Fuel injection system in a diesel engine :
Fuel-injection system is most vital the component in the working of CI engines.
The injection system has to perform the important duty of initiating and controlling the combustion process.
Injection system main purpose is to the preparation of the combustible charge and is same as carburetion.The diesel fuel injection system consists of :
- Fuel injection pump -
pressurises fuel to high pressure
- High-pressure pipe -
sends fuel to the injection nozzle
- Injection nozzle -
injects the fuel into the cylinder
- Feed pump –
sucks fuel from the fuel tank
- Fuel filter -
filtrates the fuel
Requirements of
and injection system :
- Accurate metering of the fuel injected per cycle
- Timing the injection of the fuel correctly
- To obtain maximum power, fuel economy and clean-burning
- Proper control of the rate of injection
- Proper atomization of fuel
- A rapid mixture of fuel and air
- Uniform distribution of fuel droplets
- To supply equal quantities of fuel
- No lag during the beginning and end of injection
Classification of Injection system :
- Air injection system
- Solid injection system
Air injection
system:
Fuel is forced into
the cylinder by means of compressed air to very high pressure.
The rate of fuel
admit into the combustion chamber can be controlled by varying the pressure of
air.
The fuel is metered
& pumped to the fuel valve by a camshaft is driven fuel pump.
The fuel valve is
opened by means of a mechanical linkage operated by the camshaft which controls
the timing of injection.
The fuel valve is
also connected to a high-pressure airline fed by a multi-stage compressor
which supplies air at a pressure of about 60 to 70 bar.
Solid
injection system:
Fuel is injected directly into the
combustion chamber without primary atomization and is termed as solid
injection.
It is also termed a mechanical
injection.
Solid injection systems can be
classified into four types:
- Individual pump & injector
- Unit injector system
- Common rail system
- Distributor system
Fuel injection system in a petrol engine :
Fuel-injection system is commonly
used in CI engine.
In present gasoline injection system is also coming in SI engines because following the drawbacks of the carburetion.
- Non-uniform distribution of mixture in multi-cylinder engines.
- Loss of volumetric efficiency.
A
gasoline injection system eliminates all these drawbacks.
The injection of fuel into SI engine
can be done by the following methods :
- Direct injection of fuel into the cylinder
- Injection of fuel close to the inlet valve
- Injection of fuel into the inlet manifold
There are two types of the injection system
of gasoline systems :
- Continuous Injection: In continuous injection, fuel is
continuously injected.
- Timed Injection: In timed injection, fuel is injected
only during induction stroke. Injection timing is not a critical factor in
SI engines.
Advantages of fuel-injection in an
SI engines :
- Increased volumetric efficiency
- Increase thermal efficiency
- Low exhaust emissions
- High-quality fuel distribution