Question

An auxiliary engine exhibits a tendency to hunt to such an extent that the engine speed variation prohibits the connection of the machine to the switchboard.

(a) Discuss the possible causes of hunting. (8)

(b) Explain how the problem of hunting can be rectified. (8)

Answer 1

Part (a)

Possible Causes of Hunting in an Auxiliary Engine:

Hunting refers to the instability in engine speed, where the engine oscillates between high and low speeds rather than maintaining a steady speed. The possible causes can be categorised into three main areas: fuel system issues, mechanical governor problems or electronic governor faults.

(i) Faults Related to the Fuel System:

Fluctuation of fuel pressure due to faulty fuel pump
A malfunction of the pressure regulating valve can lead to variation in fuel line pressure
Air entrapped in the system can cause pressure variations
Water in fuel oil can also lead to the hunting of engine
Faulty fuel injector - sticking needle valve can lead to the intermittent firing of the engine

(ii) Faults Related to the Mechanical Governor:

Low hydraulic oil can lead to erratic operation of the governor
Sluggish operation of the pilot valve may be due to sludge deposit
Uneven wear out of drive gear (bevel gear)
Sluggish operation of conical spring
Incorrect operation of droop lever; more droop will lead to more hunting
Sluggish operation of servo piston

(iii) Faults Related to the Electronic Governor:

Trouble with Pickup Sensor - An incorrect air gap, a slack sensor, or a defective sensor
Loose electric connection
Problem with electronic circuit - PCB
Actuator stuck
Trouble with signal amplifier/ rectifier

Part (b)

Rectification of Hunting in an Auxiliary Engine:

(i) Fuel System Faults:

Maintenance of fuel pump and fuel injectors and pressure regulating valve
Proper purification of fuel oil to remove water
Monitoring the correct temperature of fuel oil and removing entrapped air

(ii) Mechanical Governor Faults:

Maintain the correct quantity and quality of hydraulic oil
Check for wear down of drive gear
Check the condition of the conical spring. Renew if required
Minimise the droop by using the correct setting and operation of the droop lever
Clean and overhaul the pilot valve and servo piston for correct operation

(iii) Electronic Governor Faults:

Pickup sensor - adjust the air gap or properly tighten the nut or renew if defective
Tighten loose electrical connections
Renew the defective PCB
Check and rectify trouble with the amplifier/ rectifier

✓ Verified Model Answer (Text Solution)

Possible Causes of Hunting in an Auxiliary Engine:

Rectification of Hunting in an Auxiliary Engine: