Fuel injection
Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of an injector. This article focuses on fuel injection in reciprocating piston and Wankel rotary engines.
All compression-ignition engines (e.g.
The term "fuel injection" is vague and comprises various distinct systems with fundamentally different functional principles. Typically, the only thing all fuel injection systems have in common is a lack of
System functions
The fundamental functions of a fuel injection system are described in the following sections. In some systems, a single component performs multiple functions.
Pressurising fuel
Fuel injection is operated by spraying pressurised fuel into the engine. Therefore a device to pressurise the fuel is needed, such as a fuel pump.
Metering fuel
The system must determine the appropriate amount of fuel to be supplied and control the fuel flow to supply this amount.
Several early mechanical injection systems used relatively sophisticated helix-controlled injection pump(s) that both metered fuel and created injection pressure. Since the 1980s, electronic systems have been used to control the metering of fuel. More recent systems use an electronic engine control unit which meters the fuel, controls the ignition timing and controls various other engine functions.
Injecting fuel
The fuel injector is effectively a spray nozzle that performs the final stage in the delivery of fuel into the engine. The injector is located in the combustion chamber, inlet manifold or - less commonly - the throttle body.
Fuel injectors which also control the metering are called "injection valves", while injectors that perform all three functions are called unit injectors.
Direct injection systems
Direct injection means that the fuel is injected into the main combustion chamber of each cylinder.[3] The air and fuel are mixed only inside the combustion chamber. Therefore, only air is sucked into the engine during the intake stroke. The injection scheme is always intermittent (either sequential or cylinder-individual).
This can be done either with a blast of air[4] or hydraulically, with the latter method being more common in automotive engines. Typically, hydraulic direct injection systems spray fuel into the air inside the cylinder or combustion chamber. Direct injection can be achieved with a conventional helix-controlled injection pump, unit injectors, or a sophisticated common-rail injection system. The latter is the most common system in modern automotive engines.
Direct injection for petrol engines
During the 20th century, most petrol engines used either a
Common-rail injection systems
In a common rail system, fuel from the fuel tank is supplied to a common header (called the accumulator), and then sent through tubing to the injectors, which inject it into the combustion chamber. The accumulator has a high-pressure relief valve to maintain pressure and return the excess fuel to the fuel tank. The fuel is sprayed with the help of a nozzle that is opened and closed with a solenoid-operated needle valve.[5] Third-generation common rail diesels use piezoelectric injectors for increased precision, with fuel pressures up to 300 MPa or 44,000 psi.[6]
The types of common-rail systems include air-guided injection[7] and spray-guided injection.[7]
Unit injector systems
Used by diesel engines, these systems include:
Helix-controlled pump systems
This injection method was previously used in many diesel engines. Types of systems include:
- Lanova direct injection[9]
- Afterchamber injection[10]
- G-System (sphere combustion chamber)[11]
- Gardner system (hemisphere combustion chamber)[11]
- Saurer system (torus combustion chamber)[11]
- Flat piston (combustion chamber between piston and head)
Air-blast injection systems
Other systems
The M-System, used in some diesel engines from the 1960s to the 1980s, sprayed the fuel onto the walls of the combustion chamber,[12] as opposed to most other direct-injection systems which spray the fuel into the middle of the chamber.
Indirect injection systems
Manifold injection
Manifold injection systems are common in petrol-fuelled engines such as the Otto engine and the Wankel engine. In a manifold injection system, air and fuel are mixed outside the combustion chamber so that a mixture of air and fuel is sucked into the engine. The main types of manifold injections systems are multi-point injection and single-point injection.
These systems use either a continuous injection or an intermittent injection design.[13] In a continuous injection system, fuel flows at all times from the fuel injectors, but at a variable flow rate. The most common automotive continuous injection system is the Bosch K-Jetronic system, introduced in 1974 and used until the mid-1990s by various car manufacturers. Intermittent injection 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; simultaneous, in which fuel is injected at the same time to all the cylinders; or cylinder-individual, in which the engine control unit can adjust the injection for each cylinder individually.[13]
Multi-point injection
Multi-point injection (also called 'port injection') injects fuel into the intake ports just upstream of each cylinder's
Single-point injection
Single-point injection (also called 'throttle-body injection')
Diesel engines
In indirect-injected engines used by diesel engines (as well as Akroyd engines), there are two combustion chambers: the main combustion chamber, and a
Types of indirect injection used by diesel engines include:
Hot-bulb injection
History
1870s – 1930s: early systems
In 1872, George Bailey Brayton obtained a patent on an internal combustion engine that used a pneumatic fuel injection system, also invented by Brayton: air-blast injection.[21]: 413 In 1894, Rudolf Diesel copied Brayton's air-blast injection system for the diesel engine, but also improved it.[22]: 414 He increased the air blast pressure from 4–5 kp/cm2 (390–490 kPa) to 65 kp/cm2 (6,400 kPa).[23]: 415 In the meantime, the first manifold injection system was designed by Johannes Spiel in 1884, while working at Hallesche Maschinenfabrik in Germany.[24]
In 1891, the British
In 1898, German company Deutz AG started producing four-stroke petrol stationary engines[28] with manifold injection.[citation needed] The 1906 Antoinette 8V aircraft engine (the world's first V8 engine) was another early four-stroke engine that used manifold injection. The first petrol engine with direct-injection was a two-stroke aircraft engine designed by Otto Mader in 1916.[29] Another early spark-ignition engine to use direct-injection was the 1925 Hesselman engine, designed by Swedish engineer Jonas Hesselman.[30][31] This engine could run on a variety of fuels (such as oil, kerosene, petrol or diesel oil)[32] and used a stratified charge principle whereby fuel is injected towards the end of the compression stroke, then ignited with a spark plug.
The Cummins Model H diesel truck engine was introduced in America in 1933.[33] In 1936, the Mercedes-Benz OM 138 diesel engine (using a precombustion chamber) became one of the first fuel-injected engines used in a mass-production passenger car.[34]
1940s – 1950s: WWII aircraft and early direct-injection petrol engines
During
The first mass-produced petrol direct-injection system was developed by Bosch and initially used in small automotive two-stroke petrol engines. Introduced in the 1950
1950s – 1970s: manifold injection for petrol engines
Throughout the 1950s, several manufacturers introduced their manifold injection systems for petrol engines. Lucas Industries had begun developing a fuel injection system in 1941 and by 1956 it was used in the Jaguar racing cars.[41] At the 1957 24 Hours of Le Mans, the 1st to 4th placed cars were Jaguar D-Type entries using a Lucas fuel injection system.[42] Also in 1957, General Motors introduced the Rochester Ramjet option, consisting of a fuel injection system for the V8 engine in the Chevrolet Corvette. During the 1960s, fuel injection systems were also produced by Hilborn,[43] SPICA[44] and Kugelfischer.
Up until this time, the fuel injection systems had used a mechanical control system. In 1957, the American Bendix Electrojector system was introduced, which used analogue electronics for the control system. The Electrojector was intended to be available for the Rambler Rebel mid-size car, however reliability problems meant that the fuel injection option was not offered.[45][46][47][48][49] In 1958, the Chrysler 300D, DeSoto Adventurer, Dodge D-500 and Plymouth Fury offered the Electrojector system, becoming the first cars known to use an electronic fuel injection (EFI) system.[50]
The Electrojector patents were subsequently sold to Bosch, who developed the Electrojector into the Bosch
Also in 1974, Bosch introduced the
1980s – present: digital electronics and common-rail injection
Prior to 1979, the electronics in fuel injection systems used analogue electronics for the control system. The Bosch Motronic multi-point fuel injection system (also amongst the first systems where the ignition system is controlled by the same device as the fuel injection system) was the first mass-produced system to use digital electronics. The Ford EEC-III single-point fuel injection system, introduced in 1980, was another early digital fuel injection system.[53][54] These and other electronic manifold injection systems (using either port injection or throttle-body injection) became more widespread through the 1980s, and by the early 1990s they had replaced carburettors in most new petrol-engined cars sold in developed countries.
The aforementioned injection systems for petrol passenger car engines - except for the 1954-1959 Mercedes-Benz 300 SL - all used
References
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- ^ ISBN 978-3-7091-8180-5, p. 64
- ^ 1997 Chevrolet Truck Service Manual, page 6A-24, drawing, item (3) Central Sequential Muliport injector.
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- ^ "Driving the Awesome Mercedes 300 SL 'Gullwing' - slide 8/22". Wired. Retrieved 26 December 2022.
- ^ "A short history of Lucas injection". lucasinjection.com. Retrieved 1 May 2015.
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- ^ Walton, Harry (March 1957). "How Good is Fuel Injection?". Popular Science. 170 (3): 88–93. Retrieved 1 May 2015.
- ^ "Spica Fuel Injection". www.hemmings.com. Retrieved 30 October 2023.
- ^ 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.
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See also
- Carburettor
- Common rail
- Diesel engine#Fuel injection
- Jacketed fuel injection pipe
- Petrol direct injection
- Indirect injection
- Unit injector for diesel engines