210

(d) Engine speed 1200 RPM

(c) Engine speed 140<J RPM

(d) Engine speed 1200 RPM

and power output at high cylinder-head temperatures to a maximum of 32.2 at the minimum power output at low cylinder-head temperatures.

The reduced engine performance data obtained by Ward are summarized in Table 9.2. The data are arranged in four sub-tables for constant speeds of 1800, 1600, 1400 and 1200 revolutions per minute. In all cases measurements were made at cylinder-head temperatures of 900, 800, 700 and 600°C (1652, 1472, 1292 and 1112°F). with mean cycle pressures in the range 0.4 to 1.2 MN/nv (4 to 12 bar).

The results are presented graphically in Figs. 9.21 and 9.22. Each figure shows the brake power and brake specific fuel consumption at constant engine speed or constant cylinder-head temperature as a function of mean pressure in one case or engine speed in the other.

Ward carried out a series of interesting 'motoring' tests with the engine. A motoring test involves driving the engine with the dynamometer acting as a motor and measuring the power input to the engine. Motoring tests are normally carried out in evaluation of internal combustion engines to establish the friction horsepower. However, if a Stirling engine is driven that way it acts like a refrigerator and so the input work is made up partly of the mechanical friction losses and partly of the cycle work to accomplish the refrigeration effect. Ward overcame this problem by including a large volume (compressed gas bottle) in the engine dead space. This ensured there was no significant cyclic pressure variation during operation of the engine and therefore no refrigeration effect was created.

lie carried out motoring tests at different speeds and different mean pressures with the engine always at ambient temperature conditions and obtained the results presented in Fig. 9.23. This shows the motoring

Mean (ipcratinR pressure (bar) (a) Hrake power vs pressure

Mean nperalinn pressure (bar) (b) Hrake specific fuel consumption vs pressure

Fici. 9.21. Hrake power and brake specific furl eonsumption ol small Stirling air engine as a function of mean pressure at four different cylinder head temperatures and a constant engine speed of 1800 revolutions per minute.

Mean (ipcratinR pressure (bar) (a) Hrake power vs pressure

Mean nperalinn pressure (bar) (b) Hrake specific fuel consumption vs pressure

Fici. 9.21. Hrake power and brake specific furl eonsumption ol small Stirling air engine as a function of mean pressure at four different cylinder head temperatures and a constant engine speed of 1800 revolutions per minute.

Fin. 9.22. Drake power and brake specific I'ucl consumption of small Stirling air engine as a function of engine speed at different mean operating pressures and a constant cylinder-head temperature of 800 °C.

Engine speed frpm) (a) Brake power vs speed

Solar Stirling Engine Basics Explained

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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