Air Injection System – Diagram, Operation, Advantages

Fuel injection is a system of mixing fuel with air in an internal combustion engine.

The functional purposes of fuel injection systems vary, but they all share the central task of delivering fuel to the combustion process. There are several competing goals, such as:

Power, fuel emission, emission performance, reliability, smooth operation, initial cost, maintenance cost.

Fuel injection system requirements are:

i) Accurate measurement of fuel injected per cycle: The amount of fuel measured must vary to meet speed changes and engine load requirements

ii) Correctly synchronize fuel injection in the cycle: obtain maximum power, ensuring fuel economy and clean burning.

iii) Proper control of injection rate: The desired heat release pattern is achieved during combustion.

iv) Adequate atomization of the fuel into very fine droplets.

v) Adequate spray pattern to ensure rapid mixing of fuel and air.

vi) Uniform distribution of fuel droplets throughout the combustion chamber.

Air injection system:

It was first developed by Rudolf Diesel. The system layout is shown in fig. In this system, air and fuel are injected into the cylinder during fuel delivery. The air pressure required to inject the fuel is around 70 bar or higher.

A fuel pump is driven by the engine itself. (A camshaft operates the fuel pump through a cam and the power required to rotate the camshaft is taken from the main shaft of the engine with the help of gears and discharges a set amount of fuel into the injection valve as shown In Fig. 3A. 1, the injection valve is mechanically opened and the high pressure air drives the fuel charge and some air into the combustion chamber. oil pump, which is operated by a regulator. at about 70 bar by a three-stage compressor (as shown in fig.) providing intermediate cooling The compressor is also operated by the engine. the combustion chamber and atomizes it.

This type of system is rarely used in diesel engines today.

diagram of the air injection system working

The advantages and disadvantages of this system are listed below:

Benefits:

• Provides better atomization and distribution of fuel.
• As combustion is more complete, BMEP is superior to other types of injection systems.
• Allows the use of inferior fuels.

Disadvantages:

• Requires a complicated mechanism to operate the compressor
• The engine weight increases.
• Part of the power is used to drive the compressor and thus the BHP of the engine is reduced.