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 rotary piston engines.
All Diesel (compression-ignition) engines use fuel injection, and many Otto (spark-ignition) engines use fuel injection of one kind or another. Mass-produced Diesel engines for passenger cars (such as the Mercedes-Benz OM 138) became available in the late 1930s and early 1940s,being the first fuel injected engines for passenger car use. In passenger car petrol engines, fuel injection was introduced in the early 1950s, and gradually gained prevalence until it had largely replaced carburetors by the early 1990s. The primary difference between carburetion and fuel injection is that fuel injection atomizes the fuel through a small nozzle under high pressure, while a carburetor relies on suction created by intake air accelerated through a Venturi tube to draw the fuel into the airstream.
The term "fuel injection" is vague and comprises various distinct systems with fundamentally different functional principles. Typically, the only thing in common all fuel injection systems have is the lack of carburetion. There are two main functional principles of mixture formation systems for internal combustion engines: internal mixture formation, and external mixture formation. A fuel injection system that uses external mixture formation is called a manifold injection system; there exist two types of manifold injection systems: multi-point injection (port injection), and single-point injection (throttle-body injection). Internal mixture formation systems can be separated into direct, and indirect injection systems. There exist several different varieties of both direct and indirect injection systems, the most common internal mixture formation fuel injection system is the common-rail injection system, a direct injection system. The term electronic fuel injection refers to any fuel injection system having an engine control unit.
An ideal fuel injection system can precisely provide exactly the right amount of fuel under all engine operating conditions. This typically means a precise air-fuel-ratio (lambda) control, which allows, for instance: easy engine operation even at low engine temperatures (cold start), good adaptation to a wide range of altitudes and ambient temperatures, exactly governed engine speed (including idle and redline speeds), good fuel efficiency, and the lowest achievable exhaust emissions (because it allows emissions control devices such as a three-way catalyst to function properly).
In practice an ideal fuel injection system does not exist, but there is a huge variety of different fuel injection systems with certain advantages and disadvantages. Most of these systems were rendered obsolete by the common-rail direct injection system that is nowadays (2020) used in many passenger cars. Common-rail injection allows petrol direct injection, and is even better suited for diesel engine fuel direct injection. However, common-rail injection is a relatively complex system, which is why in some passenger cars that do not use diesel engines, a multi-point manifold injection system is used instead.
When designing a fuel injection system, a variety of factors has to be taken into consideration, including:
All fuel injection systems comprise three basic components: they have at least one fuel injector (sometimes called an injection valve), a device that creates sufficient injection pressure, and a device that meters the correct amount of fuel. These three basic components can either be separate devices (fuel injector(s), fuel distributor, fuel pump), partially combined devices (injection valve and an injection pump), or completely combined devices (unit injector). Early mechanical injection systems (except air-blast injection) typically used injection valves (with needle nozzles) in combination with a single (or more than one) relatively sophisticated helix-controlled injection pump(s) that both metered the fuel, and created the injection pressure. They were well-suited for intermittently injecting multi-point injection systems as well as all sorts of conventional direct injection systems, and chamber-injected systems. Advancements in the field of microelectronics allowed injection system manufacturers to significantly improve the accuracy of the fuel metering device. In modern engines, the fuel metering and injection valve actuation is usually done by the engine control unit. Therefore, the fuel injection pump does not have to meter the fuel or actuate the injection valves; it only needs to provide injection pressure. These modern systems are used in multi-point-injected engines, and common-rail-injected engines. Unit injection systems have made it into series production in the past, but proved to be inferior to common-rail injection.
The overview below illustrates the most common types of mixture formation systems in internal combustion engines. There are several different ways of characterising, grouping and describing fuel injection systems, the clade is based upon a differentiation between internal and external mixture formation systems.
In an engine with external mixture formation, air and fuel are mixed outside the combustion chamber, so that a premixed mixture of air and fuel is sucked into the engine. External mixture formation systems are common in petrol-fueled engines such as the Otto engine, and the Wankel engine. There exist two main external mixture formation systems in internal combustion engines: carburettors, and manifold injection. The following description focuses on the latter. Manifold injection systems can also be considered indirect injection, but this article primarily uses the term indirect injection to describe internal mixture formation systems that are not direct injection. There exist two types of manifold injection: single-point injection, and multi-point injection.They can use several different injection schemes.
Single-point injection uses one injector in a throttle body mounted similarly to a carburetor on an intake manifold. As in a carbureted induction system, the fuel is mixed with the air before the inlet of the intake manifold.Single-point injection was a relatively low-cost way for automakers to reduce exhaust emissions to comply with tightening regulations while providing better "driveability" (easy starting, smooth running, freedom from hesitation) than could be obtained with a carburetor. Many of the carburetor's supporting components - such as the air cleaner, 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.
Multi-point 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. Typically, multi-point injected systems use multiple fuel injectors,but some systems such as the GM central port injection use tubes with poppet valves fed by a central injector instead of multiple injectors.
Manifold injected engines can use several injection schemes: continuous, and intermittent (simultaneous, batched, sequential, and cylinder-individual).
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, 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.
In an engine with an internal mixture formation system, 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). There are two different types of internal mixture formation systems: indirect injection, and direct injection.
This article describes indirect injection as an internal mixture formation system (typical of Akroyd and Diesel engines); for the external mixture formation system that is sometimes called indirect injection (typical of Otto and Wankel engines), this article uses the term manifold injection.
In an indirect injected engine, there are two combustion chambers: a main combustion chamber, and a pre-chamber (also called an ante-chamber)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 called indirect injection. There exist several slightly different indirect injection systems that have similar characteristics. All Akroyd (hot-bulb) engines, and some Diesel (compression ignition) engines use indirect injection.
Direct injection means that an engine only has a single combustion chamber, and that the fuel is injected directly into this chamber.This can be done either with a blast of air (air-blast injection), or hydraulically. The latter method is far more common in automotive engines. Typically, hydraulic direct injection systems spray the fuel into the air inside the cylinder or combustion chamber, but some systems spray the fuel against the combustion chamber walls (M-System). Hydraulic 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 is well-suited for a huge variety of fuels, including petrol (see petrol direct injection), and diesel fuel.
In a common rail system, the fuel from the fuel tank is supplied to the common header (called the accumulator). This fuel is then sent through tubing to the injectors, which inject it into the combustion chamber. The header has a high pressure relief valve to maintain the pressure in the header 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 needle valve, operated with a solenoid. When the solenoid is not activated, the spring forces the needle valve into the nozzle passage and prevents the injection of fuel into the cylinder. The solenoid lifts the needle valve from the valve seat, and fuel under pressure is sent in the engine cylinder. 300 MPa or 44,000 lbf/in2.Third-generation common rail diesels use piezoelectric injectors for increased precision, with fuel pressures up to
In 1872, George Bailey Brayton obtained a patent on an internal combustion engine that used a pneumatic fuel injection system, also invented by Brayton: the air-blast injection. 4–5 kp/cm2 (390–490 kPa) to 65 kp/cm2 (6,400 kPa).In 1894, Rudolf Diesel copied Brayton's air-blast injection system for the diesel engine, but also improved it. Most notably, Diesel increased the air-blast pressure from
The first manifold injection system was designed by Johannes Spiel at Hallesche Maschinenfabrik in 1884.In the early 1890s, Herbert Akroyd Stuart developed an indirect fuel injection system using a 'jerk pump' to meter out fuel oil at high pressure to an injector. This system was used on the Akroyd engine and was adapted and improved by Bosch and Clessie Cummins for use on diesel engines.
In 1898, Deutz AG started series production of stationary four-stroke Otto engines with manifold injection. Eight years later, Grade equipped their two-stroke engines with manifold injection, and both Léon Levavasseur's Antoinette 8V (the world's first V8 engine of any sort, patented by Levavasseur in 1902), and Wright aircraft engines were fitted with manifold injection as well. The first engine with petrol direct injection was a two-stroke aircraft engine designed by Otto Mader in 1916.
Another early use of petrol direct injection was on the Hesselman engine invented by Swedish engineer Jonas Hesselman in 1925.Hesselman engines use the stratified charge principle; fuel is injected towards the end of the compression stroke, then ignited with a spark plug. They can run on a huge variety of fuels.
The invention of the pre-combustion chamber injection by Prosper l'Orange helped Diesel engine manufacturers to overcome the problems of air-blast injection, and allowed designing small engines for automotive use from the 1920s onwards. In 1924, MAN presented the first direct-injected Diesel engine for lorries.
Direct petrol injection was used in notable World War II aero-engines such as the Junkers Jumo 210, the Daimler-Benz DB 601, the BMW 801, the Shvetsov ASh-82FN (M-82FN). German direct injection petrol engines used injection systems developed by Bosch, Deckel, Junkers and l'Orange from their diesel injection systems.Later versions of the Rolls-Royce Merlin and Wright R-3350 used single point injection, at the time called "Pressure Carburettor". Due to the wartime relationship between Germany and Japan, Mitsubishi also had two radial aircraft engines using petrol direct injection, the Mitsubishi Kinsei and the Mitsubishi Kasei.
The first automotive direct injection system used to run on petrol was developed by Bosch, and was introduced by Goliath for their Goliath GP700, and Gutbrod for their Superior in 1952. This was basically a specially lubricated high-pressure diesel direct-injection pump of the type that is governed by the vacuum behind an intake throttle valve.The 1954 Mercedes-Benz W196 Formula 1 racing car engine used Bosch direct injection derived from wartime aircraft engines. Following this racetrack success, the 1955 Mercedes-Benz 300SL, became the first passenger car with a four-stroke Otto engine that used direct injection. Later, more mainstream applications of fuel injection favored the less-expensive manifold injection.
Throughout the 1950s, several manufacturers introduced their manifold injection systems for Otto engines, including General Motors' Rochester Products Division, Bosch, and Lucas Industries.During the 1960s, additional manifold injection systems such as the Hilborn, Kugelfischer, and SPICA systems were introduced.
The first commercial electronicially controlled manifold injection system was the Electrojector developed by Bendix and was offered by American Motors Corporation (AMC) in 1957.Initial problems with the Electrojector meant only pre-production cars had it installed so very few cars were sold and none were made available to the public. The EFI system in the Rambler worked well in warm weather, but was difficult to start in cooler temperatures.
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.The Electrojector patents were subsequently sold to Bosch, who developed the Electrojector into the Bosch D-Jetronic. The D in D-Jetronic stands for Druckfühlergesteuert, German for "pressure-sensor controlled"). The D-Jetronic was first used on the VW 1600TL/E 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.
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 L-Jetronic uses a mechanical airflow meter (L for Luft, German for "air") that produces a signal that is proportional to volume flow rate. This approach required additional sensors to measure the atmospheric pressure and temperature, to calculate mass flow rate. L-Jetronic was widely adopted on European cars of that period, and a few Japanese models a short time later.
The first digital engine management system (engine control unit) was the Bosch Motronic introduced in 1979. In 1980, Motorola (now NXP Semiconductors) introduced their digital ECU EEC-III.The EEC-III a single-point injection system.
Manifold 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 petrol passenger cars sold in first world markets are equipped with electronic manifold injection. The carburetor remains in use in developing countries where vehicle emissions are unregulated and diagnostic and repair infrastructure is sparse. Fuel injection systems are 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.
In 1995, Mitsubishi presented the first common-rail petrol direct injection system for passenger cars. It was introduced in 1997.Subsequently, common-rail direct injection was also introduced in passenger car diesel engines, with the Fiat 1.9 JTD being the first mass market engine. In the early 2000s, several car manufacturers attempted to use stratified charge concepts in their direct injection petrol engines to reduce fuel consumption. However, the fuel savings proved to be almost unnoticeable and disproportionate to the increased complexity of the exhaust gas treatment systems. Therefore, almost all car manufacturers have switched to a conventional homogeneous mixture in their direct injected petrol engines since the mid 2010s. In the early 2020s, some car manufacturers have still been using manifold injection, especially in economy cars, but also some high performance cars. Ever since 1997, car manufacturers have been using common-rail direct injection for their diesel engines. Only Volkswagen used the Pumpe-Düse system throughout the early 2000s, but they have also been using common-rail direct injection since 2010.
The diesel engine, named after Rudolf Diesel, is an internal combustion engine in which ignition of the fuel is caused by the elevated temperature of the air in the cylinder due to the mechanical compression; thus, the diesel engine is a so-called compression-ignition engine. This contrasts with engines using spark plug-ignition of the air-fuel mixture, such as a petrol engine or a gas engine.
A stratified charge engine describes a certain type of internal combustion engine, usually spark ignition (SI) engine that can be used in trucks, automobiles, portable and stationary equipment. The term "stratified charge" refers to the working fluids and fuel vapors entering the cylinder. Usually the fuel is injected into the cylinder or enters as a fuel rich vapor where a spark or other means are used to initiate ignition where the fuel rich zone interacts with the air to promote complete combustion. A stratified charge can allow for slightly higher compression ratios without "knock," and leaner air/fuel ratio than in conventional internal combustion engines.
A naturally aspirated engine, also known as a normally aspirated engine or NA, is an internal combustion engine in which air intake depends solely on atmospheric pressure and does not have forced induction through a turbocharger or a supercharger. Many sports cars specifically use naturally aspirated engines to avoid turbo lag.
Indirect injection in an internal combustion engine is fuel injection where fuel is not directly injected into the combustion chamber. In the last decade, gasoline engines equipped with indirect injection systems, wherein a fuel injector delivers the fuel at some point before the intake valve, have mostly fallen out of favor to direct injection. However, certain manufacturers such as Volkswagen, Toyota and Ford have developed a 'dual injection' system, combining direct injectors with port (indirect) injectors, combining the benefits of both types of fuel injection. Direct injection allows the fuel to be precisely metered into the combustion chamber under high pressure which can lead to greater power, fuel efficiency. The issue with direct injection is that it typically leads to greater amounts of particulate matter and with the fuel no longer contacting the intake valves, carbon can accumulate on the intake valves over time. Adding indirect injection keeps fuel spraying on the intake valves, reducing or eliminating the carbon accumulation on intake valves and in low load conditions, indirect injection allows for better fuel-air mixing. This system is mainly used in higher cost models due to the added expense and complexity.
Lean-burn refers to the burning of fuel with an excess of air in an internal combustion engine. In lean-burn engines the air:fuel ratio may be as lean as 65:1. The air / fuel ratio needed to stoichiometrically combust gasoline, by contrast, is 14.64:1. The excess of air in a lean-burn engine emits far less hydrocarbons. High air–fuel ratios can also be used to reduce losses caused by other engine power management systems such as throttling losses.
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 from manifold fuel injection systems, which inject fuel into the intake manifold.
Dieseling or engine run-on is a condition that can occur in spark-plug-ignited, gasoline powered internal combustion engines, whereby the engine keeps running for a short period after being turned off, due to the engine kicking back upon shutdown, drawing fuel through the carburetor, into the engine and igniting it without a spark.
Manifold vacuum, or engine vacuum in an internal combustion engine is the difference in air pressure between the engine's intake manifold and Earth's atmosphere.
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 of the technology offering technological development and refinement.
A backfire or afterburn is combustion or an explosion produced by a running internal combustion engine that occurs in the exhaust system, rather than inside the combustion chamber. It is also sometimes referred to as an afterfire, especially in cases where the word backfire is used to mean a fuel burn that occurs while an intake valve is open, causing the fire to move backward through the system and out through the intake instead of the exhaust. When the flame moves backward it may also be called a "pop-back." A backfire can be caused either by ignition that happens with an exhaust valve open or unburnt fuel making its way in the hot exhaust system. A visible flame may momentarily shoot out of the exhaust pipe. A backfire is often a sign that the engine is improperly-tuned.
Homogeneous Charge Compression Ignition (HCCI) is a form of internal combustion in which well-mixed fuel and oxidizer are compressed to the point of auto-ignition. As in other forms of combustion, this exothermic reaction releases energy that can be transformed in an engine into work and heat.
A glowplug is a heating device used to aid in starting diesel engines. In cold weather, high-speed diesel engines can be difficult to start because the mass of the cylinder block and cylinder head absorb the heat of compression, preventing ignition. Pre-chambered engines use small glowplugs inside the pre-chambers. Direct-injected engines have these glowplugs in the combustion chamber.
Diesel engine runaway is a rare condition affecting diesel engines, in which the engine draws extra fuel from an unintended source and overspeeds at higher and higher RPM and producing up to 10 times the engine's rated output until destroyed by mechanical failure or bearing seizure through lack of lubrication.
The Hesselman engine is a hybrid between a petrol engine and a Diesel engine. It was designed and introduced in 1925 by Swedish engineer Jonas Hesselman (1877-1957). It represented the first use of direct gasoline injection on a spark-ignition engine used to power a road going vehicle. Hesselman engines saw use in heavy trucks and buses in models produced in the 1920s and 1930s.
Internal combustion engines come in a wide variety of types, but have certain family resemblances, and thus share many common types of components.
Air-blast injection is a historical direct injection system for Diesel engines. Unlike modern designs, air-blast injected Diesel engines do not have an injection pump. A simple low-pressure fuel-feed-pump is used instead to supply the injection nozzle with fuel. At injection, a blast of compressed air presses the fuel into the combustion chamber, hence the name air-blast injection. The compressed air comes from compressed-air tanks which feed the injection nozzle. A large crankshaft-driven compressor is used to re-fill these tanks; the size of the compressor and the low rotational frequency of the engine's crankshaft means that air-blast injected Diesel engines are huge in size and mass, this, combined with the problem that air-blast injection does not allow for quick load alteration makes it only suitable for stationary applications and watercraft. Before the invention of precombustion chamber injection, air-blast injection was the only way a properly working internal air fuel mixture system could be built, required for a Diesel engine. During the 1920s, air-blast injection was rendered obsolete by superior injection system designs that allowed much smaller but more powerful engines. Rudolf Diesel was granted a patent on air-blast injection in November 1893.
Bowl Prechamber Ignition, abbreviated BPI, is a combustion process designed for Otto cycle engines running on an air-fuel mixture leaner than stochiometric . Its distinguishing feature is a special type of spark plug, capable of reliably igniting very lean air-fuel mixtures. This spark plug is called prechamber spark plug. The ignition electrodes of this spark plug are housed in a perforated enclosure, the prechamber. At the engine's compression stroke, some fuel is injected into the piston bowl; this fuel is then forced through the small holes into the prechamber due to the high pressure in the cylinder near top dead centre. Inside the prechamber spark plug, the air-fuel mixture is ignitable by the ignition spark. Flame jets occurring due to the small holes in the prechamber then ignite the air-fuel mixture in the main combustion chamber, that would not catch fire using a regular spark plug.
The MAN M-System, also referred to as M-Process and M combustion process, is a direct injection system for Diesel engines. In M-System engines, the fuel is injected onto the walls of the combustion chamber, that is solely located inside the piston, and shaped like a sphere. The M-System was rendered obsolete by modern fuel injection systems for Diesel engines. Due to its particularities, the M-System was only used for stationary applications and commercial vehicle engines, passenger car engines with this design have never been made. The letter M is an abbreviation for the German word Mittenkugelverfahren, meaning centre sphere combustion process.
Manifold injection is a mixture formation system for internal combustion engines with external mixture formation. It is commonly used in engines with spark ignition that use petrol as fuel, such as the Otto engine, and the Wankel engine. 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; this means that there is an even distribution of fuel and air across the combustion chamber, and enough, but not more air present that what is required for the fuel's complete combustion. The injection timing and measuring of the fuel amount can be controlled either mechanically, or electronically. 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, which caused a decline in manifold injection installation in newly produced cars.