Sequential Injection system

Sequential Fuel Injection (SFI), also known as Sequential Multi-Point Fuel Injection (Sequential MPFI), is a refined form of multi-point fuel injection where each fuel injector is timed to spray fuel individually in sync with the engine's firing order. This precise timing helps optimize fuel delivery by injecting fuel directly into each cylinder just before the intake valve opens, ensuring a more efficient and controlled fuel-air mixture.

How Sequential Injection Works

In a sequential fuel injection system, each cylinder’s fuel injector is controlled individually by the Engine Control Unit (ECU), based on the engine’s firing sequence:

1. Injector Timing: Each injector sprays fuel precisely when that cylinder is ready to intake, ensuring fuel is immediately available for combustion.

2. Synchronization with Firing Order: The ECU times each injector's pulse to align with the engine’s firing order. This prevents fuel from sitting on the intake valve and allows for a fresh fuel charge to enter each cylinder.

3. Real-Time Adjustments: Using inputs from various sensors (like oxygen sensors, throttle position sensors, and engine temperature sensors), the ECU adjusts the amount and timing of fuel injection for each cylinder in real time.

Components of a Sequential Injection System

1. Fuel Injectors: One injector for each cylinder, positioned on the intake manifold near the intake valve.

2. Engine Control Unit (ECU): The ECU manages the timing and quantity of fuel delivered to each cylinder by controlling the injectors based on data from sensors.

3. Sensors: Includes sensors like the camshaft position sensor (for timing each injector pulse), throttle position sensor, oxygen sensor, and temperature sensors.

4. Fuel Pump and Fuel Pressure Regulator: Ensures a steady supply and consistent fuel pressure for each injector.

Advantages of Sequential Injection

1. Improved Fuel Efficiency: Sequential injection minimizes the amount of fuel wasted by injecting only when each cylinder needs it, reducing fuel consumption.

2. Better Emissions Control: By optimizing the air-fuel mixture in real-time, SFI helps reduce harmful emissions.

3. Enhanced Throttle Response: Because fuel is injected right before combustion, there’s less delay, providing smoother and faster throttle response.

4. More Consistent Power Delivery: SFI optimizes combustion across all cylinders, providing consistent and balanced power output.

Disadvantages of Sequential Injection

1. Complex and Costly: SFI systems are more complex due to individual injector timing, making them more expensive and challenging to repair compared to simpler fuel injection systems.

2. Requires High-Quality ECU and Sensors: SFI depends heavily on accurate timing and sensor data, so faulty sensors or a malfunctioning ECU can impact performance and efficiency.

Applications of Sequential Injection

Sequential injection is commonly found in most modern vehicles, from economy cars to high-performance engines, due to its fuel efficiency, emissions control, and improved performance. It’s particularly useful in engines requiring precise fuel management and responsiveness, making it a standard in modern automotive fuel injection systems.