Thermal Efficiency

  • Thread starter EngNoob
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38
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Main Question or Discussion Point

Hi

Could any one help me with this?

How would i go about calculating the thermal efficiency of a heat engine with four processes?

I am thinking of moddeling it on the Otto or Diesel Cycle.

The data i have is.

Temp @ State/Process 1

Specific Gas Constant

Specific Heat Capacity

and i have

Pressure

Volume

for states one, two, three and four.

How would i got about figuring out the thermal efficiency? do i use a NFEE equation?

Thanks for any help.
 

Answers and Replies

95
0
Although my knowledge is limited on the subject, I assume that if the working fluid is air, then you would need some air tables to look up the enthalpy/internal energy values for each state. Once you have those values you can calculate the net work and the heat input to the engine. Your efficiency then is the ratio of the two.
 
See how much heat is transfered at the high temperature (Qh) then see how much heat is transfered at the low temperature (Qc), then use

n (thermal) = (Qh-Qc)/Qh or W/Qh
 
38
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Thanks for that, i will have a go using that formula.

However, i need to calculate work done first for a otto cycle, any ideas on that?

I have Volume, Pressure and Exp/Comp Index
 
62
2
Hi there:

Check out your post on compression and expansion.

The same input material covers this post.

Here are two plots regarding the thermal efficiency of Otto Cycle and Diesel Cycle.

Slide43.GIF

Slide50.GIF

Thanks,

Gordan
 
Last edited:
38
0
Thanks for that, understand better now, cheers...
 
62
2
EngNoob:

I am glad to be of some help to you and PF members and/or visitors ...

Thanks,

Gordan
 
Hi, I'm new by here.
The information helps.I will see something about jet engines.
But, just to make presence, leave a reply.Ok?
See you later.
 

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