How can I make the heat engine efficiency become 100%?

Question

Is it possible to make it 100%? Or in what kind of situation the heat engine efficiency could be 100%?

Answer 1

According to Carnot's Theorem Carnot's Theorem, the maximum efficiency of a cyclic heat machine working between a hot reservoir at absolute temperature $T_h$ and a cold reservoir at $T_c$ is $$\eta=\frac{W}{Q_h}=1-\frac{T_c}{T_h}$$ where $W$ is the work done and $Q_h$ is the heat entering the machine. Therefore, the efficiency increases for large $T_h$ and small $T_c$ and approaches $1$, i.e.100%, for $T_c \to 0K$, which is, however not a practical working condition.