Rajan Wilcox
Fuel flow injectors are a part of the fuel injection system, which is used to introduce fuel into an internal combustion engine. The injectors spray pressurised fuel into the engine's cylinders, where it combusts, allowing the engine to run. The amount of fuel injected is carefully controlled to maintain the correct fuel-air mixture and keep the engine running smoothly and efficiently. Fuel injection systems can be continuous, where fuel is sprayed at all times, or intermittent, where fuel is delivered in bursts.
| Characteristics | Values |
|---|---|
| Purpose | To introduce fuel into an internal combustion engine, most commonly automotive engines |
| Mechanism | Fuel is pumped at high pressure from the tank to a fuel accumulator, then passes into the fuel distributor, which sends a burst of fuel to each injector, from where it is fired into the inlet port |
| Types | Continuous injection, intermittent injection, timed injection, multi-port fuel injection, throttle body fuel injection |
| Continuous Injection | Fuel flows at all times from the fuel injectors, but at a variable flow rate |
| Intermittent Injection | Fuel is delivered in bursts to coincide with the induction stroke of the cylinder |
| Timed Injection | Controlled either mechanically or electronically |
| Multi-port Fuel Injection | Fuel injector for each cylinder, usually located so they spray at the intake valve |
| Throttle Body Fuel Injection | Also known as single-point or central fuel injection systems; electrically controlled fuel-injector valves are incorporated into the throttle body |
| Fuel Flow | Determined by the amount of time the fuel injector stays open, called the pulse width, and controlled by the ECU |
| Fuel Atomization | Fuel is atomized through a small nozzle under high pressure, creating a fine spray that can burn easily |
| Fuel/Air Mixture | Sensors monitor the mass of air entering the engine and the amount of oxygen in the exhaust to ensure the correct fuel/air mixture |
| Emissions | Fuel injectors help meet stricter emissions requirements by allowing for very careful control of the air-to-fuel ratio |
| Performance | Engines with fuel injectors are more efficient, powerful, and economical, with reduced poisonous emissions |
| Applications | Used in both gasoline and E85 applications, including in NASCAR race cars |
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What You'll Learn
- Fuel injectors are the primary means of getting gasoline into the engine cylinder
- The Bosch K-Jetronic system is the most common continuous injection system
- Fuel injection systems use either continuous or intermittent injection
- Direct injection can be achieved with a helix-controlled pump, unit injectors, or a common-rail system
- Fuel injectors atomize fuel through a small nozzle under high pressure
Fuel injectors are the primary means of getting gasoline into the engine cylinder
Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of a fuel injector. All compression-ignition engines (e.g. diesel engines) and many spark-ignition engines (i.e. petrol (gasoline) engines) use fuel injection. Fuel injectors atomize the fuel through a small nozzle under high pressure, creating a fine spray or mist that can burn easily. The amount of fuel sprayed is controlled by a mechanical or electrical control unit.
There are two popular fuel injection systems. The first is a continuous injection system, where the fuel is squirted into the inlet port all the time the engine is running. The second is timed injection (pulsed injection), where the fuel is delivered in bursts to coincide with the induction stroke of the cylinder. As with continuous injection, timed injection can also be controlled either mechanically or electronically.
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. In 1974, Bosch also introduced the L-Jetronic system, a pulsed flow system that used an air flow meter to calculate the amount of fuel required. This system was widely adopted on European cars during the 1970s and 1980s.
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The Bosch K-Jetronic system is the most common continuous injection system
Fuel injection is the introduction of fuel into an internal combustion engine, most commonly automotive engines, by means of a fuel injector. All compression-ignition engines (e.g. diesel engines) and many spark-ignition engines (i.e., petrol engines) use fuel injection. The Bosch K-Jetronic system, introduced in 1974, is the most common automotive continuous injection system. It is a mechanical injection system that uses a plunger actuated by the intake manifold pressure to control the fuel flow to the injectors. The system was used by various car manufacturers until the mid-1990s.
The K-Jetronic system is a form of mechanical fuel injection. It is a Continuous Injection System (CIS) where, unlike later L-Jetronic or "standard" Electronic Fuel Injection, the injectors do not pulse open and closed. Instead, once the system pressure is high enough, they all inject a constant spray of fuel, in all cylinders at once, with the volume varied by the system depending on various factors. The main moving part is a central plunger that is controlled by the air sensor plate. When the throttle is opened, the increase of air into the manifold causes the air sensor plate to rise and push the control plunger, which allows fuel to flow to the injectors. The K-Jetronic system is different from pulsed injection systems in that the fuel flows continuously from all injectors, while the fuel pump pressurises the fuel up to approximately 5 bar (73.5 psi). The volume of air taken in by the engine is measured to determine the amount of fuel to inject.
The K-Jetronic system was first used in the 1973.5 Porsche 911T in January 1973. It was later installed in a number of Porsche, Volkswagen, Audi, BMW, Mercedes-Benz, Rolls-Royce, Bentley, Lotus, Ferrari, Peugeot, Nissan, Renault, Volvo, Saab, TVR, and Ford automobiles. The final car to use the K-Jetronic system was the 1994 Porsche 911 Turbo 3.6. The system is known for its reliability and robustness, with fewer potential points of failure compared to other systems.
The Bosch K-Jetronic system has been described as a black art, with some people expressing hesitation or confusion about it. However, it is a well-engineered and effective fuel injection system that, when properly maintained and understood, can perform reliably and efficiently.
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Fuel injection systems use either continuous or intermittent injection
Fuel injection is the introduction of fuel into an internal combustion engine, most commonly an automotive engine, by means of a fuel injector. Fuel injection systems use either continuous or intermittent injection.
Continuous Injection
In a continuous injection system, fuel flows at all times from the fuel injectors, but at a variable flow rate. The injector acts as a spray nozzle to break up the fuel into a fine spray but does not control the fuel flow. The amount of fuel sprayed is increased or decreased by a mechanical or electrical control unit. 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
Intermittent injection systems can be sequential, batched, simultaneous, or cylinder-individual. In a sequential system, injection is timed to coincide with each cylinder's intake stroke. Batched injection involves injecting fuel to the cylinders in groups, without precise synchronization to any particular cylinder's intake stroke. In a simultaneous system, fuel is injected at the same time to all the cylinders, while in a cylinder-individual system, the engine control unit can adjust the injection for each cylinder individually.
Fuel Injectors
Fuel injectors are devices that deliver fuel into the engine. They can be mechanically or electronically controlled. In a mechanical system, the injector is spring-loaded into the closed position and is opened by fuel pressure. In an electronic system, the injector is held closed by a spring and opened by an electromagnet built into the injector body. The electronic control unit determines how long the injector stays open. Fuel injectors that control the metering are called injection valves, while those that perform all three functions (metering, injection, and ignition control) are called unit injectors.
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Direct injection can be achieved with a helix-controlled pump, unit injectors, or a common-rail system
Fuel injection is the introduction of fuel into an internal combustion engine, most commonly automotive engines, via a fuel injector. Direct injection is one method of fuel injection, and it can be achieved with a helix-controlled pump, unit injectors, or a common-rail system.
A helix-controlled pump is a type of fuel injection pump used in internal combustion engines, particularly in commercial vehicles. This system features a piston pump cylinder with control edges that regulate the supply of fuel to the pump working space via a fuel bore in the pump cylinder. The helix-controlled pump requires a significant constructional effort and overall height due to the presence of a pre-injection piston and spring arrangement.
Unit injectors are another method of direct injection, but limited information is available on this system.
The common-rail system is the most common method of direct injection in modern automotive engines. In this system, fuel from the fuel tank is supplied to a common header (the accumulator) and then sent through tubing to the injectors, which inject it into the combustion chambers. The accumulator maintains pressure through a high-pressure relief valve and returns excess fuel to the fuel tank. This system provides flexibility in emission control, power, and fuel consumption, making it advantageous for meeting stringent emission standards.
In addition to these three methods, direct injection can also be achieved through other systems such as the Bosch K-Jetronic, which was introduced in 1974 and used a continuous flow of fuel from the injectors.
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Fuel injectors atomize fuel through a small nozzle under high pressure
Fuel injection is the introduction of fuel into an internal combustion engine, most commonly an automotive engine, by means of a fuel injector. The primary difference between carburetion and fuel injection is that fuel injection atomizes the fuel through a small nozzle under high pressure, while carburetion relies on suction created by intake air. Fuel injectors are effectively spray nozzles that perform 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 injection nozzles can be categorized as hole-type or throttling pintle type and as either closed or open. Closed nozzles can be actuated hydraulically using a simple spring-biased mechanism or using servo control. Open nozzles, as well as some newer closed nozzle injector designs, can be directly actuated. Metering of the injected fuel amount is commonly carried out in either the high-pressure pump or the fuel injector. A number of different fuel metering approaches exist, including pressure metered at a constant time interval (PT), time metered at a constant pressure (TP), and time/stroke metered (TS). Most fuel injection systems use electronics to control the opening and closing of the nozzle. Electrical signals are converted into mechanical forces using some type of actuator, such as electromagnetic solenoids or active materials like piezoelectric ceramics.
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 chambers. The accumulator has a high-pressure relief valve to maintain pressure and return 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. The nozzle is an important component of the fuel injection system, as its shape and design can impact the spray pattern and efficiency of the engine. For example, the presence of a sac in the nozzle is important for equalizing fuel pressure and producing good quality sprays, but it can also lead to increased emissions if fuel is left in the sac after combustion.
The first system of fuel injection uses continuous injection, where the fuel is squirted into the inlet port all the time the engine is running. The injector acts as a spray nozzle to break up the fuel into a fine spray, and the amount of fuel sprayed is controlled by a mechanical or electrical control unit. The other popular system is timed injection (pulsed injection), where the fuel is delivered in bursts to coincide with the induction stroke of the cylinder. As with continuous injection, timed injection can also be controlled either mechanically or electronically.
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Frequently asked questions
Fuel flow injectors are electronically controlled valves that deliver fuel to the engine.
Fuel flow injectors are supplied with pressurised fuel by the fuel pump. When the injector is energised, an electromagnet moves a plunger that opens the valve, allowing the pressurised fuel to squirt out through a tiny nozzle. The nozzle atomises the fuel, turning it into a fine mist so that it can burn easily.
Carburetion relies on suction created by intake air, while fuel injection atomises the fuel through a small nozzle under high pressure. Fuel injection systems are also able to meet stricter emissions requirements as they can maintain a precise air-to-fuel ratio.
Examples of fuel flow injectors include the Bosch K-Jetronic system, the Lucas system, and the FIC Fuel Injector Clinic Injector Set for Mustang GT.
