Fuel injection system
RAGHVENDRA KUMAR PANDEY
NATIONAL INSTITUTE OD TECHNOLOGY, DURGAPUR
-:Functional requirement of an injection system:Fuel injection system is the most vital component of the engines (CI & SI).
Engine performance viz. power output, economy, etc. is greatly affected by the fuel injection system
The injection system has to perform the most important duty of initiating and controlling the engine during the
idling, cruising or during the full load so that the equivalence ratio is maintained according to the need of
For a proper running and performance ,following requirement must be met by the injection systems:a) Accurate metering of the fuel injected per cycle . This is very important an critical because e small amount
of metering errors may cause drastic variation from the desired output.
b) Timing the injection of fuel correctly in the cycle so that maximum power is obtained ensuring the fuel
economy and clean burning
c) Proper control on rate of fuel injection so that desired heat release pattern is obtained
d) Proper atomization of fuel and proper spray pattern ensuring rapid mixing of the fuel and air
e) To supply equal quantity of metered fuel to all cylinders in case of multi cylinder engines
f) No lag during beginning an d end of the injection i.e. eliminate dribbling of the fuel droplets into the
Mechanical injection system
Throttle body injection system
Common rail injection system
Multi point fuel injection
CARBURATION:The process of formation of combustible fuel- air
mixture by mixing the proper amount of fuel with
air before admission to engine cylinder is called
carburation and the device which does this job is
Preparation of charge is done outside the engine
Appropriate for petrol 4 stroke and 2 stroke (light
duty engines) because petrol is more volatile as
compare to diesel
Fuel is atomized by relying on the air speed
Factors affecting carburation:
The engine speed
Vaporization characteristics of fuel
Temperature of incoming air
Design of carburetor
Principle of carburation:A simple carburetor works on the Bernoulli’s
principle, i.e. faster the air moves lower the static
pressure and higher the dynamic pressure,
The throttle (accelerator) linkage does not directly
control the flow of liquid fuel. Instead, it actuates
carburetor mechanisms which meter the flow of air
being pulled into the engine. The speed of this flow,
and therefore its pressure, determines the amount
of fuel drawn into the airstream.
Assuming air like ideal gasu2 =sqrt(2Cp(T1-T2))
mass flow rate = (Cd)X(ᵨ2 u2)
Where Cd=coefficient of discharge for the venture.
Question :- WHY GASOLIN INJECTION [electronic fuel injection in SI engine] …..
Fuel injection system are commonly used in the CI engines but presently gasoline injection system is coming in vogue in SI
engines because of the following drawbacks of carburetion:These are following:i. Non uniform distribution of mixture in multi cylinder engine (MALDISTRIBUTION).
ii. Loss of volumetric efficiency due to restriction for the mixture flow and the possibility of back firing.
A gasoline injection system eliminates all these drawbacks. The injection of fuel in an SI engine can be done by employing
any of the following methods :A. Direct injection of fuel into the cylinder.
B. Injection of fuel close the inlet valve.
Throttle body fuel injection
C. Injection of fuel into the manifold.
Multipoint fuel injection
There are two types of gasoline (SI)injection system—
1. Continuous injection :- adopted when manifold injection is contemplated.
2. Timed injection :- fuel injected during only induction stroke over a limited period
Though use of gasoline injection system is limited because of high initial cost, complex design and increased maintenance
Direct injection into cylinder
Injection upstream near the valve
Throttle body Injection system: Similar to carburetor throttle body injection system
with a throttle valve controlling the amount of air
entering the intake manifold
Injector is placed slightly above the throttle body.
Injector spray the gasoline into the air in the intake
manifold where gasoline mixes with the air and
mixture passes through the throttle valve and enters
into the intake manifold
It may be timed or continuous type.
Multi-point fuel injection system
Throttle body injection
Multipoint fuel injection
Multipoint fuel injection
Manifold fuel injection system type.
Port fuel injection type.
Vacuum in the manifold is sensed by the Fuel metering is regulated by the engine
speed and amount of air that enters the
Volume of air is sensed by its density in the engine
Also called air mass metering or air flow
Sensed information is sent to the ECU and
and ECU sends commands to injector to Sensed information is sent to the ECU and
regulate the amount of gasoline supply for
and ECU sends commands to injector to
regulate the amount of gasoline supply for
Electronic fuel injection for SI engine
Uniform distribution in multi cylinder engines.
1) High maintenance cost.
Improved breathing capacity i.e. higher volumetric
2) Difficult in servicing.
Reduced or eliminated detonation
3) Possibility of malfunction of some sensors.
Prevent fuel loss during scavenging in case of two
Formation of the ice on the throttle plate is
Manifold wetting and mal distribution is eliminated .
Atomization of the fuel is independent of cranking
speed and therefore starting will be easier.
5) Complex design
Sensors used for electronic fuel injection
Exhaust gas sensor
Air flow sensor
Air inlet sensor
Throttle position sensor
Manifold pressure sensor
Camshaft position sensor
an electronic control unit or computer
receives the electrical pulses in the form of current or
the voltage from the various sensors
It then use the stored data to operate the injectors,
ignition system and other engine related
electronically controlled devices.
Coming to the CI Engines…
Air injection system
Fuel is forced into the cylinder by means
of compressed air
Little used nowadays because it requires
bulky multistage air compressor, which
causes increase in engine weight and
reduces the brake power output.
BUT it gives good mixing of fuel with the
air resulting higher mean effective
pressure, i.e. higher indicated power for
Fuels of high viscosity ( less expensive)
can be injected through this type of
Solid injection system
All the above system comprise mainly following components:i.
ii. Fuel feed pump to supply fuel from main fuel tank to the injection system
iii. Injection pump to meter and pressurize the fuel for the injection
iv. Governor to ensure that the amount of fuel injected is in accordance with the variation in load
Injector to take the fuel from the pump and distribute it in the combustion chamber by atomizing it into fine droplets
vi. Fuel filters to prevent dust and abrasive particles from entering the pumps and injectors
Typical fuel feed system ( individual pump and nozzle system)
Unit injector system:Pump and injector nozzle is provided in in one housing. Each cylinders is provided with one of
these unit injectors, fuel is brought up to the injectors by a low pressure pump where at proper time a rocker arm actuates
Plunger and thus injected the fuel into the cylinder.
effective stroke of plunger decides the amount of fuel injected into the cylinders.
-:Common rail injection system:In common rail injection system :-
High pressure pump supplies fuel to a fuel header
High pressure in header pushes fuel to the each nozzle located in the cylinders
At the proper time a mechanically operated valve allows fuel to enter the proper cylinder through the nozzle
Fuel pressure in the header must be that, for which the injector system is designed i.e.it must be able to penetrate
And disperse the fuel in combustion chamber
Length of push rod controls the amount of fuel entering in the combustion chamber
Common rail fuel injection system is finding increasing use in diesel engine as it has potential to drastically cut the
emission and fuel consumption. This system provide control of many important parameters linked to the injection
Also it has a wide range of applications from small to heavy duty engines.
some Important features are: Very high injection pressure of order up to 1500 bar.
Complete control over start and end of injection
Injection pressure is independent of engine speed.
Variable injection pressure can be set.
Distributer type: Pump which pressurizes the fuel also meters and times it.
The fuel pump after metering, the required amount of fuel supplies it to a rotating distributer at correct time for
supply to each cylinder.
The number of injection stroke per cycle for the pump is equal the number of cylinders.
Very economical (2/3rd less than of individual injection system)
Uniform distribution because there is only one metering system.
Stem of nozzle valve is extended to form a pin or Pintle which protrudes through the mouth of nozzle.
Provides a spray operating at low pressure, 8-10 MPa.
Spray cone angle is generally 60 degree.
It avoids weak injection and dribbling.
Pintaux nozzle: Similar to Pintle nozzle but a auxiliary hole is drilled in the nozzle body. Hence it helps in injection of small amount of
fuel through it slightly before the main injection.
The needle valve does not open fully at low speed and most of fuel is injected through the auxiliary hole.
Provides better cold starting of engine.
Single hole: At the center of nozzle body there is single hole which is closed by the nozzle valve. Order of hole is generally order of
Injection pressure is in the order of 8-10MPa and cone angle is 15 -20 degree.
Major disadvantage is that it tend to dribble
Small cone angle facilitates good mixing unless higher velocities are used.
Multi hole: Contains number of holes drilled in the tip of nozzle. Holes may vary from 4-18 in numbers and in size 35 to
Injection pressure is of order of 18-20 MPa and cone angle is greater that 20 degree.
Ability to distribute the fuel properly even with lower air motion available in open combustion chambers.
Internal combustion engine by V. Ganeshan