Mercedes Mullins
Fuel injection is a system for introducing fuel into the cylinders of an internal combustion engine. This is done by means of a pump rather than through the suction created by the movement of the pistons. Fuel injection systems are usually electronically controlled and have replaced carbureted engines in modern cars. They are more efficient, powerful, and economical, and have helped reduce harmful emissions.
| Characteristics | Values |
|---|---|
| Definition | Fuel injection is a system for injecting a precise amount of atomized fuel into the cylinders or the intake airstream of an internal combustion engine. |
| Introduction | Fuel injection was introduced in the early 1950s and gradually gained prevalence until it had largely replaced carburetors by the early 1990s. |
| Types | There are two main types of fuel injection systems: internal and external. |
| Internal | Direct and indirect injection are the two types of internal mixture formation systems. |
| External | Multi-point (or port) and single-point (or throttle body) injection are the two types of external mixture formation systems. |
| Common-rail injection | Common-rail injection is a type of direct injection that is the most common system in modern automotive engines. |
| Electronic fuel injection | Electronic fuel injection refers to any fuel injection system controlled by an engine control unit (ECU). |
| Benefits | Fuel injection systems provide more accurate fuel metering, quicker response, and reduced emissions. |
| Drawbacks | GDI engines produce more black carbon aerosols than traditional port fuel injection engines. |
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What You'll Learn
Fuel injection systems
There are two main functional principles of mixture formation systems for internal combustion engines: internal and external. A fuel injection system that uses external mixture formation is called a manifold injection system. 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, rather than at a central point within an intake manifold. Single-point injection uses one injector in a throttle body mounted similarly to a carburettor on an intake manifold.
Internal mixture formation systems can be separated into several different varieties of direct and indirect injection, the most common being the common-rail injection, a variety of direct injection. Direct injection means that the fuel is injected into the main combustion chamber of each cylinder. The 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). This can be done either with a blast of air or hydraulically, with the latter method being more common in automotive engines. Typically, hydraulic direct injection systems spray fuel into the air inside the cylinder or combustion chamber.
Indirect injection systems inject fuel 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.
The term electronic fuel injection refers to any fuel injection system controlled by an engine control unit (ECU). The ECU uses information from oxygen sensors to adjust the air-to-fuel ratio in real-time. This is called closed-loop control and was not feasible to achieve with carburetors.
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Carburettors vs fuel injection
Fuel injection is the introduction of fuel into the cylinders of an internal combustion engine by means of a pump, rather than by the suction created by the movement of the pistons. All compression-ignition engines (e.g. diesel engines) and many spark-ignition engines (i.e. petrol engines) use fuel injection.
The primary difference between carburetion and fuel injection is that fuel injection atomises the fuel through a small nozzle under high pressure, while carburetion relies on suction created by intake air. Carburettors were the most common method of fuel delivery for cars until the early 1990s when they were largely replaced by fuel injection. The 1990 Subaru Justy was the last car sold in the United States to have a carburettor.
Carburettors
The carburettor was first invented by Samuel Morey in 1826 and was used for a petroleum engine. In its most basic form, a carburettor uses a Venturi Tube that narrows in a section, decreasing air pressure and creating a vacuum. This vacuum pulls fuel into the carburettor, where the ratio is adjusted using two valves: the choke and the throttle. The choke decreases the amount of air and increases the flow of fuel, causing the engine to run lean, which is useful during winter or for a cold start. The throttle valve regulates how much of the air-fuel mixture flows into the engine.
Fuel Injection
The basic idea behind fuel injection is to precisely measure and time the injection of fuel into the intake manifold or combustion chamber. This accuracy allows for the best air-fuel ratios, which optimises combustion and increases power output and fuel economy. The system also adjusts to shifting environmental factors like temperature and altitude, assuring constant performance in various settings. Fuel injection systems assist in reducing hazardous exhaust emissions, helping automakers adhere to environmental requirements, and promoting a cleaner environment by precisely controlling the air-fuel combination.
Carburettors vs. Fuel Injection
Fuel injection has several advantages over carburettors. Fuel injection systems are more accurate, providing more precise fuel control and better fuel metering. They also provide a quicker response, smoother acceleration, and higher power output. Fuel injection is also essential for achieving strict emissions rules as it helps reduce hazardous exhaust emissions.
However, some people still prefer carburettors due to their simplicity and ease of repair. Additionally, in electronic fuel injection (EFI), one is forced to maintain a minimum of around 2.5 litres of petrol in the fuel tank, otherwise, the vehicle's engine will not start.
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Multi-point fuel injection
Fuel injection is the introduction of fuel into the cylinders of an internal combustion engine by means of a pump, rather than by the suction created by the movement of the pistons. All compression-ignition engines (e.g. diesel engines) and many spark-ignition engines (i.e. petrol or gasoline engines) use fuel injection.
The Electronic Control Unit (ECU) is the 'brain' of the MPFI system, gathering data from various sensors such as the Mass Airflow Sensor (MAF), Throttle Position Sensor (TPS), and Oxygen Sensor (O2 Sensor) to calculate the optimum fuel-air mixture. The ECU then triggers the injectors to spray precise amounts of fuel based on real-time engine data. The ECU calculates the exact amount of fuel required for each cylinder and the appropriate moment to inject it during the engine's intake stroke.
There are two main types of MPFI systems: traditional and sequential. In a traditional MPFI system, all the injectors deliver fuel simultaneously, spraying fuel into each intake port or directly into the combustion chamber at the same time. In a sequential MPFI system, the injectors deliver fuel in a sequential manner, precisely timed to the engine's firing order. This means that each injector opens just before the corresponding intake valve opens during the engine's intake stroke, allowing for better fuel atomization and more accurate fuel delivery.
MPFI systems have several advantages, including improved efficiency, performance, and reduced emissions. They also provide more accurate fuel metering and a quicker response. However, they are more expensive and complex in design compared to carburettors, and can be more tedious to repair.
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Single-point injection
Fuel injection is the introduction of fuel into the cylinders of an internal combustion engine, most commonly automotive engines, by the 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.
While single-point injection provided better driveability and reduced emissions compared to carburettors, it could not form the precise mixtures required for modern emission regulations. As a result, it is now considered obsolete technology in passenger cars. Modern manifold injection systems typically use multi-point injection (MPI) or port injection, which provides more accurate fuel metering and quicker response.
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Direct injection
The primary advantage of direct injection is that it increases engine efficiency and power output while reducing exhaust emissions. This is achieved through more precise control of the air-fuel mixture and improved combustion. During the 20th century, most petrol engines used either a carburettor or indirect fuel injection. However, in the 21st century, direct injection has become increasingly common in petrol engines due to its advantages in fuel efficiency and emissions reduction.
While direct injection offers improved performance and reduced emissions, it also has some drawbacks. One of the main issues is the aggressive build-up of carbon in the intake ports and on the back of the valves. This carbon accumulation can lead to maintenance challenges and impact the engine's performance and efficiency until it reaches its ideal operating temperature.
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Frequently asked questions
Fuel injection is a system for injecting a precise amount of atomized fuel into the cylinders or the intake airstream of an internal combustion engine.
Carburettors rely on suction created by intake air, whereas fuel injection atomizes the fuel through a small nozzle under high pressure. Fuel injection systems are also controlled by an engine control unit (ECU) which adjusts the air-to-fuel ratio in real-time.
Fuel injection systems are more efficient, powerful, and economical than carburettors. They also produce less poisonous emissions.
