Turbochargers Flashcards
State the function of Suction Filters
Removing contaminants like dust and debris Prior to Entry of the engine
State the function of the Exhaust Grids
To collect any foreign debris After the Combustion Process
State the function of the Charge Air Cooler
Used to increase the Density of the air to allowing for more air creating better combustion
With reference to Main Engine Turbochargers, Explain their function
- To make use of the exhaust gasses produced by the engine
- Turbochargers increase the engines power output by compressing the air which in turn increases the air density and then forcing it into the engine which allows the engine to burn more fuel
With reference to Main Engine Turbochargers, State TWO advantages of fitting them
- Increases engine efficiency by increasing the power out put
- As it forces more air into the engine it allows for less fuel to be used which in turn improves the fuel efficiency
With reference to Main Engine Turbochargers, Explain how they are cooled and lubricated
LUBRICATION
- Usually cooled and lubricated via the main engines LO system, the turbocharger does not have its own dedicated system
- The turbocharger will have its own oil line connected to the engines L.O system
- This lubricates the main components of the turbocharger such as the bearings and shaft before returning to the engines sump
COOLING
- As the turbocharger is lubricated the lube oil also absorbs heat generated by the turbocharger and carries it away
Explain the meaning of the term Supercharging and state how it is achieved
WHAT IT IS
- Supercharging is the process of increasing the pressure or density of the air entering the engines cylinder for combustion
- Due to the increase of air pressure to in the cylinder more fuel to be burned which allows the engines power output to increase, increasing engine efficiency
- As engine efficiency increases the fuel need will be reduced, in turn improves fuel efficiency
HOW IT IS ACHIEVED
- This state is achieved via a shaft driven blower that is directly powered from the engines crankshaft through some kind of timing chain or belt
State how you would ascertain that the Charge Air Intercooler had become fouled
- Efficiency of the ME will be reduced
- Scavenge air temperature will begin to increase
- Charge Air and Scavenge pressures will drop
State how you would ascertain that the Air Intake Suction Filters had become fouled
- Scavenge Air Pressure will begin to drop
- Incomplete combustion will occur due to the lack of air entering the engine causing a High Exhaust Temperature
- ## The lack of volume of air to the engine can cause pressure fluctuations which in turn can cause Turbocharger Surging
State TWO reasons for fitting an Exhaust Gas Turbocharger to an engine
- Increases engine efficiency by increasing the power out put
- As it forces more air into the engine it allows for less fuel to be used which in turn improves the fuel efficiency
Describe the effect of dirty or restricted Air Filters
- Engine power will be reduced due to less air being forced into the engine which in turn reduced combustion efficiency
- As there’s less air it also means the turbocharger needs to work harder which results in Turbocharger Surging
- Scavenger pressure will decrease while the Exhaust temperature will increase
Describe the effect of a dirty or restricted Exhaust Gas Turbine
- Turbochargers efficiency will decrease as it reduces exhaust gas flow rate
- Local Overheating due to high exhaust temperatures while the turbine is blocked
- Due to a restriction in the turbine it causes an uneven exhaust flow to the turbocharger leading to an unbalanced load on the rotor, this also causes excessive vibrations which isn’t ideal
Outline how the Exhaust Gas Turbine is Cleaned
WATER CLEANING (SLOW SPEED)
- Clean the turbine using water at a low pressure, as per manufactures instructions and rotate the turbine at slow speed to avoid damaging parts
DRY SHELL NUTS CLEANING (FULL SPEED)
- Use dry shell nuts to clean the turbine blades at full speed to remove stubborn build up, following manufactures guidelines
State the Immediate action to be taken when the turbocharger is repeatedly surging, give ONE reason why each action is necessary
+ Turbo surging is often caused by the engines demand of air relative to the air in the turbo (commonly happens at high loads)
- Reducing the engine load immediately
- If left unchanged engine performance will drop and in extreme cases the turbocharger may experience internal mechanical damage.
State the Immediate action to be taken when the air start manifold/branch pipe overheating local to one unit, give ONE reason why each action is necessary
+ Usually caused due to a leaking air start valve
- Inform the bridge
- Reduce engine load or even stop
- Ensure the unit has been isolated and the fuel pump has been lifted
- If left unchanged an air start explosion will occur
State the Immediate action to be taken when the low scavenge air temperature alarm activates, give ONE reason why each action is necessary
- Cooling to the scavenge space must be stopped
- An investigation then must be put in place to resolve the problem
- If left unchanged the temperature may hit the dewpoint resulting in cold corrosion
State the Immediate action to be taken when the engine misfires, fuel rail pressure low alarm activates and booster pump pressure high, give ONE reason why each action is necessary
+ Usually due to blocked filters
- Reduce engine load
- Inspect and replace filters
- If left unchanged incomplete combustion will occur leading to engine performance issues
Outline the importance of maintaining temperature of the scavenge space air above the dewpoint
- If the temperature drops below the dewpoint there is a high chance that water vapour will condense into a liquid
- Sulphur is usually always present in the scavenge space
- The water and sulphur will mix into sulphuric acid which is highly corrosive
- This is known as cold corrosion
Outline the importance of maintaining fuel at the correct viscosity for injection
- Fuel must be a specific viscosity to allow for proper atomization
- Viscosity too High, fuel may not atomize properly into the fine droplets needed for proper atomization
- Viscosity too Low, fuel may atomize to early
- Either too High or Low it will lead to poor combustion.
Outline the importance of regular on board testing of lubricating oil
- When done regularly it helps determine weather the oil still meets required performance standard
- Water Contamination due to leaks or condensation
- Metal Contamination due to engine wear which can accumulate in the oil
Outline the importance of ensuring rotation of exhaust valves
- Ensuring rotation allows the heat and pressure to be evenly distributed across the valve face and seat, preventing overheating
- As it is in constant rotation the wear caused is evenly spread across the valve seat, which in turn creates a proper seal preventing leaks
Describe how modern diesel engines are pressured charged
WITH A TURBOCHARGER
- It makes use of the exhaust gas expelled from the engine to spin a turbine
- This turbine drives a compressor which draws in fresh air and compressing it before forcing it into the engine
+ However, when the air is compressed temperature increases making it less dense
WITH AN INTERCOOLER
- The air is then passed through the intercooler which cools it down increasing air density before it enters the cylinders
+ Cooler air improves combustion and reduces engine knocking and thermal stress
State TWO reasons for cooling the charge air before it enters the engine
INCREASES AIR DENSITY
- Cooler air is denser, meaning it contains more oxygen per volume
- This allows more fuel to be burned, increasing the overall power output
IMPROVES COMBUSTION EFFICIENCY
- Denser and cooler air promotes better fuel-air mixing
- This leads to more complete combustion, reducing unburnt fuel and smoke
Describe with the aid of a sketch, the operating principles of a main engine exhaust gas turbocharger
INCLUDES SKETCH
1), Waste heat from the exhaust gases spins the exhaust turbine via the nozzle ring.
2), Leftover exhaust exits through the funnel.
3), The turbine is connected to the air compressor by a shaft which draws in fresh air through filters.
4), The compressor wheel increases air velocity (Low Pressure, High Speed)
5), The volute casing converts the air to a high pressure and low velocity air.
6), the compressed air is then forced into the engine through the charge air intercooler.
