Ideal (Carnot) Engine
An engine achieves maximum efficiency when it uses reversible processes.
Carnot's Principle: The efficiency of an engine using irreversible
processes can be no greater than the efficiency of an engine using reversible
processes that is working between the same temperatures.
For an ideal (Carnot) engine, operating between temperatures Th
and Tc, the efficiency is:
| ηc
| = 1 - |
| Tc
|  |
| Th
|
|
The efficiency is maximized when Tc is as low as possible, and
Th is as high as possible.
| Comparing this to our previous result: η
| = 1 - |
| |Qc|
| |
| |Qh|
|
|
| For an ideal (Carnot) engine:
| | |Qc|
| |
| |Qh|
|
|
= |
| Tc
| |
| Th
|
|