Fuel injection has transformed petrol engines, replacing outdated carburetors with more efficient, precise, and electronically controlled methods. The evolution of petrol fuel injection systems has led to significant advancements in performance, fuel economy, and emissions reduction.
Types of Petrol Fuel Injection Systems
Petrol injection methods vary based on fuel atomization, delivery timing, and combustion efficiency. Below are the major types, ranked from the most basic to advanced systems.
1. Single-Point Injection (SPI)
- Also known as: Throttle Body Injection (TBI).
- How it works: Uses one injector positioned in the throttle body, spraying fuel directly into the intake manifold.
- Technical Details:
- Injection Pressure: 1–3 bar
- Fuel Atomization: Moderate, limited control
- Control System: Basic electronic control unit (ECU)
- Fuel Delivery Timing: Continuous or batch injection
- Compression Ratio Supported: 8:1 – 10:1
- Advantages:
- Simple and cost-effective.
- Easier to maintain than complex systems.
- Disadvantages:
- Uneven fuel distribution across cylinders.
- Lower efficiency compared to multi-point injection.
2. Multi-Point Fuel Injection (MPFI)
- How it works: Uses individual injectors for each cylinder, delivering fuel near the intake valves.
- Technical Details:
- Injection Pressure: 3–5 bar
- Fuel Atomization: Better distribution
- Control System: ECU-controlled multiple injectors
- Fuel Delivery Timing: Batch or sequential injection
- Compression Ratio Supported: 9:1 – 11:1
- Advantages:
- Improved fuel distribution, enhancing combustion efficiency.
- Better fuel economy than SPI.
- Disadvantages:
- Requires electronic control, increasing complexity.
- Limited ability to optimize fuel-air mixture dynamically.
3. Sequential Fuel Injection (SFI)
- How it works: A refined version of MPFI that times each injector independently, synchronizing fuel delivery with intake valve opening.
- Technical Details:
- Injection Pressure: 3–5 bar
- Fuel Atomization: High precision, independent for each cylinder
- Control System: ECU-controlled sequential timing
- Fuel Delivery Timing: Precisely timed per cycle
- Compression Ratio Supported: 10:1 – 12:1
- Advantages:
- Reduces fuel waste, improving throttle response.
- Optimized power delivery due to timed injection.
- Disadvantages:
- Requires high-precision electronic control.
- Slightly more expensive than MPFI.
4. Direct Injection (DI)
- How it works: Injects fuel directly into the combustion chamber, skipping the intake manifold.
- Technical Details:
- Injection Pressure: 50–200 bar
- Fuel Atomization: Ultra-fine mist for optimal mixing
- Control System: High-pressure pump & ECU
- Fuel Delivery Timing: Stratified or homogeneous injection
- Compression Ratio Supported: 11:1 – 14:1
- Advantages:
- Superior fuel economy, extracting maximum energy per drop.
- Higher compression ratios, improving power output.
- Disadvantages:
- Carbon buildup on intake valves can occur over time.
- More expensive to manufacture.
5. Gasoline Direct Injection (GDI)
- How it works: An advanced DI system using high-pressure injectors that optimize fuel atomization.
- Technical Details:
- Injection Pressure: 100–250 bar
- Fuel Atomization: Ultra-fine mist, precisely controlled
- Control System: ECU-controlled high-pressure fuel pump
- Fuel Delivery Timing: Stratified or homogeneous injection
- Compression Ratio Supported: 12:1 – 15:1
- Advantages:
- Improved fuel efficiency, reducing fuel consumption.
- Enhanced throttle response, making acceleration smoother.
- Disadvantages:
- Requires specialized high-pressure pumps.
- Can produce higher particulate emissions, needing filters.
6. Turbocharged Direct Injection (TDI)
- How it works: Combines direct injection with turbocharging for increased performance and efficiency.
- Technical Details:
- Injection Pressure: 100–250 bar
- Fuel Atomization: Ultra-fine mist, dynamically adjusted
- Control System: ECU-controlled turbo and fuel pump
- Fuel Delivery Timing: Optimized for power and efficiency
- Compression Ratio Supported: 12:1 – 15:1
- Advantages:
- Maximizes horsepower and torque without increasing displacement.
- Improves fuel economy compared to naturally aspirated engines.
- Disadvantages:
- More complex and expensive to maintain.
- Turbo lag may reduce low-RPM responsiveness.
7. Hybrid Fuel Injection Systems
- How it works: Found in hybrid petrol-electric vehicles, combining port injection and direct injection dynamically.
- Technical Details:
- Injection Pressure: 3–250 bar
- Fuel Atomization: Variable based on driving mode
- Control System: ECU-controlled hybrid fuel system
- Fuel Delivery Timing: Adaptive per cycle
- Compression Ratio Supported: 12:1 – 15:1
- Advantages:
- Optimized fuel efficiency, switching modes based on driving conditions.
- Lower emissions, improving environmental impact.
- Disadvantages:
- Requires complex electronic control.
- More expensive than conventional systems.
Comparison of Petrol Fuel Injection Systems
| Feature | SPI | MPFI | SFI | DI | GDI | TDI | Hybrid |
|---|---|---|---|---|---|---|---|
| Injection Pressure (bar) | 1–3 | 3–5 | 3–5 | 50–200 | 100–250 | 100–250 | 3–250 |
| Fuel Atomization | Moderate | Improved | High Precision | Ultra-Fine Mist | Ultra-Fine Mist | Ultra-Fine Mist | Variable |
| Control System | Basic | ECU | ECU | High-Pressure Pump & ECU | ECU & High-Pressure Pump | ECU & Turbo | ECU & Hybrid System |
| Fuel Delivery Timing | Continuous | Batch/Sequential | Sequential | Stratified/Homogeneous | Stratified/Homogeneous | Stratified/Homogeneous | Adaptive |
| Compression Ratio Supported | 8:1 – 10:1 | 9:1 – 11:1 | 10:1 – 12:1 | 11:1 – 14:1 | 12:1 – 15:1 | 12:1 – 15:1 | 12:1 – 15:1 |
| Efficiency | Low | Moderate | High | Very High | Very High | Very High | Optimized |
| Maintenance Cost | Low | Moderate | Moderate | High | High | High | High |
Fuel injection systems have evolved significantly, improving power output, fuel economy, and emissions control.
- Basic systems (SPI, MPFI) provide affordability but limited precision.
- Advanced systems (DI, GDI, TDI) optimize fuel economy and power.
- Hybrid Fuel Injection Systems represent the future of optimized efficiency.
Each system offers trade-offs between cost, complexity, and performance, shaping the engine technology of tomorrow