Diesel engines rely on several safety cut-outs or trips to prevent damage in case of critical operating parameter deviations. Here are four common safety cut-outs and their functions:
- Overspeed Trip:
- Function: This safety cut-out protects the engine from excessive revolutions per minute (RPM).
- Operation: A speed sensor (e.g., magnetic pickup) monitors the engine’s crankshaft speed. If the RPM exceeds a preset limit (typically slightly above the engine’s rated speed), the overspeed trip activates.
- Action: The overspeed trip typically triggers one of the following actions:
- Fuel Shutoff: The fuel supply to the engine is cut off, stopping fuel injection and engine operation.
- Engine De-rating: In some systems, the engine might be de-rated (power output reduced) instead of a complete shutdown.
- Importance: Overspeeding can cause severe damage to engine components like bearings, crankshafts, and connecting rods due to excessive stress and wear.
- Low Oil Pressure Trip:
- Function: This safety cut-out protects the engine from damage due to insufficient lubrication.
- Operation: An oil pressure sensor continuously monitors the engine’s oil pressure. If the pressure falls below a predetermined minimum level, the low oil pressure trip activates.
- Action: The low oil pressure trip typically triggers a complete engine shutdown to prevent internal components from seizing due to lack of lubrication.
- Importance: Engine oil plays a crucial role in reducing friction, wear, and cooling internal components. Low oil pressure indicates a potential problem like an oil leak, worn oil pump, or insufficient oil level, all of which could lead to catastrophic engine failure if not addressed.
- High Coolant Temperature Trip:
- Function: This safety cut-out protects the engine from overheating.
- Operation: A coolant temperature sensor monitors the engine coolant temperature. If the temperature exceeds a preset limit, the high coolant temperature trip activates.
- Action: Similar to the low oil pressure trip, the high coolant temperature trip typically initiates a complete engine shutdown to prevent overheating and potential damage to cylinder heads, pistons, and other engine components.
- Importance: Engine coolant regulates the operating temperature by absorbing heat and transferring it to a radiator for dissipation. Excessive coolant temperature indicates a potential cooling system issue like a blocked radiator, malfunctioning fan, or insufficient coolant level, which could lead to engine damage if not addressed.
- High Exhaust Gas Temperature (EGT) Trip (on turbocharged engines):
- Function: This safety cut-out is specifically used in turbocharged engines to prevent excessive exhaust gas temperatures.
- Operation: A temperature sensor monitors the exhaust gas temperature after the turbocharger. If the temperature exceeds a safe limit, the high EGT trip activates.
- Action: Depending on the engine management system, the high EGT trip might initiate various actions:
- Fuel Shutoff: Similar to the overspeed trip, fuel delivery might be shut off to reduce engine power output and lower exhaust gas temperatures.
- Variable Geometry Turbocharger (VGT) Adjustment (if applicable): In engines with VGTs, the trip might adjust the turbocharger vanes to reduce boost pressure and consequently lower exhaust gas temperatures.
- Importance: Excessive exhaust gas temperatures can damage turbocharger components and potentially lead to piston and exhaust valve problems.