This question is about How correct are those comments on efficiecy of internal combustion(IC) engines which calcuate it using 2nd law of thermodynamics.The maximum efficiency of a heat engine can be determined by second law. But the second law says you can't convert heat completely into work in a cyclic manner.It is not the case with ic engines since the working substance(fuel+air) doesn't follow any cycle. So there should not be any limitation imposed by 2nd law on IC engines.

  • $\begingroup$ 1. Please explain abbreviations like "ic engine" 2. I don't see an explicit question here. $\endgroup$ – ACuriousMind Jun 23 '15 at 11:38
  • $\begingroup$ The piston goes in and the piston comes out - how is that not a cycle? $\endgroup$ – Jon Custer Jun 23 '15 at 14:20
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    $\begingroup$ You should probably take a look at wiki articles on the Otto cycle and the Diesel cycle. $\endgroup$ – user3823992 Jun 23 '15 at 15:42
  • $\begingroup$ @jon custer a thermodynamic cycle is when working substance attains its initial state. In IC engines the working substance is exhausted rather than completeing the cycle. $\endgroup$ – imgodsparticle Jun 23 '15 at 17:52
  • $\begingroup$ Yet, somehow, the Otto cycle is in every thermodynamics book. As is the steam engine. Both of which 'exhaust' the working substance as part of the cycle. $\endgroup$ – Jon Custer Jun 23 '15 at 18:13

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