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Magnifier Engine

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which is exactly the Carnot efficiency.

In practice, regenerators can be realized by using, for example, steel wool whose large surface-to-volume ratio guarantees a speedy heat exchange. Desirable characteristics of regenerators include:

- high heat capacity,

- low longitudinal heat conductance,

- low viscous losses,

3.8.1.2 The Beta Stirling Engine

In a beta-configured Stirling engine, a single cylinder is used. (See the schematics in Figure 3.13.) The lower piston is called the power piston and fits tightly in the cylinder so that gas can be compressed. The upper

Isothermal compression

10-3 m3 es2 K 2.17310s Pa

10-3 m3 es2 K 2.17310s Pa

10-3 m3 300 K 10s Pa

10-3 m3 300 K 10s Pa transfer

Isothermal expansion

Isometric heat rejection

Wi"r-23oJn r Q-r=0 2=^cJ(T2.-T2) W^ =^RT3In r Q3^ =c¿Ts-T<0¡

V_Regeneration__J

Figure 3.13 The various states of a beta Stirling cycle.

Figure 3.14 A regenerator can be fitted indicated above.
to a beta Stirling engine in the manner

piston is the displacer and fits loosely so that it is quite leaky. The function of this displacer is to move the gas from the "cold" space (Space 2) just above the power piston to the "hot" space above the displacer (Space 1).

The phases of this cycle are the same as those of the alpha cycle so we can use the same quantitative example. In Figure 3.14, we divide the 1 ^ 2 phase into two subphases: 1 ^ 2* in which the displacer comes down and moves the cold gas of Space 2 into the hot region of Space 1. Again, ideally, no energy is consumed in this subphase because the gas leaks freely through the gap between displacer and cylinder. Isometric heat addition is performed in Subphase 2* ^ 2.

The problem with this configuration is that there is no provision for the important regeneration function. This can be remedied by using an external path connecting Spaces 1 and 2, as indicated in Figure 3.14

3.8.1.3 The Implementation of the Kinematic Stirling Engine

One possible implementation of the Stirling engine is that shown in Figure 3.15. Air from a combustion blower is fed to a burner where it is mixed with fuel and ignited. The resulting hot gases are passed through an input heat exchanger that transfers heat to the working fluid in "Space #1." Gases that exit the input side of this heat exchanger still contain a considerable amount of heat that can be recovered by preheating the air coming from the combustion blower, lowerings the amount of fuel required to maintain the working fluid of the engine at the required temperature.

The cooling of the working fluid in "Space #2" is accomplished through a separate cooling heat exchanger.

As in all types of engines, a number of factors cause the specific fuel consumption of a practical Stirling engine to be much higher than the theoretical predictions and its pollutant emissions to be higher than desirable.

Further development would be necessary if this category of engines were to become popular in the automotive world. This will probably not happen because it appears that combustion engines are approaching the end of their popularity. In all probability, fuel cells will gradually take over most areas where IC engines are now dominant. Owing to the enormous size of the automotive industry, the transition from IC to FC technology must, necessarily, proceed gradually. An important intermediate step is the use of hybrid cars.

Fuel

Exhaust

Air from combustion blower

Preheating heat exchanger

Fuel

Preheating heat exchanger

Exhaust

Air from combustion blower

Cooling heat exchanger

Figure 3.15 One possible implementation of a Stirling engine.

Cooling heat exchanger

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## Solar Stirling Engine Basics Explained

The solar Stirling engine is progressively becoming a viable alternative to solar panels for its higher efficiency. Stirling engines might be the best way to harvest the power provided by the sun. This is an easy-to-understand explanation of how Stirling engines work, the different types, and why they are more efficient than steam engines.

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