Fuel Injection System: Components, Types, and Advantages

Posted on Feb 19, 2025 in Technology

Fuel Injection System: Components and Types

A fuel injection system delivers fuel into an internal combustion engine. Here’s a breakdown of the key components and types:

  1. Fuel Tank: The fuel reservoir.
  2. Fuel Pump: Typically an electric roller pump, it delivers more fuel than needed to the fuel rail. This ensures sufficient pressure and prevents fluctuations when injectors or the pressure regulator activate.
  3. Fuel Filter: Removes impurities from the fuel.
  4. Fuel Line: Connects the fuel pump to the fuel rail.
  5. Pressure Regulator: Maintains a consistent fuel pressure (between 2.5 and 3 bars) within the system.
  6. Engine Control Unit (ECU): The electronic brain that controls the fuel injection process.
  7. Fuel Injector: Precisely meters and sprays fuel into the intake manifold, near the intake valves. It’s an electromagnetic device that opens and closes based on signals from the ECU. Pulse duration is typically between 1 and 1.5 milliseconds. A spring keeps the nozzle closed when the coil is not energized.
  8. Cold Start Injector: Provides extra fuel during cold starts to ensure reliable ignition.
  9. Idle Adjustment Screw: Used to fine-tune the idle speed.
  10. Throttle Position Sensor (TPS): Corrects the fuel/air mixture for optimal combustion.
  11. Throttle Body: Controls the amount of air entering the engine.
  12. Air Flow Meter: Measures the amount of air entering the engine. A fin-mobile probe deflects proportionally to the airflow.
  13. Relay: An electrically operated switch.
  14. Lambda Probe (Oxygen Sensor): Monitors the oxygen content in the exhaust gases. It sends data to the ECU, which adjusts the fuel mixture to minimize emissions and maintain stoichiometric balance.
  15. Engine Coolant Temperature Sensor (ECTS): Provides the ECU with engine temperature data. Immediately after starting, the engine receives 2 to 3 times more fuel than normal.
  16. Thermo Switch: Another temperature-sensitive switch.
  17. Fuel Distributor/Rail: Delivers fuel to the injectors.
  18. Auxiliary Air Valve: Provides additional air to the engine during cold starts, bypassing the throttle body.
  19. Idle Mixture Adjustment Screw: Fine-tunes the air/fuel mixture at idle.

Fuel Injection Types

Fuel injection systems meter the precise amount of fuel needed at any given moment, resulting in lower emissions and improved fuel efficiency. Fuel is injected into the intake manifold, before the valves, through an autonomous system controlled hydromechanically or by electrical devices. The fuel is injected right at the entrance of the cylinder for proper balance.

Three Main Types:

  • Mechanical: Uses continuously open nozzles to deliver fuel at a constant pressure.
  • Electromechanical: A variation of mechanical injection with an electronic control system to modify fuel flow based on engine needs.
  • Electronic: Employs electromagnetic injectors controlled by an electronic system. Injection timing is adjusted based on data from various engine sensors.

Injection Points:

  • Single Point (Throttle Body Injection): Uses a single injector, similar to a carburetor, to inject fuel into the intake manifold.
  • Multipoint (Port Fuel Injection): Has one injector per cylinder, located near the intake valves.
  • Direct Injection: Injects fuel directly into the combustion chamber at high pressure, using a solenoid valve per cylinder.

Injection Timing:

  • Sequential: Injectors are activated one after another, in a specific firing order.
  • Simultaneous: All injectors spray fuel at the same time.
  • Semi-Sequential: Injectors are activated in pairs.

Advantages of Fuel Injection

  • Lower fuel consumption
  • Increased power and better acceleration
  • Improved cold starting
  • Reduced exhaust emissions

Electronic Fuel Injection with Air Flow Measurement

This system combines air flow measurement with a lambda sensor for improved mixture control and reduced emissions. Various sensors located on the engine provide signals to the electronic control module (ECU), enabling precise fuel delivery based on engine conditions. The ECU controls the injector opening time based on the amount of fuel required.