COMBUSTION CHAMBER IN CI ENGINE

- SUYASH SAXENA M225

TYPES OF COMBUSTION CHAMBERS Direct Injection (DI) Type – These also called open combustion chambers. The entire combustion space lies in themain cylinder and the fuel is injected into this volume.

Indirect Injection (IDI) Type – In this type of combustion chambers, combustion space is divided into two parts, one in the cylinder head and other in the main cylinder. Fuel is generally injected in the part which lies in cylinder head.

DIRECT INJECTION COMBUSTION CHAMBERS Shallow Depth Chamber

Hemispherical Chamber

In shallow depth chamber, depth of the cavity provided in the piston in small.

Due to this, the squish is negligible.

It is usually adopted for large engines running at low speeds.

This design also gives small squish.

However, its depth to diameter radius can be varied to obtain desired type of squish for better performance.

DIRECT INJECTION COMBUSTION CHAMBERS Cylindrical Chamber

Toroidal Chamber

This design is a modification of cylindrical chamber in the form of truncated cone.

Swirl is produced by masking the valve up to 180 deg. of circumference.

Squish produced is better than the previous two designs.

This design produces a powerful squish along with air movement.

The masking needed on the valves is small, and thus, it makes better utilisation of oxygen.

INDIRECT INJECTION COMBUSTION CHAMBERS Swirl Chamber

Swirl Chamber is provided in the cylinder head. A throat which is tangent to this chamber connects it with the main cylinder.

During compression, air flows into the swirl chamber through the throat. Tangential direction of air motion generates rotary motion inside the swirl chamber.

Fuel in injected into the chamber, and the combustion products travel back to the main cylinder at much higher velocity.

This type of chamber is used where fuel quality cannot be controlled, where reliability is more important than fuel economy.

INDIRECT INJECTION COMBUSTION CHAMBERS Pre-ignition Chamber

It consists of a pre-ignition chamber (40% of total combustion space) connected with the main cylinder through small no. of holes.

During compression, piston forces the air into pre-ignition chamber. Fuel is then injected into the chamber due to which combustion takes place.

The resulting pressure rise forces the combustion products at higher velocities through small holes into the main cylinder, where bulk of combustion takes place.

INDIRECT INJECTION COMBUSTION CHAMBERS Air-Cell ChamberThe clearance volume is divided into two parts – one in the main cylinder and rest in energy cell.

Energy cell is divided into two parts – major and minor, which are separated from each other and from the cylinder by narrow orifices.

Pressure in the energy cell is low, therefore, air is forced at high velocity into the energy cell on compression. After the injection of fuel, combustion takes place inside energy cell and hot burning gases blow out through small holes into the main chamber.

These hot gases provides swirling movement in main chamber, which results in complete combustion.

DIRECT INJECTION VS INDIRECT INJECTION

Injection Type Advantages Drawbacks

Direct InjectionMinimum heat loss during compression

Requires high fuel injection pressure.

Fine atomization because of multi-hole nozzle

Necessity of accurate metering of fuel

Indirect InjectionInjection pressure required is low

Poor Cold starting performance

Direction of spraying of fuel is not important.

Specific fuel consumption is high

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