Methods of Supercharging | Electric Motor Driven Supercharging | Ram Effect of Supercharging | Under Piston Supercharging | Kadenacy System of Supercharging || knowledgeaboutautomobile

METHODS OF SUPERCHARGING:

(i) Independently driven compressor or blower, usually driven by an electric motor.

(ii) Ram effect.

(iii) Underpiston supercharging.

(iv) Kadenacy system (applied to two stroke engines).

(v) Engine driven compressor or blower.

 Electric Motor Driven Supercharging:

In this type the compressor is driven independently usually by an electricmotor. The speed of the supercharger can be varied independent of engine speed and therefore control is comparatively easier.

Ram Effect of Supercharging:

The ram effect of supercharging system consists primarily of tuned inlet pipes.These pipes induce resonant harmonic air oscillations. The kinetic energy of these oscillations provides a ramming effect. For the efficient operation of this system, the engine speed must be kept constant.

Under Piston Supercharging:

Under piston method of supercharging has so far been confined to large marine four stroke engines of the cross head type. It utilizes the bottom side of the piston for compressing the air. The bottom ends of the cylinder are closed off and provided with suitable valves. This system gives an adequate supply of compressed air, as there are two delivery strokes to each suction stroke of the cycle.

Kadenacy System of Supercharging:

• The kadenacy system utilizes the energy in the exhaust system to cause a depression of pressure in the cylinder. This depression makes the scavenge air to flow into the cylinder. A blower may also be used with this system, but it is not an essential.
• The kadenacy system is based on the following principle: When the exhaust ports or valves are opened rapidly during the end of expansion stroke,there is, within the first interval of a few thousandths of a second, an urge or impulse in the gases to escape very rapidly from the cylinder. The escaping gases leave behind a pressure depression.
• At the above moment, the fresh charge of air (or mixture) is allowed to enter the cylinder behind the exhaust gases by suitable timing of the admission valve or ports. For the best result a proper timing and skillful design of the exhaust system is a must.
• The exhaust blow down must be rapid to get a good-sized puff. In this respect, the exhaust ports are better than valves, and the ports with square upper edges are better than those with rounded upper edges. The impulse must arrive at the exhaust duct of the concerned cylinder at the right time some 15 to 20◦, before exhaust valve closure. This will depend upon the timing of the blow down and the travel time of the wave from the source of its origin. In this method, the exhaust pressure is low (even subatmospheric during the greater part of the scavenging period). Hence, scavenging takes place against lower resistance and the intake pressure need not be high. This type of supercharging is also called exhaust pulse supercharging.