222 Engine Speed

The output power of an engine is the product of its torque and its speed; therefore, higher speed engines have higher power densities. However, piston size and weight limit the speed at which an engine can operate. The speed at which the flame front travels through the compressed gas also limits the speed. Slower speed engines are more efficient and can burn lower grade, less expensive fuels.

Engines are usually directly coupled to the generator and operate at synchronous speeds (Table 2.1). These speeds are defined by the frequency in Hz (cycles per second) of the electric grid in the country involved (usually 60 or 50 Hz). Small engines generally operate at 3600 rpm (60 Hz) or 3000 rpm (50 Hz) with 2-pole generators. Medium size engines operate at 1800 rpm (60 Hz) and 1500 rpm (50 Hz) with 4-pole generators. Large engines operate at

1200 or 900 rpm (60 Hz) or 1000 or 750 rpm (50 Hz) with 6- or 8-pole generators. Engine speed can be determined by solving this equation when frequency and number of poles are known:

TABLE 2.1

Variation of Synchronous Speed with Number of Poles and Frequency

Frequency (Hz) Two Pole Four Pole Six Pole Eight Pole

60 3600 1800 1200 900

50 3000 1500 1000 750

RPM per Hz 60 30 20 15

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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