Fuel injection is the system sending the fuel to cylinders in the gasoline engines. Work that carburetor systems make in the former type engines, injection systems in the modern engines have taken over. Injection systems in the new generation gasoline atmosferic or charged engines are used. Injection systems with the technology developing have been provided fuel saving at a serious. At the same time, its emission values are reduced to protect the environment and atmosphere.
Fuel Systems in Gasoline Engines
- Carburetor Engines
- Single Port Injection – SPI
- Multi Port Injection – MPI
- Gasoline Direct Injection – GDI
Engine fuel systems are the system sending to the cylinders the fuel basic need to create combustion time of internal combustion engines. Gasoline, diesel or LPG is used as fuel internal combustion engines used today. These systems need systems that will provide fuel to the engine continuously and in the desired amount. New injectors and injection systems with the technology developing have been found in the automotive industry.
We are going to examine fuel systems used in the diesel and gasoline motors below this section. Engine fuel systems seem very complex, you will see it is very basic and understandable when you read it under the headings. Subjects have been explained under the 2 main headings as in the diesel and gasoline motors.
What does the Engine Control Unit work?
The Engine Control Unit (ECU) which controls the injection mounts are benefited the air system components to calculate the engine load.
We can briefly examine the fuel systems 4 main under the headings in order of development.
1- Carburetor Systems is engine fuel systems used in former vehicles. It is the system sending to the intake manifold and then to the cylinders by taking the fuel from the fuel tank with the vacuum effect air entering to the intake manifold.
2- Single Point Injection (SPI) It is similar to a carburetor system. Differently, it uses an injector to give the fuel. The injector connected to the throttle injects the fuel over the throttle body.
3- Multi Port Injection (MPI) has been produced that will be an injector in each cylinder. It injects fuel into each cylinder to the area where the intake valve is located.
4-) Gasoline Direct Injection (GDI) It is the most advanced and efficient injection system. It gives the fuel directly to the combustion chamber of the engine. It can inject the fuel at the time of suction, compression and even combustion.
1- Carburetor Engines
The air sucked in by the suction power of the pistons in the cylinder, while passing through the carburetor, drags some gasoline along with it and evaporates it, and the resulting gas mixture enters the cylinders and is ignited by sparks emitted from the spark plugs. Carburetor adjusts automatically the air to be sucked and the rate of the gasoline to be mixed with additional mechanisms.
Carburetor simply consists of a narrowing air pipe in the middle and a gasoline tank connected to this pipe by several thin channels. Throat to air pipe, narrowing area of throat is called “venturi”. While according to laws of physics air sucked to the engine passes from venturi gains speed and consists of low pressure in this section. Low pressure (vacuum) consisting provides the fuel in the tank gasoline to be sucked and mixed with the air to move towards the cylinder or cylinders. Because of that, the main fuel channel is opened to venturi. There is a throttle valve in the section of the throat after the venturi, which is used to regulate the amount of air to be taken into the engine, and therefore the amount of air-fuel mixture, according to the direction of the air flow. Throttle works with action of the gas pedal in the vehicles. When driver steps to the gas pedal actually increases the opening of the throttle.
Gasoline is sent with the help of fuel pump to tank in the carburetor. A float valve is located here to keep the amount of gasoline at a steady level in the tank. Modern carburetors are equipped with many complex systems in order to ensure that the gasoline engine used in cars can operate at the desired power and speed according to changing conditions. Amount and rate of air-fuel mixture can’t be controlled because the density of gasoline and air and other physical properties are different. Despite many developed system, it has been understood that carburetors can’t achieve efficiency at the excellent level and the fuel injection system has taken its place in many modern vehicles today.
2- Single Point Injection – SPI
Single point injection systems can be described as a slightly developed version of carburetors. Fuel is injected into the intake fuel manifold by an injector connected to the throttle body. This fuel injected is given by mixing with air from intake valves to cylinders. This system that has started to be used since 1980 has been used generally in cars and vans made in America. These system parts which used in a small amount of European cars have not been reproduced due to their costs. It has not been produced by thinking about cost of parts due to not avantaged according to the carburetor.
3 – Multi Port Injection – MPI
Another name of multi port injection system is port fuel injection (PFI). It began to be produced in the 2000. There is a special injector for each cylinder. These injectors inject the fuel to the intake valve. With the opening of the intake, air-fuel mixture is given to the cylinder. In this system, injectors make to spray in that same time. However, the sequential fuel injection produced later, injects in the injector whose suction time comes. Engine control unit in the sequential injection system opens separately each injector.
Low pressure fuel pump located in the gasoline tank sends the fuel to the fuel log that injectors are connected. Thanks to the pressure regulating valve, the fuel stays at a constant pressure in the log. Injector taking command from the engine control unit opens and injects point that the intake manifold encounters with the cylinder head so that before the intake valve.
In this injection system, fuel pressure in the low pressure like the sequential fuel injection is about 3-5 bars. This pressure is sufficient to inject fuel.
4 – Gasoline Direct Injection – GDI
Direct gasoline injection systems are the most advanced and efficient among injection systems. The most fundamental difference of this system from other injection systems is to inject the fuel direction to the combustion chamber.
How does this injection system work?
The fuel that low pressure fuel pump receives, it pressurizes and gives it to the high-pressure pump, which is coupled to the engine and takes its movement from the crankshaft. Thanks to the high pressure pump, the fuel reaches 50-120 bars. There are injectors to the combustion chamber connected to each cylinder. These injectors are operated through the solenoid. Solenoid acts as a valve. By opening the solenoid, the fuel to coming injector overcomes the spring pressure inside and by pushing the needle valve up, it injects in way pulvarize the fuel to the combustion chamber through the nozzles. Later, by closing the solenoid valve, it cuts off the fuel to the coming injector.
Sensors calculating the combustion quality and load engine in the car send information to the engine control unit. By opening the solenoids of injectors the engine control unit on these informations, it decides how much fuel will be sent. So, the engine control unit adjusts solenoid opening time and open time according to the load of the engine. Parts that determine the load of the engine have been examined under the heading of air systems. These are sensors of MAF and MAP. To explain briefly, MAF sensor measures mass of air entering the engine. MAP sensor measures vacuum value consisting in the manifold and sends it to the engine control unit. In the oxygen sensors connecting to the end of the exhaust manifold measure the combustion quality and declares to the engine control unit amount of the air fuel mixture.
For more information, visit www.flowaytech.com/about-us/