Scavenging and Turbocharging

Scavenging and turbocharging

“Pulse” system:

The Pulse system takes advantage of the higher pressures and temperatures of the exhaust gases during Blow—down period and with rapidly opening of exhaust valves or ports.

The gases leave the cylinder at high velocity as pressure energy is effectively converted into kinetic energy to create a pressure wave or pulse in the exhaust pipe.

The pipe so constructed in small diameter is quickly pressurised and boosted up to form a pressure pulse.

The pulsating pressure waves reach up to the turbine nozzles and further expansion takes place.

The pressure in the exhaust pipe before the turbine shows a cyclic variation as is evident from the pressure crank angle diagram.

Advantages of pulse system:

1) High available energy at turbine.

2) Good performance at low speed & part load.

3) Good turbocharger acceleration.

4) Highly responsive to any changing load due to small volume of exhaust ducting

5) Required no scavenge assistance at any changing load

Disadvantages:

1. The exhaust grouping is complicated.

2. Different sizes of exhaust pipes are needed for spare.

3. Exhaust tuning and grouping requires special attention to avoid back flow and incorrect tuning could seriously affect the engine performance.