With a neat sketch explain the operation of an electrical fuel injection system used in a SI engine ?

 

⚙️ Operation of an Electronic Fuel Injection (EFI) System in an SI Engine

(With Neat Sketch Explanation)

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🚗 What is an Electronic Fuel Injection (EFI) System?

An EFI system is used in Spark Ignition (SI) engines to deliver the correct amount of fuel to the engine cylinders electronically, based on engine conditions. It replaces conventional carburetors with electronic sensors, actuators, and a control unit.

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📈 Main Objectives:

• Optimize fuel efficiency

• Ensure complete combustion

• Reduce emissions

• Improve engine performance

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🔩 Main Components of EFI System:

Component	Function
Fuel Tank	Stores fuel
Fuel Pump	Pumps fuel to injectors
Fuel Filter	Removes dirt/particles
Fuel Injector	Atomizes and sprays fuel into intake manifold or cylinder
Electronic Control Unit (ECU)	Brain of the system – controls fuel injection based on sensor data
Throttle Position Sensor (TPS)	Measures how much the throttle is open
Manifold Absolute Pressure (MAP) Sensor	Measures pressure inside the intake manifold
Engine Coolant Temperature (ECT) Sensor	Detects engine temperature
Oxygen (O₂) Sensor	Measures residual oxygen in exhaust to monitor AFR
Crankshaft Position Sensor	Helps time the injection event

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🔄 Working Principle:

1. Fuel Delivery:

   • Fuel from the tank is pressurized by the fuel pump and passed through a filter to remove impurities.

2. Air Intake Measurement:

   • Mass Air Flow (MAF) or MAP sensor measures incoming air.

   • TPS and crankshaft position sensor help determine engine load and speed.

3. Signal to ECU:

   • Sensors send signals to the ECU, which calculates the ideal air-fuel ratio for the operating condition.

4. Fuel Injection:

   • ECU sends signals to the injectors, which spray fuel directly into the intake manifold or cylinder.

   • The injected fuel mixes with air and is drawn into the combustion chamber.

5. Ignition:

   • The spark plug ignites the air-fuel mixture at the correct moment, completing the combustion process.

6. Feedback Loop:

   • The O₂ sensor monitors exhaust gases to help the ECU fine-tune the mixture in real time.

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🖼️ Neat Sketch: EFI System Layout

        +--------------------+     
        |     Fuel Tank      |
        +--------+-----------+
                 |
            +----v----+       Intake Air
            | Fuel    |       --->  
            |  Pump   |         +---------------------+
            +----+----+         | Air Filter          |
                 |              +---------------------+
            +----v----+                |
            | Fuel    |           +----v-----+
            | Filter  |           | Throttle |
            +----+----+           | Body     |
                 |                +----+-----+
           +-----v------+              |
           | Fuel Rail  |         +---v---+  
           +-----+------+         | Intake|  
                 |                | Manifold  
          +------+-------+        +---+---+
          | Fuel Injector|            |
          +------+-------+        +---v---+
                 |                |Cylinder|
                 |                +--------+
         +-------v--------+
         | ECU (Computer) |
         +----------------+

 Sensors connected to ECU:
 - Throttle Position Sensor
 - MAP / MAF Sensor
 - Crankshaft Position Sensor
 - Coolant Temp Sensor
 - Oxygen Sensor

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✅ Advantages of EFI over Carburetor:

• More precise fuel control

• Better fuel efficiency

• Lower emissions

• Easier cold starting

• Smoother engine performance

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🧠 Conclusion:

The Electronic Fuel Injection (EFI) system plays a critical role in modern SI engines by ensuring accurate, responsive, and cleaner fuel delivery. Controlled by the ECU, it adjusts fuel supply dynamically based on various engine and environmental parameters, ensuring optimal power, economy, and emission control.