scavenge

Uniflow scavenging

This article does not cite any references or sources. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (November 2006)

In automotive usage, scavenging is the process of pushing exhausted gas-charge out of the cylinder and drawing in a fresh draught of air ready for the next cycle.

This process is essential in having a smooth-running internal combustion engine. Modifying the exhaust system, (i.e. modifying the exhaust gas velocity by changing exhaust tube diameters) can detract from the "ideal" scavenging effects, and reduce fuel efficiency and power if not properly planned out and executed.

To increase scavenging potential, the entire path from intake to exhaust (i.e. all powertrain parts) to tailpipe must be tuned in sync with each other. This will ensure that the air flow is never interrupted. The acceleration and deceleration of this exhaust gas is what will hinder the scavenging potential.

For example, fast flowing heads and a tunnel ram intake combined with a poorly planned camshaft and exhaust system will cause the air to "slow down" and "speed up" throughout its journey, thus reducing its scavenging potential. So, to increase scavenging potential, the air must maintain a positive linear acceleration curve.

There are three types of scavenging on the basis of the flow of air:

1. Direct or cross scavenging
2. Loop scavenging, using Schnuerle porting
3. Uniflow scavenging

Cross flow scavenging

In this method, the transfer port (or inlet port for the engine cylinder) and exhaust port are situated on the opposite sides of the engine cylinder (as was done in case of two-stroke cycle engines). The piston crown is shaped as a deflector piston, so that the fresh charge was intended to move upwards and push out the burnt gases in the form of cross flow. as shown in (a)

Types of scavenging

Backflow or loop scavenging

In this method, the inlet and outlet ports are situated on the same side of the engine cylinder. The fresh charge, while entering into the engine cylinder, forms a loop and pushes out the burnt gases. as shown in (b)

Uniflow scavenging

In this method, the fresh charge, while entering from one side (or sometimes two sides) of the engine cylinder pushes out the gases through the exit valve situated on the top of the cylinder. In uniflow scavenging, both the fresh charge and burnt gases move in the same upward direction. as shown in (c)

See also

• Engine tuning
• Inertial supercharging effect
• Kadenacy effect
• Reciprocating engines

This engineering related article is a stub. You can help Wikipedia by expanding it. v t e

This article about an automotive technology is a stub. You can help Wikipedia by expanding it. v t e