30-10 Knowledge Check

Why can’t any realistic engine convert all the energy from fossil fuels or nuclear fuel into work output, according to the laws of thermodynamics?

• Because engines are not powerful enough

• Because some energy is always lost as heat

• Because fuel is not pure enough

• Because engines are too expensive to build

Which of the following correctly represents the formula for the thermal efficiency of a heat engine?

• η_thermal = W_NET / Q_sup

• η_thermal = Q_sup / W_NET

• η_thermal = W_OUT / Q_in

• η_thermal = Q_in / W_OUT

Explain the process by which energy is transferred from fuel to the propeller in a surface ship using a mechanical drive.

• The energy is converted from chemical to electrical, then to mechanical energy.

• The energy is converted from chemical to mechanical energy by the engine, then transmitted through reduction gears and shafts to the propeller.

• The energy is converted from mechanical to chemical energy by the propeller.

• The energy is transmitted directly from the fuel to the propeller without conversion.

Which of the following statements best describes the efficiency of engines and ship propellers?

• Engines are most efficient at low RPMs, while ship propellers are most efficient at high RPMs.

• Both engines and ship propellers are most efficient at high RPMs.

• Engines are most efficient at high RPMs, while ship propellers are most efficient at low RPMs.

• Both engines and ship propellers are most efficient at low RPMs.

Why does electric drive introduce new types of losses in ship propulsion systems?

• Because it uses more fuel

• Due to electrical transmission losses (I²R losses)

• Because it increases friction in reduction gears

• Due to increased propeller inefficiencies

Which of the following is NOT mentioned as a recent electric drive ship class in the Navy?

• Zumwalt Class

• Columbia Class

• Arleigh Burke Class

• Both Zumwalt and Columbia Classes

At what speed do most propulsion systems operate most efficiently, according to the text?

• At the lowest possible speed

• At the highest possible speed

• At a middle speed

• At a speed just below maximum

At high speed, what happens to drag and fuel economy for an aircraft?

• Drag decreases and fuel economy improves

• Drag takes over and fuel economy falls off quickly

• Drag remains constant and fuel economy stays the same

• Drag is not affected and fuel economy increases

Which type of engine is commonly used in jets according to the course overview?

• Split Shaft Gas Turbine

• Turbofan

• Reciprocating Internal Combustion Engine

• Nuclear Powered Steam Plant

What does the efficiency of a heat engine describe?

• The total amount of heat energy produced by the engine

• The ratio of useful work output to the total heat energy input

• The speed at which the engine operates

• The temperature difference between the heat source and the heat sink