Fuel Injection Systems
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Introduction
 Fuel injection is a system for admitting fuel into an internal combustion
engine.
 It has become the primary fuel delivery system used in automotive engines,
having replaced carburetors during the 1980s and 1990s.
 The primary difference between carburetors and fuel injection is that fuel
injection atomizes the fuel by forcibly pumping it through a small nozzle
under high pressure, while a carburetor relies on suction created by intake
air accelerated through a Venturi-tube to draw the fuel into the airstream.
 Fuel injection systems are for diesel and gasoline applications.
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Functions of FIS
 It filters the fuel ensuring oil free from dirt.
 It measures the correct quantity of the fuel to be injected in each cylinder.
 It times the injection process in relation to the crank shaft revolution.
 It regulates the fuel supply.
 It atomizes the fuel under high pressure for better mixing with hot air
leading to an efficient combustion.
 It distributes the atomized fuel properly in the combustion chamber.
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Major Parts of FIS
 Fuel tank – the part is where the fuel is stored.
 Fuel pump – it pumps fuel from the fuel tank to the fuel injection system.
 Injection pump – this part is a meter and pressurize fuel for injection.
 Governor – supply fuel in accordance to the load.
 Fuel injector – supplies fuel from the injection pump to the cylinders.
 Fuel filter – to filter dirt, duct and abrasive particles from blocking the
injection system.
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Types of FIS based on the location of Fuel Added
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Types of FIS based on the location of Fuel Added
Used for petrol
 Throttle Body Fuel Injection
 Multi-Port Injection
 Sequential Injection
 Direct Injection
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Throttle Body Fuel Injection
 Also known as single port injection
system.
 It is the earliest type of fuel injection.
 TBFI works by adding the correct
amount of fuel to the air before it is
distributed to the individual cylinders.
 The advantage of TBFI is that it is
inexpensive and easy to maintain.
Additionally, since this injector has a
fairly high flow rate, it is not as easy to
clog up. Throttle body systems are
very robust.
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Throttle Body Fuel Injection
 It is rarely used today. The maintenance cost is higher.
 TBFI systems are not as fuel efficient as modern systems. There is a lot of fuel
in the air mixture that is being sent to engine cylinders. This can result in
unburned fuel being sent out through the exhaust.
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Multi-Port Injection
 Also called multi point fuel injection
(MPFI) system.
 Multiport injection simply moved the
injectors further down towards the
cylinders. The injector is located at the
end of this port, right before it’s sucked
through the valve and into the cylinder.
 The advantage of this system is that fuel
is distributed more accurately, with each
cylinder receiving its own spray of fuel.
 Each injector is smaller and more
accurate, offering an improvement in
fuel economy.
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Multi-Port Injection
 The downside is that all injectors spray at the same time, while the cylinders
fire one after the other. This means that there will be leftover fuel in between
intake periods.
 Multiport systems work great when the vehicle is traveling at a consistent
speed. But when you are quickly accelerating or removing your foot from the
throttle, this design reduces either fuel economy or performance.
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Sequential Injection
 Sequential fuel delivery systems are very similar to multiport systems except
fuel deliver timing. Instead of all injectors firing at the same time, they
deliver fuel one after the other. The timing is matched to engine cylinders,
allowing the engine to mix the fuel right before the valve opens to suck it in.
This design allows for improved fuel economy and performance.
 Because fuel only remains in the port for a short amount of time, sequential
injectors tend to last longer and remain cleaner than other systems. Because
of these advantages, sequential systems are the most common type of fuel
injection in vehicles today.
 The fuel / air mixture is sucked into the cylinder only moments after the
injector opens. If it is dirty, clogged, or unresponsive, the engine will be
starved of fuel.
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Direct Injection
 Also called gasoline direct injection (GDI) system.
 Direct injection is a more advanced version of multiport systems, where fuel
is injected directly into the combustion chamber instead of the intake port.
 Direct injection improves combustion efficiency, increases fuel economy and
lowers emissions.
 One of the problems with direct ignition engines, shoots from small particles
of oil/dirt that can blow back from the crankcase ventilation system and
deposit onto the walls of the intake port and the back of the valve. Carbon
sticks to the valve. The buildup can become significant enough that a piece
can break off and damage the catalytic converter. It also can cause ignition
problems.
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Direct Injection
Throttle body
injection
Multiport
injection
Direction
injection
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Types of FIS based on the Fuel Atomization Method
Mainly used for diesel
 Air Injection System
 Solid or Mechanical Injection System
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Air Injection System
 In this Injection system, the fuel will be injected into the cylinder by means of
compressed air. So it needs an additional compression system for the
Injection System. Due to this additional system, the weight of the engine will
increase which will result in the reduced brake power output.
 Nowadays little in use.
 The following are the advantages of the Air Injection system
 High viscosity fuel can be used which are comparatively less expensive
than the fuel used by the Solid Injection System.
 Can achieve higher Mean Effective Pressures (MEP) due to the good
mixing of fuel with the air.
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Solid Injection System
 In this Injection system, the fuel will be directly injected into the cylinder
without the aid of the compressed air.
 In this Solid Injection System, there are three different types of Injection
Systems,
 Individual pump injection system
 Common rail injection system
 Distributor injection system
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Individual Pump Injection System
 As the name employs, the system has an independent high pressure pump for
each cylinder with meters, pumps and controls the timing of fuel injection.
 Each cylinder is provided with one injector and the pump. The fuel is brought
to the individual pump from storage tank through filters and low pressure
pump.
 The high pressure pump is equipped with control mechanism of injecting
fuel at the proper time, a rocker arm actuates the plunger and thus injects the
fuel in to the cylinder. This is the most popular fuel injection system.
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Individual Pump Injection System
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Common Rail Injection System
 Also known as CRDI system
 This system consists of a high pressure pump which distributes fuel to a
common rail or header to which all the fuel injectors are connected.
 In common rail system, the fuel injectors are operated mechanically.
 The metering and timing of fuel injection is accomplished by the spray valve.
Then amount of fuel to be injected in to the cylinder.
 The quantity of the fuel injected depends on the duration of valve opening
size and number of holes in the nozzle tip, fuel pressure and air pressure in
the cylinder.
https://www.youtube.com/watch?v=0ZYtDkn0b9g
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Common Rail Injection System
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Distributor Injection System
 In this system, a metering and high pressure pump is used to pump the
metered quantity of fuel in to the rotating distributor which distributes the
fuel to the individual cylinders at the correct timing.
 The number of injection strokes per cycle for the pump is equal to the
number of cylinders.
 The fuel is fed to high pressure pump from storage tank through course filter,
low pressure pump and the fine filter.
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Distributor Fuel Injection System
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References
 Youtube.com
 https://www.youtube.com/watch?v=Qf05MIFxX9c
 Google.com
 https://electricalfundablog.com/electronic-fuel-injection-system-efi/
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Multi-Port Injection
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