Q1: Knocking tendency in a petrol engine decreases with increasing

ANS:D - engine speed

Increasing engine speed can potentially increase the knocking tendency in a petrol engine due to several factors related to combustion dynamics and thermodynamics:

1. Increased Turbulence and Mixing: At higher engine speeds, the airflow and turbulence within the combustion chamber increase. This can result in better mixing of the air-fuel mixture, but it can also create localized hot spots and uneven distribution of temperature and pressure, which may promote knocking.
2. Reduced Residence Time: Higher engine speeds mean shorter combustion cycles and reduced residence time for the air-fuel mixture within the combustion chamber. This shorter residence time may not allow for complete combustion of the air-fuel mixture, leading to the presence of unburned fuel and increased knocking tendency.
3. Increased Cylinder Pressure and Temperature: As engine speed increases, the speed of the piston also increases, leading to higher pressures and temperatures within the combustion chamber during the compression stroke. Higher pressures and temperatures can increase the likelihood of auto-ignition and knocking, especially if the fuel mixture is prone to pre-ignition.
4. Advanced Ignition Timing: At higher engine speeds, ignition timing may need to be advanced to optimize combustion efficiency and power output. However, advancing ignition timing too much can lead to premature ignition of the air-fuel mixture, causing knocking.
5. Increased Mechanical Stresses: Higher engine speeds result in increased mechanical stresses on engine components, including the piston, connecting rods, and crankshaft. These mechanical stresses can create vibrations and harmonics within the engine, potentially affecting combustion stability and promoting knocking.

Overall, while increasing engine speed can enhance power output and performance, it also presents challenges related to combustion stability, combustion efficiency, and mechanical stresses that can influence knocking tendency in a petrol engine. Engine design, fuel quality, and tuning parameters such as ignition timing and air-fuel ratio must be carefully optimized to minimize knocking at higher engine speeds.