ICE-14 — Common Rail

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

In this lesson you will learn:

• The structure and operation
• The advantage of pressure control
• Multiple-injection strategy

1. Structure and Operation

Common rail stores fuel at high pressure in a single rail and delivers it from there to each injector.

FACT — Components: fuel tank, low-pressure feed pump, high-pressure pump, common rail, pressure sensor and per-cylinder electro-hydraulic injectors. Fuel pressure is held in the rail independent of injection.

2. Pressure Control

FACT — The key advantage is that injection pressure can be controlled independently of engine speed and load — unlike older pump-nozzle systems where pressure was speed-limited.

3. Multiple Injection

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

INTERPRETATION — Multiple injection shapes heat release to manage the NOx/soot balance — a core emissions-calibration tool (ICE-41).

4. Trade-offs

FACT — Higher injection pressure improves atomization and reduces soot, but increases pump work (parasitic loss) and cost. Pressure is optimized for the emissions/efficiency balance.

5. Summary

• Common rail stores fuel in a shared high-pressure rail.
• Pressure is controlled independently of speed.
• Multiple injection manages combustion and emissions.

6. Sources

• Bosch, Diesel-Engine Management
• Bosch Automotive Handbook

Next Lesson

• ICE-15 — Turbocharging: exhaust-driven forced induction.