisture form the gas outlet casing and from the air manifold.

    Note: Recommended hours for replacement of bearing unit depend upon the class of turbocharger, it varies from 6,000 to 16,000 hours. 

10. Prevention of turbocharger from getting dirty.

    (a) Avoid suction of contaminated air.

    (b) Improve the performance of air filter.

    (c) Keep the combustion in good condition.

    Note: Carbon which sticks on the back of blower impeller is mainly from turbine side through backward flowing. To prevent the sticking of carbon, it is necessary to keep the combustion is in good condition at all times. Sticking of carbon is notable specially in case of remarkable change in load.

11. Washing procedure of blower.

In some marine engine burning heavy fuel oil equipped with washing unit, be sure to wash the blower by use of its washing unit, once in about five days otherwise turbocharger blower may foul and exhaust temperature will rise and shorten the life of fuel injection valve.

              Carry out this washing while the engine is running on more then 50% load.

              It is possible to clean the blower and turbine sides by injection Teepol and water solution. The connecting point for injecting Teepol solution at blower side is equipped on the blower-casing.

(a)    Open the drain cock of inter-cooler inlet air duct or tube.

(b)   Turn the knob of the blower washer over counter-clockwise to detach the cover, pour blower washing into the washer by the specified quantity and attach the cover.

(c)  Open the cock of the washer for about 5 seconds. By this, washings is sprayed against the blower to accomplish washing.

(d) After washing by use of the blower washings, pour fresh water of the same quantity as blower washing into the blower washer and carry out water spraying in the same way such as (c).

(e)  After washing is over, close the cock of the washer.

(f) If the indication of boost air pressure gauge is not restored, wait next 10 minute and then repeat the above procedure.

(g)  after washing of the blower, preform load running of engine for more than one hour.

(h) If there is no restoration of boost air pressure even if the above procedure had been carried out, overhaul and clean blower side and turbine side of turbocharger.

        Note: For one-time use, quantity of blower washing Teepol and water solution is about 0.3 litre (water with Teepol or detergent powder).

POSSIBLE CAUSES FOR FAULTS OR TURBOCHARGER

1. Exhaust gas temperature higher than normal:

    (a) High intake air temperature when running without air cooler.

    (b) Fault in injection system.

    (c) Lack of air due to dirt in air filter.

    (d) Blower dirty.

    (e) Exhaust back pressure too high.

    (f) Turbine blading damaged.

    (g) Leaking gas or air pipe between engine and turbocharger.

   (h) Air cooler dirty, insufficient cooling water. Cooling water temperature too high and insufficient venting. 

2. Turbocharging pressure lower than normal:

    (a) Air receiver not air-tight.

    (b) Ducting between engine and turbine; not gas light.

    (c) False indication by pressure gauge or connection to it is leaking.

    (d) Air filter dirty, accounting pressure loss.

    (e) Turbocharger dirty.

    (f) Labyrinth seal damaged.

    (g) Turbine blading damaged.

    (h) Nozzle ring damaged.

    (i) Exhaust back pressure too high.

3. Turbocharging pressure higher than normal:

    (a) Fault in injection system.

    (b) Output of engine higher than expected.

    (c) Incorrect indication by pressure gauge.

    (d) Dirty or partially blocked nozzle ring.

4. Turbocharger vibrate:

    (a) Appreciable unbalance in the shaft due to very dirty charger of damaged turbine blading.

    (b) Distorted or misaligned shaft.

    (c) Defective bearings.

    (d) Incorrect assembly of the bearing, especially of the damping springs.

5. Noise during running and turbocharging not developing rated R.P.M:

    (a) Bearing damaged.

    (b) Rotor rubbing.

    (c) Turbocharger dirty.

    (d) Foreign bodies in the turbocharger.

6. Gas casing leaking:

    (i) Cracks: (a) Thermal stresses occur with uneven cooling, with lack of water or with excessive furring.

    (ii) Corrosion: (a) When the water drain is closed water can gather in the gas outlet casing e.g. when the engine is at rest water may enter via the chimney.

        (b) Rain water acts corrosively with the sulphur residue from the fuel.

        (c) Sea water some time promotes corrosion.

        (d) Copper pipes should not be directly connected to the cast iron casings.

        (e) Anti-corrosion plug used up.

    (iii) Erosion: (a) This danger only occurs if cooling water has a high sand content.

        (b) Baffle plates at the cooling water inlet are missing.

    (iv) Cavitation: (a) No orifiees in the cooling water inlet pipes.

        (b) The inner diameter of the cooling water inlet pipe should correspond to the connection on the turbocharger. 

7. Bearing oil becomes dark very quickly:

    (a) Exhaust gas entering in bearing housing.

    (b) Sealing air duct blocked.

    (c) Shaft seal on turbine side damaged.

    (d) Guard in balance duct blocked.

    (e) Clearance in sealing bush too high.

    (f) Unsuitable lubricating oil.

    (g) Too high oil temperature.

8. Losses of lubricating oil:

    (a) Clearance in the sealing bushes too high.

    (b) The balance passages blocked.

    (c) Bearing covers plugs either missing or not tight enough.

    (d) Individual nuts on studs for bearing cover not tight enough.

9. Moisture in charger or in bearing housing:

    (a) Ingress of water through the ducts and condensation in the bearing housing due to high humidity of air and very cold cooling water or considerable changes in temperature when the turbocharger is not running.