A fuel injector in a diesel engine consists of a solenoid (a type of electromagnet), a nozzle, and a needle within the injector body. Modern diesel engines are direct injection, meaning fuel is delivered directly into the combustion chamber. In the cylinder, air is compressed by the upward movement of the piston.
Fuel injectors are responsible for regulating the direct injection of fuel into the diesel engine's combustion chamber. Here, the fuel is mixed with air and spontaneously combusts.
Fuel injection is the introduction of fuel in an internal combustion engine, most commonly automotive engines, by the means of a fuel injector.
All compression-ignition engines (e.g. diesel engines), and many spark-ignition engines (i.e. petrol (gasoline) engines, such as Otto or Wankel), use fuel injection of one kind or another. Mass-produced diesel engines for passenger cars (such as the Mercedes-Benz OM 138) became available in the late 1930s and early 1940s, being the first fuel-injected engines for passenger car use. In passenger car petrol engines, fuel injection was introduced in the early 1950s and gradually gained prevalence until it had largely replaced carburettors by the early 1990s.[ 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 accelerated through a Venturi tube to draw fuel into the airstream.
The term fuel injection is vague and comprises various distinct systems with fundamentally different functional principles. The only thing all fuel injection systems have in common is the absence of carburetion.
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 exist two types of manifold injection systems: multi-point (or port) and single-point (or throttle body) injection.
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. The term electronic fuel injection refers to any fuel injection system controlled by an engine control unit.
Injecting fuelThe fuel injector is effectively a spray nozzle that performs the final stage in the delivery of fuel into the engine. The injector is located in the combustion chamber, inlet manifold or – less commonly – the throttle body.Fuel injectors which also control the metering are called injection valves, while injectors that perform all three functions are called unit injectors.
Direct injection systemsDirect injection means that the fuel is injected into the main combustion chamber of each cylinder. As air and fuel are mixed only inside the combustion chamber, air alone is sucked into the engine during the intake stroke. The injection scheme is always intermittent (either sequential or cylinder-individual).Fuel is injected directly into the combustion chamber either with a blast of air or hydraulically, with the former rendered obsolete in automotive engines in the early 20th century by the invention of the precombustion chamber.Typically, hydraulic direct injection systems spray fuel into the air inside the cylinder or combustion chamber. Direct injection can be achieved with a conventional helix-controlled injection pump, unit injectors, or a sophisticated common-rail injection system. The last is the most common system in modern automotive engines.
Common-rail injection systemsMain article: Common-rail injectionIn 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 the 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.[5] Third-generation common-rail diesels use piezoelectric injectors for increased precision, with fuel pressures up to 300 MPa or 44,000 psi.
The types of common-rail systems include air-guided injection and spray-guided injection.Unit injector systems Main article: Unit injector Used by diesel engines, these systems include: Pumpe-Düse Pump-rail-nozzle system Helix-controlled pump systems This injection method was previously used in many diesel engines. Types of systems include: Lanova direct injectionAfterchamber injection G-System (sphere combustion chamber) Gardner system (hemisphere combustion chamber) Saurer system (torus combustion chamber) Flat piston (combustion chamber between piston and head) Air-blast injection systems
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