What are the effects of knocking in SI engine?

When knocking combustion occurs, high-frequency pressure oscillations can be observed. The SI engine can be damaged by knocking combustion in different ways: piston crown melting, piston ring sticking, cylinder bore scuffing, piston ring-land cracking, cylinder head gasket leakage and cylinder head erosion.

What is SI engine turbulence?

The turbulent field in an engine is produced by high shear flows that occur during the intake process and/or near top dead center (TDC) of the compression stroke for engines that have large squish regions (i.e. a region of small clearance between the cylinder head and the piston crown).

What causes turbulence in an IC engine?

Turbulence is caused by modified piston. Turbulence enhances mixing and probably produces a leaning effect. The turbulence in the combustion chamber makes the charge into homogeneous and increases the combustibility of fuel. So brake thermal efficiency of modified piston is 2\% more than the normal piston.

What is the effect of knocking?

Knocking combustion causes major engine damage, and also reduces the efficiency. The variation of pressure signal is gradually increased and smoothly reduced to minimum during normal combustion. The rapid rise of pressure signal has occurred during knocking combustion.

What are the factors affecting knocking?

Factors affecting Detonation or Knocking in SI engine:

• Compression ratio: The pressure and temperature at the end of compression increases with increase in compression ratio.
• Supercharging:
• Increasing inlet temperature:
• Increase in load:
• Advancing the spark:
• Flame travel distance:
• Spark plug location:
• Engine size:

What is swirl in engine?

Swirl is usually defined as organized rotation of the charge about the cylinder axis. Swirl can be created by bringing the intake flow into the cylinder with an initial angular momentum [2]. It is well known that the in-cylinder air motion strongly affects the combustion process and consequently their performance.

What is scavenging in IC engine?

Scavenging is the process of replacing the exhaust gas in a cylinder of an internal combustion engine with the fresh air/fuel mixture (or fresh air, in the case of direct-injection engines) for the next cycle. Scavenging is equally important for both two-stroke and four-stroke engines.

How is knocking produced in a petrol engine?

knocking, in an internal-combustion engine, sharp sounds caused by premature combustion of part of the compressed air-fuel mixture in the cylinder. These pressure waves force parts of the engine to vibrate, which produces an audible knock.

What do you mean by knocking in SI engines differentiate between knocking phenomenon in SI and CI engines?

In S.I. engines detonation is caused by the auto-ignition of end gas towards the end of combustion whereas knocking in CI engines is due to auto-ignition of the first charge at the start of combustion.

How much turbulence does it take to knock out an engine?

In SI engine therefore, generally limited to 100 mm Decreasing the turbulence of the mixture decreases the flame speed and hence increases the tendency to knock. Turbulence depends on the design of combustion chamber and one engine speed.

What is knocking in an SI engine?

Knocking in SI engine – Since air fuel mixture is added to SI engine,sometimes here the last charge left at the end of piston gets ignited due to high temperature and hence it generates a flame front in opposite direction of the original one caused by the spark.

Why do large engines have a greater knocking tendency?

Large engines have a greater knocking tendency because flame requires a longer time to travel across the combustion chamber. In SI engine therefore, generally limited to 100 mm Decreasing the turbulence of the mixture decreases the flame speed and hence increases the tendency to knock.

How does the turbulence of a mixture affect the knock-out rate?

Decreasing the turbulence of the mixture decreases the flame speed and hence increases the tendency to knock. Turbulence depends on the design of combustion chamber and one engine speed. i. Molecular Structure