Calculator · Thermal Engineering
Carnot Efficiency
Two reservoirs at T_H and T_C bound every heat engine running between them. Enter both absolute temperatures and read the reversible limit, plus the work and rejected heat of a stated heat input.
Inputs
Ideal cycle limits: reversible Carnot models between two reservoirs, and ideal air-standard Otto, Diesel and Brayton cycles with constant specific heats. Real machines fall below these values.
Results
Carnot efficiency η_C
The ideal limit: no engine between these reservoirs can do better.
| Heat input Q_H | 100 kJ |
|---|---|
| Work output W | 70 kJ |
| Heat rejected Q_C | 30 kJ |
| Carnot efficiency η_C | 70 % |
Assumptions
- · reversible cycle
- · two reservoirs
Explore in the Lab
The full cycle state travels; the Lab adds the state diagram and the comparison view.
Technical reference
η_C = 1 − T_C / T_H
W = η_C · Q_H
Q_C = Q_H − W
- T_H
- hot reservoir temperature (absolute)[K]
- T_C
- cold reservoir temperature (absolute)[K]
- r
- compression ratio[—]
- r_c
- cutoff ratio[—]
- r_p
- pressure ratio[—]
- γ
- heat-capacity ratio cp/cv[—]
Temperatures are absolute (kelvin); equal or inverted reservoirs are refused.
This is the reversible ideal limit — every real engine between the same reservoirs is less efficient.