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What is fuel injection and how it works

Modern cars use various fuel injection systems. The injection system as the name implies provides fuel injection.

The injection system is used on both gasoline and diesel engines. However, the design and operation of the injection systems of gasoline and diesel engines differ significantly.

In gasoline engines, a uniform air-fuel mixture is formed by injection, which is forcibly ignited by a spark. In diesel engines, fuel is injected at high pressure, a portion of the fuel is mixed with compressed (hot) air and ignites almost instantly. The injection pressure determines the size of the portion of the injected fuel and, accordingly, the engine power. Therefore, the greater the pressure, the higher the engine power.

The fuel injection system is an integral part of the fuel system of a car. The main working body of any injection system is the nozzle ( injector ).

Petrol engine injection systems

Depending on the method of formation of the air-fuel mixture, the following systems of central injection, distributed injection and direct injection are distinguished. Central and distributed injection systems are pre-injection systems, i.e. they are injected without reaching the combustion chamber – in the intake manifold.

The central injection ( single injection ) is carried out by a single nozzle installed in the intake manifold. In fact, this is a carburetor with a nozzle. Currently, central injection systems are not produced but are still found in cars. The advantages of this system are simplicity and reliability, and the disadvantages are increased fuel consumption, low environmental performance.

The distributed injection system ( multi-point injection system ) involves the supply of fuel to each cylinder with a separate nozzle. The formation of the fuel-air mixture occurs in the intake manifold. It is the most common injection system for gasoline engines. It is distinguished by moderate fuel consumption, low levels of harmful emissions, low requirements for fuel quality.

Promising is the direct injection system . Fuel is injected directly into the combustion chamber of each cylinder. The system allows you to create the optimal composition of the fuel-air mixture at all engine operating modes, increase the compression ratio, thereby ensuring complete combustion of the mixture, fuel economy, increasing engine power, and reducing harmful emissions. On the other hand, it is distinguished by the complexity of the design, high operational requirements (it is very sensitive to fuel quality, especially to the sulphur content in it).

To reduce emissions of particulate matter into the atmosphere with exhaust gases, a combined injection system is used, combining a direct injection system and a distributed injection system on a single internal combustion engine.

Gasoline engine injection systems can be mechanically or electronically controlled. The most advanced is electronic injection control, which provides significant fuel economy and reduction of harmful emissions.

The fuel injection in the system can be continuous or pulsed ( discrete ). Promising from the point of view of efficiency is pulse fuel injection, which is used by all modern systems.

In the engine, the injection system is usually combined with the ignition system and forms a combined injection and ignition system (for example, Motronic, Fenix systems ). The coordinated operation of the systems is provided by the engine management system.

Diesel engine injection systems

Fuel injection in diesel engines can be performed in two ways: into the preliminary chamber or directly into the combustion chamber.

Engines with injection into the preliminary chamber are distinguished by a low noise level and smooth operation. But at present, direct injection systems are preferred. Despite the increased noise level, such systems have high fuel efficiency.

The decisive structural element of the diesel engine injection system is the high-pressure fuel pump (TNVD).

Various designs of injection systems are installed on passenger cars with a diesel engine: with in-line injection pump, with distribution injection pump, pump nozzles, Common Rail. Progressive injection systems – pump nozzles and the Common Rail system.

In the pump-nozzle injection system, the functions of creating high pressure and fuel injection are combined in one device – the pump-nozzle. The nozzle pump has a permanent (non-disconnectable) drive from the engine camshaft, therefore it is subject to intense wear. This quality pump nozzle directs the preferences of automakers towards the Common Rail system.

The operation of the Common Rail injection system is based on the supply of fuel to the injectors from a common high-pressure accumulator – a fuel rail (common rail means a common rail). Another name for the system is the battery injection system. To reduce the noise level, improve self-ignition and reduce harmful emissions in the system, multiple fuel injection is implemented – preliminary, main and additional.

Diesel injection systems can be mechanically or electronically controlled. In mechanical systems, the pressure, volume and moment of fuel are regulated mechanically. Electronics forms a diesel control system.

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