Basic Knowledge About Engine

1. What are the starting speed and minimum stable speed of a diesel engine?

Answer: The lowest speed at which a diesel engine can start and ignite is called the starting speed, also known as the ignition speed.

After the engine starts and runs, the lowest speed at which each cylinder can continuously and evenly ignite to maintain stable operation (generally 1/3 to 1/4 of the rated speed) is called the minimum stable speed of the diesel engine.

2. Why do diesel engines need governors or speed limiters? How are they classified?

Answer: Under constant external load, a typical diesel engine operates at a stable speed. However, the external load on a diesel engine often changes during operation, and increases or decreases in external load will cause the engine speed to decrease or increase. To ensure that the diesel engine can still operate stably at a given speed under varying external loads, or to limit its speed from exceeding the maximum allowable value, a governor or speed limiter is required. This allows the governor to automatically adjust the fuel supply when the external load changes, without direct human intervention, to meet the requirements of stable operation or speed limitation of the diesel engine.

Governors can be classified according to the range and function of the speed they regulate, into constant-speed governors, all-speed governors, and speed limiters; and according to the way they act on the fuel quantity regulating mechanism, into direct-acting and indirect-acting governors.

In direct-acting governors, the centrifugal force generated by the flyweights is directly used to move the fuel quantity regulating mechanism. In indirect-acting governors, the centrifugal force generated by the flyweights is only used to control a certain amplifier (called a servo mechanism), and then the amplified power from the servo mechanism is used to indirectly push or pull the fuel quantity regulating mechanism to regulate the speed of the diesel engine.

3. Why must the governor of a power generation diesel engine be a constant-speed governor?

Answer: All diesel engines working with generators require a stable speed to ensure the stability of the generator's frequency, thus meeting the requirements for parallel operation and power supply. Due to the increase or decrease in electrical equipment usage, the external power demand frequently changes during operation, causing the external load on the diesel engine to constantly fluctuate. Without a governor to promptly and accurately adjust the fuel injection quantity, the diesel engine's speed will change accordingly. If the external load suddenly decreases, the diesel engine speed will suddenly increase, posing a risk of overspeeding; if the external load increases, the diesel engine speed will decrease, which will not meet the requirements for stable output frequency and parallel operation. For this reason, the governor for a power generation diesel engine must be a single-control governor, i.e., a constant-speed governor.