Fuel injection: Difference between revisions

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Fuel injection is a system for admitting fuel into an internal combustion engine. It has become the primary fuel delivery system used in automotive engines, having replaced carburetors during the 1980s and 1990s. A variety of injection systems have existed since the earliest usage of the internal combustion engine.

The primary difference between carburetors and fuel injection is that fuel injection

Modern fuel injection systems are designed specifically for the type of fuel being used. Some systems are designed for multiple grades of fuel (using sensors to adapt the tuning for the fuel currently used). Most fuel injection systems are for gasoline or diesel applications.

Objectives

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 is optimized. There are several competing objectives such as:

• Power output
• Fuel efficiency
• Emissions performance
• Ability to accommodate alternative fuels
• Reliability
• Driveability and smooth operation
• Initial cost
• Maintenance cost
• Diagnostic capability
• Range of environmental operation
• Engine tuning

The modern digital electronic fuel injection system is more capable at optimizing these competing objectives consistently than earlier fuel delivery systems (such as carburetors). Carburetors have the potential to atomize fuel better (see Pogue and Allen Caggiano patents).^{[dubious – discuss]}

Benefits

Benefits of fuel injection include smoother and more consistent transient throttle response, such as during quick throttle transitions, easier cold starting, more accurate adjustment to account for extremes of ambient temperatures and changes in air pressure, more stable idling, decreased maintenance needs, and better fuel efficiency.

Fuel injection also dispenses with the need for a separate mechanical choke, which on carburetor-equipped vehicles must be adjusted as the engine warms up to normal temperature. Furthermore on spark ignition engines (direct) fuel injection has the advantage of being able to facilitate stratified combustion which have not been possible with carburetors.

It is only with the advent of multi-point fuel injection certain engine configurations such as inline five cylinder gasoline engines have become more feasible for mass production, as traditional carburetor arrangement with single or twin carburetors could not provide even fuel distribution between cylinders, unless a more complicated individual carburetor per cylinder is used.

Fuel injection systems are also able to operate normally regardless of orientation, whereas carburetors with floats are not able to operate upside down or in zero gravity, such as encountered on airplanes.

Environmental benefits

Fuel injection generally increases engine fuel efficiency. With the improved cylinder-to-cylinder fuel distribution of multi-point fuel injection, less fuel is needed for the same power output (when cylinder-to-cylinder distribution varies significantly, some cylinders receive excess fuel as a side effect of ensuring that all cylinders receive sufficient fuel).

Exhaust

Alfa Romeo tested one of the first electronic injection systems (Caproni-Fuscaldo) in Alfa Romeo 6C 2500 with "Ala spessa" body in 1940 Mille Miglia. The engine had six electrically operated injectors and were fed by a semi-high-pressure circulating fuel pump system.^[5]

Development in diesel engines

All diesel engines (with the exception of some tractors and

Development in gasoline/petrol engines

Mechanical injection

The invention of mechanical injection for gasoline-fueled aviation engines was by the French inventor of the

The first post-World War I example of direct gasoline injection was on the Hesselman engine invented by Swedish engineer Jonas Hesselman in 1925.^[6][7] Hesselman engines used the ultra lean burn principle and injected the fuel in the end of the compression stroke and then ignited it with a spark plug, it was often started on gasoline and then switched over to run on diesel or kerosene. The Hesselman engine was a low compression design constructed to run on heavy fuel oils.

Direct gasoline injection was applied during the

Immediately following the war, hot rodder Stuart Hilborn started to offer mechanical injection for race cars, salt cars, and midgets,^[8] well-known and easily distinguishable because of their prominent velocity stacks projecting upwards from the engines on which they were used.

The first automotive direct injection system used to run on gasoline was developed by

In 1956, Lucas developed its injection system, which was first used for Jaguar racing cars at Le Mans. The system was subsequently adopted very successfully in Formula One racing, securing championships by Cooper, BRM, Lotus, Brabham, Matra and Tyrrell in the years 1959 through 1973.^[9] While the racing systems used a simple fuel cam for metering, a more sophisticated Mk 2 vacuum based shuttle metering was developed for production cars. This mechanical system was used by some Maserati, Aston Martin, and Triumph models between 1963 and 1975.^[10]

During the 1960s, other mechanical injection systems such as Hilborn were occasionally used on modified American

A system similar to the Bosch inline mechanical pump was built by SPICA for Alfa Romeo, used on the Alfa Romeo Montreal and on U.S. market 1750 and 2000 models from 1969 to 1981. This was designed to meet the U.S. emission requirements with no loss in performance and it also reduced fuel consumption.

Electronic injection

The first commercial electronic fuel injection (EFI) system was Electrojector, developed by the

Chrysler offered Electrojector on the 1958 Chrysler 300D, DeSoto Adventurer, Dodge D-500, and Plymouth Fury, arguably the first series-production cars equipped with an EFI system. It was jointly engineered by Chrysler and Bendix. The early electronic components were not equal to the rigors of underhood service, however, and were too slow to keep up with the demands of "on the fly" engine control. Most of the 35 vehicles originally so equipped were field-retrofitted with 4-barrel carburetors. The Electrojector patents were subsequently sold to Bosch.

Bosch developed an electronic fuel injection system, called

.

Bosch superseded the D-Jetronic system with the

L-Jetronic systems for 1974, though some cars (such as the Volvo 164) continued using D-Jetronic for the following several years. In 1970, the Isuzu 117 Coupé

was introduced with a Bosch-supplied D-Jetronic fuel injected engine sold only in Japan.

In Japan, the

Subaru EA81 engine installed in the Subaru Leone. Honda followed in 1984 with their own system, called PGM-FI in the Honda Accord, and the Honda Vigor using the Honda ES3 engine

.

The limited production Chevrolet Cosworth Vega was introduced in March 1975 using a Bendix EFI system with pulse-time manifold injection, four injector valves, an electronic control unit (ECU), five independent sensors and two fuel pumps. The EFI system was developed to satisfy stringent emission control requirements and market demands for a technologically advanced responsive vehicle. 5000 hand-built Cosworth Vega engines were produced but only 3,508 cars were sold through 1976.^[21]

The Cadillac Seville was introduced in 1975 with an EFI system made by Bendix and modelled very closely on Bosch's D-Jetronic. L-Jetronic first appeared on the 1974 Porsche 914, and uses a mechanical airflow meter (L for Luft, German for "air") that produces a signal that is proportional to "air volume". This approach required additional sensors to measure the atmospheric pressure and temperature, to ultimately calculate "air mass". L-Jetronic was widely adopted on European cars of that period, and a few Japanese models a short time later.

In 1980,

Freescale) introduced the first electronic engine control unit, the EEC-III.^[22] Its integrated control of engine functions (such as fuel injection and spark timing) is now the standard approach for fuel injection systems. The Motorola technology was installed in Ford

North American products.

Ellimination of carburetors

In the 1970s and 1980s in the U.S. and Japan, the respective federal governments imposed increasingly strict

exhaust emission

regulations. During that time period, the vast majority of gasoline-fueled automobile and light truck engines did not use fuel injection. To comply with the new regulations, automobile manufacturers often made extensive and complex modifications to the engine carburetor(s). While a simple carburetor system is cheaper to manufacture than a fuel injection system, the more complex carburetor systems installed on many engines in the 1970s were much more costly than the earlier simple carburetors. To more easily comply with emissions regulations, automobile manufacturers began installing fuel injection systems in more gasoline engines during the late 1970s.

The

Closed loop fuel injection systems improved the air/fuel mixture control with an exhaust gas oxygen sensor. Although not part of the injection control, a catalytic converter

further reduces exhaust emissions.

Fuel injection was phased in through the latter 1970s and 80s at an accelerating rate, with the German, French, and U.S. markets leading and the UK and Commonwealth markets lagging somewhat. Since the early 1990s, almost all gasoline passenger cars sold in

first world

markets are equipped with electronic fuel injection (EFI). The carburetor remains in use in developing countries where vehicle emissions are unregulated and diagnostic and repair infrastructure is sparse. Fuel injection is gradually replacing carburetors in these nations too as they adopt emission regulations conceptually similar to those in force in Europe, Japan, Australia, and North America.

Many motorcycles still utilize carburetored engines, though all current high-performance designs have switched to EFI.

NASCAR finally replaced carburetors with fuel-injection, starting at the beginning of the 2012 NASCAR Sprint Cup Series season.^[23][24][25]

System components

System overview

The process of determining the necessary amount of fuel, and its delivery into the engine, are known as fuel metering. Early injection systems used mechanical methods to meter fuel, while nearly all modern systems use electronic metering.

Determining how much fuel to supply

The primary factor used in determining the amount of fuel required by the engine is the amount (by weight) of air that is being taken in by the engine for use in combustion. Modern systems use a mass airflow sensor to send this information to the engine control unit.

Data representing the amount of power output desired by the driver (sometimes known as "engine load") is also used by the

closed loop

operation.

Supplying the fuel to the engine

Fuel is transported from the fuel tank (via fuel lines) and pressurised using fuel pump(s). Maintaining the correct fuel pressure is done by a fuel pressure regulator. Often a

fuel rail

is used to divide the fuel supply into the required number of cylinders. The fuel injector injects liquid fuel into the intake air (the location of the fuel injector varies between systems).

Unlike carburettor-based systems, where the

G-forces, vehicles are often provided by an anti-surge vessel, usually integrated in the fuel tank

, but sometimes as a separate, small anti-surge tank.

EFI gasoline engine components

Note: These examples specifically apply to a modern EFI gasoline engine. Parallels to fuels other than gasoline can be made, but only conceptually.

• Injectors
• Fuel Pump
• Fuel Pressure Regulator
• Engine control unit
• 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:
  UEGO sensor

Engine control unit

Main article: engine control unit

The engine control unit is central to an EFI system. The ECU interprets data from input sensors to, among other tasks, calculate the appropriate amount of fuel to inject.

Fuel injector

When signalled by the engine control unit the fuel injector opens and sprays the pressurised fuel into the engine. The duration that the injector is open (called the pulse width) is proportional to the amount of fuel delivered. Depending on the system design, the timing of when injector opens is either relative each individual cylinder (for a sequential fuel injection system), or injectors for multiple cylinders may be signalled to open at the same time (in a batch fire system).

Target air/fuel ratios

The relative proportions of air and fuel vary according to the type of fuel used and the performance requirements (i.e. power, fuel economy, or exhaust emissions).

See

air-fuel ratio, stoichiometry, and combustion

.

Various injection schemes

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Single-point injection

Single-point injection uses a single injector at the

throttle body

(the same location as was used by carburetors).

It was introduced in the 1940s in large aircraft engines (then called the

General Motors, Central Fuel Injection by Ford, PGM-CARB by Honda, and EGI by Mazda

). Since the fuel passes through the intake runners (like a carburetor system), it is called a "wet manifold system".

The justification for single-point injection was low cost. Many of the carburetor's supporting components- such as the air cleaner, intake manifold, and fuel line routing- could be reused. This postponed the redesign and tooling costs of these components. Single-point injection was used extensively on American-made passenger cars and light trucks during 1980-1995, and in some European cars in the early and mid-1990s.

Continuous injection

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. K-Jetronic was used for many years between 1974 and the mid-1990s by BMW, Lamborghini, Ferrari, Mercedes-Benz, Volkswagen, Ford, Porsche, Audi, Saab, DeLorean, and Volvo. Chrysler used a continuous fuel injection system on the 1981-1983 Imperial.

In piston aircraft engines, continuous-flow fuel injection is the most common type. In contrast to automotive fuel injection systems, aircraft continuous flow fuel injection is all

TCM system. The Bendix system is a direct descendant of the pressure carburetor

. However, instead of having a discharge valve in the barrel, it uses a flow divider mounted on top of the engine, which controls the discharge rate and evenly distributes the fuel to stainless steel injection lines to the intake ports of each cylinder. The TCM system is even more simple. It has no venturi, no pressure chambers, no diaphragms, and no discharge valve. The control unit is fed by a constant-pressure fuel pump. The control unit simply uses a butterfly valve for the air, which is linked by a mechanical linkage to a rotary valve for the fuel. Inside the control unit is another restriction, which controls the fuel mixture. The pressure drop across the restrictions in the control unit controls the amount of fuel flow, so that fuel flow is directly proportional to the pressure at the flow divider. In fact, most aircraft that use the TCM fuel injection system feature a fuel flow gauge that is actually a pressure gauge calibrated in gallons per hour or pounds per hour of fuel.

Central port injection

From 1992 to 1996

General Motors implemented a system called Central Port Injection or Central Port Fuel Injection. The system uses tubes with poppet valves from a central injector to spray fuel at each intake port rather than the central throttle-body^{[citation needed]}. Fuel pressure is similar to a single-point injection system. CPFI (used from 1992 to 1995) is a batch-fire system, while CSFI (from 1996) is a sequential system.^[26]

Multiport fuel injection

Multiport fuel injection injects fuel into the intake ports just upstream of each cylinder's intake valve, rather than at a central point within an intake manifold. MPFI (or just MPI) systems can be sequential, in which injection is timed to coincide with each cylinder's intake stroke; batched, in which fuel is injected to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke; or simultaneous, in which fuel is injected at the same time to all the cylinders. The intake is only slightly wet, and typical fuel pressure runs between 40-60 psi.

Many modern EFI systems utilize sequential MPFI; however, in newer gasoline engines, direct injection systems are beginning to replace sequential ones.

Direct injection

See also: Common rail

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In a direct injection engine, fuel is injected into the combustion chamber as opposed to injection before the

intake valve (petrol engine) or a separate pre-combustion chamber (diesel engine).^[27]

In a

piezoelectric injectors for increased precision, with fuel pressures up to 1,800 bar or 26,000 psi

.

Direct fuel injection costs more than indirect injection systems: the injectors are exposed to more heat and pressure, so more costly materials and higher-precision electronic management systems are required.

Diesel engines

Most diesel engines (with the exception of some tractors and scale model engines) have fuel injected into the combustion chamber.

Earlier systems, relying on simpler injectors, often injected into a sub-chamber shaped to swirl the compressed air and improve combustion; this was known as

toroidal

) in the crown of the piston.

Throughout the early history of diesels, they were always fed by a mechanical pump with a small separate chamber for each cylinder, feeding separate fuel lines and individual injectors.^{[citation needed]} Most such pumps were in-line, though some were rotary.

Most modern diesel engines use common rail or unit injector direct injection systems.

Gasoline engines

Main article: gasoline direct injection

Modern gasoline engines also utilise direct injection, which is referred to as gasoline direct injection. This is the next step in evolution from multi-point fuel injection, and offers another magnitude of emission control by eliminating the "wet" portion of the induction system along the inlet tract.

By virtue of better

lean burn) mixtures, and hence avoid throttling losses at low and part engine load. Some direct-injection systems incorporate piezoelectronic

fuel injectors. With their extremely fast response time, multiple injection events can occur during each cycle of each cylinder of the engine.

Swirl injection

Swirl injectors are used in liquid rocket, gas turbine, and diesel engines to improve atomization and mixing efficiency.

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The circumferential velocity component is first generated as the propellant enters through helical or tangential inlets producing a thin, swirling liquid sheet. A gas-filled hollow core is then formed along the centerline inside the injector due to centrifugal force of the liquid sheet. Because of the presence of the gas core, the discharge coefficient is generally low. In swirl injector, the spray cone angle is controlled by the ratio of the circumferential velocity to the axial velocity and is generally wide compared with nonswirl injectors.[28]

Maintenance hazards

Fuel injection introduces potential hazards in engine maintenance due to the high fuel pressures used. Residual pressure can remain in the fuel lines long after an injection-equipped engine has been shut down. This residual pressure must be relieved, and if it is done so by external bleed-off, the fuel must be safely contained. If a high-pressure diesel fuel injector is removed from its seat and operated in open air, there is a risk to the operator of injury by hypodermic jet-injection, even with only 100 psi (6.9 bar) pressure.^[29] The first known such injury occurred in 1937 during a diesel engine maintenance operation.^[30]

Notes

1. ^ ^{a b} Hartmann, Gerard (5 August 2007). "Les moteurs et aéroplanes Antoinette" (PDF) (in French). hydroretro.net. Archived from the original (PDF) on 14 December 2014. Retrieved 1 May 2015. {{cite web}}: Unknown parameter |trans_title= ignored (|trans-title= suggested) (help)
2. ISBN 978-91-7886-074-6
   .
3. ISBN 978-91-86442-76-7
   .
4. ^ "The Direct Injection Engine Will Likely Power Your Next Car". HybridKingdom.com. 2009. Retrieved 1 May 2015.
5. ^ "1940 6C 2500 Touring "Ala Spessa"" (in Italian). digilander.libero.it. Retrieved 20 January 2014.
6. ISBN 91-7886-074-1
   .
7. ISBN 91-86442-76-7
   .
8. ^ Circle Track, 9/84, pp.82-3.
9. ^ "A short history of Lucas injection". lucasinjection.com. Retrieved 1 May 2015.
10. ^ "Petrol Injection Mk II". Lucas Service Training Centre. Retrieved 1 May 2015.
11. ^ ^{a b} Walton, Harry (March 1957). "How Good is Fuel Injection?". Popular Science. 170 (3): 88–93. Retrieved 1 May 2015.
12. ^ Davis, Marlan (October 2010). "What You Need To Know About Mechanical Fuel Injection". Hot Rod Magazine. Retrieved 1 May 2015.
13. ^ Ingraham, Joseph C. (24 March 1957). "Automobiles: Races; Everybody Manages to Win Something At the Daytona Beach Contests". The New York Times. p. 153. Retrieved 1 May 2015.
14. ^ "1957 cars". Consumer Reports. 22: 154. 1957.
15. ISBN 978-0-89689-278-1
    . Retrieved 1 May 2015.
16. ^ "An Invitation to Happy Motoring... (Excerpts from the 1957 Rambler Rebel Owner's Manual)". AMX-files.com. Archived from the original on 28 March 2009. Retrieved 1 May 2015.
17. ^ ^{a b} Auto Editors of Consumer Guide (22 August 2007). "Rambler Measures Up". Retrieved 1 May 2015. {{cite web}}: |author= has generic name (help)
18. ISBN 978-1-55788-365-0
    .
19. ^ Kendall, Leslie. "American Musclecars: Power to the People". Petersen Automotive Museum. Archived from the original on 27 October 2011. Retrieved 1 May 2015.
20. ^ "Celica Parts Catalogue" (in Japanese). Toyota. Retrieved 20 January 2014.
21. ^ 1975 Chevrolet Cosworth Vega Overhaul Supplement - general information
22. ^ "A Timeline Overview of Motorola History 1928-2009" (PDF). Motorola. Archived from the original (PDF) on 20 June 2011. Retrieved 20 January 2014.
23. ^ Ryan, Nate (2 November 2011). "NASCAR sets fuel injection for '12 but keeping restrictor plates". USA Today. Retrieved 20 January 2014.
24. ^ "NASCAR Moves to Fuel Injection, Bosch First Approved Supplier". Auto Service World. 18 July 2011. Retrieved 20 January 2014.
25. ^ "Bosch to provide oxygen sensors for fuel injection". NASCAR.com. Archived from the original on 25 December 2011. Retrieved 20 January 2014.
26. ^ 1997 Chevrolet Truck Service Manual, page 6A-24, drawing, item (3) Central Sequential Muliport injector.
27. ^ "IC Engines". Global Fuel Economy Initiative. Archived from the original on 6 October 2012. Retrieved 1 May 2014.
28. ^ Ji-Hyuk, Im; Seongho, Cho; Youngbin, Yoon; Insang, Moon (2010). "Comparative Study of Spray Characteristics of Gas-Centered and Liquid-Centered Swirl Coaxial Injectors". Journal of Propulsion and Power.
29. ^ Agha, F.P. (1978). "High-pressure paint gun injuries of hand: clinical and roentgen aspects". NY State Journal of Medicine. 78: 1955–6.
30. doi:10.1001/jama.1937.92780370004012c
    .

Further reading

Patents

• U.S. patent 3,430,616 — Fuel Injection Control System — Otto Glöckler, et al.
• U.S. patent 3,500,801 — Actuator Circuit for Electronic Precision Fuel Metering Systems — E. David Long and Keith C. Richardson
• U.S. patent 3,504,657 — Cold Start Fuel Enrichment — Dieter Eichler, et al.
• U.S. patent 3,548,791 — Precision Fuel Metering ... — E. David Long
• U.S. patent 4,069,795 — Start-up Control for Fuel Injection System — E. David Long and Keith C. Richardson

External links

• History of the D Jetronic system
• High Quality Fuel System Repairs Guide
• How Fuel Injection Systems Work