ICE-12 — Fuel Injection

ASSUMPTION — Injection pressure values are typical orders of magnitude that vary by technology; exact values must be verified from OEM data.

In this lesson you will learn:

• Port vs direct injection
• Diesel common rail logic
• Injection pressure/timing importance

1. Why Injection?

Delivering the right amount of fuel, at the right time, well atomized, is critical for efficiency, emissions and driveability. Electronic injection replaced the carburetor for this precision.

FACT — Electronic fuel injection lets the ECU precisely set fuel quantity and timing every cycle — the core enabler of modern emission regulations.

2. Port vs Direct (Gasoline)

• MPI — fuel into the intake port; low pressure, homogeneous mixture.
• GDI — fuel into the cylinder; high pressure, charge cooling, better efficiency.

FACT — GDI reduces knock tendency via in-cylinder vaporization cooling, allowing higher compression ratio, but is prone to particulates (may need a GPF).

3. Diesel Injection

Diesel injects fuel into hot compressed air at very high pressure; modern systems use common rail.

FACT — In common rail, fuel is stored at high pressure in a single rail; injection pressure is controlled independently of engine speed and multiple injections are possible (ICE-14).

4. Injection Timing and Multiple Injection

• Pilot — reduces ignition delay and combustion noise.
• Main — primary power production.
• Post — raises exhaust temperature to aid DPF regeneration.

INTERPRETATION — Multiple injection shapes heat release to manage the NOx/soot balance — the heart of calibration (ICE-40, ICE-41).

5. Summary

• MPI is homogeneous; GDI is in-cylinder.
• Diesel uses common rail high-pressure, speed-independent injection.
• Timing and multiple injection manage combustion and emissions.

6. Sources

• Bosch, Gasoline-Engine Management and Diesel-Engine Management

Next Lesson

• ICE-13 — The Ignition System.