(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
(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