Unit injector : Nozzle types, Electronic Fuel

Injection system (EFI), GDI, MPFI, DTSI,

Unit Injection System
• In the unit injector system (UIS), the fuelinjection pump, high-
pressure solenoid valve and injection nozzle form a single unit.
• The compact construction – with very short high-pressure lines
integrated in the component between pump and nozzle – makes it
easier to deliver higher injection pressures compared with other fuel-
injection systems because the compression volume 1) and thus the
compression losses are lower.
• The peak pressure in the UIS currently varies, depending on the type
of pump, between 1,800 and 2,200 bar.
 Nozzle
• The nozzle sprays the liquid fuel

• The functions of the nozzle are

• Atomization
• Distribution of fuel to the required are
• Non impingement on the wall
• No dribbling
Types of Nozzles
 Single Hole Nozzle
• The single hole nozzle requires a high
injection pressure and this type of nozzle
has a tendency to dribble.
• The spray cone angle is usually narrow, and
this gives poor mixing unless the velocity is
high.
 Pintle Nozzle
• The pintle nozzle has been developed to avoid
weak injection and dribbling.
• The spindle is provided with a pintle capable of
protruding in and out.
• Pintle nozzle results in good atomization and
reduced penetration.
 Multi-Hole Nozzle
• A multi-hole nozzle, where the
number of holes may vary from 4 to
18, allows a proper mixing of air and
fuel.
• The advantage lies with the ability to
distribute the fuel properly even with
lower air motion within the chamber.
 Pintaux Nozzle
• The pintaux nozzle is a pintle nozzle
with an auxiliary hole drilled into the
nozzle body.
• At low speed, the needle vale does not
lift fully and most of the fuel is
injected through this auxiliary hole.
• A modem gasoline injection system uses pressure form an
electric fuel pump to spray fuel into the engine intake manifold.
 Advantages of Fuel injection system
• Improved atomization: Fuel is force into the intake manifold under
pressure that helps break fuel droplets into a fine mist.
• Better fuel distribution: Equal flow of fuel vapors into each cylinder.
• Smoother idle: Lean fuel mixture can be used without rough idle because
of betel fuel distribution and low speed atomization.
• Low emissions: Lean efficient air-fuel mixture reduces exhaust pollution.
• Better cold weather drivability: Injection provides better control of
mixture enrichment than a carburetor.
• Increased engine power: Precise metering of fuel to each cylinder and
increased air flow can result in more horsepower output.
• Fewer parts: Simple, late model, electronic fuel injection system have
fewer parts than modern computer-controlled carburetors.
 Classification of Gasoline Injection Systems
• Single – or multi-point injection
• Indirect or direct injection
 Single Point Fuel Injection
(Throttle Body Injection – TBI)
• Injector located inside
throttle body, sits on
top of inlet manifold.
• Injector sprays fuel
from above throttle
valve.
• ECU controls injector
opening.
Single-Point or Throttle Body Injection
• The first and simple kind of Fuel Injection was the Single-Point
injection. Here the carburetor is replaced by one or two fuel injector
nozzles in the throttle body, which is the throat of the engine’s air
intake manifold.
• Single-Point Injection was a stepping stone to the more complex
multi-point system for some manufacturers. They are economical and
easier to service.
 Multi Point Fuel Injection
• Injector located in each branch of
inlet manifold, below throttle
valve.

• Injectors spray fuel directly into

each port.

• ECU controls opening of injectors.

Port or Multi-Point Fuel Injection
• In Multi-point Fuel injection a separate injector nozzle is devoted to each cylinder,
right outside its intake port, due to which the system is also called Port Injection
System. When the fuel vapor is shot close to the intake port it makes sure that fuel
is drawn completely into the cylinder.
• The major benefit is that MPFI meters fuel more precisely than the TBI designs
do. It is better at achieving the desired fuel/air ratio and improving all related
aspects. Also, it nearly eliminates the possibility of the fuel to condense or to get
collected in the intake manifold. The TBI and carburetors are designed in such a
way that the intake manifold conducts the engine’s heat which is the measure to
vaporize liquid fuel.
• It is not necessary on engines that are equipped with MPFI where the intake
Manifold can be made out of lighter-weight material, even plastic. MPFI system
results in increased fuel economy. Standard metal intake Manifolds have to be
positioned on top of the engine to conduct heat, but in case of MPFI it can be
positioned more creatively, granting the engineers design flexibility.
(a) Single-point or Throttle Body (b) Port or Multi-Point (c) Direct Engine Fuel
Injection System
• A multi-point injection
system, also called port
injection, has an injector in
the port (air-fuel passage)
going to each cylinder.
• Gasoline is sprayed into each
intake port and toward each
intake valve. Thereby, the
term multipoint (more than
one location fuel injection is
used.
 Sequential Fuel Injection
• Sequential Fuel Injection, also known as the Sequential Port Fuel
Injection (SPFI) or Timed Injection, is a type of Multi-Port Injection.
Although the MPFI has multiple injectors, they all spray their fuel at
the same time or in groups. This may result in “hanging around” of the
fuel in a port for as long as 150 milliseconds at the time of engine
idling.
• It may not seem like much, but it’s sufficient of a limitation that the
engineers addressed it i.e. Sequential fuel injection triggers every
injector nozzle separately. They are basically timed like the spark
plugs and spray the fuel immediately before or as their intake valve
opens. Although seems like a minor step, the efficiency and emission
improvements come in exceptionally small doses.
 Direct Injection
• Direct Injection injects fuel straight into the combustion chambers, past the
valves.
• Direct Injection system is common in diesel engines and is beginning to pop
up in gasoline engine designs, sometimes called DIG for Direct Injection
Gasoline.
• Fuel proportioning is still more accurate than in the other injection system.
• The Direct Injection grants engineers an additional variable to influence
precisely how combustion occur in the cylinders.
• The discipline of engine design scrutinizes how the fuel/air mixture swirls
around in the cylinders and how the explosion travels from the ignition
point.
• Direct Injection is one that can be used in low-emission lean-burn engines.
 Architecture of Electronic Fuel Injection System

Components of the Electronic Fuel Injection System include:

• Sensors
• Electronic Control Unit (ECU)
• “Check Engine” Light / “Service Engine Soon” Light
• Fuel Injectors
• Fuel Pump
 Sensors
• Engine Temperature Sensor
• Intake Temperature Sensor
• Exhaust Temperature Sensor
• Engine Speed Sensor
• Throttle Position Sensor
• Probe which is responsible for the measurement of the fuel concentration in
the fuel/air mixture
• Actuators are components that obtain information from ECU and they act in
the feeding system, varying the volume of fuel that the engine receives.
• It uses following actuators:
• Fuel Injector
• Spark Plug
• Throttle
 Electronic Injectors
• The injectors can survive the excessive temperature and pressure of
combustion by using the fuel that passes through it as a coolant.
Electronic Injectors
• An indirect injection system sprays fuel
into the engine intake manifold.
• Most gasoline injection systems are of
this type
• Direct injection forces fuel into the
engine combustion chambers.
• Dieses injection systems are direct type.
Electronic Control Unit
• The Electronic Control Unit is responsible for the measurement of
the sensors and the estimation of the action for each actuator with
regard to timing restrictions.
• It is defined that a turn of the engine i.e. 360° is completed once in
every 5 micro seconds for 12,000 rpm.
• The actuator of throttle valve considers the position of 0° as a pulse of
1 milli second and 90° as a pulse of 2 milli seconds, within a period of
25 milli seconds.
• Considering these timing constraint, the reading of the sensors and the
calculation of the acting times for the actuators should be processed in
at most 15 milli seconds.
Block Diagram of Electronic Fuel Injection System
How EFI System Works
• The Fuel Injection System consists of many sensors positioned all
around your vehicle.
• Every time you start your vehicle, the Electronic Control Unit (ECU)
scans each and every one of these sensors to verify their functionality.
• The sensors continuously detect the values of numerous parameters
like air pressure, air temperature, throttle angle, air density, fuel
temperature, fuel pressure, oil pressure, coolant temperature, exhaust
temperature, crankshaft angle, timing, engine rpm, speed, etc.
• All these data are processed through the ECU (Electronic Control
Unit) to establish the amount of time the Fuel Injectors are open,
injecting fuel into your engine’s intake ports.
Fuel System Block Diagram
 Electronic Control Unit
• In automotive electronics, electronic control unit (ECU) is generic
term for any embedded system that control one or more of the
electrical systems or subsystems in a motor vehicle.
• An engine control unit (ECU), also known as power-train control
module (PCM), or engine control module (ECM) is a type of
electronic control unit that determines the amount of fuel, ignition
timing and other parameters an internal combustion engine needs to
keep running, it does this by reading values from multidimensional
maps which contain values calculated by sensor devices monitoring
the engine.
 Working of ECU
• Control of fuel injection: ECU will determine the quantity of fuel to
inject based on a number of parameters. If the throttle pedal is pressed
further down, this will open the engine. The ECU will inject more air
to be pulled into the engine. The ECU will inject more fuel according
to how much air is passing into the engine. If the engine has not
warmed up yet, more fuel will be injected.
• Control of ignition timing: a spark ignition engine requires a spark to
initiate combustion in the combustion chamber. An ECU can adjuct
the exact timing of the spark (called ignition timing) to provide better
power and economy.
 Working of ECU
• Control of idle speed: most engine
systems have idle speed control built
into the ECY. The engine RPM is
monitored by the crankshaft position
sensor which plays a primary role in the
engine timing functions for fuel
injection, spark events, and valve
timing. Idle speed is controlled by
programmable throttle stop or an idle air
bypass control stepper motor.
Common rail and Pressure sensor
• The term “common rail” refers to the fact that all of the fuel injectors
are supplied by a common fuel rail which is nothing more than a
pressure accumulator where the fuel is store at high pressure. This
accumulator supplies multiple fuel injectors with high pressure fuel.
 Sensor System

• Monitors engine operating condition and

reports this information to ECM
(computer)
• Sensors are electrical devices that
change resistance or voltage with change
in condition such as temperature,
pressure and position.
 Engine Sensors
• Oxygen Sensor measures the oxygen content
in engine exhaust.
• Mounted on the exhaust system before the
catalytic converter.
• Voltage output of O2 sensor changes with the
change in oxygen content of exhaust.
• Lean mixture decreases the voltage
• Rich mixture increases the voltage
• Signal is sent to ECM and the ECM changes
the time that an injector is open or close.
Engine Sensors
Throttle position sensor (TPS)
• Variable resister connected to the throttle
plate
• Change in throttle angle = change in
resistance
• Based on the resistance, ECM richness or
leans the mixture.
 Engine Sensors
Engine Temperature Sensor
• Monitors the operating temperature of the
engine
• Exposed to engine coolant
• Engine cold = Low Resistance = Rich Mixture
• Engine Hot = High Resistance = Lean Mixture
 Engine Sensors
Mass Air Flow Sensor (MAF)
• Measures the amount of outside air entering the engine
• Contains an air flap or door that operates a variable resistor
• Help computer to determine how much fuel is needed.
 Engine Sensors
• Inlet Air Temperature Sensor
• Measures the temperature of air entering the engine
• Cold air (more dense) = More fuel for proper AF ratio.
Engine Sensors
Crankshaft Position Sensor
• Detects engine speed
• Changes injector timing and duration
• Higher engine speed = more fuel
Throttle Body Injection
• Uses one or two injectors
• Injectors (pulse) spray fuel into the top of
throttle body air horn
• Atmoized fuel mixes with air and drawn
into the engine
• Fuel pressure regulaor is spring loaded and
I part of the housing
• Fuel is being injected whenever the engine
is running, also called CIS: Continuous
injection system.
 Electronic Fuel Injection
EFI Multi port Injection System
• Injector is pressed into the runner
(port) in the intake manifold
• Injector sprays toward an engine
intake valve.
• Each cylinder has its own injector
EFI Direct fuel Injection System
• Injectors are pressed into the
combustion chamber and spray fuel
directly into the combustion chamber.
Applications of Electronic Fuel Injection System

• The applications include:

• EFI System incorporates the state of the art control software routine
for emission, fuel consumption and performance demands
• The System also incorporates a technology of Smart Ignition for
control of the ignition system, by providing OEMs the flexibility to
achieve best in class fuel consumption
Advantages of Electronic Fuel Injection System

• The advantages are:

• Enhancement of volumetric efficiency of the engine
• Direct fuel injection into the cylinder eliminates manifold wetting
• Good atomization of fuel even at low speed as atomization is independent of
cranking speed
• Less knocking because of the improved atomization and vaporization
• Ice formation at throttle plate is eliminated
• Fuels of low volatility can be used as distribution is independent of vaporization
• As variation of fuel/air ratio is almost negligible it results in good engine
performance
• The height of engine can be less as the position of injection unit is not so critical
Disadvantages of Electronic Fuel Injection System
• The disadvantages include:
• High maintenance cost
• Difficulty in servicing
• Possibility of malfunction of some sensors
 GDI
• Gasoline Direct Injection (GDI) provides the basis for a cleaner and
more economical engine generation. At the same time, it contributes to
the current engine downsizing trend.
• Provides exact flow and original spray pattern for optimal
performance
• Enhances a homogeneous and lean-burn combustion
• Key enabler for engine downsizing, while maintaining desired
horsepower
• High-pressure fuel is injected directly into the combustion chamber
• Maintains new-car smoothness and drivability
 What is DTSI?
• DTSi, or Digital Twin Spark Ignition System, is a technology developed
and patented by Bajaj Auto Limited.
• It was first used in their Pulsar and Avenger models.
• At the time of its introduction to the market, it was considered revolutionary
as it both saved fuel and improved engine performance.
• The DTSi engine gives twice the power of a regular two-stroke engine
along with a significant power boost, and it has a sizable power-to-weight
ratio as compared to a few four-stroke engines. It can also adjust idling
speed and even cuts off fuel feed when the throttle is released and thus
controls the enrichment of the air-fuel mixture for cold starts and
acceleration.
How Does DTSi Engine Work?
• The DTSi engine employs two spark plugs to ignite the air-fuel mixture
alternatively so as to increase the flame diameter and burn the fuel
instantaneously. This process of firing the spark, coupled with the swirl caused in
the air-fuel mixture results in incomplete combustion. The Digital Twin Spark
Ignition system controls this process electronically.
• The two spark plugs are fixed on opposite ends of the combustion chamber,
creating efficient and speedy combustion. It is an electronic system with a static
spark advance and no moving parts, and therefore no wear and tear occur. The
system is mapped by an integrated digital electronic box that also controls valve
timings and fuel injection.
• It has two plugs per cylinder and has the combustion chambers, and piston heads
positioned to produce a broad and fast flame front to ignite the air-fuel mixture.
This technology enables lesser ignition advance and leaner mixtures and thus can
provide both a lightweight and powerful engine.
Main Features of DTSi Engine
• Great balance and a comfortable, compact design.
• High specific power.
• Integrated electronic twin spark ignition coupled with an injection fuel
system.
• Digital electronic ignition.
• Two plugs per cylinder and two ignition distributors.
Advantages of DTSi Engine
• Engine parts being not subjected to wear, have a long life. This means fewer expenses for part replacement
such as piston rings and valve stems. Buying a bike with DTSi engine is easy with Two wheeler loans.
• Better handling and comfort levels due to fewer vibrations and noise in the bike. This DTSi engine gives you
a smoother ride than most other bikes.
• The specific fuel consumption is less due to the DTSi technology, so it offers better mileage than other bikes.
• The engine does not overheat, and you can go long rides without any discomfort.
• The engine’s thermal efficiency is higher.
• It can bear higher loads due to its increased power.
• The engine will easily start in cold weather, winter season, low temperatures and so on because of the high
compression ratio. This ensures that you do not have to get worried about your bike not starting in cold
weather.
• The twin spark technology causes an increase in the diameter of the flame, resulting in instantaneous fuel
combustion, leading to better work output due to the increased work it exerts on the piston.
• Increased and enhanced throttle response.
• Resistant to breakdowns and temperature fluctuations, making it a sturdy, dependable bike for commute
purposes.