Mercedes Mullins
The fuel injection system in a car is a mechanism that injects a calibrated spray of fuel into the engine's combustion chamber. All modern cars use fuel injection systems, which have been the primary means of getting fuel into the engine cylinder since the 1990s. The system works by using an electronically controlled valve, which is supplied with pressurised fuel by the fuel pump. When the injector is activated, an electromagnet moves a plunger that opens the valve, allowing the pressurised fuel to be atomised and squirted through a tiny nozzle. The amount of fuel supplied to the engine is determined by how long the injector stays open, which is controlled by the engine control unit (ECU).
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What You'll Learn
The evolution of fuel injectors
Fuel injectors are a relatively new technology in the automotive industry, but the concept of injection systems has been around for over a century. The earliest recorded use of fuel injectors was in 1902 when French aviator Leon Levavasseur implemented a prototype version of an injection system in his Antoinette 8V aircraft. During World War I, fuel-injected plane designs were used in combat, and fuel injection continued to be used in aircraft design after the war.
In the 1920s, injection systems gained popularity in diesel engines across various automobiles, and this trend continued into the 1950s. Mass-produced diesel engines for passenger cars, such as the Mercedes-Benz OM 138, became available in the late 1930s and early 1940s, becoming the first fuel-injected engines for passenger car use. In 1957, GM introduced its first fuel-injected model as an option, and in 1958, the Chrysler 300D, DeSoto Adventurer, Dodge D-500, and Plymouth Fury offered the Electrojector system, becoming the first cars known to use an electronic fuel injection (EFI) system.
In the 1960s and 1970s, mechanical fuel injection was used by many manufacturers in their higher-performance sports cars and sports saloons. The 1970s also saw the introduction of the L-Jetronic system, a pulsed-flow system that used an airflow meter to calculate the amount of fuel required. This system was widely adopted in European cars during the 1970s and 1980s and laid the foundation for modern EFI systems.
The 1980s witnessed the rapid increase and spread of electronic fuel injectors in Europe, and by the end of the decade, the last car sold in the United States with a carburetor engine was the 1990 Subaru Justy. The following year, the 1991 Subaru Justy was manufactured and sold with a new fuel injector, marking a significant shift towards fuel injection technology in the American market. By the early 1990s, fuel injection systems had largely replaced carburetors in passenger car petrol engines.
Over time, the design of fuel injectors has evolved from single-point injection to multi-point injection. Single-point injection, also known as throttle-body injection, uses one injector in a throttle body, similar to a carburetor. Multi-point injection, on the other hand, uses multiple fuel injectors and delivers fuel directly before the intake valve, maximizing efficiency and allowing for longer-lasting designs. Today, all cars sold in the United States are equipped with fuel injection systems, and these systems continue to evolve to meet stricter emissions requirements and improve fuel efficiency.
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How fuel gets into the cylinder
Fuel injection systems have been used in cars since the 1950s, and all cars sold in the United States today have them. Fuel injection systems are controlled by an engine control unit (ECU) and are designed to carefully control the air-to-fuel ratio, which is necessary for effective catalytic converters.
Fuel injection systems can be separated into two main types: internal and external mixture formation systems. External mixture formation systems are called manifold injection systems. There are two types of manifold injection systems: multi-point (or port) and single-point (or throttle body) injection. Multi-point injection systems inject fuel into the intake ports just upstream of each cylinder's intake valve, usually with a fuel injector for each cylinder. Single-point injection systems, on the other hand, use one injector in a throttle body, similar to a carburettor.
Internal mixture formation systems can be further separated into several different varieties of direct and indirect injection, the most common being the common-rail injection, a variety of direct injection. In common-rail injection, fuel from the fuel tank is supplied to a common header (the accumulator) and then sent through tubing to the injectors, which inject the fuel into the combustion chambers.
In direct injection, fuel is injected directly into the cylinder. This can be achieved with a conventional helix-controlled injection pump, unit injectors, or a common-rail injection system. The latter is the most common system in modern automotive engines. In petrol engines, direct injection is always indirect, with petrol injected into the inlet manifold or inlet port rather than directly into the combustion chambers. This ensures that the fuel is well mixed with the air before it enters the chamber.
In indirect injection, the fuel is not injected directly into the cylinder. Instead, it is injected into a pre-chamber or specially shaped pre-combustion chamber, which is connected to the main combustion chamber.
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Multi-port fuel injection
In a multi-port fuel injection system, each injector sprays fuel directly at the intake valve of the corresponding cylinder. This provides more accurate fuel metering and a quicker response compared to single-point injection. The fuel injectors are typically mounted in the intake manifold, and the amount of fuel supplied to the engine is controlled by the engine control unit (ECU) via the pulse width, or the amount of time the injector stays open.
One example of a multi-port fuel injection system is the Sequential Central Port Injection (SCPI) system found in GM's Vortec engines. This system employs sequential fuel injection, where each injector nozzle is triggered independently, spraying fuel immediately before or as the intake valve opens. This further improves efficiency and emissions compared to basic multi-port fuel injection systems, where all injectors spray fuel at the same time or in groups.
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Throttle body fuel injection
Throttle body injection (TBI) is a step up from a carburetor and is found on older vehicles. The setup uses one or two throttle body-mounted injectors to spray fuel into the intake manifold. The injectors deliver fuel into the air above the throttle plates. From there, the air-fuel mixture enters the intake manifold, where it is distributed to the engine's individual cylinders. The amount of fuel injected is controlled by a flap valve located in the engine's air intake. The flap opens and closes in response to airflow — as you open the throttle, the 'suck' from the cylinders increases the airflow and the flap rises.
The gas pedal in your car is connected to the throttle valve, which regulates how much air enters the engine. When you press on the gas pedal, the throttle valve opens up more, letting in more air. The engine control unit (ECU) then increases the fuel rate in anticipation of more air entering the engine. The ECU is the computer that controls all of the electronic components on the engine. It uses information from oxygen sensors to adjust the air-to-fuel ratio in real-time, a process called closed-loop control.
The fuel injector is an electronically controlled valve. It is supplied with pressurized fuel by the fuel pump in your car and is capable of opening and closing many times per second. When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to squirt out through a tiny nozzle. The nozzle is designed to atomize the fuel — to make as fine a mist as possible so that it can burn easily.
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Direct vs. indirect injection
Direct injection and indirect injection systems differ in the way fuel is injected into the engine. Direct injection systems inject fuel directly into the combustion chamber, usually on top of the piston, which is designed to control the spread of combustion. On the other hand, indirect injection systems inject fuel into a pre-combustion chamber or an air cell, where initial combustion takes place, and the fuel-air mixture is then expelled into the main combustion chamber.
Indirect injection systems, also known as IDI, were more common in the 1980s and 1990s and are still used in some applications today. They feature high compression ratios and unique-looking cylinder heads that house the pre-chambers. IDI systems have a high rate of air swirl, a lower risk of blockage due to self-cleaning pintle injectors, and do not require as much pressure. However, they have lower thermal efficiency and higher fuel consumption.
Direct injection systems, also known as DI, are the most common type of fuel injection system in modern engines. They offer better thermal efficiency, making them more economical. DI systems also have the advantage of being better for cold starts due to their smaller combustion space. However, they tend to be louder, more prone to blockages due to smaller injection holes, and have lower power output.
Multi-port injection, also known as indirect injection, is the most common type of fuel injection system found in vehicles. It utilizes one fuel injector per cylinder, which is mounted on the intake manifold. The fuel injector sprays fuel directly into the intake runner behind the intake valve, cleaning carbon deposits from the valve face.
Dual injection systems, which combine both direct and indirect injection, have been shown to increase fuel economy, reduce emissions, and increase engine power.
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Frequently asked questions
A fuel injection system is a method of delivering fuel to an engine's combustion chamber. It replaced the carburetor, which was previously the device that supplied fuel to the engine. Fuel injection systems are more efficient, powerful, and economical than carburetors, and they produce less poisonous emissions.
A fuel injector is an electronically controlled valve. It is supplied with pressurized fuel by the fuel pump in the car. When the injector is energized, an electromagnet moves a plunger that opens the valve, allowing the pressurized fuel to be atomized and squirt out through a tiny nozzle. The amount of fuel supplied to the engine is determined by how long the fuel injector stays open, which is controlled by the Engine Control Unit (ECU).
There are two main functional principles of mixture formation systems for internal combustion engines: internal and external. External mixture formation systems, also known as manifold injection systems, can be further divided into multi-point (or port) injection and single-point (or throttle body) injection. Internal mixture formation systems can be separated into direct and indirect injection, with common-rail injection being the most common type of direct injection.
