With reference to the operation of an air starting system of a large medium speed marine diesel engine fitted with individual air starting valves:
(a) state the checks to be carried out if the engine will not start when initiating the start sequence;(6)
(b) list FOUR safety devices fitted to the air start system.(4)
Air Starting System for Large Medium Speed Marine Diesel Engine
An air starting system utilizes compressed air to initiate the rotation of a large diesel engine.
1. High Pressure air system | Engine Start | Gardner Denver – Reavell
Components of an Air Starting System
- Air Compressors: These compress atmospheric air to high pressure (typically around 28-42 bar) and store it in air receivers.
- Air Receivers: These are large pressure vessels that store compressed air for starting the engine. 1. Solutions for starting air – KAESER KOMPRESSOREN www.kaeser.com
- Starting Air Valves: Located on the cylinder heads, these valves admit compressed air into the cylinders. 1. Air Start Valve Explained – saVRee www.savree.com
- Air Distribution System: A network of pipes and valves that distributes compressed air to the starting air valves. 1. Air Start Valve Explained – saVRee www.savree.com
- Control System: Manages the timing and sequence of air admission to the cylinders.
Operating Principle
- Compressed Air Storage: Air compressors charge the air receivers to the required pressure.
- Starting Sequence: When the start command is given, the control system activates the starting air valves in a predetermined sequence.
- Air Admission: Compressed air is injected into the engine cylinders, forcing the pistons downwards and initiating rotation. 1. Air Start Valve Explained – saVRee www.savree.com
- Engine Start: As the engine gains speed, the starting air valves close automatically, and the engine continues to run on its own combustion process.
Advantages of Air Starting Systems
- Reliable: Proven technology with a high success rate.
- Powerful: Can start large, heavy-duty engines. 1. Marine Air Systems marinedieselspecialists.com
- Simple: Relatively few components compared to other starting methods.
Disadvantages of Air Starting Systems
Environmental concerns: Compressed air systems can contribute to noise pollution. 1. Noise Mitigation in Pneumatic Systems – Leveraging the Power of Pneumatic Mufflers – Electricsolenoidvalves.com www.electricsolenoidvalves.com
High air consumption: Requires large air compressors and receivers.
Noise and vibration: Can be noisy during the starting process.
Individual Air Starting Valves
Individual air starting valves are mounted directly on the cylinder head of each cylinder in a diesel engine. They are responsible for admitting compressed air into the cylinder to initiate the starting process.
1. Air Start Valve Explained – saVRee
Key features and advantages:
- Precise control: Each cylinder has its own valve, allowing for precise control of air timing and quantity.
- Reliability: Less prone to failures compared to systems with a single distributor.
- Efficiency: Can optimize the starting process for different engine conditions.
- Maintenance: Individual valves are easier to access and maintain.
However, this system requires more components and can be more complex compared to systems using a single distributor.
Troubleshooting a Failed Engine Start
When a diesel engine fails to start using an air starting system, several checks should be carried out:
Air Supply System:
- Air pressure: Verify sufficient air pressure in the air receivers.
- Starting valves: Check for proper operation and sealing of individual starting valves.
- Air distribution pipes: Inspect for blockages or leaks.
- Filters and strainers: Ensure they are clean and not restricting air flow.
Engine and Starting System:
- Engine compression: Check for adequate compression in all cylinders.
- Starter motor (if applicable): Ensure the starter motor is functioning correctly and engaging the flywheel.
- Timing: Verify correct timing of fuel injection and starting air.
- Fuel system: Ensure sufficient fuel supply and proper injection.
- Lubrication system: Check for adequate oil pressure and lubrication.
Control System:
- Solenoid valves: Verify proper operation of the starting air solenoid valves.
- Timing control: Check the timing sequence of air admission to the cylinders.
- Safety interlocks: Ensure all safety interlocks are functioning correctly.
Additional Checks:
- Engine temperature: Verify that the engine is within the recommended starting temperature range.
- Air intake system: Check for restrictions or obstructions in the air intake.
By systematically checking these components, you can identify the root cause of the starting failure and take corrective actions.
Safety Devices in Air Starting Systems
Air starting systems incorporate several safety devices to prevent accidents and protect the engine:
Pressure Relief Devices
- Bursting disc: Designed to rupture at a predetermined pressure to prevent catastrophic failure of the air system. 1. When To Use Safety Relief Valve vs Rupture Disc www.steriflowvalve.com
- Relief valve: Similar to a bursting disc but provides a controlled release of excess pressure. 1. When To Use Safety Relief Valve vs Rupture Disc www.steriflowvalve.com
Flame Arrestors
- Flame traps: Prevent ignition of the air-fuel mixture in the event of a backfire.
Other Safety Devices
- Non-return valves: Prevent backflow of air. 1. Non-return valve – Formula Air www.formula-air.com
- Moisture traps: Remove moisture from the compressed air to prevent corrosion and ice formation.
- Temperature sensors: Monitor air temperature to prevent overheating.
- Pressure gauges: Indicate air pressure levels. 1. Air Pressure Gauge – How It Works | Tameson.com tameson.com
- Safety interlocks: Prevent the engine from starting under unsafe conditions (e.g., low oil pressure, high water temperature).
These safety devices work together to protect the engine and personnel from potential hazards associated with high-pressure air systems.