fuel injection

mechanical system to inject atomized fuel directly into the cylinders of an internal-combustion engine

avoids the need for a carburetor

Fuel Injection is a method to precisely meter fuel into an internal combustion engine, where the fuel is then burned in air to produce heat. Carburetors were the predominant method to meter fuel prior to the widespread use of fuel injection, however various injection schemes have existed since the earliest usage of the internal combustion engine. Prior to 1980, nearly all gasoline engines used carburetors. Since 1990, all gasoline passenger cars sold in the United States use electronic fuel injection (Electronic fuel injectionEFI).

Benefits - An engine’s air/fuel ratio must be precisely controlled under all operating conditions to achieve optimum engine performance. Modern EFI systems exceed the overall performance available from a carburetor in this regard. The two fundamental improvements are:#Reduced response time to rapidly changing inputs, e.g., rapid throttle movements.#Deliver an equal quantity of fuel to each cylinder of the engine.These two features result in the following performance benefits::*Automobile emissions controlEmissions:**Significantly reduced "engine out" or "feedgas" emissions (the chemical products of engine combustion).:** A reduction in final tailpipe emissions (≈ 0.99%) resulting from the ability to accurately condition the "feedgas" in a manner that maximizes the function of the catalytic converter. :*General Engine Operation :**Smoother function during quick throttle transitions.:**Engine starting.:**Extreme weather operation.:**Reduced maintenance interval.:**A slight increase in fuel economy.:*Power Output:**Fuel injection often produces more power than an equivalent carbureted engine. However, fuel injection alone does not increase maximum engine output. Increased airflow is necessary to oxidize more fuel, which generates more output. The combustion process converts the fuel's chemical energy into heat; whether the fuel arrived via EFI or a carburetor is not significant. Fuel injection components are smaller than a carburetor and do not require a drag-inducing venturi to momentarily lower the pressure of the incoming air and suck in fuel. This permits more design freedom to arrange the components in a manner that improves the air's path into the engine. In contrast, a carburetor's potential mounting locations are limited because it is larger, it must be carefully oriented with respect to gravity, and it must be an equal distance from each of the engine's cylinders. These design constraints impose packaging limitations that compromise the air's induction path. :**Fuel injection is more likely to increase efficiency than power. When cylinder-to-cylinder fuel distribution is improved (common with EFI), less fuel is required to generate the same power output. This increases efficiency - (BSFC, brake specific fuel consumption). When distribution is less than ideal (and it always is under one condition or another), more fuel than necessary is metered to the rich cylinders in order to provide enough fuel to the lean cylinders. Power output is asymmetrical with respect to air/fuel ratio. In other words, burning extra fuel in the rich cylinders does not reduce their power nearly as quickly as burning too little fuel in the lean cylinders. The standard calibration compromise is to run the rich cylinders "even richer" of the optimal air/fuel ratio, and the leaner cylinders will then be rich enough to generate their maximum output. An analogy is that of painting a wall. One coat of paint may not cover very well. The second coat dramatically improves the appearance, however some areas got more paint than necessary. ''Deviations from perfect air/fuel distribution, however subtle, dramatically impact emissions, much more so than efficiency or power, by forfeiting combustion events at the stoichiometric air/fuel ratio. Grosser distribution problems begin to negatively impact efficiency, and the worst distribution issues finally effect power. The hierarchy of negative functional impact with regard to inceasingly poorer air/fuel distribution is: emissions, efficiency, and power.''Injection systems have evolved significantly since the mid 1980s. Current EFI systems provide an accurate and cost effective method of metering fuel. The emission and subjective performance characteristics have steadily improved with the advent of modern digital controls, which is why EFI systems have replaced carburetors in the marketplace. EFI is becoming more reliable and less expensive through widespread usage. At the same time, carburetors are less available and more expensive. Marine applications are rapidly adopting EFI as reliability improves. If this trend continues, it is conceivable that virtually all internal combustion engines, including garden equipment and snow throwers, will eventually use EFI. The 1990 Subaru Justy was the last carbureted passenger car sold in the U.S. A carburetor's fuel metering system is less expensive when emission regulations are not a requirement, as is the case in developing countries. EFI will undoubtedly replace carburetors in these nations too as they adopt emission regulations similar to Europe and the U.S.

Basic Function - The fuel injector, which acts as the dispensing nozzle, injects liquid fuel directly into the engine. This usually requires an external pump. These are only two of many components that comprise a complete fuel injection system. The process of determining the amount of fuel, and its delivery into the engine, are known as fuel-metering. Early injection systems used mechanical methods to meter fuel. Modern systems, nearly all EFI, use an electronic injector to inject the fuel, and a CPU to calculate the quantity of fuel. A carburetor uses minute differences in air pressure to emulsify (premix fuel with air), and then to push the mixture into the engine’s air intake. The carburetor itself generates its own air pressure differences using the venturi principle. A carburetor is a self-contained fuel metering system, and is cost competitive when compared to injection, which requires several additional components in order to duplicate the carburetor's function. A point worth noting in times of diagnostic ambiguity is that a single carburetor replacement can accomplish what might require numerous repair attempts to identify which of the several injection components are malfunctioning.

Gasoline or Diesel - The calibration, and often the design, of a fuel injection system differ depending on the type of fuel: propane (Liquified petroleum gasLPG), gasoline, alcohol, methane (natural gas), hydrogen or Petroleum dieseldiesel. The vast majority of fuel injection systems are for gasoline or diesel applications and to a lesser extent for Liquified petroleum gasLPG, and in the past, the designs were quite different. With the advent of EFI, the two systems have grown similar in concept, but the nature of the fuels and their respective combustion characteristics will continue to require differences in their systems.

Diesel

*At one time, nearly all diesel engines used high-pressure "mechanical injection", i.e., not "electronic injection".

*Diesels are rapidly adopting EFI, which is based on an electronic fuel injector similar to a modern gasoline application.

Gasoline

*Prior to EFI, it was extremely rare for an automobile engine to be equipped with fuel injection. If it was, it was most likely a low-pressure mechanical system of "immature" technology. These early systems were generally used on exotic performance vehicles, or for racing.

*Robert Bosch GmbH, and Bendix CorporationBendix introduced the first electronic injection systems starting in the 1950s, and they were quite dissimilar to today's EFI. (#Evolution)

Detailed Function - :Note: The following description applies to a modern EFI gasoline engine. Parallels to a diesel can be made, but only conceptually. Typical EFI Components

Injectors

Fuel Pump

Fuel Pressure Regulator

ECU - Electronic Control Unit; includes a digital CPU, and circuitry to communicate with sensors and control outputs.

Wiring Harness

Various Sensors (Some, of the sensors required are listed here.):*Crank/Cam Position: Hall effect sensor:*Airflow: Mass airflow sensorMAF sensor, or inferred with a MAP sensor:*Exhaust Gas Oxygen: O2 Sensor, Oxygen sensor, EGO sensor, UEGO sensorA contemporary EFI system requires a number of sensors to measure the engine's operating conditions. A CPU interprets these conditions in order to calculate the precise amount of fuel, among numerous other tasks. The desired “fuel flow rate” depends on several conditions, with the engine’s “air flow rate” being the elemental factor. The electronic fuel injector is normally closed and opens to flow fuel as long as an electric pulse is applied to the injector. The pulse’s duration (pulsewidth) is proportional to the amount of fuel desired. When the pulse is applied, pressurized fuel passes from the fuel line, through the open injector, into the engine’s air intake, usually just ahead of the intake valve. Since the nature of fuel injection dispenses fuel in discrete amounts, and since the nature of the 4-stroke-cycle engine has discrete induction (air-intake) events, the CPU calculates and dispenses fuel in discrete amounts. The fuel quantity is tailored for each individual induction event. In other words, every induction event, of every cylinder, of the entire engine, is a separate calculation, and each injector receives a unique pulsewidth based on that cylinder’s fuel requirements. It is necessary to know the amount (actual mass) of air the engine "breathes" during each induction event. This is proportional to the intake manifold’s air pressure, which is proportional to throttle position. The amount of air inducted, known as "air-charge", can be determined using one of several methods, but they are beyond the scope of this topic. (See Mass airflow sensorMAF sensor, or MAP sensor.):Note: The right pedal is not the gas pedal; it is the air pedal. The throttle pedal determines the air, and in turn, the airflow determines the fuel. The same is true for carburetors.The three elemental ingredients for combustion are fuel, air and ignition systemignition. The sensors and CPU interpret the air mass in order to calculate the fuel mass. The nominal (chemically correct) air/fuel ratio is 14.64:1, by weight, for gasoline. This "molar balanced" ratio is called stoichiometry. 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). :Note: The stoichiometric ratio changes as a function of the fuel; diesel, gasoline, ethanol, methanol, propane, methane (natural gas), or hydrogen. Additionally, "flexible fuel vehicles" permit refueling with gasoline, and/or an alcohol, resulting in all possible blends in the tank. These EFI systems must be able to identify the blend and compensate accordingly. Additionally, final pulsewidth is inversely proportional to fuel line pressure and injector size. A larger capacity injector, or higher fuel line pressure, will inject more fuel for the same pulsewidth. Compensation for these and many other factors are addressed in the CPU's software.In summary, the vehicle operator opens the engine’s throttle (right pedal), the sensors measure airflow, the CPU calculates the desired air/fuel ratio, and then outputs a pulsewidth providing the precise mass of fuel for efficient combustion. This process is repeated every time an intake valve opens. The modern EFI system treats each injection as series of discrete events, which when all strung together, perform one, smooth, seamless experience. An oversimplified analogy is that it is not unlike a motion picture that appears to move from a series of individual images.

Pulsewidth Calculation - These calculations are based on a 4-stroke-cycle, 5.0L, V-8, gasoline engine. The data used are real.Calculate injector pulsewidth from airflow.:First, the CPU determines airflow from the sensors. (The various methods to determine airflow are beyond the scope of this topic. See Mass airflow sensorMAF sensor, or MAP sensor.)::*1) (lb-air/min) × (min/rev) × (rev/4-intake-stroke) = (lb-air/intake-stroke) = (air-charge)::::Min/revolution is the reciprocal of engine speed (RPM) – minutes cancel. ::::Factor in the number of induction events per engine rev, minding whether its a 2-stroke or 4-stroke engine. ::*2) (lb-air/intake-stroke) × (fuel/air) = !(lb-fuel/intake-stroke)::::Fue l/air? is the desired mixture ratio, usually stoichiometric, but often different depending on engine conditions. ::*3) (lb-fuel/intake-stroke) × (1/injector-size) = !(pulsewidth/intake-stroke):::: Injector-size? is the flow capacity of the injector, which in this example is 24-lbs/hour. 'All three terms above combined . . . '''::*(lbs-air/min) × (min/rev) × (rev/4-intake-stroke) × (fuel/air) × (1/injector-size) = !(pulsewidth/intake-stroke)'Sub stituting? real variables for the 5.0L engine at idle.'''::*(0.55 lb-air/min) × (min/700 rev) × (rev/4-intake-stroke) × (1/14.64) × (h/24-lb) × (3,600,000 ms/h) = (2.0 ms/intake-stroke)'Substituting real variables for the 5.0 L engine at maximum power.::*(28 lb-air/min) × (min/5500 rev) × (rev/4-intake-stroke) × (1/11.00) × (h/24-lb) × (3,600,000 ms/h) = (17.3 ms/intake-stroke):Injector pulsewidth typically ranges from 2-msecs/engine-cycle at idle, to 20-msecs/engine-cycle at wide-open throttle. The pulsewidth accuracy is approximately 0.01 msecs; injectors are very precise devices. The final pulsewidth will change if fuel line pressure changes, which effectively changes injector flow capacity.To calculate a fuel-flow rate from pulsewidth . . . '''::*(Fuel flow rate) ≈ (pulsewidth) × (engine speed) × (number of fuel injectors) ::::Looking at it another way:::*(Fuel flow rate) ≈ (throttle position) × (rpm) × (cylinders) ::::Looking at it another way:::*(Fuel flow rate) ≈ (air-charge) × (fuel/air) × (rpm) × (cylinders) 'Substituting real variables for the 5.0L engine at idle.'''::*(2.0 ms/intake-stroke) × (hour/3,600,000-ms) × (24lb-fuel/hour) × (4-intake-stroke/rev) × (700-rev/min) × (60-min/hour) = (2.24 lb-fuel/hour)'Substituting real variables for the 5.0L engine at maximum power, and minding the units.::*(17.3-ms/intake-stroke) × (hour/3,600,000-ms) × (24-lb-fuel/hour) × (4-intake-stroke/rev) × (5500-rev/min) × (60-min/hour) = (152-lb-fuel/hour):The fuel consumption rate is 68 times greater at maximum engine output than at idle. This dynamic range of fuel flow is typical of naturally aspirated passenger car engines. The dynamic range is greater on supercharged or turbocharged engines. It is interesting to note that 15 gallons of gasoline will be consumed in 37 minutes if maximum output is sustained. On the other hand, this engine could continuously idle for almost 42 hours on the same 15 gallons.

Various Injection Schemes -

Indirect injection - This may be single point where the fuel is injected using one or more nozzles, located centrally either just upstream or just downstream of the throttle housing, or multi point''' where each cylinder has its own injector in the inlet manifold. The nozzles may be opened using the pressure in the fuel system or there may be a solenoid on the injector that will pulse it open and closed in a duty cycle according to the desired fuel requirement.

Throttle-body injection - Electronic ''throttle-body injection'' (normally called TBI, though Ford Motor CompanyFord used the abbreviation, ''CFI'') was introduced in the early 1980s as a transition technology to fully electronic port injection. The system injects fuel into the throttle-body (a ''wet system''), because fuel passes through the intake runners like a carburetor system. This system had all the drawbacks of a carburetor, and all the drawbacks of early automotive electronics as well. Computer-controlled TBI was inexpensive, and was primarily a transition phase from carburetors to port fuel injection.

Central port injection - General Motors developed a new "in-between" technique called ''central port injection'' or CPI. It uses tubes from a central injector to spray fuel at the intake port rather than the throttle-body (it is a ''dry system''). However, fuel is continuously injected to all ports simultaneously, which is less than optimal.

Sequential central point injection - GM refined the CPI system into a ''sequential central port injection'' (SCPI) system in the mid-1990s. It used valves to meter the fuel to just the cylinders that were in the intake phase. This worked well on paper, but the valves had a tendency to stick. Fuel injector cleaner sometimes worked, but the system remained problematic.

Multi-port fuel injection - The goal of all fuel injection systems is to carefully meter the amount and timing of fuel to each cylinder. This is achieved with the more sophisticated fuel injection systems, often called ''multi-port fuel injection'' (MFI) or ''sequential port fuel injection'' (''SFI''). On gasoline applications, the system uses a single injector per cylinder and injects fuel immediately ahead of the intake poppet valvevalves.

Direct injection - ''See also: Gasoline Direct Injection''Since mid-2000s, many diesel engines feature direct injection (DI). The injection nozzle is placed inside the combustion chamber itself and the piston incorporates a depression (often toroidal) which is where initial combustion takes place. Direct injection diesel engines are generally more efficient and cleaner than indirect injection engines, but tend to be noisier; which is being addressed in newer common rail designs.Some hi-tech petrol engines utilize this system as well. This can improve the engine's volumetric efficiency by permitting more design freedom for the air induction system. The injector also features distinct spray modes to better manage combustion characteristics.

Evolution -

Pre-Emission Era - Frederick William Lanchester joined the Forward Gas Engine Company Birmingham, England in 1889. He carried out what were possibly the earliest experiments with fuel injection. Indirect fuel injection has been used in diesel engines since the mid 1920s, almost from their introduction (due to the higher energy required for diesel to evaporate). The concept was adapted for use in petrol-powered aircraft during World War II, and direct injection was employed in some notable designs like the Daimler-Benz DB 603 and later versions of the Wright R-3350 used in the B-29 Superfortress.A mechanical gasoline injection system developed by Robert Bosch GmbHBosch was first used in a automobilecar in 1955 with the introduction of the Mercedes-Benz 300SL. An electronic fuel injection system was also developed by the Bendix Corporation, but development was abandoned as being too impractical at the time; there did not yet exist solid state sensors or mass-produced transistors suitable for further development. The patents were subsequently sold to Bosch.In 1957, Chevrolet introduced a mechanical fuel injection option for its !GM_Small-Block_engine#283283 V8 engine, made by General Motors' Rochester, New YorkRochester division. This system used a single central plunger to feed fuel to all eight cylinders, in contrast to Mercedes' individual plunger for each of the six cylinders, but it nevertheless produced 283 hp (211 kW) from 283 in³ (4.6 L), making it the first production engine in history to exceed 1 hp/in³ (45.5 kW/L).Fuel injection systems such as Hilborn were occasionally used on modified American V8 engines in high performance automobiles of the 1960s, in drag racing, oval racing, and road racing. The primary motivation behind these systems was, however, to reduce the airflow restriction in the air intake at wide-open throttle by eliminating the venturi, with little attention to low speed or closed throttle operation. Therefore, these racing-derived systems were generally quite unsuitable for street use, although occasionally an individual would take up the challenge of adapting such an engine.

Post Emission Era - In 1968, in the United States, the Environmental Protection Agency began to restrict exhaust emissions and enacted a series of automobile emissions control laws coming into effect over the next several years. This change became the primary driver behind the adoption of fuel injection systems on a mass scale. Bosch developed the first production electronic fuel injection system, called D-Jetronic (D for Druck, the German word for pressure), which was first used on the Volkswagen_Type_4Volkswagen 411 in 1967. This was a speed/density system, using intake manifold pressure and engine speed to calculate fuel requirements. The system used all analog discrete electronics and an electro-mechanical pressure sensor, but the sensors were susceptible to vibration and dirt. These systems were adopted by VolkswagenVW, Mercedes-Benz, Porsche, Saab automobileSaab and Volvo. Lucas licensed the system and production units for Jaguar_(car)Jaguar. Bosch replaced this with a mass-flow system, initially using a mechanical airflow meter to judge how much fuel to inject. This system, L-Jetronic (L for Luft, German for air), first appeared on the 1974 Porsche 914, and was very widely adopted on European cars of that period. It was also licensed by Japanese firms and appeared on Japanese cars a short time later. In 1975, California's emissions regulations, the most stringent in the world, required manufacturers to resort to a catalytic converter, which act as a "catalyst", when exposed to gasoline combustion byproducts; no other technology available could meet the California regulations. An oxidation catalyst was designed into the vehicle's exhaust system. When hot products of combustion, unburned hydrocarbons and carbon monoxide, are exposed to the catalyst material (platinum and/or palladium), these compounds are nearly all oxidized into water and carbon dioxide. Stricter legislation to reduce compounds called oxides of nitrogen occurred in 1980. This required a reduction catalyst (rhodium) to redoxreduce the various nitrogen oxides into free nitrogen and oxygen. The introduction of the catalyst reduced tailpipe emission to approximately 10% of the pre-regulated 1960 level. Nearly all vehicles of this vintage used a carburetor. Catalytic converters will not tolerate exposure to tetraethyl lead, an octane ratingoctane enhancer in gasoline, and they will become almost totally ineffective after only a short time. Unleaded fuel became available with the introduction of catalysts. In order to take maximum advantage of a catalyst's chemical process, excellent air/fuel ratio control is essential, which the EFI systems accomplished in two stages. The first systems were "open loop", and then by 1980 "closed loop" systems began to appear. The early fuel injection systems were "open loop". This was generally fine, as long as all the components of the system were clean and within operational parameters. However, the electro-mechanical sensors often deteriorate with time, or became dirty, and it was impossible to emissions compliance over the life of the vehicle. Soon, even more stringent emissions legislation occurred. In order to address these issues, "closed loop" feedback control of EFI appeared in 1980. Closed loop fuel control is accomplished with the Lambda-Sond sensor, commonly referred to as the exhaust gas oxygen sensor, or EGO sensor, or O₂ sensor. This sensor resembled a spark plug without an electrode and is designed into the exhaust system upstream of the catalyst. The EGO sensor measures the oxygen content in the exhaust. Oxygen, or the lack of it, is proportional to the air/fuel mixture ingested into the engine. "Closed loop feedback" fuel control made possible by digital EFI systems reduced exhaust emissions to less than 1% of the 1960 models. Unleaded fuel protects the catalytic converter so this level of emission performance is durable for tens of thousands of miles. Starting in 1982, Robert Bosch GmbHBosch used a mass airflow meter on their L-Jetronic system, changing the name to LH-Jetronic (L for Luft, or air, and H for Heiße-leitung, or hot-wire), as the first true sensor for actual air mass involved the use of a heated platinum wire. The LH-Jetronic system is also notable in that it was the first system to abandon an analog ECU (using mainly AF components) in favor of a digital computer, which is now the prevailing form of ECU. This further refined air/fuel ratio control. The introduction of microprocessor controls allowed the integration of fuel injection and ignition control, with systems first appearing in 1982 (The Bosch Motronic system, which oddly reverted to using a mechanical airflow sensor until the mid-to-late 1980s). Full engine management systems came shortly afterwards, with control of all engine systems under the control of a single computer. In 2005, many new cars had multiple computers on board controlling every aspect of the car.

External links -

auto.howstuffworks.com - How Fuel Injection Systems WorkCategory:Engine fuel system technologyCategory:Engine technology

!:Category:Enginesde:Kraftstoff einspritzungfr:Injection? directeid:Injeksi bahan !bakarja:燃料ࢥ 2;射装置sv:B ränsleinsprutning

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