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.
a. measuring the speed and
b. control the a amount of fuel supply to the engine.
2. Function of governor ?
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.
3. 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 rapid swing
Large droop slower response to change in speed.
4. Types of governors.
a. Mechanical governor.
b. Hydraulic governor
c. Inertia governor [fitted on older slow speed engine]
d. Electronic governor
5. What is compensation ?
The use of temporary speed droop to prevent over correction of the fuel supply is called compensation.
It required two actions-
a. Droop application – as the fuel supply is changed
b. Droop removal – as the engine response to the fuel change and returns to original speed .
6. 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.
7. Why fitted over speed trip 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.
8. Why hydraulic servo governor is widely used ?
Hydraulic governor is widely used because of their
a. sensitivity
b. isochronous and
c. having grater power to move the fuel control mechanism of the engine .
9. What is hunting ?
It is a fluctuation of engine speed due to the over correction of the fuel supply. (too much increase or decrease fuel supply)
10. Cause of engine hunting ?
It is unavoidable time lag between the movement of the governor act and the movement of engine response.
11. 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.
12. What will happen when over speed occurred ?
Engine revolving and reciprocating parts may damage due to inertia effects.
13. 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.
14. Why speed droop governor is used at G/E ?
It is fitted to get load sharing ability isochronous governor gives constant speed, thus can not sharing the load.
AVR is fitted at alternator.
15. Why over speed trip provided although governor fitted ?
Governor only control the engine speed in prescribed limits. When accidental sudden load change that from full load to no load, 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.
16. How to operate/act Isochronous governor ?
It maintains constant speed without hunting. Speed droop for it is temporary
It acts 2 actions
1. Droop application (as fuel supply is changed)
2. Droop removal (as engine responses to fuel change and returns to original speed)
Sensitivity : Ability to control the engine speed, within narrow limits
Stability : Governor is stable, when there is only one radius of rotation of flywheel for each speed, at which governor operates within the sped range.
17) Why Inertia type Governor is not used nowadays ?
1) Although very simple type, it requires an engine speed increase of 5% or more to make it operate
2) In some cases, increase of engine speed will bring into or near to critical speed that can cause severe vibration.
Governor Maintenance
Periodically check oil level
Change the governor oil
Grease the linkage and joint
OVER SPEED TRIP Speed rise more than 10 to 15% above the full load speed, shut down the engine. Reset the engine before starting the engine.
OVER SPEED GOVERNOR Not effective certain limit up to 110% of normal speed. 10% above normal speed shut off fuel supply to engine and 5% below normal speed automatically recut in fuel supply to engine.