Troubleshooting Engine No-Start with Individual Air Start Valves (Large/Medium Speed Marine Diesel Engine)
(a) Checks to Perform if Engine Won’t Start:
If a large/medium speed marine diesel engine with individual air start valves fails to start during the initiation sequence, a systematic approach is crucial. Here are some key checks to conduct:
1. Air System Checks:
- Air Pressure Verification: Verify sufficient air pressure in the receivers using the pressure gauges. Ensure the pressure meets the manufacturer’s minimum requirements for starting.
- Drain Trap Inspection: Check the drain traps at the air receivers and individual air lines for accumulated water condensation. Drain any collected water to prevent it from entering the cylinders and hindering combustion.
- Leak Inspection: Visually inspect the air lines and connections for leaks. Listen for any hissing noises that might indicate compressed air escaping. Repair or tighten loose connections promptly.
- Start Valve Operation: Verify that all individual air start valves are fully open during the starting sequence. You can use visual inspection (if accessible) or listen for the characteristic air flow through the valves.
2. Engine System Checks:
- Fuel System: Ensure proper fuel supply to the cylinders. Check for clogged filters, low fuel level, or issues with the fuel injection system.
- Starting System: Verify that the starting sequence is initiated correctly and all components like the starting motor (if electric) are functioning properly.
- Engine Alarms: Look for any engine alarms that may offer clues about the no-start condition. Consult the engine manual for alarm interpretations.
- Engine Overcrank Protection: If the engine cranked excessively during the previous starting attempt, the overcrank protection may have triggered. Allow the system to reset before attempting another start.
3. Additional Checks:
- Engine Room Ventilation: Ensure adequate ventilation to avoid excessive exhaust fumes that might hinder proper air intake during starting.
- Lubricating Oil Level and Condition: Check the oil level and its condition. Low oil level or degraded oil can affect engine starting and performance.
(b) Four Safety Devices in the Air Start System:
The air start system incorporates several safety features to prevent accidents and equipment damage:
- Non-Return Valve: This valve allows compressed air to flow only in one direction, from the receivers to the engine. It prevents pressurized air from flowing back into the compressor after the start sequence.
- Pressure Relief Valve: This valve protects the air system from overpressure by automatically venting excess air back to the atmosphere if the pressure exceeds a safe limit.
- Starting Air Isolation Valve: This valve allows isolating the entire air start system from the receivers for maintenance or repairs. This ensures no pressurized air flows to the engine while work is being done.
- Engine Starting Interlocks: These interlocks prevent accidental engine starting under unsafe conditions. Examples include:
- Neutral Gear Interlock: Engine can’t start unless the transmission is in neutral, avoiding sudden jolts.
- Low Lube Oil Pressure Interlock: Prevents starting if oil pressure is insufficient to adequately lubricate internal components.
- Engine Overcrank Protection: Limits cranking duration to prevent overheating the starter motor and engine.
By conducting these checks and following a structured approach, you can identify the cause of the no-start condition and take appropriate corrective actions to get the engine running safely and efficiently. Remember to consult the engine manufacturer’s manual for specific troubleshooting procedures and safety precautions.