MDE Unit 6 Q1

A crankcase is the housing that encloses the crankshaft and lower part of the piston assembly in a reciprocating engine. In essence, it forms the backbone of the engine.  

1. What is a Crankcase and Why are they Important? – Jaytrac

Functions of a Crankcase:

• Houses crankshaft and connecting rods: Provides a rigid structure to support the rotating and reciprocating components.   1. What is a Crankcase and Why are they Important? – Jaytrac jaytrac.co.uk
• Contains lubricating oil: Acts as a reservoir for engine oil, ensuring proper lubrication of internal components.   1. What is and how does the lubrication system of a diesel engine work? – Talleres Nasio www.talleresnasio.com
• Provides mounting points: Serves as a base for attaching other engine components like cylinder blocks, oil pump, and filters.
• Strength and rigidity: Must be robust to withstand the forces generated during engine operation.   1. What is a Crankcase and Why are they Important? – Jaytrac jaytrac.co.uk

Marine Diesel Engine Crankcase Considerations:

• Vibration and Shock: Marine engines are subjected to significant vibration and shock due to the vessel’s movement. Crankcases for marine applications are often reinforced to handle these forces.
• Corrosion Resistance: The marine environment exposes engines to saltwater and humidity, requiring corrosion-resistant materials and coatings.
• Space Constraints: Marine engine rooms are often compact, necessitating careful design of the crankcase to fit within the available space.
• Weight Considerations: For vessels focused on speed or fuel efficiency, reducing engine weight is crucial, influencing crankcase design.

Additional features:

• Oil sump: The lower part of the crankcase that collects used oil.
• Oil baffles: Internal structures to prevent oil sloshing and foaming.
• Oil pickup pipe: Connects the oil pump to the oil sump.
• Crankcase breather: Allows for pressure equalization and prevents blow-by gases from building up.   1. Crankcase ventilation system – Wikipedia en.wikipedia.org

By understanding the specific requirements of marine environments, crankcase designs are optimized for durability, performance, and reliability.

Crankcase relief valves are safety devices designed to protect the engine from damage in the event of an internal explosion or excessive pressure buildup.  

1. Crankcase Explosion Relief Valve Explained – saVRee

Functions of a Crankcase Relief Valve:

• Pressure Relief: If pressure within the crankcase exceeds a predetermined level, the valve opens to release the excess pressure, preventing potential damage to the engine.   1. Crankcase Explosion Relief Valve Explained – saVRee www.savree.com
• Flame Arrestor: Many relief valves incorporate a flame arrester to prevent the ignition of flammable gases outside the crankcase, reducing the risk of fire.   1. Crankcase Explosion Relief Valve Explained – saVRee www.savree.com
• Rapid Closure: The valve is designed to close quickly after the pressure is relieved to prevent the ingress of air into the crankcase.

By incorporating crankcase relief valves, engine manufacturers enhance the safety and reliability of their products.

A crankcase relief valve should ideally operate only in emergency situations. However, several factors can trigger its activation:

Overpressure Conditions:

• Blow-by gases: Excessive blow-by gases from the combustion chambers can increase crankcase pressure.   1. Blow-by in Diesel Engines: Causes, Diagnosis, and Common Questions supertechonline.ca
• Oil foaming: Excessive aeration of the engine oil can create pressure buildup.
• High engine loads: Heavy loads can generate increased pressure within the crankcase.
• Engine overheating: High temperatures can lead to increased pressure due to thermal expansion of gases.

Malfunction of Engine Components:

• Piston ring failure: Severe wear or breakage of piston rings can allow combustion gases to enter the crankcase.
• Breather system blockage: Obstruction in the crankcase ventilation system can trap pressure.

External Factors:

• Fire: External heat sources can increase crankcase pressure.

It’s crucial to investigate the cause of a relief valve activation to prevent recurring issues and potential engine damage.

To prevent catastrophic failures and protect personnel, various safety detection systems can be fitted to engine crankcases.  

1. Catastrophic Engine Damage Led to OSV Fire -NTSB

Oil Mist Detectors

• Function: Continuously monitors the crankcase atmosphere for oil mist concentration.   1. Specs Specsvision 5C Crank Case Oil Mist Detector – Lavastica International www.lavastica.com
• Alarm: Triggers an alarm if oil mist levels exceed a predetermined threshold.   1. Specs Specsvision 5C Crank Case Oil Mist Detector – Lavastica International www.lavastica.com
• Early warning: Provides early indication of potential engine problems like wear or seal failure.

Crankcase Pressure Sensors

• Monitors pressure: Continuously measures pressure within the crankcase.
• Abnormal pressure detection: Alerts the operator if pressure levels exceed normal operating parameters.
• Potential issues: Can indicate problems like blow-by gases or blockages in the ventilation system.

Temperature Sensors

• Overheating detection: Monitors the temperature of critical components within the crankcase.
• Early warning: Provides early indication of potential bearing failures or other heat-related issues.

Vibration Sensors

• Abnormal vibration detection: Monitors engine vibrations for any unusual patterns.   1. What is a Continuous Vibration Monitor? – Grace Technologies www.graceport.com
• Potential issues: Can indicate imbalances, bearing wear, or other mechanical problems.

Combination Systems

• Comprehensive monitoring: Some systems combine multiple sensors for a more complete assessment of engine health.
• Early warning: Provides early detection of a wide range of potential issues.

By implementing these safety detection systems, engine operators can take proactive measures to prevent engine failures and ensure the safety of personnel.