Two stroke cross head engine V/S Four stroke trunk type engine as a method of propulsion

Two stroke cross head engine

ADVANTAGES OF TWO STROKE CROSS HEAD ENGINE

• More power output at the same swept volume.
• Better starting efficiency as every revolution has a power stroke.
• Early detection of abnormal condition due to slow speed.
• Governor require less attention as the engine is moving in slow speed.
• Simple reversing mechanism can be used in two stroke cross head engine.
• No reduction gear is required as the engine is slow speed engine.
• Lower mean temperature of working parts of the engine.
• Less crankcase oil contamination problem as stuffing box is provided to prevent the unburnt particle reach crankcase.
• Low lube oil consumption.
• Lighter flywheel.
• Less side thrust on cylinder liner due to crosshead effect.

Disadvantages of two stroke cross head engine.

• Low mean effective pressure (MEP) for same specific fuel oil consumption (SFOC).
• Poor scavenging as there is no seperate stroke for scavenging.
• More chances of scavenge fire.
• Vibration problem also occur due to long stroke.
• Air compressors needs to run during manoeuvring time.
• More weight to power ratio.
• Less cargo spaces.
• Seperate cylinder lubrication.

Four stroke trunk type engine.

Advantages of four stroke trunk type engine.

• Higher mean effective pressure (MEP) for same specific fuel oil consumption (SFOC).
• Better scavenging efficiency since it has seperate stroke for scavenging.
• Reduced air consumption and air compressor running time.
• Reduction in size for same power gives less overhaulling time.
• Vibration not considerable.
• More cargo spaces.

Disadvantages of  four stroke trunk type engine.

• Less power output as one power stroke per every two revolution.
• Inefficient starting.
• Abnormal condition can't be detected easily.
• Governor require extra care as running speed vary from medium to high.
• Reversing is not so simple as two valves and one fuel pump has to be reversed.
• Reduction gear required.
• Higher mean temperature and exhaust temperature.
• Pronounced crankcase oil contamination problem, due to crankcase trunk type.
• Heavier flywheel.
• Higher lube oil consumption.
• Higher noise level.

Four stroke engine as a method of propulsion is favourable for ship where head room is less like ferries, and small passanger vessels.