Fuel injection

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Fuel Injection is a method or system for metering fuel into an internal combustion engine. The fuel is then burned in air to produce heat, which in turn is converted to mechanical work by the engine. In modern automotive applications, fuel injection is typically only one of several important tasks performed by an engine management system.

For gasoline engines, carburetors were the predominant method to meter fuel prior to the widespread use of fuel injection, however various fuel injection schemes have existed since the earliest usage of the internal combustion engine.

Prior to 1980, nearly all gasoline engines used carburetors. Since 1990, almost all gasoline passenger cars sold in the United States use electronic fuel injection (EFI).

The functional objectives for fuel injection systems can vary. All share the central task of supplying fuel to the combustion process, but it is a design decision how a particular system will be optimized. There are several competing objectives such as:

• power output
• fuel efficiency
• emission output
• ability to accomodate alternative fuels
• durability
• reliability
• driveability and smooth operation
• initial cost
• maintenance cost
• diagnostic capability
• range of environmental operation
• cruising range
• passenger/cargo capacity

Certain combinations of these goals are conflicting, and it is impractical for a single engine control system to fully optimize all criteria simultaneously. In practice, automotive engineers strive to best satisfy a customer's needs in a competitive manner. The modern digital EFI system is far more capable at optimizing these competing objectives than a carburetor.

Contents 1 Benefits 2 Regulatory Motivation 3 Basic Function 4 Type of Fuel 5 Detailed Function 5.1 Typical EFI Components 5.2 Functional Description 5.3 Sample Pulsewidth Calculations 5.3.1 Calculate Injector Pulsewidth From Airflow 5.3.2 Calculate Fuel-Flow Rate From Pulsewidth 6 Various Injection Schemes 6.1 Throttle Body Injection (TBI or CFI) 6.2 Continuous Injection 6.3 Central Port Injection (CPI) 6.4 Sequential Central Point Injection (SCPI) 6.5 Multi-Port Fuel Injection (PFI or EFI or SEFI) 6.6 Direct Injection 7 Evolution 7.1 Pre-Emission Era 7.2 Post Emission Era 8 External links

Benefits

An engine's air/fuel ratio must be accurately controlled under all operating conditions to achieve the desired engine performance, emissions, driveability and fuel economy. Modern EFI systems meter fuel with great precision, and when used in conjunction with an Exhaust Gas Oxygen Sensor (EGO sensor), they are also very accurate. The advent of digital closed loop fuel control, based on feedback from an EGO sensor, permit EFI to significantly out perform a carburetor. The two fundamental improvements are:

1. Reduced response time to rapidly changing inputs, e.g., rapid throttle movements.
2. Deliver an accurate and equal mass of fuel to each cylinder of the engine, dramatically improving the cylinder-to-cylinder distribution of the engine.

These two features result in the following performance benefits:

• Exhaust Emissions
  • Significantly reduced "engine out" or "feedgas" emissions (the chemical products of engine combustion).
  • A reduction in the final tailpipe emissions (≈ 0.99%) resulting from the ability to accurately condition the "feedgas" in a manner that maximizes the effectiveness 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 permit oxidizing more fuel, which generates more heat, which in turn generates more output. The combustion process converts the fuel's chemical energy into heat energy, whether the fuel arrived via EFI or a carburetor is not significant. Airflow is often improved with fuel injectors, which are much smaller than a carburetor. Their smaller size permits more design freedom to improve the air's path into the engine. In contrast, a carburetor's mounting options are limited because it is larger, it must be carefully oriented with respect to gravity, and it must be approximately equal distance from each of the engine's cylinders. These design constraints generally compromise airflow into the engine.
  • A carburetor relies on a drag inducing venturi in order to create a local air pressure difference, which forces the fuel into the air stream. The flow loss caused by the venturi is small in comparison to other flow losses in the induction system. In a well-designed carbureted induction system, the venturi in and of itself is not a significant airflow restriction.
  • 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. Engine efficiency is known as the BSFC, or brake specific fuel consumption. When cylinder-to-cylinder distribution is less than ideal (and it always is under one condition or another, and worse on carburetor systems), more fuel than necessary is metered to the rich cylinders in order to provide sufficient 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 power nearly as quickly as burning too little fuel in the lean cylinders. The standard fuel metering compromise is to run the rich cylinders "even richer" of the optimal air/fuel ratio, in order to provide enough fuel to the leaner cylinders. The net power output improves with all the cylinders making maximum power. An analogy is that of painting a wall. One coat of paint may not cover very well. The second coat dramatically improves the appearance of the poorly covered areas, but some extra paint is consumed on areas that were already well covered.
  • Deviations from perfect air/fuel distribution, however subtle, significantly impact emissions, by forfeiting combustion events at the chemically ideal, stoichiometric air/fuel ratio. Grosser distribution problems eventually begin to negatively impact efficiency, and the grossest distribution issues finally affect power. The hierarchy of negative functional impact with regard to increasingly 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 becoming less available, and more expensive. Even marine applications are 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.

It should be noted that a carburetor's fuel metering system is a less expensive alternative when strict 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, Japan and North America.

Regulatory Motivation

Throughout the 1950s and 1960s, various federal, state and local governments conducted studies into the numerous sources of air pollution. These studies ultimately attributed a significant portion of air pollution to the automobile, and concluded air pollution is not bounded by local political boundaries. At that time, the primary source of emission regulations was legislated at the local level. The ineffective scope of local regulations was gradually superseded with more strategically comprehensive state and federal regulations. By 1967 the state of California (Governor Reagan), created the California Air Resources Board, and in 1970, the U.S. Environmental Protection Agency was formed. Both agencies now create and enforce emission regulations from automobiles, as well as many other sources.

Additionally, similar studies and regulations were simultaneously developed in Europe and Japan.

The primary source of internal combustion engine emissions is the incomplete combustion of a miniscule fraction of the total fuel consumed. The unburned portion of fuel is so small, the lost energy is trivial to fuel efficiency, and therefore commercially insignificant to the final customer. Auto manufacturers were eventually motivated by emission regulations to address this issue.

The modern EFI system evolved to gain deliberate control of the small fraction of unburned fuel. The ultimate combustion goal is to match each molecule(s) of fuel with a corresponding molecule(s) of oxygen so that neither has any molecules remaining after combustion - (see stoichiometry). This is a gross oversimplification of complex combustion chemistry that occurs in a difficult to manage environment. However, it accurately describes the magnitude of the fuel metering task, as well as the precision of a modern EFI system.

Basic Function

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 (non electronic, or mechanical fuel injection). Modern systems are nearly all electronic, and use an electronic solenoid (the injector) to inject the fuel. An electronic engine control unit calculates the mass of fuel to inject.

The fuel injector acts as the fuel-dispensing nozzle. It injects liquid fuel directly into the engine's air stream. In almost all cases this requires an external pump. The pump and injector are only two of several components in a complete fuel injection system.

In contrast to an EFI system, a carburetor directs the induction air through a venturi, which generates a minute difference in air pressure. The minute air pressure differences both emulsify (premix fuel with air) the fuel, and then acts as the force to push the mixture from the carburetor nozzle into the induction air stream. As more air enters the engine, a greater pressure difference is generated, and more fuel is metered into the engine. A carburetor is a self-contained fuel metering system, and is cost competitive when compared to a complete EFI system.

An EFI system requires several peripheral components in addition to the injector(s), in order to duplicate all the functions of a carburetor. A point worth noting during times of fuel metering repair is that EFI systems are prone to diagnostic ambiguity. A single carburetor replacement can accomplish what might require numerous repair attempts to identify which one of the several EFI system components is malfunctioning. On the other hand, EFI systems require little regular maintenance; a carburetor typically require seasonal and/or altitude adjustments.

Type of Fuel

The calibration, and often the design, of a fuel injection system differs depending on the type of fuel: propane (LPG), gasoline, ethanol, methanol, methane (natural gas), hydrogen or diesel. The vast majority of fuel injection systems are for gasoline or diesel applications, and in the past, their components and designs were quite different. With the advent of "electronic" fuel injection, the diesel and gasoline hardware have grown quite similar. EFI's programmable software has permitted common hardware to be used across some of the fuels.

• Diesel Fuel
  • 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 in basic construction to a modern gasoline injector, although utilizing considerably higher injection pressures.
• Gasoline Fuel
  • Prior to EFI, it was extremely rare for a gasoline engine to be equipped with fuel injection. If it was, it was most likely a low-pressure mechanical system of relatively "immature" technology. These early systems were generally used on exotic performance vehicles, or for racing.
  • Robert Bosch GmbH, and Bendix introduced the first electronic injection systems starting in the 1950s, and they were quite dissimilar to today's EFI. (#Evolution)
• Alternative Fuels (propane (LPG), ethanol, methanol, methane (natural gas), hydrogen)
  • The basic components of a gasoline EFI system can also be used with alternative fuels, with appropriate modification. Unique fuel metering values (the calibration contained within the software instructions) are required to accommodate each type of fuel.
  • "Flexible fuel vehicles" are vehicles that are capable of operating on both gasoline and alcohol (usually ethanol). These vehicles automatically determine the blend ratio of the two fuels present in the fuel tank and adjust the injector calculations "on the fly". Flexible fuel vehicles have a single fuel tank where a blend of both fuels can coexist.
  • "Bi-fuel" vehicles also operate on two types of fuel, but since the fuels are not functionally compatible with each other, they are stored in separate tanks, and the engine burns only one fuel at a time.

Detailed Function

Note: The following examples specifically apply to a modern EFI gasoline engine. Parallels to fuels other than gasoline 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: MAF sensor, sometimes this is inferred with a MAP sensor
• Exhaust Gas Oxygen: O2 Sensor, Oxygen sensor, EGO sensor, UEGO sensor

Functional Description

A 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 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 fundamental 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. The pulse is applied once per engine cycle, which permits pressurized fuel to flow from the fuel supply 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 fuel in discrete amounts. The injected fuel mass is tailored for each individual induction event. In other words, every induction event, of every cylinder, of the entire engine, is a separate fuel mass calculation, and each injector receives a unique pulsewidth 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 one of several methods, but this is beyond the scope of this topic. (See MAF 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 air mass determines the fuel mass. The same is true for carburetors, only carburetors were volume, not mass based devices. With some recent systems, the right pedal isn't even an "air pedal"... it has evolved to a "power demand pedal" - it isn't connected to the throttle at all, it signals the CPU how far the driver has depressed the pedal, and the CPU determines how far to open the throttle using an electric motor. This has many benefits some of which include: controlling emissions during transients, cruise control, traction control, engine start/cranking, driveline clunk, idle speed control, air conditioning load compensation, etc.

The three elemental ingredients for combustion are fuel, air and ignition. 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, final pulsewidth 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 pulsewidth will meter 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 CPU's software.

In summary, the vehicle operator opens the engine's throttle (right pedal), atmospheric pressure forces air into the engine past sensors that indicate air mass flow. The CPU interprets these signals from the sensors, calculates the desired air/fuel ratio, and then outputs a pulsewidth providing the exact mass of fuel for optimal combustion. This process is repeated every time an intake valve opens.

The modern EFI system treats each injection as a discrete event, 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.

Sample Pulsewidth Calculations

Note: These calculations are based on a 4-stroke-cycle, 5.0L, V-8, gasoline engine. The variables used are real data.

Calculate Injector Pulsewidth From Airflow

First the CPU determines the air mass flow rate from the sensors - lb-air/min. (The various methods to determine airflow are beyond the scope of this topic. See MAF sensor, or MAP sensor.)

• (lb-air/min) × (min/rev) × (rev/4-intake-stroke) = (lb-air/intake-stroke) = (air-charge)

- min/rev is the reciprocal of engine speed (RPM) – minutes cancel.

- rev/4-intake-stroke for an 8 cylinder 4-stroke-cycle engine.

• (lb-air/intake-stroke) × (fuel/air) = (lb-fuel/intake-stroke)

- fuel/air is the desired mixture ratio, usually stoichiometric, but often different depending on operating conditions.

• (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 if the fuel pressure across the injector is 40 psi.

Combining the above three terms . . .

• (lbs-air/min) × (min/rev) × (rev/4-intake-stroke) × (fuel/air) × (1/injector-size) = (pulsewidth/intake-stroke)

Substituting 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 ms/engine-cycle at idle, to 20 ms/engine-cycle at wide-open throttle. The pulsewidth accuracy is approximately 0.01 ms; injectors are very precise devices.

Calculate 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 5.0 L engine at idle.

• (Fuel flow rate) = (2.0 ms/intake-stroke) × (hour/3,600,000 ms) × (24lb-fuel/hour) × (4-intake-stroke/rev) × (700 rev/min) × (60 min/h) = (2.24 lb/h)

Substituting real variables for the 5.0L engine at maximum power, and minding the units.

• (Fuel flow rate) = (17.3 ms/intake-stroke) × (hour/3,600,000-ms) × (24 lb/h fuel) × (4-intake-stroke/rev) × (5500-rev/min) × (60-min/hour) = (152 lb/h)

The fuel consumption rate is 68 times greater at maximum engine output than at idle. This dynamic range of fuel flow is typical of a naturally aspirated passenger car engine. The dynamic range is greater on a supercharged or turbocharged engine. 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

Throttle Body Injection (TBI or CFI)

Throttle-body injection (called TBI by General Motors and CFI by Ford) was introduced in the mid 1980's as a transition technology to individual port injection. The TBI system centrally injects fuel at the throttle body (the same location where a carburetor introduced fuel). The induction mixture passes through the intake runners like a carburetor system. The justification for the TBI/CFI phase was low cost. Many of the carburetor's supporting components could be reused such as the air cleaner, intake manifold and fuel line routing. This postponed the redesign and tooling costs of these components, which were later redesigned for the next phase of fuel injection's evolution, which is individual port injection, commonly known as EFI. TBI was used by GM on heavy duty trucks all the way through OBD-I (ending in 1995).

Continuous Injection

Bosch's K-Jetronic or CIS used a continuous injection method. Gasoline was pumped through a large control valve called a fuel distributor, which sat atop a control vane mounted in the air intake pathway. The fuel went from there to the injectors on each cylinder's intake port (which were simply nozzles with no valves in them). The system worked by varying fuel mixture based on the amount of air flowing past the control vane. This system was used for many years by Mercedes Benz, Volkswagen and Volvo. There was also a variant of the system called KE-Jetronic that used an oxygen sensor to fine-tune the mixture.

Central Port Injection (CPI)

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

Sequential Central Point Injection (SCPI)

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.

Multi-Port Fuel Injection (PFI or EFI or SEFI)

The goal of all fuel injection systems is to carefully meter the amount of fuel to each cylinder. On most gasoline applications, the system uses a single injector per cylinder and injects fuel immediately ahead of the intake valves.

Direct Injection

See also: Gasoline Direct Injection

Recently many diesel engines feature direct injection (DI). The injection nozzle is placed inside the combustion chamber and the piston incorporates a depression (often toroidal) 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 recently designed hi-tech petrol engines utilize direct injection as well. This is the next step in evolution from multi port fuel injection and offers another magnitude of emission control by eliminating the "wet" portion of the induction system.

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 commercially 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.

One of the first commercial gasoline injection systems was a mechanical system developed by Bosch and introduced in 1955 on the Mercedes-Benz 300SL.

An early electronic fuel injection system was developed by the Bendix Corporation, but a commercial application was impractical at the time; there did not yet exist solid-state sensors or mass-produced transistors. The patents were subsequently sold to Bosch.

In 1957, Chevrolet introduced a mechanical fuel injection option for its 283 V8 engine, made by General Motors' Rochester division. This system used a single, central plunger to feed fuel to all eight cylinders through distribution tubes. The engine 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). In contrast, Mercedes' used six individual plungers to feed fuel to each of the six cylinders.

During the 1960's, other mechanical injection systems such as Hilborn were occasionally used on modified American V8 engines in various racing applications such as drag racing, oval racing, and road racing. These racing-derived systems were not suitable for everyday street use.

Post Emission Era

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 411 in 1967. This was a speed/density system, using engine speed and intake manifold air density to calculate "air mass" flow rate and thus fuel requirements. The system used all analog, discrete electronics, and an electro-mechanical pressure sensor. The sensor was susceptible to vibration and dirt. This system was adopted by VW, Mercedes-Benz, Porsche, Saab and Volvo. Lucas licensed the system for production with Jaguar.

Bosch replaced the D-Jetronic system with the L-Jetronic system. L-Jetronic uses a mechanical airflow meter (L for Luft, German for air) which produces a signal that is porportional to "air volume". This approach required additional sensors to correct for barometer and temperature, to utlitmately determine "air mass". This system first appeared on the 1974 Porsche 914. L-Jetronic was widely adopted on European cars of that period, as well as a few Japanese models a short time later.

In 1975, California's emissions regulations, the most stringent in the world, required manufacturers to resort to using a catalytic converter. A catalyst promotes a reaction without itself becoming consumed in the reaction. In this case, an oxidation catalyst was designed into the vehicle's exhaust system to promote reactions of the exhaust constituents in the presence of heat. When hot products of combustion, such as 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 reduce the various nitrogen oxides into free nitrogen and oxygen. The reduction catalyst was used in additiona to the oxidation catalyst.

Eventually the two features were combined into what is now commonly called a "3-way" catalyst. The "3" comes from its ability to catalyze the three regulated exhaust emissions; unburned hydrocarbons, carbon monoxide, and oxides of nitrogen.

In order to take maximum advantage of a 3-way catalyst's chemical process, excellent air/fuel ratio control is essential. EFI systems improved fuel control in two major stages. The first stage was open loop fuel control, and then by 1980, the second stage known as closed-loop fuel control began to appear.

Open loop injection systems actually provided less acurate air/fuel ratio control than a carburetor due to manufacturing tolerance issues, but still provided excellent cylinder-to-cylinder fuel distribution. In order to improve the air/fuel ratio control as well, closed loop feedback control of EFI appeared in 1980.

Closed loop control is accomplished with a Lambda-Sond sensor, commonly referred to as the exhaust gas oxygen sensor, or EGO sensor, or O₂ sensor. This sensor is mounted in the exhaust system nearly always upstream of the catalyst. The EGO sensor detects excess oxygen in the exhaust. Oxygen, or the lack of it, is a directional indicator of the air/fuel mixture's deviation from the desired stoichiometric air/fuel ratio.

"Closed loop" air/fuel ratio control, along with the catalytic converter, reduced exhaust emissions to less than 0.1% compared to a 1960, unregulated automobile.

In 1982, Bosch introduced 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", not "air volume". The mass air sensor utilizes a heated platinum wire, and the rate of the wire's cooling is proportional to the "air mass" flowing across the wire. Additional temperature and pressure sensors are not required to calculate the final "air mass" with LH-Jetronic.

The LH-Jetronic system is also notable in that it was the first system to abandon an all analog Electronic Control Unit in favor of digital CPU, which is now the prevailing form of ECU. This further refined air/fuel ratio control.

The introduction of digital microprocessor controls facilitated the integration of both the fuel control and the ignition control, with combined 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 there after, with control of all powertrain sub-systems in a single digital computer.

External links

• How Fuel Injection Systems Work
• The role of spray technology in fuel injectionde:Direkteinspritzung

es:Inyección de combustible fr:Injection directe id:Injeksi bahan bakar ja:燃料噴射装置 pl:Wtrysk paliwa pt:Injecção electrónica sv:Bränsleinsprutning