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    INTRODUCTION

    MPFI stands for multi-point or multi-port fuel injection system.The term MPFI is used

    to specify a technology used in Gasoline/petrol Engines. This system is a replacement

    of carburettors and used in almost all the vehicles with slight modifications. Fuel

    injection is a system for admitting fuel into an internal combustion engine. The primary

    difference between carburettors and fuel injection is that fuel injection atomizes the fuel

    by forcibly pumping it through a small nozzle under high pressure, while a carburettor

    relies on suction created by intake air rushing through a venturi to draw the fuel into the

    airstream. MPFI system injects fuel into individual cylinders, based on commands

    from the on board Engine management system computer. These techniques result not

    only in better power balance amongst the cylinders but also in higher output from

    each one of them. In the MPFI system, there is separate supply of fuel to each

    individual cylinder regulated by electronic control module or electronic control unit

    depending on the input from various sensors. Carburettors were the predominant

    method used to meter fuel on gasoline engines before the widespread use of fuel

    injection. A variety of injection systems have existed since the earliest usage of the

    internal combustion engine.

    One of the first commercial gasoline injection systems was a mechanical system

    developed by Bosch and introduced in 1952 on the Goliath GP700 and Gutbrod

    Superior 600.

    The first commercial electronic fuel injection (EFI) system was Electrojector,developed by the Bendix Corporation and was to be offered by American

    Motors Corporation (AMC) in 1957. The system incorporated electronic control

    module or on board computer for the purpose of metering & supplying of fuel

    depending upon the input from various sensors.

    At present the modifications are going in the basic construction and reliability

    of engine control unit which is the heart of the modern electronically controlled

    multipoint fuel injection systems. Automotive leader BOSCH has contributed a

    lot in the development of fuel injection systems and majority of patents filed by

    it are blessings to the current automotive sector.

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    HISTORY OF SUPERSESSION OF CARBURETTORS

    CARBURETTOR

    THROTTLE BODY INJECTION OR SINGLE POINT INJECTION

    MULTIPOINT FUEL INJECTION SYSTEM

    At first, carburettors were replaced with throttle body fuel injection systems (also

    known as single point or central fuel injection systems) that incorporated electrically

    controlled fuel-injector valves into the throttle body. These were almost a bolt-in

    replacement for the carburettor, so the automakers didn't have to make any drastic

    changes to their engine designs.

    Gradually, as new engines were designed, throttle body fuel injection was replaced by

    multi-port fuel injection (also known as port, multi-point or sequential fuel injection).

    These systems have a fuel injector for each cylinder, usually located so that they spray

    right at the intake valve. These systems provide more accurate fuel metering and

    quicker response.

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    FACTORS CONTRIBUTED TOWARDS REPLACEMENT

    Failure to meet the condition of stochiometry was one among the prime reasons

    that paved the way for gasoline injection systems.When efficient combustion

    does not take place, extra fuel nor extra oxygen molecules remain; each fuel

    molecule is matched with the appropriate number of oxygen molecules. This

    balanced condition is called stochiometry. In the case of carburettors, the air-

    fuel mixture was supplied to the intake manifold of the multi-cylinder engine.

    The fuel due to the inertia continued to flow in the straight direction resulting

    into pudding of fuel near the corner, thus the charge entering the end cylinders

    will be rich and the fuel entering the cylinders close to the supply will be lean in

    nature. The problem is known as misdistribution of fuel.

    The second reason was the inability to meet the increasingly strict exhaust

    emissions, imposed by the federal government in the year 1970 & 1980 in U.S.

    So in order to more easily comply with government emissions controlregulations, automobile manufacturers, beginning in the late 1970s, furnished

    more of their gasoline-fuelled engines with fuel injection systems, and fewer

    with complex carburettor systems. There are three primary types of toxic

    emissions from an internal combustion engine: Carbon Monoxide (CO), unburnt

    hydrocarbons (HC), and oxides of nitrogen (NOx). CO and HC result from

    incomplete combustion of fuel due to insufficient oxygen in the combustion

    chamber. NOx, in contrast, results from excessive oxygen in the combustion

    chamber. The opposite causes of these pollutants makes it difficult to control all

    three simultaneously. Once the permissible emission levels dropped below a

    certain point, catalytic treatment of these three main pollutants became

    necessary. This required a particularly large increase in fuel metering accuracy

    and precision, for simultaneous catalysis of all three pollutants requires that the

    fuel/air mixture be held within a very narrow range of stoichiometry.

    As a result the fuel injection was phased in through the latter '70s and '80s at an

    accelerating rate, with the US, French and German markets leading and the UK

    and Commonwealth markets lagging somewhat, and since the early 1990s,

    almost all gasoline passenger cars sold in first world markets like the United

    States, Canada, Europe, Japan, and Australia have come equipped with

    electronic fuel injection (EFI).

    Fuel injection systems have evolved significantly since the mid-1980s. Currentsystems provide an accurate, reliable and cost-effective method of metering fuel

    and providing maximum engine efficiency with clean exhaust emissions, which

    is why EFI systems have replaced carburettors in the marketplace. EFI is

    becoming more reliable and less expensive through widespread usage. At the

    same time, carburettors are becoming less available, and more expensive. Even

    marine applications are adopting EFI as reliability improves. Virtually all

    internal combustion engines, including motorcycles, off-road vehicles, and

    outdoor power equipment, may eventually use some form of fuel injection.

    FUNCTIONAL OBJECTIVES

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    The functional objectives of a fuel injection system can vary. There are several

    competing objectives such as:

    Power output Fuel efficiency

    Emissions performance

    Ability to accommodate alternate fuels

    Reliability

    Driveability and smooth operation

    Initial cost

    Maintenance cost

    In a MPFI system, there is separate supply of fuel to each individual cylinder, thus the

    more accurate controlling of the fuel supply as well as metering is realized. Fuel

    injection generally increases engine fuel efficiency. With the improved cylinder-to-

    cylinder fuel distribution, less fuel is needed for the same power output.

    A fuel-injected engine often produces more power than an equivalent carburetted

    engine. Fuel injection alone does not necessarily increase an engine's maximum

    potential output. Increased airflow is needed to burn more fuel, which in turn releases

    more energy and produces more power. The combustion process converts the fuel's

    chemical energy into heat energy, whether the fuel is supplied by fuel injectors or acarburettor. However, airflow is often improved with fuel injection, the components of

    which allow more design freedom to improve the air's path into the engine.

    MPFI SYSTEM:

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    MPFI stands for multipoint fuel injection system

    In this system there is a separate supply of fuel to each individual cylinder by

    the help of fuel injector housed either near to the intake valve or into the intake

    port depending upon whether it is a direct injection into the engine cylinder or it

    is an indirect injection.

    Earlier systems were using the mechanical means to meter the fuel but recent

    developments in the engine control unit or engine control module has resulted in

    the electronically based fuel metering and fuel supply system. The EFI systems

    possess the ECU which calculates the pulse width for the injectors i.e. the time

    for which the injectors are to be kept open.

    The process of determining the necessary amount of fuel, and its delivery into

    the engine, are known as fuel metering. It is done by the ECU or ECM.

    The typical components of an electronically controlled multipoint fuel injection

    system are:-

    -Injectors

    -Fuel Pump

    -Fuel Pressure Regulator

    -ECM - Engine Control Module; includes a digital computer and circuitry to

    communicate with sensors and control outputs.

    -Wiring Harness

    -Various Sensors

    In case of MPFI system the pulse width of the injector is calculated by the ECM

    and determines the amount of fuel to be injected in the cylinder. The air supply

    should also be in matching and in accordance with the fuel injected in order to

    meet the conditions of stoichiometry. The air supply is calculated by the throttlebody and position of throttle determines the air inflow.

    FUNCTIONAL DESCRIPTION:

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    Central to an EFI system is a computer called the Engine Control Unit (ECU),

    which monitors engine operating parameters via various sensors. The ECU

    interprets these parameters in order to calculate the appropriate amount of fuel

    to be injected, among other tasks, and controls engine operation bymanipulating fuel and/or air flow as well as other variables. The optimum

    amount of injected fuel depends on conditions such as engine and ambient

    temperatures, engine speed and workload, and exhaust gas composition.

    The electronic fuel injector is normally closed, and opens to inject pressurized

    fuel as long as electricity is applied to the injector's solenoid coil. The duration

    of this operation, called the pulse width, is proportional to the amount of fuel

    desired. The electric pulse may be applied in closely controlled sequence with

    the valve events on each individual cylinder (in a sequential fuel injection

    system), or in groups of less than the total number of injectors (in a batch firesystem). The solenoid is energized as the electric supply is provided to it; this in

    turn lifts the pintle or nozzle valve of its seat. When the electric supply to the

    injector is disconnected, the restraining spring holds the pintle in its original

    position. Fuel metering can be very effectively controlled by the solenoid

    operated fuel injector. The prerequisite for the fuel injector is that the opening

    and closing of the fuel injector should be purely instantaneous without causing

    any dribbling of fuel droplets inside the engine cylinder.

    Since the nature of fuel injection dispenses fuel in discrete amounts, and since

    the nature of the 4-stroke engine has discrete induction (air-intake) events, the

    ECU calculates fuel in discrete amounts. In a sequential system, the injected

    fuel mass is tailored for each individual induction event. Every induction event,

    of every cylinder, of the entire engine, is a separate fuel mass calculation, and

    each injector receives a unique pulse width based on that cylinder's fuel

    requirements. It is necessary to know the mass of air the engine "breathes"

    during each induction event. This is proportional to the intake manifold's air

    pressure/temperature, which is proportional to throttle position. The amount of

    air inducted in each intake event is known as "air-charge", and this can be

    determined using several methods. (See MAF sensor, and MAP sensor).

    The three elemental ingredients for combustion are fuel, air and ignition.

    However, complete combustion can only occur if the air and fuel is present in

    the exact stoichiometric ratio, which allows all the carbon and hydrogen from

    the fuel to combine with all the oxygen in the air, with no undesirable polluting

    leftovers. Oxygen sensors monitor the amount of oxygen in the exhaust, and the

    ECU uses this information to adjust the air-to-fuel ratio in real-time.

    To achieve stoichiometry, the air mass flow into the engine is measured and

    multiplied by the stoichiometric air/fuel ratio 14.64:1 (by weight) for gasoline.The required fuel mass that must be injected into the engine is then translated to

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    the required pulse width for the fuel injector. The stoichiometric ratio changes

    as a function of the fuel; diesel, gasoline, ethanol, methanol, propane, methane

    (natural gas), or hydrogen.

    Deviations from stoichiometry are required during non-standard operating

    conditions such as heavy load, or cold operation, in which case, the mixture

    ratio can range from 10:1 to 18:1 (for gasoline). In early fuel injection systems

    this was accomplished with a thermo time switch.

    Pulse width is inversely related to pressure difference across the injector inlet and

    outlet. For example, if the fuel line pressure increases (injector inlet), or the manifold

    pressure decreases (injector outlet), a smaller pulse width will admit the same fuel. Fuel

    injectors are available in various sizes and spray characteristics as well. Compensation

    for these and many other factors are programmed into the ECU's software.

    WORKING REPRESENTATION OF MPFI SYSTEM

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    CALCULATIONS FOR PULSE WIDTH OF AN INJECTOR:

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    The pulse width of a fuel injector is the time for which the fuel injector is kept open.

    Thus the amount of fuel entering into the engine cylinder is directly proportional to the

    pulse width which is calculated by the electronic control module or electronic control

    unit for each individual cylinder for a particular operating condition.

    Minutes / Revolution is the reciprocal of engine speed (RPM)

    The term Revolutions / Stroke = 1 / 2, whether it is a four-stroke or a two-stroke

    engine.

    Mass Fuel / Mass Air is the desired mixture ratio, usually stoichiometric, but often

    different depending on operating conditions.

    1 / (Mass Fuel / Minute) is the flow capacity of the injector, or its size.

    TWO- TYPES OF MPFI SYSTEM:

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    The D-MPFI system is the manifold fuel injection system. In this type, the vacuum in

    the intake manifold is first sensed. In addition, it senses the volume of air by its density.

    As air enters into the intake manifold, the manifold pressure sensor detects the intake

    manifold vacuum and sends the information to the ECU. The speed sensor also sends

    information about the rpm of the engine to the ECU. The ECU in turn sends commandsto the injector to regulate the amount of gasoline supply for injection. When the injector

    sprays fuel in the intake manifold the gasoline mixes with the air and the mixture enters

    the cylinder.

    L-MPFI SYSTEM

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    The L-MPFI system is a port fuel injection system. In this type the fuel metering is

    regulated by the engine speed and the amount of air that actually enters the engine. This

    is called air mass metering or airflow metering.

    As air enters into the intake manifold, the air flow sensor measures the amount of airand sends information to the ECU. Similarly the speed sensor sends the information

    about the speed of the engine of the ECU. The ECU processes the information received

    and sends appropriate commands to the injector, in order to regulate the amount of

    gasoline supply for injection. When injection takes place, the gasoline mixes with the

    air and the mixture enters the cylinder.

    SINGLE POINT INJECTION SYSTEM VERSUS MPFI SYSTEM

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    In the single point injection system or throttle body injection there is either one

    or two fuel injectors mounted over the top of the throat of the throttle body. The

    fuel gets mixed with the air and the air- fuel mixture is discharged to the various

    cylinders.

    Whereas in the case of a multipoint fuel injection system there is an individual

    injector for each individual cylinder spraying either into the intake port or into

    the engine cylinder depending on whether it is a direct injection or the indirect

    injection. The figure showing the direct as well as indirect injection is given

    below:

    Single-point injection, called Throttle-body injection (TBI) by General Motors

    and Central Fuel Injection (CFI) by Ford, was introduced in the 1940s in large

    aircraft engines (then called the pressure carburettor) and in the 1980s in theautomotive world. The SPI system injects fuel at the throttle body (the same

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    location where a carburettor introduced fuel). The induction mixture passes

    through the intake runners like a carburettor system, and is thus labelled a "wet

    manifold system". Fuel pressure is usually specified to be in the area of 10-15

    psi. The justification for single-point injection was low cost.

    The multi-point fuel injection system can be either pulsed or continuous

    injection system. In the pulsed injection system fuel is supplied intermittently in

    pulses whereas in the case of continuous injection system the amount of fuel to

    be injected is a function of the pressure of the fuel line. In a continuous

    injection system, fuel flows at all times from the fuel injectors, but at a variable

    flow rate. This is in contrast to most fuel injection systems, which provide fuel

    during short pulses of varying duration, with a constant rate of flow during each

    pulse. Continuous injection systems can be multi-point or single-point, but not

    direct.The most common automotive continuous injection system is Bosch's K-

    Jetronic introduced in 1974.

    In general for MPFI system controlled electronically, an ECU in is controlled by

    the data input from a set of SENSORS located all over the Engine and its

    Auxiliaries. These detect the various operating states of the Engine and the

    performance desired out of it. Such Sensors constantly monitor : 1) Ambient

    Temperature, 2) Engine Coolant Temp., 3) Exhaust/manifold temp., 4) Exhaust

    O2 content, 5) Inlet manifold vacuum, 6) Throttle position, 7) Engine rpm, 8)

    Vehicle road speed, 9) Crankshaft position, 10) Camshaft position, etc. Based

    on a programmed interpretation of all this input data, the ECU gives the

    various commands to the Engines fuel intake and spark ignition timing

    systems, to deliver an overall satisfactory performance of the Engine from start

    to shut down, including emission control.

    The sensors are basically the thermistor type and send the signal in the form of

    varying voltage to the electronic control unit. The oxygen sensor mounted in the

    exhaust manifold is the important sensor determining the nature of combustion

    i.e. whether it is complete or incomplete combustion by tracing out the amount

    of oxygen contained in the exhaust from the engine.

    ADVANTAGES OF MPFI SYSTEM:

    Improved Fuel Consumption--Vehicles with carburettors do not get nearly thefuel economy of those with multi-point fuel injection. The underlying reason is

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    that fuel delivery systems of these older vehicles are less precise. A multipoint

    fuel injection system, which uses one fuel injector for each cylinder of the

    engine, delivers just the right amount of gasoline to each cylinder. Thus,

    gasoline is not wasted in the process. Over time, the gasoline saved with a

    multi-point fuel injection system saves the vehicle owner loads of money.

    Emissions--Emissions test results are an important factor today. A car from this

    century emits a small fraction of what a vehicle emitted even a few decades ago.

    Multi-point injection systems are better for the environment because the

    emissions of hazardous chemicals being released when fossil fuels are burned

    are minimized. As mentioned above, the more precise delivery of fuel to the

    engine means that fewer toxious by products are released when the fuel

    combusts within the engine. The implements within the engine meant to cleanthe exhaust have been fine-tuned in a multi-point system to work more

    efficiently. Therefore, the engine--and the air--is cleaner as a result of multi-

    point systems.

    The ECU stores a default code for each sensor; thus in the case of any

    malfunction or fault in the sensor, the default value is used in the worst case

    conditions so that the engine continues to run satisfactorily.

    Better Performance--The performance of an engine suffers with the use of a

    carburettor, but multipoint fuel injection allows for far better engine

    performance. This is due to a few factors. Instead of allowing for additional air

    intake, multi-point injection atomizes the air that is taken through a small tube.

    Because multipoint injectors are usually controlled by computers, each function

    of a carburettor is performed by a different system component. These systems

    also improve the cylinder-to-cylinder distribution of an engine, which allows it

    to conserve energy.

    1) More uniform A/F mixture will be supplied to each cylinder; hence the

    difference in power developed in each cylinder is minimum. Vibration from the

    engine equipped with this system is less; due to this the life of enginecomponents is improved.

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    (2) No need to crank the engine twice or thrice in case of cold starting as

    happens in the carburettor system.

    (3) Immediate response, in case of sudden acceleration / deceleration.

    (4) Since the engine is controlled by ECM* (Engine Control Module), more

    accurate amount of A/F mixture will be supplied and as a result complete

    combustion will take place. This leads to effective utilization of fuel supplied

    and hence low emission level.

    (5) The mileage of the vehicle will be improved.

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