A Stirling-Cycle Engine. The Stirling cycle is similar to the Otto cycle, except that the...

A Stirling-Cycle Engine. The Stirling cycle is similar to the Otto cycle, except that the compression and expansion of the gas are done at constant temperature, not adiabatically as in the Otto cycle. The Stirling cycle is used in external combustion engines (in fact, burning fuel is not necessary; any way of producing a temperature difference will do-solar, geo-thermal, ocean temperature gradient, etc.), which means that the gas inside the cylinder is not used in the combustion process. Heat is supplied by burning fuel steadily outside the cylinder,  instead of explosively inside the cylinder as in the Otto cycle. For this reason Stirting-cycle engines are quieter than Otto-cycle engines, since there are no intake and exhaust valves (a major source of engine noise). While small Stirling engines are used for a variety of purposes, Stirling engines for automobiles have not been successful because they are larger, heavier, and more expensive than conventional automobile engines. In the cycle, the working fluid goes through the following sequence of steps (Fig.):

Figure:

(i). Compressed isothermally at temperature T1 from the initial state a to state b, with a compression ratio r.

(ii) Heated at constant volume to state at temperature T,

(iii). Expanded isothermally at T2 to state d.

(iv). Cooled at constant volume back to the initial state a.

Assume that the working fluid is n moles of an ideal gas(for which C1 is independent of temperature). (a) Calculate Q, W, and ΔU each of the processes a → b, b →c, c → d, and d → a. (b). In the Stirling cycle, the heat transfers in the processes b → c and d → c do not involve external heal sources but rather use regenerator The same substance that transfers heat to the gas inside the cylinder in the process b → c also absorbs heat back from the gas process d → a. Hence the heat transfers and Qb→c and Qd→a role in determining the efficiency of the engine; Explain last statement by comparing the expressions for Qb→ c and Qd→ a calculated in part (a). (c) Calculate the efficiency of a Stalin cycle engine in terms of the temperatures T1 and T2 A. How does compare to the efficiency of a Carnot-cycle engine- opening Between these same two temperatures? (Historically, the in cycle was devised before the Carnot cycle.) Does this result violate second law of thermodynamics? Explain. Unfortunately, actual Stirling-cycle engines cannot achieve this efficiency due to problems with the heat-transfer processes and pressure losses in the engine.