Safety Interlocks for Direct Air Start Medium Speed Diesel Engines (a)
Here are FOUR safety interlocks commonly fitted to a direct air start medium speed diesel engine to prevent inadvertent starting during maintenance:
- Starting Air Isolation Valve: This is a manually operated valve that isolates the entire air start system from the receivers. When closed, no compressed air can flow to the engine’s air start valves, preventing accidental starting.
- Neutral Gear Interlock: This interlock prevents the engine from starting unless the transmission is in neutral. This avoids sudden jerks and potential damage to the drivetrain if the engine were to start unexpectedly in gear.
- Engine Stop Switch: A physical switch that cuts off fuel supply or electrical power to the engine, immediately stopping it or preventing it from starting. This allows for quick shutdown in case of emergencies during maintenance.
- Crankshaft Position Sensor Interlock: This electronic interlock uses a sensor to detect the crankshaft position. In some systems, the engine may not start unless the crankshaft is positioned at a specific top dead center (TDC) for a particular cylinder, ensuring the engine is in a safe starting position.
Air Start Valve Opening Period on a Four-Stroke Diesel Engine (b)
In a four-stroke diesel engine, the opening period of the air start valve is precisely controlled in relation to the crank angle, inlet, and exhaust valves to ensure efficient starting:
- Crank Angle: The air start valve typically opens slightly before the piston reaches Top Dead Center (TDC) of the compression stroke. This timing ensures sufficient compressed air is present in the cylinder when the piston begins its downward power stroke.
- Inlet Valve: The inlet valve on a four-stroke engine remains closed during the compression and combustion strokes. Therefore, the air start valve operates during a period when the inlet valve is closed.
- Exhaust Valve: The exhaust valve typically closes just before TDC of the compression stroke. The air start valve opens shortly after the exhaust valve closes, ensuring no remaining exhaust gases are pushed back out and the cylinder receives a full charge of clean air for starting.
Overall, the precise timing of the air start valve opening maximizes the compressed air available for initiating combustion during the power stroke, leading to efficient engine starting.