All modern cars are now equipped with fuel injection systems (FIS) replacing carburetors. FIS is a combination of various components that co-ordinate and work together to deliver optimum engine performance. Failure of any single component can lead to improper functioning of the system and sometimes results in serious engine issues. This article is about the major components of FIS and their working process.
- Electronic control unit (ECU): It is the heart of the fuel injection system. It collects information from other components and checks if they are functioning properly.
- Sensors: There are different types of sensors in FIS like oxygen sensor, airflow sensor, coolant temperature sensor, throttle position sensor, engine speed sensor, etc., that act like brain of ECU.
They collect information on many factors like air pressure, air temperature, throttle angle, air density, fuel temperature, fuel pressure, oil pressure, coolant temperature, exhaust temperature, crankshaft angle, timing, engine rpm, speed of the vehicle, etc., and help ECU in processing the collected information.
- Injectors: They inject fuel and air mixture into cylinders.
- Pump: It is the component that transfers fuel from tank to injectors.
- Pressure regulator: It makes sure that fuel is supplied to injectors continuously and proper pressure is maintained.
- Rail: It connects fuel pump and fuel injectors.
- Filters: They are located in fuel rail. They filter the fuel flowing through the fuel rail.
- Check engine light: ECU scans all the sensors to verify their functionality before start of the engine. This check engine light indicates the scanning progress. Check engine light turns on when the scanning takes place and turns off when the scanning is completed. It is commonly located on the dashboard of the car.
Working of fuel injection system
The primary job of fuel injection system is to provide right amount of fuel and air mixture to the injector and at the right time. This is achieved with the optimum functioning of all the components mentioned above.
The entire working process of the system can be explained in two stages.
Measuring and sending right amount of fuel to injector
- The first step in fuel injection process is to send right amount of fuel to injectors. For this, components like fuel pump, pressure regulator, rail and filter are involved.
- ECU, with the help of information provided by crankshaft position sensor, identifies which cylinder needs fuel. It then sends this signal to fuel pump that is present in fuel tank.
- Fuel pump collects certain amount of fuel from tank and sends it to the pressure regulator where the fuel gets electrically pressurized. Pressure regulator also makes sure that the fuel is sent to the corresponding injector with the required pressure and no fuel is left out in the rail.
- Pressurized fuel then enters the rail, passes through the filters present in it which remove all the solid and unwanted particles present in the fuel. Thus filtered fuel enters the injector.
Injecting fuel and air mixture into combustion chamber
- Fuel injector now contains right amount of pressurized fuel but it is not injected into combustion chamber until the injector receives signal from ECU.
- ECU estimates the right time to inject fuel into combustion chamber by considering various factors like how much air is required, how much vacuum is present, temperature of air, temperature of fuel, temperature of engine, etc., using sensors and calculates the amount of time that the valve of the injector should be open (this time will generally be some milliseconds) to spray right amounts of mixture.
- Once the injector receives the signal, it opens its valve and sprays the fuel and air mixture with required pressure in to the combustion chamber.
An engine’s performance is purely based on the amount of fuel and air mixture. While both carburetor and FIS do the same job of feeding fuel and air mixture to the engine, the electronics used in FIS will calculate and constantly adjust the proportions resulting in a controlled fuel injection. This not only leads to higher power output but also increases the fuel efficiency of the vehicle and reduces toxic emissions.