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Manifold injection is a mixture formation system for
internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...
s with external mixture formation. It is commonly used in engines with
spark ignition A spark-ignition engine (SI engine) is an internal combustion engine, generally a petrol engine, where the combustion process of the air-fuel mixture is ignited by a spark from a spark plug. This is in contrast to compression-ignition engines, ty ...
that use
petrol Gasoline (; ) or petrol (; ) (see ) is a transparent, petroleum-derived flammable liquid that is used primarily as a fuel in most spark-ignited internal combustion engines (also known as petrol engines). It consists mostly of organic co ...
as fuel, such as the
Otto engine The Otto engine was a large stationary single-cylinder internal combustion four-stroke engine designed by the German Nicolaus Otto. It was a low-RPM machine, and only fired every other stroke due to the Otto cycle, also designed by Otto. Typ ...
, and the
Wankel engine The Wankel engine (, ) is a type of internal combustion engine using an Eccentric (mechanism), eccentric rotary combustion engine, rotary design to convert pressure into rotating motion. It was invented by German engineer Felix Wankel, and desi ...
. In a manifold-injected engine, the fuel is injected into the intake manifold, where it begins forming a combustible air-fuel mixture with the air. As soon as the intake valve opens, the piston starts sucking in the still forming mixture. Usually, this mixture is relatively homogeneous, and, at least in production engines for passenger cars, approximately
stoichiometric Stoichiometry refers to the relationship between the quantities of reactants and products before, during, and following chemical reactions. Stoichiometry is founded on the law of conservation of mass where the total mass of the reactants equal ...
; this means that there is an even distribution of fuel and air across the combustion chamber, and enough, but not more air present than what is required for the fuel's complete combustion. The injection timing and measuring of the fuel amount can be controlled either mechanically (by a fuel distributor), or electronically (by an
engine control unit An engine control unit (ECU), also commonly called an engine control module (ECM), is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It does this by re ...
). Since the 1970s and 1980s, manifold injection has been replacing carburettors in passenger cars. However, since the late 1990s, car manufacturers have started using
petrol direct injection Gasoline direct injection (GDI), also known as petrol direct injection (PDI), is a mixture formation system for internal combustion engines that run on gasoline (petrol), where fuel is injected into the combustion chamber. This is distinct fro ...
, which caused a decline in manifold injection installation in newly produced cars. There are two different types of manifold injection: *the ''multi-point injection'' (MPI) system, also known as ''port injection'', or ''dry manifold system'' *and the ''single-point injection'' (SPI) system, also known as ''throttle-body injection'' (TBI), ''central fuel injection'' (CFI), ''electronic gasoline injection'' (EGI), and ''wet manifold system'' In this article, the terms multi-point injection (MPI), and single-point injection (SPI) are used. In an MPI system, there is one fuel injector per cylinder, installed very close to the intake valve(s). In an SPI system, there is only a single fuel injector, usually installed right behind the throttle valve. Modern manifold injection systems are usually MPI systems; SPI systems are now considered obsolete.


Description

In a manifold injected engine, the fuel is injected with relatively low pressure (70...1470 kPa) into the intake manifold to form a fine fuel vapour. This vapour can then form a combustible mixture with the air, and the mixture is sucked into the cylinder by the piston during the intake stroke. Otto engines use a technique called ''quantity control'' for setting the desired engine
torque In physics and mechanics, torque is the rotational equivalent of linear force. It is also referred to as the moment of force (also abbreviated to moment). It represents the capability of a force to produce change in the rotational motion of th ...
, which means that the amount of mixture sucked into the engine determines the amount of torque produced. For controlling the amount of mixture, a
throttle valve A throttle is the mechanism by which fluid flow is managed by constriction or obstruction. An engine's power can be increased or decreased by the restriction of inlet gases (by the use of a throttle), but usually decreased. The term ''throttle'' ...
is used, which is why quantity control is also called intake air throttling. Intake air throttling changes the amount of air sucked into the engine, which means that if a stoichiometric (\lambda \approx 1) air-fuel mixture is desired, the amount of injected fuel has to be changed along with the intake air throttling. To do so, manifold injection systems have at least one way to measure the amount of air that is currently being sucked into the engine. In mechanically controlled systems with a fuel distributor, a vacuum-driven piston directly connected to the control rack is used, whereas electronically controlled manifold injection systems typically use an
airflow sensor Flow measurement is the quantification of bulk fluid movement. Flow can be measured in a variety of ways. The common types of flowmeters with industrial applications are listed below: * a) Obstruction type (differential pressure or variable area ...
, and a
lambda sensor An oxygen sensor (or lambda sensor, where lambda refers to air–fuel equivalence ratio, usually denoted by λ) or probe or sond, is an electronic device that measures the proportion of oxygen (O2) in the gas or liquid being analysed. It was ...
. Only electronically controlled systems can form the stoichiometric air-fuel mixture precisely enough for a
three-way catalyst A catalytic converter is an exhaust emission control device that converts toxic gases and pollutants in exhaust gas from an internal combustion engine into less-toxic pollutants by catalyzing a redox reaction. Catalytic converters are usually ...
to work sufficiently, which is why mechanically controlled manifold injection systems such as the Bosch K-Jetronic are now considered obsolete.Konrad Reif (ed.): ''Ottomotor-Management'', 4th edition, Springer, Wiesbaden 2014, , p. 101


Main types


Single-point injection

As the name implies, a single-point injected (SPI) engine only has a single fuel injector. It is usually installed right behind the throttle valve in the throttle body. Therefore, single-point injected engines bear very close resemblance to carburetted engines, often having the exact same intake manifolds as their carburetted counterparts. Single-point injection has been a known technology since the 1960s, but has long been considered inferior to carburettors, because it requires an injection pump, and is thus more complicated.Kurt Lohner, Herbert Müller (auth): ''Gemischbildung und Verbrennung im Ottomotor'', in Hans List (ed.): ''Die Verbrennungskraftmaschine'', Band 6, Springer, Wien 1967, , p. 64 Only with the availability of inexpensive digital engine control units ( ECUs) in the 1980s, single-point injection became a reasonable option for passenger cars. Usually, intermittently injecting, low injection pressure (70...100 kPa) systems were used that allowed the use of low-cost electric fuel injection pumps. A very common single-point injection system used in many passenger cars is the
Bosch Mono-Jetronic Bosch may refer to: People * Bosch (surname) * Hieronymus Bosch (c. 1450 – 1516), painter * Van den Bosch, a Dutch toponymic surname * Carl Bosch, a German chemical engineer and nephew of Robert Bosch * Robert Bosch, founder of Robert Bosch GmbH ...
, which German motor journalist
Olaf von Fersen Olaf or Olav (, , or British ; Old Norse: ''Áleifr'', ''Ólafr'', ''Óleifr'', ''Anleifr'') is a Scandinavian and German given name. It is presumably of Proto-Norse origin, reconstructed as ''*Anu-laibaz'', from ''anu'' "ancestor, grand-father" a ...
considers a "combination of fuel injection and carburettor". Single-point injection systems helped car manufacturers to easily upgrade their carburetted engines with a simple and inexpensive fuel injection system. However, single-point injection does not allow forming very precise mixtures required for modern emission regulations, and is thus deemed an obsolete technology in passenger cars.


Multi-point injection

In a multi-point injected engine, every cylinder has its own fuel injector, and the fuel injectors are usually installed in close proximity to the intake valve(s). Thus, the injectors inject the fuel through the open intake valve into the cylinder, which should not be confused with direct injection. Certain multi-point injection systems also use tubes with poppet valves fed by a central injector instead of individual injectors. Typically though, a multi-point injected engine has one fuel injector per cylinder, an electric fuel pump, a fuel distributor, an airflow sensor,Konrad Reif (ed.): ''Ottomotor-Management'', 4th edition, Springer, Wiesbaden 2014, , p. 103 and, in modern engines, an
engine control unit An engine control unit (ECU), also commonly called an engine control module (ECM), is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It does this by re ...
.Bosch (ed.): ''Kraftfahrtechnisches Taschenbuch'', 25th edition, Springer, Wiesbaden 2003, , p. 610 The temperatures near the intake valve(s) are rather high, the intake stroke causes intake air swirl, and there is much time for the air-fuel mixture to form. Therefore, the fuel does not require much atomisation. The atomisation quality is relative to the injection pressure, which means that a relatively low injection pressure (compared with direct injection) is sufficient for multi-point injected engines. A low injection pressure results in a low relative air-fuel velocity, which causes large, and slowly vapourising fuel droplets. Therefore, the injection timing has to be precise if unburnt fuel (and thus high HC emissions) are undesired. Because of this, continuously injecting systems such as the Bosch K-Jetronic are obsolete. Modern multi-point injection systems use electronically controlled intermittent injection instead.


Injection controlling mechanism

In manifold injected engines, there are three main methods of metering the fuel, and controlling the injection timing.


Mechanical controlling

In early manifold injected engines with fully mechanical injection systems, a gear-, chain- or belt-driven injection pump with a mechanic "analogue" engine map was used. This allowed injecting fuel intermittently, and relatively precisely. Typically, such injection pumps have a three-dimensional cam that depicts the engine map. Depending on the throttle position, the three-dimensional cam is moved axially on its shaft. A roller-type pick-up mechanism that is directly connected to the injection pump control rack rides on the three-dimensional cam. Depending upon the three-dimensional cam's position, it pushes in or out the camshaft-actuated injection pump plungers, which controls both the amount of injected fuel, and the injection timing. The injection plungers both create the injection pressure, and act as the fuel distributors. Usually, there is an additional adjustment rod that is connected to a barometric cell, and a cooling water thermometer, so that the fuel mass can be corrected according to air pressure, and water temperature.Kurt Lohner, Herbert Müller (auth): ''Gemischbildung und Verbrennung im Ottomotor'', in Hans List (ed.): ''Die Verbrennungskraftmaschine'', Band 6, Springer, Wien 1967, , p. 233 Kugelfischer injection systems also have a mechanical centrifugal crankshaft speed sensor.Kurt Lohner, Herbert Müller (auth): ''Gemischbildung und Verbrennung im Ottomotor'', in Hans List (ed.): ''Die Verbrennungskraftmaschine'', Band 6, Springer, Wien 1967, , p. 234 Multi-point injected systems with mechanical controlling were used until the 1970s.


No injection-timing controlling

In systems without injection-timing controlling, the fuel is injected continuously, thus, no injection timing is required. The biggest disadvantage of such systems is that the fuel is also injected when the intake valves are closed, but such systems are much simpler and less expensive than mechanical injection systems with engine maps on three-dimensional cams. Only the amount of injected fuel has to be determined, which can be done very easily with a rather simple fuel distributor that is controlled by an intake manifold vacuum-driven airflow sensor. The fuel distributor does not have to create any injection pressure, because the fuel pump already provides pressure sufficient for injection (up to 500 kPa). Therefore, such systems are called "unpowered", and do not need to be driven by a chain or belt, unlike systems with mechanical injection pumps. Also, an engine control unit is not required.Konrad Reif (ed.): ''Ottomotor-Management'', 4th edition, Springer, Wiesbaden 2014, , p. 302 "Unpowered" multi-point injection systems without injection-timing controlling such as the Bosch K-Jetronic were used from the mid-1970s until the early 1990s in passenger cars.


Electronic control unit

Engines with manifold injection, and an electronic
engine control unit An engine control unit (ECU), also commonly called an engine control module (ECM), is a type of electronic control unit that controls a series of actuators on an internal combustion engine to ensure optimal engine performance. It does this by re ...
are often referred to as engines with electronic fuel injection (EFI). Typically, EFI engines have an engine map built into discrete electronic components, such as
read-only memory Read-only memory (ROM) is a type of non-volatile memory used in computers and other electronic devices. Data stored in ROM cannot be electronically modified after the manufacture of the memory device. Read-only memory is useful for storing sof ...
. This is both more reliable and more precise than a three-dimensional cam. The engine control circuitry uses the engine map, as well as airflow, throttle valve, crankshaft speed, and intake air temperature sensor data to determine both the amount of injected fuel, and the injection timing. Usually, such systems have a single, pressurised fuel rail, and injection valves that open according to an electric signal sent from the engine control circuitry. The circuitry can either be fully analogue, or digital. Analogue systems such as the
Bendix Electrojector The Bendix Electrojector is an electronically controlled manifold injection (EFI) system developed and made by Bendix Corporation. In 1957, American Motors (AMC) offered the Electrojector as an option in some of their cars; Chrysler followed in 1 ...
were niche systems, and used from the late 1950s until the early 1970s; digital circuitry became available in the late 1970s, and has been used in electronic engine control systems since. One of the first widespread digital engine control units was the Bosch
Motronic Motronic is the trade name given to a range of digital engine control units developed by Robert Bosch GmbH (commonly known as Bosch) which combined control of fuel injection and ignition in a single unit. By controlling both major systems in a si ...
.


Air mass determination

In order to mix air and fuel correctly so a proper air-fuel mixture is formed, the injection control system needs to know how much air is sucked into the engine, so it can determine how much fuel has to be injected accordingly. In modern systems, an air-mass meter that is built into the throttle body meters the air mass, and sends a signal to the engine control unit, so it can calculate the correct fuel mass. Alternatively, a manifold vacuum sensor can be used. The manifold vacuum sensor signal, the throttle position, and the crankshaft speed can then be used by the engine control unit to calculate the correct amount of fuel. In modern engines, a combination of all these systems is used. Mechanical injection controlling systems as well as unpowered systems typically only have an intake manifold vacuum sensor (a membrane or a sensor plate) that is mechanically connected to the injection pump rack or fuel distributor.Kurt Lohner, Herbert Müller (auth): ''Gemischbildung und Verbrennung im Ottomotor'', in Hans List (ed.): ''Die Verbrennungskraftmaschine'', Band 6, Springer, Wien 1967, , p. 229


Injection operation modes

Manifold injected engines can use either continuous or intermittent injection. In a continuously injecting system, the fuel is injected continuously, thus, there are no operating modes. In intermittently injecting systems however, there are usually four different operating modes.Konrad Reif (ed.): ''Ottomotor-Management'', 4th edition, Springer, Wiesbaden 2014, , p. 107


Simultaneous injection

In a simultaneously intermittently injecting system, there is one single, fixed injection timing for all cylinders. Therefore, the injection timing is ideal only for some cylinders; there is always at least one cylinder that has its fuel injected against the closed intake valve(s). This causes fuel evaporation times that are different for each cylinder.


Group injection

Systems with intermittent group injection work similarly to the simultaneously injection systems mentioned earlier, except that they have two or more groups of simultaneously injecting fuel injectors. Typically, a group consists of two fuel injectors. In an engine with two groups of fuel injectors, there is an injection every half crankshaft rotation, so that at least in some areas of the engine map no fuel is injected against a closed intake valve. This is an improvement over a simultaneously injecting system. However, the fuel evaporation times are still different for each cylinder.


Sequential injection

In a sequentially injecting system, each fuel injector is a fixed, correctly set, injection timing that is in sync with the spark plug firing order, and the intake valve opening. This way, no more fuel is injected against closed intake valves.


Cylinder-specific injection

Cylinder-specific injection means that there are no limitations to the injection timing. The injection control system can set the injection timing for each cylinder individually, and there is no fixed synchronisation between each cylinder's injector. This allows the injection control unit to inject the fuel not only according to firing order, and intake valve opening intervals, but it also allows it to correct cylinder charge irregularities. This systems disadvantage is that it requires cylinder-specific air-mass determination, which makes it more complicated than a sequentially injecting system.


History

The first manifold injection system was designed by Johannes Spiel at Hallesche Maschinenfabrik. Deutz started series production of stationary four-stroke engines with manifold injection in 1898. Grade built the first two-stroke engine with manifold injection in 1906; the first manifold injected series production four-stroke aircraft engines were built by Wright and Antoinette the same year (
Antoinette 8V The Antoinette 8V was an early French eight-cylinder, liquid-cooled, V engine, the first series production gasoline-fueled, spark plug ignition engine of any kind produced with manifold injection. It was typically rated at . First produced in ...
).Richard van Basshuysen (ed.): ''Ottomotor mit Direkteinspritzung und Direkteinblasung: Ottokraftstoffe, Erdgas, Methan, Wasserstoff'', 4th edition, Springer, Wiesbaden 2017, , p. 7 In 1912, Bosch equipped a watercraft engine with a makeshift injection pump built from an oil pump, but this system did not prove to be reliable. In the 1920s, they attempted to use a Diesel engine injection pump in a petrol-fuelled Otto engine. However, they were not successful. In 1930 Moto Guzzi built the first manifold injected Otto engine for motorcycles, which eventually was the first land vehicle engine with manifold injection.Olaf von Fersen (ed.): ''Ein Jahrhundert Automobiltechnik. Personenwagen'', VDI-Verlag, Düsseldorf 1986, . p. 257 From the 1930s until the 1950s, manifold injections systems were not used in passenger cars, despite the fact that such systems existed. This was because the carburettor proved to be a simpler and less expensive, yet sufficient mixture formation system that did not need replacing yet. In ca. 1950,
Daimler-Benz The Mercedes-Benz Group Aktiengesellschaft, AG (previously named Daimler-Benz, DaimlerChrysler and Daimler) is a German Multinational corporation, multinational automotive corporation headquartered in Stuttgart, Baden-Württemberg, Germany. It ...
started development of a petrol direct injection system for their Mercedes-Benz sports cars. For passenger cars however, a manifold injection system was deemed more feasible. Eventually, the Mercedes-Benz W 128, W 113, W 189, and W 112 passenger cars were equipped with manifold injected Otto engines.Kurt Lohner, Herbert Müller (auth): ''Gemischbildung und Verbrennung im Ottomotor'', in Hans List (ed.): ''Die Verbrennungskraftmaschine'', Band 6, Springer, Wien 1967, , p. 230Kurt Lohner, Herbert Müller (auth): ''Gemischbildung und Verbrennung im Ottomotor'', in Hans List (ed.): ''Die Verbrennungskraftmaschine'', Band 6, Springer, Wien 1967, , p. 231 From 1951 until 1956, FAG Kugelfischer Georg Schäfer & Co. developed the mechanical Kugelfischer injection system. It was used in many passenger cars, such as the
Peugeot 404 The Peugeot 404 is a large family car produced by French automobile manufacturer Peugeot from 1960 to 1975. A truck body style variant was marketed until 1988. Styled by Pininfarina, the 404 was offered initially as a saloon, estate, and pickup ...
(1962),
Lancia Flavia The Lancia Flavia (Tipo 815/819/820) is an executive car produced by Lancia in Italy from 1961 to 1971. Production continued as the Lancia 2000 from 1971 to 1975. The Flavia was launched with a 1,500 cc engine at the 1960 Turin Motor Sho ...
iniezione (1965),
BMW E10 The BMW 02 Series is a range of compact executive cars produced by German automaker BMW between 1966 and 1977, based on a shortened version of the New Class Sedans. The first 02 Series produced was the 1600-2 (later renamed 1602) in 1966. In 1 ...
(1969), Ford Capri RS 2600 (1970),
BMW E12 The BMW E12 is the first generation of 5 Series executive cars, which was produced from 1972 to 1981 and replaced the saloon models of the BMW New Class range. Initial models were powered by inline-four engines, using either a carburettor or fue ...
(1973),
BMW E20 The BMW 02 Series is a range of compact executive cars produced by German automaker BMW between 1966 and 1977, based on a shortened version of the New Class Sedans. The first 02 Series produced was the 1600-2 (later renamed 1602) in 1966. In 1 ...
(1973), and the BMW E26 (1978).Olaf von Fersen (ed.): ''Ein Jahrhundert Automobiltechnik. Personenwagen'', VDI-Verlag, Düsseldorf 1986, . p. 258 In 1957,
Bendix Corporation Bendix Corporation is an American manufacturing and engineering company which, during various times in its existence, made automotive brake shoes and systems, vacuum tubes, aircraft brakes, aeronautical hydraulics and electric power systems, av ...
presented the
Bendix Electrojector The Bendix Electrojector is an electronically controlled manifold injection (EFI) system developed and made by Bendix Corporation. In 1957, American Motors (AMC) offered the Electrojector as an option in some of their cars; Chrysler followed in 1 ...
, one of the first electronically controlled manifold injection systems.Kurt Lohner, Herbert Müller (auth): ''Gemischbildung und Verbrennung im Ottomotor'', in Hans List (ed.): ''Die Verbrennungskraftmaschine'', Band 6, Springer, Wien 1967, , p. 243 Bosch built this system under licence, and marketed it from 1967 as the D-Jetronic. In 1973, Bosch introduced their first self-developed multi-point injection systems, the electronic
L-Jetronic Jetronic is a trade name of a manifold injection technology for automotive petrol engines, developed and marketed by Robert Bosch GmbH from the 1960s onwards. Bosch licensed the concept to many automobile manufacturers. There are several variation ...
, and the mechanical, unpowered
K-Jetronic Jetronic is a trade name of a manifold injection technology for automotive petrol engines, developed and marketed by Robert Bosch GmbH from the 1960s onwards. Bosch licensed the concept to many automobile manufacturers. There are several variations ...
.Konrad Reif (ed.): ''Ottomotor-Management'', 4th edition, Springer, Wiesbaden 2014, , p. 289 Their fully digital
Motronic Motronic is the trade name given to a range of digital engine control units developed by Robert Bosch GmbH (commonly known as Bosch) which combined control of fuel injection and ignition in a single unit. By controlling both major systems in a si ...
system was introduced in 1979. It found widespread use in German luxury saloons. At the same time, most American car manufacturers stuck to electronic single-point injection systems.Olaf von Fersen (ed.): ''Ein Jahrhundert Automobiltechnik. Personenwagen'', VDI-Verlag, Düsseldorf 1986, . p. 262 In the mid-1980s, Bosch upgraded their non-Motronic multi-point injection systems with digital engine control units, creating the KE-Jetronic, and the LH-Jetronic. Volkswagen developed the digital "Digijet" injection system for their "Wasserboxer" water-cooled engines, which evolved into the Volkswagen Digifant system in 1985.Olaf von Fersen (ed.): ''Ein Jahrhundert Automobiltechnik. Personenwagen'', VDI-Verlag, Düsseldorf 1986, . p. 263 Cheap single-point injection systems that worked with either two-way or three-way catalyst converters, such as the Mono-Jetronic introduced in 1987, enabled car manufacturers to economically offer an alternative to carburettors even in their economy cars, which helped the extensive spread of manifold injection systems across all passenger car market segments during the 1990s.Konrad Reif (ed.): ''Ottomotor-Management'', 4th edition, Springer, Wiesbaden 2014, , p. 288 In 1995, Mitsubishi introduced the first petrol direct injection Otto engine for passenger cars, and the petrol direct injection has been replacing the manifold injection since, but not across all market segments; several newly produced passenger car engines still use multi-point injection.Konrad Reif (ed.): ''Ottomotor-Management'', 4th edition, Springer, Wiesbaden 2014, , p. 3


References

{{Aircraft piston engine components Engine components Fuel injection systems