Engine Performance Flashcards
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
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
State the immediate action to be taken in the event of Turbocharger surging during heavy weather, giving a reason for the action
+ Surging occurs due to sudden load fluctuations, for example when the propeller momentarily leaves the water
- Gradually reduce engine load
- If left unchanged engine performance will decrease as well as possible mechanical damage
State the immediate action to be taken in the event of Excessive vibrations from the turbocharger at full speed, giving a reason for the action
- Gradually reduce engine load
- If left unchanged mechanical damage will occur to the turbocharger
+ However if reducing the load does not work, the turbo likely has already sustained mechanical damage
State the immediate action to be taken in the event of Overheating of air start branch pipe to one cylinder during manoeuvring, giving a reason for the action
+ 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 in the event of High Main bearing temperature, giving a reason for the action
- Engine load is immediately reduced and stopped if possible to prevent anymore heat generation and reduce stress
- If left unchanged a crankcase explosion is likely to occur
Explain how a typical power indicator card may be used to assess the power developed in the cylinder
1) Use the diagram and calculate the Mean Effective Pressure (Pm)
2) Take Pm and times it by the Area of the piston (A)
3) (Pm x A = Force), which moves the piston, which creates the Length (L)
4) Work Done can then be calculated via this equation… (Pm x A x L)
5) Power is equal to Work Done overtime, therefore (Pm x A x L x Revs/s) = Power
+ Revs/s 2 Stroke = 60
+ Revs/s 4 Stroke = 120
This is known as PLAN
State the effect of Early Injection
- Higher Peak Cylinder Pressure (Higher Pmax)
- Shock Loading of bearings
- Increased mechanical stress on engine components
State the effect of Late Injection
- Lower Peak Cylinder Pressure (Lower Pmax)
- After Burning which also leads to High Exhaust temperatures
- Turbocharger Surging may also occur due to the higher exhaust temperatures
Explain why the correct Tappet Clearances are essential, with reference to inlet and exhaust valves on a 4 Stroke Engine
WHY IT IS IMPORTANT
- Ensures the inlet and exhaust valves open and close at the correct time for efficient combustion
- It also allows for Thermal Expansion, these valves expand as they heat up so the clearance compensates for this to prevent improper seating
CONSEQUENCES OF INCORRECT CLEARANCE
- Drop in efficiency due to incorrect timing
- Excessive wear of engine components such as camshaft, rocker arm and valve spindles
State the results of the Tappet Clearance being too Large
-Valve will Open Late & Close Early
- Reduces Maximum Lift (Valve doesn’t open as much as it should)
- Creates Shock Loads throughout the valve spindle as the tappet may strike the cam lobe with more force than intended
State the results of the Tappet Clearance being too Small
- Valve will Open Early & Close Late
- Increases Maximum Lift (Valve opens too much)
-Thermal Expansion may push the valve off its the seat allowing gas to escape
With reference to a small diesel engine that requires the use of a starting handle, State the procedure for starting
+ Pre Checks such as Fuel, Oil & Coolant levels
+ Pre Checks such as double checking all correct valves have been opened
- Start by inserting the handle into the slot
- Open Decompression Lever (helps reduce the amount of effort required)
- Wind the handle in a clockwise direction, until you feel resistance
- Close Decompression Lever
- Pull the handle which should start the engine
State 8 Reasons why the small diesel engine (starting handle) that would cause difficulties in starting
- Insufficient Fuel
- Dirty or Clogged Air Filter
- Dirty or Clogged Fuel Filter
- Not Turning the Handle Fast Enough
- Incorrect Tappet Clearance
- Faulty Fuel Pump
- In Cold Conditions
- Exhaust or Intake is Blocked
- Air has Entered the Fuel System
- Valves not Open Fully
- Jacket Water Heating isn’t on
