Q1: __________ cycle is the most efficient thermodynamic cycle.

ANS:D - Carnot

The Carnot cycle is the most efficient thermodynamic cycle. Explanation:

1. Carnot Cycle: The Carnot cycle is an idealized thermodynamic cycle that operates between two temperature reservoirs, a high-temperature source (TH) and a low-temperature sink (TL). It consists of four reversible processes: isothermal heat addition, adiabatic expansion, isothermal heat rejection, and adiabatic compression. The Carnot cycle is characterized by its maximum theoretical efficiency, which is determined solely by the temperatures of the heat reservoirs and is independent of the working fluid.
2. Efficiency: The efficiency of a thermodynamic cycle is defined as the ratio of the work output to the heat input. The Carnot cycle achieves the highest efficiency of any thermodynamic cycle operating between the same temperature reservoirs. Its efficiency (η) is given by the formula: η=1−TH​TL​​ where TH​ is the absolute temperature of the high-temperature reservoir and TL​ is the absolute temperature of the low-temperature reservoir.
3. Reason for Efficiency: The Carnot cycle achieves maximum efficiency because it operates reversibly and without any internal irreversibilities. It utilizes all the heat input from the high-temperature reservoir to perform work and rejects heat to the low-temperature reservoir in a reversible manner.
4. Comparison with Other Cycles:
   • Diesel Cycle: The Diesel cycle is commonly used in diesel engines and consists of two adiabatic processes and two constant-pressure processes. While the Diesel cycle is more efficient than the Otto cycle due to its higher compression ratio, it is less efficient than the Carnot cycle.
   • Otto Cycle: The Otto cycle is commonly used in spark-ignition engines (e.g., gasoline engines) and consists of two adiabatic processes and two constant-volume processes. It is less efficient than the Diesel cycle and the Carnot cycle.
   • Rankine Cycle: The Rankine cycle is commonly used in steam power plants and consists of four processes: isentropic compression, constant-pressure heat addition, isentropic expansion, and constant-pressure heat rejection. While the Rankine cycle is highly practical and widely used, its efficiency is limited by the temperature difference between the steam entering and leaving the turbine.