Problem Set 7

What is the primary energy conversion in a diesel power plant?

Thermal to mechanical to electrical

Which engine cycle best represents a diesel engine?

Diesel cycle

What is the typical compression ratio range for stationary diesel engines?

12–24

Which component converts engine mechanical output to electricity?

Alternator

What is the function of the governor in a diesel generator set?

To control speed against load changes

Which fuel injection system is widely used in modern diesel engines for precise control?

Common-rail injection

What parameter is primarily indicated by cetane number of diesel fuel?

Ignition quality

Which method is commonly used to start large stationary diesel engines?

Compressed air starting

What is the purpose of an intercooler in a turbocharged diesel engine?

To reduce intake air temperature and increase density

Which arrangement typically couples the alternator to the diesel engine?

Direct flexible coupling

What is the brake specific fuel consumption unit used in plant performance?

kg/kWh

Which efficiency compares electrical output to fuel energy input?

Overall plant efficiency

What is the role of a day tank in diesel power plants?

To provide immediate fuel supply to engine

Which system removes heat from the engine jackets?

Cooling water system

What is the principal purpose of turbocharging a diesel engine in power plants?

To increase power density and efficiency

Which type of alternator is most common in gensets?

Synchronous alternator

What does the AVR control in a diesel generator?

Excitation and terminal voltage

Which property of diesel fuel affects injection spray and atomization?

Viscosity

What is the usual frequency of grid-synchronized diesel plants in many countries?

50 Hz or 60 Hz

Which parameter is maintained by the governor droop characteristic?

Load sharing among parallel units

What is the function of the jacket water heat exchanger in a closed-loop cooling system?

To exchange heat between jacket water and raw cooling water

Which device protects the engine from overspeed during load rejection?

Overspeed trip

What is the typical range of overall electrical efficiency for medium-speed diesel power plants?

35–48%

Which component filters particulate contaminants from diesel fuel before injection?

Fuel filter/water separator

What is the main purpose of the lube oil cooler?

To maintain oil viscosity within limits

Which monitoring parameter detects incomplete combustion in a diesel cylinder?

Exhaust gas temperature

What does “black start” refer to in diesel power plants?

Starting without external power supply

Which emission is primarily reduced by Exhaust Gas Recirculation?

NOx

What is the normal power factor target for grid-parallel diesel generators?

0.8–0.9 lagging

Which protection isolates the generator during internal faults?

Differential protection

What is the role of the pre-lube pump during engine start-sequence?

To establish oil pressure before cranking

Which starting method uses stored compressed air admitted to cylinder heads?

Air-start system

What is indicated by a high differential cylinder exhaust temperature?

Misfiring or injector fault

Which parameter must be synchronized before closing generator breaker to the grid?

Frequency, voltage, and phase angle

What is the purpose of a fuel day tank high-level alarm?

To prevent overflow and spillage

Which system recovers heat from engine jackets and exhaust for CHP plants?

Heat recovery for hot water/steam

What typically causes diesel engine “runaway”?

External fuel source like oil mist ingestion

Which maintenance practice extends injector life?

Maintaining fuel cleanliness and proper filtration

What is the advantage of medium-speed diesels in power plants?

Better efficiency and durability than high-speed

Which cooling configuration minimizes raw water fouling?

Closed-loop jacket water with plate cooler

What is the function of the crankcase breather (PCV) in diesels?

To vent blow-by gases and reduce pressure

Which parameter primarily influences NOx formation in diesel combustion?

High flame temperature and residence time

What is the usual unit of alternator apparent power rating?

kVA

Which device is used to regulate fuel quantity in common-rail systems?

Rail pressure control valve and electronic injectors

What is the effect of turbocharging on specific fuel consumption at rated load?

Decreases SFC

Which parameter indicates alternator rotor field health?

Field current and insulation resistance

What does the term “derating” mean for diesel generators in hot climates?

Reduced allowable output due to ambient conditions

Which protection trips a generator on reverse power flow to the prime mover?

32 relay

What is the immediate action when low lube oil pressure alarm occurs during running?

Reduce load and shut down if pressure not restored

Which emission is largely influenced by fuel sulfur content?

SO₂

What is the purpose of a jacket water expansion tank?

To accommodate thermal expansion and remove air

Which material is commonly used for cylinder liners in heavy-duty diesels?

Cast iron alloy

What indicates poor air filtration in a diesel power plant?

Clean intake manifold (low compressor fouling)

Which maintenance metric tracks engine wear via oil analysis?

Wear metals in lube oil

What is the typical speed of a 50 Hz, four-pole diesel generator?

1500 rpm

Which control ensures equal kW sharing among multiple generators?

Speed governor droop

What ensures equal reactive power sharing in parallel operation?

Voltage droop (AVR droop)

Which parameter best indicates turbocharger health?

Exhaust gas temperature spread and compressor/turbine speed

What is the most likely cause of white exhaust smoke at start?

Unburnt fuel due to low cylinder temperature

Which cooling configuration uses a radiator and fan for remote installations?

Once-through seawater

What is the purpose of a crankcase explosion relief valve?

To release pressure and prevent crankcase explosion damage

Which factor primarily increases particulate matter emissions?

High injection pressure and poor atomization

What is the consequence of prolonged low-load operation (“wet stacking”)?

Carbon deposits and unburnt fuel in exhaust

Which instrument measures insulation resistance of generator windings?

Megger

What is the recommended frequency for load bank testing standby generators?

Annually

Which system separates water from diesel fuel to protect injectors?

Fuel/water separator

What is the primary hazard of hydrogen sulfide in some fuels?

Toxicity and corrosion

Which operation mode reduces fuel consumption at partial loads for multiple gensets?

Sequential starts/stop (N+1) with load following

What is the typical diesel LHV used for heat rate calculations?

42–43 MJ/kg

Which parameter is minimized by correct fuel injector spray pattern?

NOx

What is the function of the engine tachometer?

To measure speed (rpm)

Which device prevents reverse current into the battery during charging?

Rectifier/diode in charger

What is the advantage of electronic governors over mechanical types?

Faster, precise speed control

Which cause leads to high exhaust backpressure?

Clogged silencer/particulate filter

What is the effect of high backpressure on engine performance?

Reduced power and higher exhaust temperature

Which test estimates friction power by cylinder cut-out on multi-cylinder engines?

Morse test

What is the function of the air filter in diesel power plants?

To remove dust and debris from intake air

Which device ensures correct fuel pressure to injectors?

Fuel pump

What is the main purpose of the silencer?

To reduce exhaust noise

Which safety device stops the engine in case of overspeed?

Overspeed trip

Which parameter shows the thermal efficiency of the diesel engine?

Brake thermal efficiency

What is the main reason for fuel heating in cold climates?

To reduce fuel viscosity for proper injection

Which part stores compressed air for engine starting?

Air receiver tank

What is the purpose of the flywheel in diesel engines?

To smooth out torque fluctuations

Which instrument measures engine cylinder pressure?

Pressure transducer

Which gas is a major product of incomplete combustion?

Carbon monoxide (CO)

Which control maintains voltage during varying load?

Automatic voltage regulator (AVR)

Which part prevents fuel leakage from injectors?

Injector nozzle seals

What does the term “load sharing” mean in parallel generators?

Distributing load equally among units

Which part protects the engine from excessive temperature?

Thermostat

Which maintenance activity prolongs engine life?

Regular oil change

Which device measures generator frequency?

Frequency meter

Which emission control device reduces particulate matter?

Diesel particulate filter

Which part converts mechanical energy to rotational energy?

Crankshaft

Which component stores energy to assist starting?

Battery

Which type of fuel pump is used in medium-speed engines?

Inline or rotary type

Which instrument monitors exhaust gas temperature?

EGT sensor

Which part helps in lubricating moving engine parts?

Oil pump

Which system removes heat from lube oil?

Lube oil cooler

Which part ensures proper timing of fuel injection?

Timing gear or ECU