Katerina Swanson
Fuel injection is the process of introducing fuel into an internal combustion engine. The majority of modern cars are equipped with fuel injection systems or injector motors, which have largely replaced carburetor motors. Fuel injection systems have been around since the 1950s, but they have evolved significantly over the past hundred years, becoming more efficient and eco-friendly. Today, fuel injection systems are controlled electronically, offering greater accuracy and the ability to meet strict emission standards.
| Characteristics | Values |
|---|---|
| Types of Fuel Injection | Direct Injection, Sequential Injection, Simultaneous Injection, Batched Injection, Single-Point Injection, Multi-Point Injection |
| How it works | Fuel is injected into the main combustion chamber of each cylinder |
| Fuel Injector | An electronically controlled valve that is supplied with pressurized fuel by the fuel pump in the car |
| Carburetor | A device that mixes air and fuel in the required ratio before letting it into the combustion chamber |
| Fuel Injector Pulse Width | The amount of time the fuel injector stays open, controlled by the ECU |
| Common in | All cars sold in the United States, most new petrol cars |
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What You'll Learn
Injector technology
Fuel injection is the process of introducing fuel into an internal combustion engine, most commonly an automotive engine, by means of a fuel injector. The basics of combustion may not have changed, but the way a car gets fuel into the engine has become more complex.
Fuel injection systems are classified according to different characteristics. The main types of manifold injections systems are multi-point injection and single-point injection. Single-point injection, also called throttle-body injection, uses one injector in a throttle body mounted similarly to a carburettor on an intake manifold. It was a relatively low-cost way for automakers to reduce exhaust emissions and provide better "driveability" (easy starting, smooth running, no engine stuttering). Multi-point injection systems depend on nozzle synchronization: simultaneous, batched, and sequential. In a common-rail system, the most common system in modern automotive engines, 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.
In recent decades, there have been three basic types of fuel injection used in cars: throttle body injection (TBI), port or multi-port fuel injection (MFI), and direct injection. All modern diesel engines use direct injection, while gasoline direct injection (GDI) has become increasingly commonplace.
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Carburettors
A carburettor (or carburetor in American English) is a device that mixes air and fuel in the required ratio before letting it into the combustion chamber. It is a technically simple, inexpensive, and easy-to-maintain device that does not require electricity. Instead, it uses the engine's natural air suction.
Before the new era of microchips and complicated automotive electronics, carburettors dominated the market. However, starting in the 1980s, injector technology made a comeback, and carburettors gradually became less common in cars. By the early 1990s, fuel injection systems had largely replaced carburettors in passenger car petrol engines. Today, carburettors are still in use, but mainly in simpler engines for scooters, motorboats, chainsaws, or lawn mowers.
The primary difference between carburetion and fuel injection is that fuel injection atomises the fuel through a small nozzle under high pressure, while carburettors rely on suction created by intake air. Fuel injection systems are also more accurate and can meet strict emission standards. They help save fuel, provide more power at lower engine speeds, and increase overall stability.
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Direct injection
The first GDI engine to reach production was introduced in 1925 for a low-compression truck engine. Several German cars used a Bosch mechanical GDI system in the 1950s, however, usage of the technology remained rare until an electronic GDI system was introduced in 1996 by Mitsubishi for mass-produced cars. GDI has seen rapid adoption by the automotive industry in recent years, increasing in the United States from 2.3% of production for model-year 2008 vehicles to approximately 50% for model-year 2016.
The 'charge mode' of a direct-injected engine refers to how the fuel is distributed throughout the combustion chamber. The homogeneous charge mode has the fuel mixed evenly with the air throughout the combustion chamber, as per manifold injection. The stratified charge mode creates a small zone of fuel/air mixture around the spark plug, which is surrounded by air in the rest of the cylinder. This results in less fuel being injected into the cylinder, leading to very high overall air-fuel ratios.
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Multi-point injection
In MPI, fuel is injected at low pressure into the inlet air manifold, just upstream of each cylinder's intake valve. The suction created by the piston sucks the atomized fuel and air into the engine through the intake valve opening. This is in contrast to direct injection, where fuel is injected directly into the combustion chamber at high pressure, allowing for more precise control over the spray pattern and injection timing.
MPI typically uses multiple fuel injectors, but some systems, such as GM's central port injection system, use tubes with poppet valves fed by a central injector instead of multiple injectors. The Bosch K-Jetronic system, introduced in 1974, is an example of a continuous manifold injection system, where fuel flows at all times from the fuel injectors but at a variable flow rate. This system was used by various car manufacturers until the mid-1990s.
The Bosch Motronic multi-point fuel injection system was the first mass-produced system to use digital electronics for control. It was among the first systems where the ignition and fuel injection systems were controlled by the same device. The Ford EEC-III single-point fuel injection system, introduced in 1980, was another early digital fuel injection system.
There are different types of multi-point injection systems depending on the nozzle synchronization: simultaneous, batched, and sequential. In simultaneous injection, multiple nozzles work together to inject fuel simultaneously, which is simpler and more reliable than single-point injection systems. Batched-type injector nozzles work in pairs in rotation, depending on the cylinder phase, saving more fuel. Sequential injection is the most common and effective system, coordinating each nozzle separately with its cylinder phase, so fuel is sprayed only when the intake valve opens.
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Sequential injection
Fuel injection is the process of introducing fuel into an internal combustion engine, most commonly in automotive engines. The first mass-produced diesel passenger cars with fuel injection systems were introduced in the late 1930s and early 1940s. However, these early injection systems were inefficient and were soon overtaken by carburetor motors. Carburetor motors mix air and fuel in the required ratio before letting it into the combustion chamber. They are technically simple, inexpensive, and easy to maintain, but they do not offer the same accuracy and emission standards as modern fuel injection systems.
Modern fuel injection systems are electronically controlled and offer greater accuracy, improved fuel efficiency, and enhanced stability. They are also better equipped to meet strict emission standards. Today, most new petrol cars are equipped with fuel injection systems or injector motors, which have largely replaced carburetor motors.
Overall, sequential injection is a highly effective fuel injection system that offers numerous benefits over traditional carburetor systems and other types of fuel injection. It is an essential component of modern automotive engines, helping to improve fuel efficiency and reduce emissions.
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Frequently asked questions
Fuel injection is the process of introducing fuel into an internal combustion engine. It is done through a fuel injector, which is an electronically controlled valve.
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 is designed to atomise the fuel, creating a fine mist that can burn easily. The amount of fuel supplied to the engine is determined by how long the fuel injector stays open, which is called the pulse width.
There are several types of fuel injection, including single-point injection, multi-point injection, direct injection, and sequential injection. Single-point injection replaces the carburettor with one or two fuel injector nozzles in the throttle body. Multi-point injection devotes a separate injector nozzle to each cylinder. Direct injection means that the fuel is injected directly into the combustion chamber, and sequential injection triggers each injector nozzle independently.
Yes, fuel injection systems are now standard in all cars sold in the United States and many other countries. Fuel injection has been gradually replacing carburettors since the 1980s, and modern injector systems are controlled electronically, making them more accurate and eco-friendly.
