The Electronic Fuel Injection (EFI) system uses the ECU as the control center. Various sensors are installed in different parts of the engine to measure the engine's operating parameters. According to the program set in the computer, the system controls injectors to inject a precise amount of fuel so that the engine can obtain the optimum mixture under operating conditions.
The EFI system is an advanced fuel injection device used to eliminate carburetors. The technology of electronically controlled fuel injection is popular in vehicle engines. The fuel atomization is improved during the formation of the air-fuel mixture.
What's more, this system allows precise control of fuel injection in response to changing operating conditions so that we can get better combustion, resulting in increased power, lower fuel consumption and compliance with emissions regulations.
According to the way inlet airflow is tested, the system can be divided into three types: mass-controlled, velocity-density and throttle-velocity. The mass-controlled type is further divided into hot wire, plate and Carmen vortex types.
According to the injection position, there are two types of direct injection and inlet injection. The inlet channel injection type is divided into single-point injection and multi-point injection according to the installation position of the injector.
The single point injection system is a central injection unit fitted above the throttle, with one to two injectors finishing the injection. It uses sequential injection. The structure is simple, with few faults and easy maintenance and adjustment. It is widely used in ordinary cars and trucks.
The multi-point injection system is equipped with a central injection unit at the intake valve of each cylinder. The ECU controls the injection.
This type of system has good fuel distribution uniformity, but the control system is complex and expensive. It is mainly used in high and medium-level cars.
In the electronically controlled petrol injection systems that have now been put into use, intermittent injection is popular. This method is divided into simultaneous and non-simultaneous injections depending on the injection phases of the injectors.
The simultaneous injection is divided into independent injection sequential injection and group injection. Simultaneous injection means that the injectors of each cylinder are connected in parallel. All injectors are controlled by the same command from the computer to inject fuel and stop at the same time.
The group injection means that the injectors of each cylinder are divided into several groups. The same group of injectors injects or stops at the same time.
The sequential injection means that each injector is controlled separately by the computer. It injects fuel in the working order of engine's each cylinder.
In the open-loop control system (without oxygen sensors), the optimum fuel supply parameters for each engine operating condition, determined in the laboratory, are stored in advance.
It determines the operating condition and calculates the optimum fuel injection when the engine is working, based on the input signals from the sensors in the system.
The accuracy is directly dependent on the set reference data and the accuracy of the injector adjustment calibration. Optimum control cannot be achieved when the operating conditions are outside the predefined range.
In the closed-loop control system (with the oxygen sensor), the exhaust pipe is equipped with an oxygen sensor. According to the change of the oxygen content in the exhaust gas, the system determines the actual air-fuel ratio in the cylinder.
In the next step, the computer compares the value with the standard one. It corrects the fuel injection according to the error. The air-fuel ratio control is highly accurate.
The electronic fuel injection system consists of three main parts: the air supply system, fuel system and control system.
The mass flow injection system has an air filter, an air flow meter, a throttle body, an air valve and a pressure regulator. It is designed to provide clean air for the engine and control the amount of air supplied during normal engine working.
The working principle is that the air is filtered through the air filter. It enters the intake manifold through the airflow meter and throttle body. The air is then distributed to the cylinders through the intake manifold.
The fuel system consists mainly of the fuel tank, fuel pump, fuel filter, pressure regulator and injectors. The function is to supply fuel at a certain pressure to the injectors, which in turn inject fuel according to computer commands.
The working principle is that the electric fuel pump sucks the petrol out of the tank. The fuel passes the filter. The regulator regulates the pressure.
According to the computer command, the fuel is delivered through the fuel pipe to the injector, which injects fuel into the air intake pipe. The excess petrol supplied by the fuel pump flows back to the fuel tank via the return pipe.
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Lauritz Carolsfeld 
January 06, 2022