Sylvie Willis
The four-stroke fuel injection system is a type of internal combustion engine that is commonly used in automotive engines. It was first introduced in the 1997 Mitsubishi 6G74 V6 engine and has since become the standard for many petrol engines. The four strokes refer to the intake, compression, power, and exhaust strokes that the piston undergoes to create one combustion cycle. During the compression stroke, the direct fuel injector injects gasoline under high pressure into the cylinder, and this air-fuel mixture is ignited by a spark plug, causing combustion. This process is slightly different in diesel engines, which do not have spark plugs, as the diesel fuel ignites due to the high temperature of the compressed air.
| Characteristics | Values |
|---|---|
| Type of engine | Four-stroke internal combustion engine |
| Components | Pistons, crankshaft, cylinder, valves, piston rings, spark plug, combustion chamber |
| Process | Intake, compression, power, exhaust (four strokes) |
| Fuel injection | Fuel injectors supply atomized fuel through a nozzle to the cylinder |
| Fuel injection timing | Every second revolution of the crankshaft |
| Fuel injection system | Continuous or intermittent injection design |
| Fuel type | Gasoline or diesel |
| Ignition | Spark plug or high temperature of compressed air |
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What You'll Learn
Injector location
The location of the injector in a 4-stroke engine is crucial for the proper functioning of the engine. The injector's position ensures that fuel is delivered directly into the cylinder during the compression stroke. This compression stroke occurs once every two revolutions of the crankshaft in a 4-stroke engine, as opposed to every revolution in a 2-stroke engine.
The injector's location in the 4-stroke engine allows for the precise delivery of fuel under very high pressure. This high-pressure injection contributes to the engine's overall performance and efficiency. By injecting fuel directly into the cylinder, the engine can achieve a more complete combustion process, resulting in improved power output and fuel economy.
The injector location also plays a role in the engine's ability to regulate the amount of fuel injected per stroke. This regulation ensures that the engine receives the optimal amount of fuel required for combustion, further enhancing efficiency and performance. Additionally, the injector location facilitates the atomization of the fuel, creating a fine spray that mixes with air in the cylinder, resulting in a more efficient and complete burn.
In modern engines, the injector location is designed to accommodate electronically controlled injection systems. These systems, known as "Common Rail" fuel systems, utilize a high-pressure booster pump to supply fuel to the injectors. The injectors can be mechanically or electronically opened, or by fuel pressure pushing against a spring, ensuring precise control over fuel delivery.
Overall, the injector location in a 4-stroke engine is carefully engineered to optimize fuel delivery, combustion efficiency, and overall engine performance. The location of the injector, in combination with other engine components, contributes to the engine's ability to generate power and maintain fuel efficiency.
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Injector operation
The injectors themselves can be opened mechanically, electronically, or by fuel pressure acting against a spring. The function of the injector is to supply a fine spray of atomized fuel through a nozzle to the cylinder. This process is similar for both two-stroke and four-stroke engines, with the primary difference being the frequency of fuel injection.
In a four-stroke engine, the intake stroke marks the beginning of the combustion cycle, where air and fuel enter the engine's combustion chamber. The specifics of this step depend on the engine type. In port-fuel-injected (PFI) engines, the piston moves down the cylinder, drawing an air-fuel mixture into the combustion chamber. In gasoline-direct-injected engines (GDI), fuel can be injected as the piston moves down to create a homogeneous mixture or in a smaller amount near the end of the compression stroke.
During the compression stroke, the intake and exhaust valves are closed, and the piston moves up, compressing the air trapped in the cylinder. In GDI engines, the direct fuel injector injects gasoline at a very high pressure into the cylinder during this stage, just before the piston reaches the top position. This high-pressure injection results in a fine spray of atomized fuel, ensuring efficient combustion.
The spark between the spark plug electrodes then ignites the air-fuel mixture, leading to a rapid expansion of gases, which forces the piston back down the cylinder during the power stroke. This downward movement provides the energy required to turn the wheels of a car. Finally, in the exhaust stroke, the exhaust valve opens, allowing the piston to expel the exhaust gases from the cylinder while applying a fresh coating of oil.
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Fuel injection systems
There are two main types of fuel injection systems: continuous injection and intermittent injection. Continuous injection systems involve fuel flowing constantly from the fuel injectors, but at variable flow rates. The Bosch K-Jetronic system is an example of a continuous injection design. Intermittent injection systems, on the other hand, can be further categorised into sequential, batched, simultaneous, and cylinder-individual types. Sequential injection involves timing the fuel injection to coincide with each cylinder's intake stroke. Batched injection injects fuel to the cylinders in groups without precise synchronisation to any particular cylinder's intake stroke. Simultaneous injection delivers fuel to all cylinders at the same time, while cylinder-individual injection allows the engine control unit to adjust the injection for each cylinder independently.
The design and placement of the fuel injectors can vary between engines. In conventional port fuel injection systems, the injector is installed in the intake port, above the intake valve. In contrast, gasoline direct-injected engines have the injector nozzle protruding into the combustion chamber. This allows for the injection of fuel during the piston's downward movement to create a homogeneous mixture or near the end of the compression stroke. The compression stroke is when the piston moves up, compressing the air trapped in the cylinder, and the fuel is injected under high pressure.
The evolution of fuel injection systems has led to the development of common rail systems, which have become prevalent in modern engines. These systems use a high-pressure booster pump to supply fuel to the injectors, which can be driven by the engine, an electric motor, or a combination of both. The introduction of electronic control systems has also enhanced the precision and adaptability of fuel injection, allowing for more efficient and environmentally friendly engines.
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Fuel injection history
Fuel injection is the introduction of fuel into an internal combustion engine, most commonly automotive engines, via a fuel injector. The fundamental function of a fuel injection system is to spray pressurised fuel into the engine.
The history of fuel injection dates back to the early 1900s, with the first fuel-injected compression-ignition engine constructed in 1902 and entering production in 1906. This engine, called the Antoinette 8V, was designed by French inventor and aviation pioneer Léon Levavasseur. It was an air-cooled V8 engine with eight litres of displacement, providing 50 horsepower.
In 1885, British engineer Herbert Akroyd Stuart accidentally spilled a flask of kerosene into a pot of molten tin, resulting in a blaze. This incident led to the discovery that hot kerosene vapours ignite more easily than liquid kerosene. This ultimately led to the construction of the hot-bulb engine, which entered production under licence in 1891.
Rudolf Diesel's prototype engine first ran in 1894, and mass-produced diesel engines for passenger cars became available in the late 1930s and early 1940s, becoming the first fuel-injected engines for passenger car use. In the 1940s, racers and hot-rodders began experimenting with mechanical fuel injection, and by the 1950s, Mercedes-Benz had embraced it. In 1955, Stirling Moss drove a Mercedes-Benz 300SLR with a Bosch direct-injected aircraft engine to victory in the Mille Miglia, a 1,000-mile endurance race.
In 1957, the American Motors Corporation introduced the Rambler, featuring an electronic fuel injection system called the Electrojector. However, it had issues, especially in cold weather, and only 35 units were delivered to consumers. By the late 1960s, European automakers like Porsche, Peugeot, Audi, and BMW began experimenting with mechanical fuel injection for production vehicles. In the 1970s, Bendix, an American corporation, developed the first electronic fuel injection (EFI) system for a production vehicle.
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Fuel injection in spark-ignition engines
Fuel injection is the introduction of fuel into an internal combustion engine by means of a fuel injector. In the case of spark-ignition engines, fuel is injected into the combustion chamber, which is distinct from manifold injection systems, where fuel is injected into the intake manifold. This is known as gasoline direct injection (GDI) or petrol direct injection (PDI). GDI helps increase engine efficiency, power output, and reduce emissions.
GDI was first introduced in 1925 for a low-compression truck engine. However, its usage remained rare until the introduction of an electronic GDI system by Mitsubishi in 1996 for mass-produced cars. GDI has seen rapid adoption in recent years, with many modern engines now being fitted with electronically controlled injection systems.
In spark-ignition engines, the fuel injector injects fuel under very high pressure into the cylinder during the compression stroke, when the piston is closer to the top. The spark between the spark plug electrodes then ignites the air-fuel mixture. This results in a power stroke, where the pressure of the hot gases created during combustion pushes the piston down with great force, providing the energy to turn the wheels in a car.
The injection timing depends on the piston speed. At higher piston speeds, the injection and ignition timing need to be advanced very precisely. At low piston speeds, the relative air-fuel velocity is low, which can cause the fuel to not vaporize properly, resulting in a rich mixture that does not combust properly and causes carbon build-up.
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Frequently asked questions
A four-stroke fuel injector is a type of fuel injector used in four-stroke engines, which are commonly found in passenger vehicles. Four-stroke engines are known for being more fuel-efficient, running cleaner, and providing more torque compared to two-stroke engines.
The process of fuel injection in a four-stroke engine varies depending on the type of engine. In port-fuel-injected (PFI) engines, the piston moves down the cylinder while the intake valve draws an air-fuel mixture into the combustion chamber. In gasoline-direct-injected engines (GDI), fuel can be injected while the piston moves down to create a homogeneous mixture or injected near the end of the compression stroke. During the compression stroke, the direct fuel injector injects gasoline under high pressure into the cylinder. The air-fuel mixture is then ignited by a spark plug, leading to combustion and the power stroke.
There are two main types of fuel injection systems: continuous injection and intermittent injection. Continuous injection systems have fuel flowing at all times from the injectors, but at variable flow rates. Intermittent injection systems can be sequential, batched, simultaneous, or cylinder-individual, depending on the timing and synchronization of fuel injection with the cylinder's intake stroke.
