Ameer Randolph
Fuel injection is the process of introducing fuel into an internal combustion engine, usually an automotive engine, via a fuel injector. The fuel injector is mounted in the intake manifold and sprays fuel directly at the intake valves. The amount of air drawn into the engine indicates how much power it is producing, and fuel injectors can be timed to open simultaneously or individually for each cylinder. The introduction of fuel injection systems has allowed modern cars to keep up with emissions and fuel efficiency laws.
| Characteristics | Values |
|---|---|
| Purpose | To introduce fuel into an internal combustion engine |
| Engine type | Compression-ignition engines (diesel engines) and spark-ignition engines (petrol engines) |
| Fuel type | Gasoline |
| First mass-produced use | 1930s and 1940s in diesel engines; 1950s in petrol engines |
| Injection type | Continuous injection, intermittent injection, multi-port injection, throttle body fuel injection, direct injection, simultaneous injection, cylinder-individual injection, sequential injection, batched injection |
| Fuel flow | Variable flow rate |
| Common systems | Bosch K-Jetronic system, Fiat Multijet straight-four engine, common-rail system |
| Fuel metering | Precise |
| Engine control | Engine Control Unit (ECU) |
| Sensors | Mass airflow sensor, oxygen sensor, throttle position sensor, engine speed sensor |
| Injector type | Piezoelectric injectors |
| Injector function | Monitor and adjust fuel for each cylinder |
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What You'll Learn
Injector pulse width
Fuel injection is the process of introducing fuel into an internal combustion engine, usually an automotive engine, via a fuel injector. Fuel injectors have been the primary method of getting fuel into the engine cylinder of modern cars since the 1990s. The fuel injector atomises the fuel through a small nozzle under high pressure.
The engine control unit (ECU) is the computer that controls all the electronic components of the engine. It is equipped with a range of sensors that help it monitor the engine's operating conditions. These include the mass airflow sensor, which tells the ECU the mass of air entering the engine, and the throttle position sensor, which monitors the throttle valve position to determine how much air is entering the engine. The ECU can then adjust the fuel rate accordingly.
The ECU also controls the timing of the fuel injectors. In a multi-port system, the fuel injectors can either open simultaneously or sequentially, with each injector opening just before the intake valve for its cylinder (sequential multi-port fuel injection). Sequential fuel injection allows the system to respond more quickly to sudden changes made by the driver.
The pulse width of a fuel injector refers to the amount of time that the injector is open and injecting fuel into the cylinder. The engine speed sensor is one of the factors used to calculate the pulse width. The pulse width must be adjusted to provide the correct amount of fuel for the engine's operating conditions.
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Sequential fuel injection
Fuel injection is the process of introducing fuel into an internal combustion engine, usually an automotive engine, via a fuel injector. Fuel injectors have been used as the primary means of getting gasoline into the engine cylinder of modern cars since the 1990s.
In sequential fuel injection, each injector nozzle is triggered independently, spraying fuel immediately before or as the intake valve opens. This is timed in a similar way to spark plugs. This system provides more accurate fuel metering and a quicker response. The engine control unit (ECU) monitors a range of input sensors to ensure the correct amount of fuel is provided for every operating condition. Sequential fuel injection systems can respond more quickly to sudden changes by the driver, as they only have to wait until the next intake valve opens, rather than for the next complete revolution of the engine.
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Continuous injection systems
Fuel injection is the introduction of fuel into an internal combustion engine, most commonly an automotive engine, via a fuel injector. Fuel injectors are cylinders that deliver fuel into the engine. The injector is located in the combustion chamber, inlet manifold, or throttle body.
Fuel injection systems can be categorised into continuous injection and intermittent injection designs. This response will focus on the continuous injection system, which is characterised by a constant but variable flow of fuel from the injectors. The Bosch K-Jetronic system, introduced in 1974, is the most common automotive continuous injection system. It was utilised by various car manufacturers until the mid-1990s.
In a continuous injection system, fuel flows continuously from the fuel injectors, but at varying rates. This system provides a more precise fuel metering and a faster response compared to throttle body fuel injection. The fuel injectors are typically mounted in the intake manifold, positioned to spray fuel directly at the intake valves. Each cylinder has its own fuel injector, ensuring a more accurate and immediate fuel delivery.
The engine control unit (ECU) plays a crucial role in continuous injection systems. It monitors various input sensors, such as the mass airflow sensor, oxygen sensor, and throttle position sensor, to adjust the fuel rate accordingly. This ensures that the correct amount of fuel is delivered for different operating conditions. The ECU also controls the ignition timing and other engine functions, making it a central component in the engine's performance and efficiency.
While continuous injection systems offer advantages in terms of precision and responsiveness, they are not without drawbacks. One disadvantage is that they require more sophisticated engineering and electronics compared to intermittent injection systems. This complexity can make continuous injection systems more costly to manufacture and maintain. Additionally, the constant flow of fuel, even at low engine loads, can lead to slightly higher fuel consumption and emissions.
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Injection valves
The primary function of injection valves is to supply each cylinder with the precise amount of fuel needed for combustion. This is achieved through a process called atomisation, where the fuel is sprayed into the engine cylinder as a fine mist through a nozzle with small holes. This atomisation allows the fuel to burn more effectively in the combustion chamber, resulting in improved engine performance and fuel efficiency.
The operation of injection valves is carefully controlled to ensure the accurate delivery of fuel. The engine control unit (ECU) calculates the required fuel quantity based on various sensor inputs, such as mass airflow, throttle position, and oxygen levels in the exhaust. By adjusting the opening time and duration of the injection valve, the ECU ensures that the precise amount of fuel is injected into the cylinder.
The design of injection valves includes a precision bore hole and a valve seat, which work together to optimise atomisation and control the flow rate of the fuel. This design ensures that the fuel is delivered in a finely misted state, promoting a more complete and efficient combustion process. The ECU's ability to adjust the opening time of the valve is crucial for maintaining the correct fuel-to-air ratio, which is essential for optimal engine performance.
Troubleshooting and maintenance of injection valves are important to identify and rectify any potential issues. HELLA, a renowned automotive company, provides comprehensive guidelines for checking the functionality of injection valves, including continuity tests, short circuit inspections, and measurement techniques. By following these procedures, mechanics and qualified personnel can ensure the proper functioning of injection valves, maintaining the engine's performance, fuel efficiency, and emissions compliance.
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Direct injection
The first GDI engine to reach production was introduced in 1925 for a low-compression truck engine. However, usage of the technology remained rare until an electronic GDI system was introduced in 1996 by Mitsubishi for mass-produced cars. Since then, GDI has seen rapid adoption by the automotive industry, with approximately 50% of model year 2016 vehicles in the United States featuring GDI technology.
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.
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Frequently asked questions
Fuel injectors are responsible for introducing fuel into an internal combustion engine, usually an automotive engine. They are the primary means of getting gasoline into the engine cylinder so that it can combust and the car can be driven.
Fuel injectors are mounted in the intake manifold so that they spray fuel directly at the intake valves. A pipe called the fuel rail supplies pressurised fuel to all of the injectors. The engine control unit (ECU) is equipped with sensors to monitor factors such as engine speed, mass airflow, and throttle position to calculate the pulse width and ensure the correct amount of fuel is provided.
Carburetors rely on suction created by intake air, whereas fuel injectors atomize the fuel through a small nozzle under high pressure. Fuel injection systems are also able to respond more quickly to sudden changes by the driver.
