Scavenging in IC Engine

Scavenging in IC Engine is a process to remove the exhaust air (Burnt gases) from the combustion chember and supply fresh fuel air mixture in the chember. Scavenging process is used in both two stroke and four stroke engine to remove exhaust air and supply of air or air fuel mixture. 

Scavenging Process

Scavenging is also said as a process of clearing the cylinder after each expansion stroke. The Scavenging process is used in two stroke engine which does not used piston to push exhaust gas like four stroke engine. In two stroke engine air enter in cylinder through bottom dead centre and scavenging the exhaust gas through the cylinder.

Better scavenging process includes better combustion of fuel which lead better engine performance.

What is Scavenging Angle?

Scavenging Angle is the Crank Angle by which both inlet and exhaust port are open.

Types of Scavenging

There are three types of Scavenging in Engine

• Uniflow Scavenging

• Cross-flow Scavenging

• Loop or Reverse Scavenging

Uniflow Scavenging : 

Uniflow Scavenging are mainly used in large vehicle of two Stroke Engine like large marine vehicle. It Involve one or two intake port at side of cylinder and one exhaust port at cylinder head. In operation fuel air mixture enters through intake port and take combustion and exhaust gas move upward to exhaust port. Uniflow Scavenging process has minimum air loss and minimum fuel consumption result in better efficiency of engine.

Cross-flow Scavenging : 

Cross-flow Scavenging are mainly used in low speed engine. It is less efficient in high speed engine. 

Cross-flow Scavenging

In cross flow Scavenging Intake and exhaust port are placed at opposite side of cylinder. When charge inter through intake port, It redirect the charge upward and pushing exhaust gas downward and exhaust through exhaust port.

Loop or Reverse Scavenging : 

Loop or Reverse Scavenging are mainly used in high speed engine like racing cars and bikes. It is less efficient in low speed engine. 

Loop or Reverse Scavenging

In loop or Reverse Scavenging Intake and exhaust port are placed at same side of cylinder. It's intake port is large which contains maximum charge and exhaust port is comparitably small which creates rapid expulsion of exhaust gas. It creates loop movement of Inlet charge and force to push exhaust gas out of the cylinder through exhaust port.

Results of Incomplete Scavenging

• Incomplete Scavenging lead to low oxygen supply which leads incomplete combustion which eventually increase fuel consumption and low efficiency of engine.

• Incomplete Scavenging also leads to contamination of lubricating oil which result in increase wear of piston and cylinder.