What is governor ?
- Governor is a device which controls the speed of engine automatically in the prescribed limits.
- The governor does its job in two steps.
- By measuring the speed and
- By controlling the a amount of fuel supply to the engine.
What is the function of governors ?
- To adjust the rate of fuel supply in such a way as to keep the engine running at a steady speed regardless of the load.
- To control the engine running at a steady speed under all conditions of load.
What is governor droop?
- When considering the engine and governor combination, the difference between the no load speed and full load speed is called governor droop.
- Small droop results in rapid swing.
- Large drop results in slower response to change in speed.
What are the types of governors ?
- Mechanical governor.
- Hydraulic governor.
- Inertia governor [fitted on older slow speed engine]
- Electronic governor.
What is compensation ?
- The use of temporary speed droop to prevent over correction of the fuel supply is called compensation.
It require two actions:
- Droop application – as the fuel supply is changed
- Droop removal – as the engine response to the fuel change and returns to original speed .
What types of governor used in G/E and M/E ?
- G/E governor is a droop speed governor with over speed trip.
- M/E governor is a constant speed governor with over speed trip.
Why over speed trip is fitted in main engine ?
- It is fitted to control the sudden load change and sudden increase in speed. e.g severe load change when loss of propeller in heavy sea .
- Thus, to prevent engine parts damage, over speed trip is provided.
- Set the speed 15% more than MCR.
- It is attached at camshaft through gearing.
- If engine speed rise more than 10 to 15% above the rated speed, It shut of fuel & stops the engine.
- The mechanism has to be manually reset before engine start again.
Why hydraulic servo governor is widely used ?
- Hydraulic governor is widely used because of their:
- sensitivity
- isochronous and
- having grater power to move the fuel control mechanism of the engine .
What is hunting of governor ?
- It is a fluctuation of engine speed due to the over correction of the fuel supply. (too much increase or decrease fuel supply)
What is the cause of engine hunting ?
- It is unavoidable time lag between the movement of the governor act and the movement of engine response.
What is isochronous governor ?
- It is a constant speed governor.
- It is able to maintain exactly constant speed without hunting.
- This type of governor that has proportional and reset is called isochronous governor.
What will happen when over speed occurred ?
- Engine revolving and reciprocating parts may damage due to inertia effects.
Why will you test G/E over speed trip ?
- It can be tested by increasing the engine speed by speed adjuster at no load condition.
- Over speed trip will cut-out the fuel supply at 115% of normal speed.
Why speed droop governor is used at G/E ?
- It is fitted to get load sharing ability since isochronous governor gives constant speed, thus cannot share the load.
- AVR is fitted at alternator.
Why over speed trip provided although governor fitted ?
- Governor only control the engine speed in prescribed limits.
- When accidental sudden load change from full load to no load happens, engine speed become too high above 15% of rated speed.
- Due to time delay of governor control, engine parts may become damage.
- Thus to prevent this effect over speed trip must be provided to shut down the engine by cutting fuel.
Note: It need to reset before restart the engine.
How to operate/act isochronous governor ?
- It maintains constant speed without hunting.
- Speed droop for it is temporary
It has 2 actions:
- Droop application (as fuel supply is changed)
- Droop removal (as engine responses to fuel change and returns to original speed)
What is sensitivity ?
- Ability to control the engine speed, within narrow limits
Why Inertia type Governor is not used nowadays ?
- Although very simple type, it requires an engine speed increase of 5% or more to make it operate.
- In some cases, increase of engine speed will bring into or near to critical speed that can cause severe vibration.
What are the governor maintenance carried out on ships ?
- Periodically check oil level
- Change the governor oil
- Grease the linkage and joint
Reference:
Oral Guide by – MIN ZAR TAR