1. Cause: Petrol knocking occurs when the air-fuel mixture in the combustion chamber ignites too early, resulting in a sudden and uncontrolled burn. This rapid combustion creates shockwaves that produce a knocking or pinging sound.
2. Factors Influencing Petrol Knocking:
- High Compression Ratio: Higher compression ratios increase the pressure and temperature inside the cylinder, making the fuel more susceptible to knocking.
- Incorrect Ignition Timing: If the spark plug fires too early or too late, it can cause the fuel to ignite at an inappropriate time, leading to knocking.
- Low-Octane Fuel: Petrol with a low octane rating is more likely to knock compared to higher-octane fuel, which has a higher resistance to knocking.
Diesel Knocking:
1. Cause: Diesel knocking, also known as diesel engine knock or diesel engine clatter, is a distinct sound produced by diesel engines when the combustion process is not smooth or efficient. It is caused by rapid pressure changes in the combustion chamber.
2. Factors Influencing Diesel Knocking:
- Poor Fuel Injection Timing: Improper injection timing can lead to diesel knocking, especially if the fuel is injected too early or too late.
- Incorrect Nozzle Spray Pattern: If the fuel is not properly atomized or sprayed in the correct pattern, it can cause incomplete combustion and result in knocking sounds.
- Inadequate Cetane Number: Cetane number indicates a diesel fuel's ignition quality. A low cetane number can cause delayed ignition, leading to diesel knocking.
- Worn or Damaged Engine Components: Over time, engine components such as injectors, pistons, and bearings can wear, leading to increased clearances that can cause knocking noises.
While both petrol knocking and diesel knocking are undesirable engine noises, they have different causes and are influenced by different factors related to the fuel and engine design.
