What is sensitivity of a governor?

Short Answer:

The sensitivity of a governor is the measure of how effectively the governor responds to a small change in engine speed. It shows how much the sleeve of the governor moves for a given change in speed. A sensitive governor quickly detects even minor speed variations and adjusts the fuel supply accordingly to maintain a constant mean speed of the engine.

In simple terms, a governor with high sensitivity will have a large sleeve lift even for a small change in engine speed, ensuring smoother operation and better control. However, too much sensitivity may cause instability and continuous fluctuations in speed.

Detailed Explanation:

Sensitivity of a Governor

The sensitivity of a governor is one of the most important characteristics used to judge its performance. It helps in understanding how efficiently the governor controls the speed of an engine by adjusting the fuel supply based on changes in load conditions. When the load on an engine changes, the speed tends to either increase or decrease. The governor detects this change and modifies the fuel input to bring the speed back to the desired value.

The sensitivity defines the degree to which the governor reacts to these speed variations. It is expressed in terms of the difference between the maximum and minimum equilibrium speeds and the mean equilibrium speed.

Mathematically, sensitivity can be represented as:

Where,

  • Change in speed of governor = (Maximum equilibrium speed – Minimum equilibrium speed)
  • Mean equilibrium speed = (Maximum equilibrium speed + Minimum equilibrium speed) / 2

The higher the sensitivity, the more quickly the governor can detect and correct changes in engine speed.

Working of Sensitivity in a Governor

When the load on an engine decreases, its speed increases because less power is required. The governor senses this rise in speed through centrifugal force acting on the rotating balls. The balls move outward, which in turn raises the sleeve. The upward movement of the sleeve operates a mechanism that reduces the fuel supply to the engine. As a result, the speed decreases and returns to the mean speed.

Similarly, when the load increases, the engine speed drops. The centrifugal force on the balls reduces, causing them to move inward. This movement lowers the sleeve, which increases the fuel supply to bring the speed back to normal.

In both cases, the distance moved by the sleeve for a given change in speed represents the sensitivity of the governor. A greater sleeve movement for a small speed change means the governor is more sensitive.

High and Low Sensitivity

  1. High Sensitivity:
    A highly sensitive governor reacts very quickly to even small speed changes. It produces a large sleeve movement for a small change in speed. While this ensures fine control, too much sensitivity can make the engine unstable, causing continuous oscillations of speed known as hunting.
  2. Low Sensitivity:
    A governor with low sensitivity does not react much to speed changes. It remains almost inactive for small speed variations, which leads to poor control of the engine speed.

Hence, a practical governor must have moderate sensitivity — enough to maintain constant speed but not so high as to cause instability.

Example of Sensitivity Calculation

Suppose a governor has a maximum equilibrium speed of 310 rpm and a minimum equilibrium speed of 290 rpm. Then:

  • Mean equilibrium speed = (310 + 290) / 2 = 300 rpm
  • Change in speed = 310 – 290 = 20 rpm

Now,

This means the governor has a sensitivity of 6.67%, showing how effectively it can control speed variations.

Factors Affecting Sensitivity

Several factors influence the sensitivity of a governor:

  1. Mass of rotating balls: Heavier balls generate greater centrifugal force, increasing sensitivity.
  2. Spring stiffness: In spring-controlled governors, softer springs make the governor more sensitive.
  3. Friction: Higher friction in linkages and sleeves reduces sensitivity.
  4. Type of governor: Different designs (Porter, Proell, Hartnell, etc.) offer varying sensitivity levels.
Conclusion:

The sensitivity of a governor plays a vital role in maintaining the stability and performance of an engine. It indicates how effectively the governor can control the speed under changing load conditions. A perfectly sensitive governor would react instantly to even the smallest speed variation, but in practical cases, moderate sensitivity is preferred to avoid hunting and ensure steady operation. Hence, proper design and adjustment of the governor are essential to achieve balanced sensitivity and smooth engine performance.