The cycle of the internal combustion engine can be approximated (modeled) by the

Question

The cycle of the internal combustion engine can be approximated (modeled) by the Otto cycle, which is the cyclic process through which an ideal gas can be taken that we discussed in class. Look up the equation for the efficiency of the Otto cycle in the text (Eq. 20.6), noting that r = Vmax/Vmin is the compression ratio for the engine and is the specific heat ratio for the gas.

1.If the temperature of the gas in a particular internal combustion engine is 1350oC after combustion, and the air-fuel mixture enters the engine at 27oC, what is the maximum possible efficiency that could be achieved for a heat engine that operates between these temperatures (according to the laws of physics)?

2.If the compression ratio for the actual engine is 8 and = 1.4 (diatomic gas), what is the maximum possible efficiency that this particular engine, which is modeled by the Otto cycle, can be expected achieve? In other words, what would the predicted efficiency of this Otto cycle be? Compare this to the result of Part A.

Explanation / Answer

(1) efficiency= 1- Tcold/Thot

Tcold =27o C = 300K

Thot =1350o C=1623

e= 1- 300/1623 =0.815

so efficiency= 81.5 %

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