Marine Engineering Study Materials

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 ?

1. Mechanical governor.
2. Hydraulic governor.
3. Inertia governor [fitted on older slow speed engine]
4. 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:

1. Droop application – as the fuel supply is changed
2. 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:

1. sensitivity
2. isochronous and
3. 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:

1. Droop application (as fuel supply is changed)
2. 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