Fuel injection is the introduction offuel in aninternal combustion engine, most commonlyautomotive engines, by the means of a fuel injector. This article focuses on fuel injection inreciprocating piston andWankel rotary engines.
All compression-ignition engines (e.g.diesel engines), and many spark-ignition engines (i.e.petrol (gasoline) engines, such asOtto orWankel), use fuel injection of one kind or another. Mass-produced diesel engines for passenger cars (such as theMercedes-Benz OM 138) became available in the late 1930s and early 1940s, being the first fuel-injected engines for passenger car use.[1] In passenger car petrol engines, fuel injection was introduced in the early 1950s and gradually gained prevalence until it had largely replacedcarburetors by the early 1990s.[2] The primary difference between carburetion and fuel injection is that fuel injectionatomizes the fuel through a small nozzle under high pressure, while carburetion relies onsuction created by intake air accelerated through aVenturi tube to draw fuel into the airstream.
The termfuel injection is vague and comprises various distinct systems with fundamentally different functional principles. The only thing all fuel injection systems have in common is the absence ofcarburetion. There are two main functional principles of mixture formation systems for internal combustion engines:internal andexternal. A fuel injection system that uses external mixture formation is called amanifold injection system. There exist two types of manifold injection systems:multi-point (orport) andsingle-point (orthrottle body) injection. Internal mixture formation systems can be separated into several different varieties ofdirect andindirect injection, the most common being thecommon-rail injection, a variety of direct injection. The termelectronic fuel injection refers to any fuel injection system controlled by anengine control unit.
The fundamental functions of a fuel injection system are described in the following sections. In some systems, a single component performs multiple functions.
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.
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 electronicengine control unit which meters the fuel and controls theignition timing and various other engine functions.
The fuel injector is effectively aspray nozzle that performs the final stage in the delivery of fuel into the engine. The injector is located in thecombustion chamber,inlet manifold or – less commonly – thethrottle body.
Fuel injectors which also control the metering are calledinjection valves, while injectors that perform all three functions are calledunit injectors.
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 last is the most common system in modern automotive engines.
During the 20th century, most petrol engines used either acarburettor or indirect fuel injection. Use of direct injection in petrol engines has become increasingly common in the 21st century.
In a common-rail system, fuel from the fuel tank is supplied to a common header (called theaccumulator), and then sent through tubing to the injectors, which inject it into the combustion chambers. 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 asolenoid-operatedneedle valve.[5] Third-generation common-rail diesels usepiezoelectric injectors for increased precision, with fuel pressures up to 300 MPa or 44,000 psi.[6]
The types of common-rail systems includeair-guided injection[7] andspray-guided injection.[7]
Used by diesel engines, these systems include:
This injection method was previously used in many diesel engines. Types of systems include:
TheM-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.
Manifold injection systems are common in petrol-fuelled engines such as theOtto engine and theWankel 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 aremulti-point injection andsingle-point injection.
These systems use either acontinuous injection or anintermittent 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 theBosch K-Jetronic system, introduced in 1974 and used until the mid-1990s by various car manufacturers. Intermittent injection systems can besequential, 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; orcylinder-individual, in which the engine control unit can adjust the injection for each cylinder individually.[13]
Multi-point injection (also called 'port injection') injects fuel into the intake ports just upstream of each cylinder'sintake valve, rather than at a central point within an intake manifold.[14] Typically, multi-point injected systems use multiple fuel injectors,[15] but some systems, such as GM's central port injection system, use tubes with poppet valves fed by a central injector instead of multiple injectors.[16]
Single-point injection (also called 'throttle-body injection')[17] uses one injector in athrottle body mounted similarly to acarburettor on anintake manifold. As in a carburetted induction system, the fuel is mixed with the air before entering the intake manifold.[15] Single-point injection was a relatively low-cost way for automakers to reduceexhaust emissions to comply with tightening regulations while providing better "driveability" (easy starting, smooth running, no engine stuttering) than could be obtained with a carburettor. Many of the carburettor's supporting components—such as the air filter, intake manifold, and fuel line routing—could be used with few or no changes. 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.In the US, the G10 engine in the 2000 Chevrolet Metro became the last engine available on an American-sold vehicle to use throttle body injection.
In indirect-injected diesel engines (as well as Akroyd engines), there are two combustion chambers: the main combustion chamber, and apre-chamber (also called an ante-chamber)[18] that is connected to the main one. The fuel is injected only into the pre-chamber (where it begins to combust), and not directly into the main combustion chamber. Therefore, this principle is calledindirect injection. There exist several slightly different indirect injection systems that have similar characteristics.[19]
Types of indirect injection used by diesel engines include:
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 390–490 kPa (57–71 psi) to 6,400 kPa (920 psi).[23]: 415 In the meantime, the first manifold injection system was designed by Johannes Spiel in 1884, while working atHallesche Maschinenfabrik in Germany.[24]
In 1891, the BritishHerbert-Akroyd oil engine became the first engine to use a pressurised fuel injection system.[25][26] This design, called ahot-bulb engine used a 'jerk pump' to dispensefuel oil at high pressure to an injector. Another development in early diesel engines was the pre-combustion chamber, which was invented in 1919 by Prosper l'Orange[27] to avoid the drawbacks of air-blast injection systems. The pre-combustion chamber made it feasible to produce engines in size suitable for automobiles andMAN Truck & Bus presented the first direct-injected diesel engine for trucks in 1924.[20] Higher pressure diesel injection pumps were introduced byBosch in 1927.
In 1898, German companyDeutz AG started producing four-stroke petrolstationary engines[28] with manifold injection.[citation needed] The 1906Antoinette 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 1925Hesselman 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 astratified charge principle whereby fuel is injected towards the end of the compression stroke, then ignited with aspark plug.
TheCumminsModel H diesel truck engine was introduced in America in 1933.[33] In 1936, theMercedes-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]
DuringWorld War II, several petrol engines for aircraft used direct-injection systems, such as the EuropeanJunkers Jumo 210,Daimler-Benz DB 601,BMW 801, and theShvetsov ASh-82FN (M-82FN). The German direct-injection systems were based on diesel injection systems used by Bosch, Deckel, Junkers and l'Orange.[35] By around 1943, theRolls-Royce Merlin andWright R-3350 had switched from traditional carburettors to fuel-injection (called "pressure carburettors" at the time), however these engines used throttle bodymanifold injection, rather than the direct-injection systems of the German engines. From 1940, theMitsubishi Kinsei 60 series engine used a direct-injection system, along with the relatedMitsubishi Kasei engine from 1941. In 1943, a low-pressure fuel injection system was added to theNakajima Homare Model 23 radial engine.[36]
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 1950Goliath GP700 small saloon, it was also added to theGutbrod Superior engine in 1952. This mechanically-controlled system was essentially a specially lubricated high-pressure diesel direct-injection pump of the type that is governed by the vacuum behind an intake throttle valve.[37] A Bosch mechanical direct-injection system was also used in the straight-eight used in the 1954Mercedes-Benz W196 Formula One racing car. The first four-stroke direct-injection petrol engine for a passenger car was released the following year, in theMercedes-Benz 300SL sports car.[38] However the engine suffered lubrication problems due to petrol diluting the engine oil,[39][40] and subsequent Mercedes-Benz engines switched to a manifold injection design. Likewise, most petrol injection systems prior to the 2000s used the less-expensive manifold injection design.
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 the1957 24 Hours of Le Mans, the 1st to 4th placed cars wereJaguar D-Type entries using a Lucas fuel injection system.[42] Also in 1957, General Motors introduced theRochester 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 byHilborn,[43]SPICA[44] andKugelfischer.
Up until this time, the fuel injection systems had used a mechanical control system. In 1957, the AmericanBendix Electrojector system was introduced, which used analogue electronics for the control system. The Electrojector was intended to be available for theRambler Rebel mid-size car, however reliability problems meant that the fuel injection option was not offered.[45][46][47][48][49] In 1958, theChrysler 300D,DeSoto Adventurer,Dodge D-500 andPlymouth 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 BoschD-Jetronic.[51] The D-Jetronic was produced from 1967-1976 and first used on theVW 1600TL/E. The system was a speed/density system, using engine speed and intake manifold air density to calculate the amount of fuel to be injected. In 1974, Bosch introduced theK-Jetronic system, which used a continuous flow of fuel from the injectors (rather than the pulsed flow of the D-Jetronic system). K-Jetronic was a mechanical injection system, using a plunger actuated by the intake manifold pressure which then controlled the fuel flow to the injectors.[52]
Also in 1974, Bosch introduced theL-Jetronic system, a pulsed flow system which used anair flow meter to calculate the amount of fuel required. L-Jetronic was widely adopted on European cars during the 1970s and 1980s. As a system that uses electronically-controlled fuel injectors which open and close to control the amount of fuel entering the engine, the L-Jetronic system uses the same basic principles as modern electronic fuel injection (EFI) systems.
Prior to 1979, the electronics in fuel injection systems usedanalogue electronics for the control system. TheBosch Motronic multi-point fuel injection system (also amongst the first systems where theignition system is controlled by the same device as the fuel injection system) was the first mass-produced system to usedigital electronics. TheFord 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 eitherport injection orthrottle-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 1954–1959Mercedes-Benz 300 SL – all usedmanifold injection (i.e. the injectors located at the intake ports or throttle body, instead of inside the combustion chamber). This began to change when the first mass-producedpetrol direct injection system for passenger cars was acommon rail system introduced in the 1997Mitsubishi 6G74 V6 engine.[55][56] The first common-rail system for a passenger car diesel engine was theFiat Multijet[broken anchor] straight-four engine,[57] introduced in the 1999Alfa Romeo 156 1.9 JTD model. Since the 2010s, many petrol engines have switched to direct-injection (sometimes in combination with separate manifold injectors for each cylinder). Similarly, many modern diesel engines use a common-rail design.
Stratified charge injection was used in several petrol engines in the early 2000s, such as theVolkswagen 1.4 FSI engine introduced in 2000. However, the stratified charge systems were largely no longer in use by the late 2010s, due to increased exhaust emissions of NOx gasses and particulates, along with the increased cost and complexity of the systems.
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