Diesel engines and gas engines use salient pole alternators. Salient pole alternators have poles that project outward from the rotor, which makes them less efficient than cylindrical pole alternators. However, salient pole alternators are less expensive to manufacture and are easier to maintain.
Here are some of the advantages and disadvantages of salient pole alternators:
Advantages:
Less expensive to manufacture
Easier to maintain
Can be used at lower speeds
Disadvantages:
Less efficient than cylindrical pole alternators
Can produce more noise
Can be more difficult to balance
Cylindrical pole alternators have smooth, cylindrical rotors. They are more efficient than salient pole alternators, but they are also more expensive to manufacture and maintain. Cylindrical pole alternators are typically used in high-speed applications, such as power generation.