Fuel injection is a technology used in internal combustion engines to mix the fuel with air prior to combustion.
As in a traditional carburetor, fuel is converted to a fine spray and mixed with air. However, where a traditional carburetor forces the incoming air through a venturi to pull the fuel into the air stream, a fuel injection system forces the fuel through nozzles under pressure to inject the fuel into the air stream without requiring a venturi.
The use of a venturi reduces volumetric efficiency by approximately 15%, which results in a reduction in engine power. Thus, a fuel injection system increases the power that an engine with the same engine displacement will produce. Additionally, fuel injection allows for more precise control over the mixture of fuel and air, both in proportion and in uniformity.
The fuel injection system may be purely mechanical, purely electronic or a mix of the two. Early systems were mechanical but from about 1980 onward more and more systems were completely electronic. By the middle of the decade, nearly all new passenger vehicles were equipped with electronic fuel injection. The Muitsubishi Lancer was one of the the last passenger cars sold in Australia with a carburetor.
The modern electronic systems that cars are equipped with today utilise a number of sensors to monitor engine conditions, and an electronic control unit (ECU) to accurately calculate the needed amount of fuel. Thus fuel injection can increase fuel efficiency and reduce emissions.
EFI systems employ electronically controlled injectors to spray the fuel into the intake system.
There are 2 basic systems - throttle-body injection, also called single-point injection. And multi-point injection.
Throttle-body injection sprays fuel into the air as it passes through to the intake manifold.
Multi-point injection has an injector for each cylinder, which sprays fuel directly into the intake valve port. The whole system has:
- a fuel tank to store the fuel;
- a fuel pump to circulate fuel, and provide pressure in the system;
- a fuel filter to clean the fuel and protect the injectors;
- a fuel rail, or pipe, to supply the injectors with fuel;
- injectors which spray into the intake valve ports;
- a pressure regulator to control pressure in the system;
- a throttle-body, with a throttle valve to control the flow of air to the engine;
- an air cleaner, ducting and an airflow meter, to provide clean, measured air;
- and a plenum chamber, or surge chamber, to dampen the flow of air.
There is also an electronic control unit - a computer that receives data from sensors around the engine. It processes this data, and uses the results to operate the injectors.
