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WorksheetsPower Plant Diesel Prelim Assessment
Total questions: 45
Worksheet time: 23mins
The Carnot cycle achieves maximum efficiency mainly because:
It uses atmospheric air as the working medium always
All processes are reversible and without friction losses
It allows expansion at uniform pressure conditions
It avoids compression losses in practical operations
In a conventional two-stroke diesel engine, fuel injection is mainly:
Controlled through electronic sensors and computers
Regulated by a mechanical camshaft and fuel pump unit
Activated by hydraulic actuators with manual levers
Adjusted according to exhaust valve timing settings
During isothermal expansion in an ideal gas cycle, why is the heat supplied considered equal to the work done by the gas?
Because the internal energy of the gas remains unchanged at constant temperature
Because the gas absorbs heat only at high pressures
Because pressure stays constant while volume increases
Because the internal energy of the gas increases as temperature rises
The Carnot cycle is important in thermodynamics because it:
Explains the working of jet engines
Sets the theoretical maximum efficiency of heat engines
Describes compression ignition in diesel engines
Represents the cycle of two-stroke engines
Exhaust Gas Recirculation (EGR) in marine engines is mainly used to:
Improve turbocharger performance
Reduce NOx emissions
Increase engine torque
Lower compression ratio
The Brayton cycle is most commonly applied in which system?
Diesel engines
Jet engines and gas turbines
Gasoline engines
Refrigeration units
Turbocharging in main diesel engines improves efficiency by:
Reducing the need for cylinder lubrication requirement
Increasing scavenging air pressure and mass air supply
Reducing piston stroke length in the moving assembly
Avoiding exhaust back pressure during gas expulsion
If the compression ratio of a diesel engine is reduced, the most likely outcome would be:
Increased thermal efficiency
Reduced temperature, making ignition harder
Faster combustion
Lower exhaust gas pressure
Why is the **Carnot cycle** not practical for real engines despite its maximum efficiency?
Lack of isothermal processes in reality
High fuel cost
Difficulty in maintaining reversible processes
Overuse of turbocharging
A vessel operator must choose between an ME-C and ME-E engine. If the primary goal is **enhanced fuel efficiency and lower operating costs**, which should be selected?
ME-C (High Pressure)
ME-C (Low Pressure)
ME-E series engine
Carnot cycle engine
In diesel ICEs fuel is ignited by compression, while in ECEs fuel is:
Burned in a separate chamber to heat a working fluid
Directly injected into the cylinder with spark plugs
Ignited by a glow coil inside the piston
Used only to lubricate moving parts
What is the working fluid difference between most ICEs and ECEs?
ICE - helium; ECE - diesel only
ICE - air/fuel mixture; ECE - water/steam
ICE - steam; ECE - compressed air
ICE - oxygen; ECE - nitrogen
How do Stirling engines (ECEs) differ from ICEs in principle?
ECE - heat and cool a working gas externally; ICE - ignite fuel internally
Both rely on spark plugs for ignition
ICE - use sealed gas; ECE - burn fuel inside the piston
Both cannot be used in marine systems
Which advantage is more associated with ECEs compared to ICEs in shipping?
Smaller size and faster response
Greater fuel flexibility and cleaner combustion
Higher emissions and more fuel demand
Easier maintenance and fewer parts
Which disadvantage is more associated with ECEs compared to ICEs?
Shorter lifespan and lower reliability
Higher emissions than ICEs
Cannot use multiple fuels
Bulky systems with slower response time
Where does fuel combustion take place in ICEs compared to ECEs?
ICE - inside the combustion chamber; ECE - outside the cylinder in a boiler
ICE - outside the cylinder; ECE - inside the piston
ICE - in the intake; ECE - in the condenser
ICE - at constant volume; ECE - at constant pressure
Which factor makes diesel engines more fuel-efficient than gasoline engines?
Use of spark ignition
Higher compression ratio
Lower torque output
Faster combustion speed
Comparing internal and external combustion engines, the main operational difference is:
Both burn fuel outside
ICE burns fuel inside the chamber, ECE burns outside
ICE always uses steam
ECE does not need fuel
Why are steam engines less favored in modern shipping compared to diesel engines?
They cannot use coal
They are larger, heavier, and less responsive
They produce more NOx emissions
They lack power output
A marine engineer chooses between an ICE and an ECE. If the ship requires quicker startup and load changes, which should be selected?
Steam engine
Stirling engine
Internal combustion engine
External boiler engine
When comparing ICE and ECE in the shipping industry, which statement is accurate?
ICE is compact for ships, ECE is bulkier but fuel flexible
ICE is heavier but more fuel flexible
ECE produces higher torque at lower emissions always
Both have equal response times
Why do diesel engines not require spark plugs?
They use glow plugs
They have larger cylinders
Fuel ignites due to high compression temperature
Diesel is highly volatile
Gasoline engines generally operate at:
Low RPM and high torque
Higher RPM with faster throttle response
Constant torque at all speeds
Low noise levels and low power
Which emission is usually higher in gasoline engines compared to diesel engines?
NOx
Carbon monoxide (CO) and hydrocarbons (HC)
Particulate matter
Sulfur oxides
Which is a disadvantage of diesel engines compared to gasoline engines?
Lower torque
Higher noise and vibration
Slower throttle response
Higher hydrocarbon emissions
Why are diesel engines commonly used in heavy-duty marine applications?
High torque at low RPM and fuel efficiency
Faster acceleration
Quieter operation
Lighter construction
Which factor explains why diesel engines produce higher torque at lower RPM compared to gasoline engines?
Lower compression ratio
Spark plug ignition
Higher compression ratio and denser fuel
Lighter piston design
Between gasoline and diesel engines, which design aspect explains the difference in durability?
Diesel engines are built stronger for high compression
Gasoline engines use stronger crankshafts
Diesel engines rely on spark ignition
Gasoline fuel is denser and protective
What explains the higher initial cost of diesel engines compared to gasoline engines?
Fuel price differences
Stronger build and emission systems
Simpler ignition system
Smaller displacement requirements
How do diesel and gasoline engines differ in terms of fuel efficiency and noise levels?
Diesel engines are quieter but less efficient
Diesel engines are more efficient but noisier
Gasoline engines are more efficient and noisier
Both are equally efficient and quiet
Which design factor explains why two-stroke diesel engines dominate large ships over four-stroke engines?
Quieter operation
Higher power output and efficiency per revolution
Lower compression ratio
Use of spark ignition
Why are two-stroke marine engines typically more fuel-efficient than four-stroke ones?
They use spark ignition
They require less air intake
They allow longer strokes and higher expansion
They burn gasoline fuel
How does turbocharging improve the charging process and overall performance of marine diesel engines?
Increases air pressure, improving efficiency and power
Reduces exhaust gas recirculation
Lowers compression ratio
Prevents NOx formation
How does the use of EGR (Exhaust Gas Recirculation) in marine diesel engines affect the air supply process in relation to emission compliance?
Reduces particulate matter
Lowers NOx formation by recirculating exhaust gases
Increases combustion temperature
Saves fuel costs
Why is a four-stroke diesel engine more suitable for naval ships that operate under varying load conditions?
Provides versatility and smoother operation
Limited efficiency at high loads
Requires spark ignition for flexibility
Relies on steam for stable output
If a ferry uses a four-stroke engine, what trade-off is evident compared to a two-stroke cargo ship engine?
Smoother operation but lower fuel efficiency
Higher torque but noisier operation
Faster power delivery but less reliable
Equal efficiency but more vibrations
Between reciprocating and rotary motion in engines, which is more common and why?
Rotary, due to higher torque
Reciprocating, provides reliable energy conversion
Rotary, due to simpler design
Both are equally common in marine engines
Which trade-off explains the choice of four-stroke diesel engines in ferries compared to two-stroke engines in tankers?
Four-stroke is smoother but less fuel efficient
Four-stroke is cheaper but less reliable
Two-stroke is quieter but less durable
Two-stroke is smoother but uses more fuel
How does the difference in crankshaft revolutions per power cycle between two-stroke and four-stroke marine diesel engines affect their power output and suitability for large ships?
Two-stroke requires two revolutions, leading to smoother but less powerful operation
Two-stroke completes a cycle in one revolution, giving higher power output for large vessels
Four-stroke completes a cycle in one revolution, giving higher torque at low RPM
Both require the same revolutions, so power output is unaffected
How does the ignition method in marine diesel engines differentiate them from gasoline engines in terms of design and efficiency?
Spark plug ignition makes diesel engines lighter but less durable
Compression ignition needs higher compression, improving efficiency
External furnace heating makes diesel engines more compact
Pilot flame allows both diesel and gasoline engines to operate the same way
Why is marine diesel engine power output measured in horsepower (HP) or kilowatts (kW), rather than in units like tons per hour or bar?
Tons per hour measures fuel, not engine power
Bar measures pressure, not usable output
HP or kW directly reflect the engine's mechanical output for propulsion
Newtons measure force but not continuous engine performance
Which part of the engine houses the cylinders and supports major components?
Crankshaft
Cylinder block
Piston crown
Turbocharger
The cylinder head sits on top of the cylinder block and contains:
Crankshaft and bearings
Valves, injectors, and coolant passages
Piston rings
Oil pump
The Carnot cycle achieves maximum efficiency mainly because:
All processes are reversible and without friction losses
It uses atmospheric air as the working medium always
It allows expansion at uniform pressure conditions
It avoids compression losses in practical operations
During isothermal expansion in an ideal gas cycle, why is the heat supplied considered equal to the work done by the gas?
Because the internal energy of the gas remains unchanged at constant temperature
Because the gas absorbs heat only at high pressures and heat generates
Because pressure stays constant while volume increases as being used
Because the internal energy of the gas increases as temperature rises
