The Carnot efficiency represents the maximum theoretical efficiency that a heat engine can achieve operating between two temperature reservoirs. It is based on the principles of thermodynamics and is a consequence of the second law of thermodynamics.
The second law of thermodynamics states that heat cannot spontaneously flow from a colder body to a hotter body. This principle implies that a heat engine must reject some amount of heat to a lower temperature reservoir in order to do work. The Carnot cycle, which is an idealized thermodynamic cycle, achieves maximum efficiency by operating reversibly and extracting the maximum possible work from the heat input.
Any real heat engine will have various sources of inefficiencies, such as friction, heat losses, and irreversibilities. These inefficiencies lead to a decrease in the overall efficiency of the engine compared to the ideal Carnot efficiency. Therefore, it is not possible for a real heat engine to surpass the efficiency of a Carnot engine.
Several factors contribute to the inefficiencies in real engines. For example, in an internal combustion engine, energy losses occur due to friction in the moving parts, incomplete combustion of fuel, and heat losses through the exhaust and cooling systems. In a power plant, inefficiencies arise from the conversion of heat to mechanical energy, losses in transmission and generation, and the finite temperature differences in the heat exchange processes.
Efforts are continuously made to improve the efficiency of practical heat engines, but they will always be limited by the underlying principles of thermodynamics. The Carnot efficiency sets the upper bound for the efficiency of any heat engine operating between two given temperature reservoirs.