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Fuel injection is a system for mixing fuel with air in an internal combustion engine. It has become the primary fuel delivery system used in gasoline automotive engines, having almost completely replaced carburetors in the late 1980s. The first use of direct gasoline injection was on the Hesselman engine invented by Swedish engineer Jonas Hesselman in 1925.[1][2]

A fuel injection system is designed and calibrated specifically for the type(s) of fuel it will handle. The majority of fuel injection systems are for gasoline or diesel applications. With the advent of electronic fuel injection (EFI), the diesel and gasoline hardware has become similar. EFI's programmable firmware has permitted common hardware to be used with multiple different fuels. For gasoline engines, carburetors were the predominant method to meter fuel before the widespread use of fuel injection. However, a wide variety of injection systems have existed since the earliest usage of the internal combustion engine.

The primary functional difference between carburetors and fuel injection is that fuel injection atomizes the fuel by forcibly pumping it through a small nozzle under high pressure, while a carburetor relies on low pressure created by intake air rushing through it to add the fuel to the airstream.

The fuel injector is only a nozzle and a valve: the power to inject the fuel comes from farther back in the fuel supply, from a pump or a pressure container.

History and development

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. In 1896 E.J. Pennington had detailed a crude form of fuel injection in the patent for his motorcycle (U.S. patent 574262).[citation (source) needed]. Herbert Akroyd Stuart developed the first system laid out on modern lines (with a highly-accurate 'jerk pump' to meter out fuel oil at high pressure to an injector. This system was used on the hot bulb engine and was adapted and improved by Robert Bosch for use on diesel engines- Rudolf Diesel's original system using a cumbersome and less efficient 'air-blast' system using highly compressed air.

Fuel injection was in widespread commercial use in diesel engines by the mid-1920s. Because of its greater immunity to wildly changing g-forces on the engine, the concept was adapted for use in gasoline-powered aircraft during World War II, and direct injection was employed in some notable designs like the Daimler-Benz DB 603, the BMW 801, the Shvetsov ASh-82FN (M-82FN) 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. This was basically a high pressure diesel direct injection pump with an intake throttle valve set up. (diesels only change amount of fuel injected to vary output, there is no throttle). This system used a normal gasoline fuel pump, to provide fuel to a mechanically driven injection pump, which had separate plungers per injector to deliver a very high injection pressure directly into the combustion chamber. When combined with Desmo valves in racing the 300 SL was capable of over 100 horsepower per liter, still better than what's commonly possible today without a turbo.

Another mechanical system, also by Bosch, (CIS) but injecting the fuel into the port above the intake valve was later used by Porsche from 1969 until 1973 for the 911 production range in the USA and until 1975 on the Carrera RS 2.7 and RS 3.0 street models in Europe. Porsche continued using it on its racing cars into the late seventies and early eighties. Porsche racing variants such as the 911 RSR 2.7 & 3.0, 904/6, 906, 907, 908, 910, 917 (in its regular normally aspirated or 5.5 Liter/1500 HP Turbocharged form), and 935 all used Bosch or Kugelfischer built variants of injection. The Kugelfischer system was also used by the BMW 2000/2002 Tii and some versions of the Peugeot 404/504 and Lancia Flavia. Lucas also offered a mechanical system which was used by some Maserati, Aston Martin and Triumph models between ca. 1963 and 1973. The first factory electronic fuel injection, a true multi-point system, with dual 2-bbl. throttles, was optional on 1958 Chrysler products, both Hemi and wedge engines. It was jointly engineered by Chrysler and Bendix.

A system similar to the Bosch inline mechanical pump was built by SPICA for Alfa Romeo, used on the Alfa Romeo Montreal and on US market 1750 and 2000 models from 1969 until 1981. This was specifically designed to meet the US emission requirements, and allowed Alfa to meet these requirements at no loss in performance and with a reduction in fuel consumption.

In 1957, Chevrolet introduced a mechanical fuel injection option, made by General Motors' Rochester Products division, for its 283 V8 engine. This system directed the inducted engine air across a "spoon shaped" plunger that moved in proportion to the air volume. The plunger connected to the fuel metering system which mechanically dispensed fuel to the cylinders via distribution tubes. This system was not a "pulse" or intermittent injection, but rather a constant flow system, metering fuel to all cylinders simultaneously from a central "spider" of injection lines. The fuel meter adjusted the amount of flow according to engine speed and load, and included a fuel reservoir, which was similar to a carburetor's float chamber. With its own high-pressure fuel pump driven by a cable from the distributor to the fuel meter, the system supplied the necessary pressure for injection. However, this was "port" injection, in which the injectors are located in the intake manifold, very near the intake valve. (Direct fuel injection is a fairly recent innovation for automobile engines. As recent as 1954 in aforementioned Mercedes-Benz 300SL or the Gutbrod in 1953) The highest performance version of the fuel injected engine was rated at 283 bhp (211.0 kW) from 283 cubic inches (4.6 L). This made it among the early production engines in history to exceed 1 hp/in³ (45.5 kW/L), after Chrysler's Hemi engine and a number of others.

During the 1960s, 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.[citation (source) needed] These racing-derived systems were not suitable for everyday street use, having no provisions for low speed metering or even starting (fuel had to be squirted into the injector tubes while cranking the engine in order to start it). However they were a favorite in the aforementioned competition trials in which essentially wide-open throttle operation was prevalent.


The first commercial electronic fuel injection (EFI) system was Electrojector, developed by the Bendix Corporation and was to be offered by American Motors (AMC) in 1957.[3] A special muscle car model, the Rambler Rebel, showcased AMC's new 327 cu in (5.4 L) engine. The Electrojector was an option and rated at 288 bhp (214.8 kW)[4] Initial press information about the Bendix system in December 1956 was followed in March 1957 by a price bulletin that pegged the option at US$395, but due to supplier difficulties, fuel-injected Rebels would only be available after June 15.[5] This was to have been the first production EFI engine, but Electrojector's teething problems meant only pre-production cars were so equipped and none were made available to the public.[6] The EFI system in the Rambler was a far more-advanced setup than the mechanical types then appearing on the market and the engines ran fine in warm weather, but suffered hard starting in cooler temperatures.[5]

Chrysler offered Electrojector on the 1958 300D, the D500, and the DeSoto Adventurer, arguably the first series-production cars equipped with an EFI system, but the early electronic components were not equal to the rigors of underhood service, and were too slow to keep up with the demands of "on the fly" engine control. Most 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 D-Jetronic (D for Druck, German for "pressure"), which was first used on the VW 1600TL 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.[citation (source) needed] This system was adopted by VW, Mercedes-Benz, Porsche, Citroën, Saab, and Volvo. Lucas licensed the system for production with Jaguar.

Bosch superseded the D-Jetronic system with the K-Jetronic and L-Jetronic systems for 1974, though some cars (such as the Volvo 164) continued using D-Jetronic for the following several years. The Cadillac Seville was introduced in 1977 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 barometer 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 1982, Bosch introduced a sensor that directly measures the air mass flow into the engine, on their L-Jetronic system. Bosch called this LH-Jetronic (L for Luftmasse and H for Hitzdraht, German for "air mass" and "hot wire", respectively). The mass air sensor utilizes a heated platinum wire placed in the incoming air flow. The rate of the wire's cooling is proportional to the air mass flowing across the wire. Since the hot wire sensor directly measures air mass, the need for additional temperature and pressure sensors is eliminated. The LH-Jetronic system was also the first fully digital EFI system, which is now the standard approach.[citation (source) needed] The advent of the digital microprocessor permitted the integration of all powertrain sub-systems into a single control module.

See also


  1. Scania fordonshistoria 1891-1991 av Björn-Eric Lindh, 1992. ISBN 91-7886-074-1(Translated title: Vehicle history of Scania 1891-1991)
  2. Volvo – Lastbilarna igår och idag av Christer Olsson, 1987. ISBN 91-86442-76-7 (Translated title: Volvo trucks yesterday and today)
  3. Ingraham, Joseph C. "Automobiles: Races; Everybody Manages to Win Something At the Daytona Beach Contests" The New York Times, March 24, 1957. Page 153. Retrieved on December 15 2007.
  4. Holder, William (2006). Extreme Muscle Cars: The Factory Lightweight Legacy. Krause Publications, 16. ISBN 9780896892781. Retrieved on 2009-12-26. 
  5. 5.0 5.1 "Rambler Measures Up" by the Auto Editors of Consumer Guide, retrieved on December 15 2007.
  6. American Musclecars: Power to the People, retrieved on December 15 2007.

External links

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