Heat engines- exam 2

In plain English, explain the first law of thermodynamics.

Energy cannot be created nor destroyed, only converted

1. In plain English, explain the second law of thermodynamics. 

Law of entropy- things naturally go from order to disorder over time

What is entropy? Explain this concept using a sand pile versus a sand castle. Be able to distinguish between a high entropy and a low entropy state in your explanation.

It's a measure of disorder; a sand castle has low entropy because it is organized and structured, a sand pile is high entropy because it is random and messy

What is a heat engine?

A machine  that turns into helpful work; it takes in heat and uses some to do work.

What is the role of the source, sink, and the working fluid?

Source: provides heat to the engine; sink: absorbs waste heat that the engine cannot use; working fluid: moves heat through the engine to produce work

What fluids are commonly used as working fluids in a heat engine?

Water/steam, air, refrigerants, and oil

Use the example of a water wheel to illustrate the components of a heat engine

Source (high water), working fluid (flowing water), wheel (engine mechanism), sink (low water)

Distinguish between internal and external combustion engines—list an example of both.

ICE: burns fuel inside the engine (car engine); ECE: burns fuel outside to heat a working fluid (steam engine)

Describe how a thermal energy flow is created in a heat engine and how some of the heat is transformed to work.

Heat source: adds energy to the working fluid; working fluid expands: pushing parts; work is done: as movement is created; waste heat: is released to the heat sink

we call the simple equation QH equals W plus QC. Explain how this equation is related to the first law of thermodynamics.

The total energy (QH) is either used for work (W) or lost as waste heat (QC)- no energy is created or destroyed.

What part of the heat engine is in a high entropy state and a low state? How does this correspond to the heat engine system's highest quality and lowest quality energy?

High entropy (low quality energy)- heat sink (QC)- waste heat spreads out, hard to use; low entropy (high quality energy)- heat source (QH)- concentrated heat, can do work; as energy moves through the turbine it goes from high quality (USEFUL) to low quality (LESS USEFUL) due to increasing entropy

How is the second law of thermodynamics related to the efficiency of a heat engine?

Some energy is always lost as wasted heat so that no engine can be 100% efficient; some energy goes to the sink as waste heat (higher entropy) and the remaining energy can be used for work (lower entropy)

Explain how the maximum efficiency is calculated for a heat engine

(QH (source)- QC (sink))/ W (work)

Describe what happens with strokes in a 4-stroke engine?

The intake value opens, and the piston moves down to draw in air and fuel

Describe what happens with induction in a 4-stroke engine?

Intake valve closes and the piston moves up, compressing the air-fuel mixture

Describe what happens with power in a 4-stroke engine?

The spark plug ignites the compressed mixture, causing an explosion that pushes the piston down, creating power.

Describe what happens with compression exhaust in a 4-stroke engine?

Exhaust valve opens, and the piston moves up again to push out the  waste gases.

Explain why the gas temperature in the chamber increases during the compression stage.

Compressing a gas increases its energy (volume gets smaller), making it hotter.

What is the purpose of a motor oil in an ICE?

Cools the engine by carrying heat away

Describe the transformation of energy that takes place during the power stroke.

The spark plug ignites compressed air-fuel mixture, C.E. It is the fuelthat  turns into heat energy, causes a small explosion, creates M.E. by pushing the piston down

Explain the difference between a four-cylinder and a V6 engine

4: smaller, lighter, and more fuel-efficient, but less powerful; V6: more powerful, smoother, and better for higher speeds or heavy loads, but uses more fuel

What is better for the environment, a four-cylinder or a V6 engine?

4 cylinder because it uses less fuel

What is a turbo charger? Explain how this improves the performance of a four-cylinder engine.

It forces more air into the engine's cylinder allowing it to burn more fuel and produce more power