Carnot Engine: Efficiency, Law of Thermodynamics, 6 Stroke

In summary, the Carnot engine is a hypothetical engine that does not obey the laws of thermodynamics because it has a 100% efficiency. However, there is no engine that has come close to this level of efficiency. The process of Carnot cannot be used for a 6 stroke engine, even hypothetically. It is impossible to construct a Carnot cycle engine in real life due to practical difficulties and the fact that it is a purely theoretical concept. The maximum efficiency of a Carnot engine is 1- Tc/Th, but this is not achievable in practical situations due to the absence of a truly reversible process. Therefore, 100% efficiency is not possible for any engine, including the Carnot engine.
  • #1
monty37
225
1
the carnot engine does not obey any law of thermodynamics,because it has
100% efficiency,now do we have any engine that has come close to this hypothetical
engine?(in terms of efficiency ) can this process of carnot be used for a 6 stroke engine?(hypothetically)
 
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  • #2
monty37 said:
the carnot engine does not obey any law of thermodynamics,because it has
100% efficiency,now do we have any engine that has come close to this hypothetical
engine?(in terms of efficiency ) can this process of carnot be used for a 6 stroke engine?(hypothetically)

Which thermodynamic law did Carnot engine break?? And where did you read that its efficiency is 100%?
 
  • #3
Here's a http://hyperphysics.phy-astr.gsu.edu/hbase/thermo/carnot.html" where you practice some calculations.
 
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  • #4
well my engineering book of thermodynamics says that carnot engine(imaginary)
is supposed to have 100% efficiency,the perfect engine.
thus it disobeys the 2nd law,which states that heat cannot be totally converted
to work?
 
  • #5
It's also a fact that it's impossible to construct a Carnot cycle engine in real life for that very reason. Carnot only really demonstrates the 1st law, its a purely paper concept and so doesn't have to obey the 2nd law as its idealised. It's also why other cycles are compared to Carnot efficieny.

Also a Carnot engine isn't actually 100% efficient, its just the best possible efficiency (which is why it says 100%) between two heat reservoirs. The Carnot efficieny is 1- Tc/Th.
 
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  • #6
monty37 said:
well my engineering book of thermodynamics says that carnot engine(imaginary)
is supposed to have 100% efficiency...
Could you quote the passage for us? You clearly misread it.
 
  • #7
xxChrisxx said:
Also a Carnot engine isn't actually 100% efficient, its just the best possible efficiency (which is why it says 100%) between two heat reservoirs. The Carnot efficieny is 1- Tc/Th.
That doesn't make sense - why would the book say that an engine with 65% efficiency (for example) is 100% efficient? I think what we have here is a complete misread.
 
  • #8
russ_watters said:
That doesn't make sense - why would the book say that an engine with 65% efficiency (for example) is 100% efficient? I think what we have here is a complete misread.

As between the two temperatues, a Carnot Cycle will extract the maximum possible efficiency compared to a Rankine cycle for example. Thats the only reason why I can think that a book would say its 100% efficient. The book chose a poor (and misleading) choice of words if it does indeed say that.

Like you said though, its probably a misread.
 
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  • #9
monty37 said:
well my engineering book of thermodynamics says that carnot engine(imaginary)
is supposed to have 100% efficiency,the perfect engine.
thus it disobeys the 2nd law,which states that heat cannot be totally converted
to work?

The thermal efficiency is always less than unity. Carnot is just the best theoretical efficiency (not practical though). It's typically used in thermodynamics to help understand the general concept of the second law.

It doesn't break any laws of thermodynamics, but it can not exist practically since there is no such thing as a truly reversible process.

CS
 
  • #10
the lines go like this
" is it that we cannot achieve 100%efficiency due to practical difficulties or is there
any theoritical problem about it? to decide about this sadi carnot imagined the
concept of an ideal engine in which no energy loss takes place"

so do you mean to say even theoritically ,100%efficiency is not possible,but they
have not listed any loss in case of carnot engine.
 
  • #11
Yeah, you misread that, though it may be a little poorly worded. It is saying that Carnot envisioned how the perfect thermodynamic enegine could work. "No losses" doesn't mean no heat of rejection (just no friction, heat transfer, etc.) and isn't meant to imply 100% efficiency.

Anyway, yes, it means 100% efficiency is not possible: Carnot efficiency is the maximum that is theoretically possible.
 
  • #12
Maybe think of it this way: If you could reject heat to a sink at absolute zero, then your Carnot engine would be 100% efficient.

With normal everyday heat sinks at something like normal environmental temperatures (500 to 550 R), the efficiency is going to be a lot less.
 

1. What is a Carnot Engine?

A Carnot Engine is a theoretical heat engine that operates on the principles of thermodynamics. It was first proposed by French physicist Sadi Carnot in the early 19th century.

2. How does a Carnot Engine achieve high efficiency?

A Carnot Engine operates on the Carnot Cycle, which is a reversible cycle that consists of two isothermal processes (constant temperature) and two adiabatic processes (no heat exchange). This cycle allows for maximum conversion of heat energy into work, resulting in high efficiency.

3. What is the Law of Thermodynamics in relation to Carnot Engines?

The Law of Thermodynamics states that energy cannot be created or destroyed, only transferred or converted from one form to another. In the case of Carnot Engines, the law is used to explain the limits of efficiency and the impossibility of achieving 100% efficiency.

4. What is the 6 Stroke Concept in Carnot Engines?

The 6 Stroke Concept is a proposed modification to the traditional 4 stroke engine used in cars. It aims to improve efficiency by adding two additional strokes - a water injection stroke and a steam expansion stroke - in order to utilize the waste heat from the exhaust and increase the work output.

5. Are Carnot Engines used in practical applications?

No, Carnot Engines are purely theoretical and have not been successfully implemented in practical applications. However, the principles and concepts of Carnot Engines have greatly influenced the development of modern heat engines and power plants.

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