ICE-11 — The Diesel Engine

ASSUMPTION — This lesson covers general architecture; no specific OEM engine code or exact values are given.

In this lesson you will learn:

• The compression-ignition principle
• Differences from gasoline
• The emissions-control chain

1. Working Principle

The diesel (Diesel cycle) engine inducts only air and compresses it heavily. At the end of compression the air exceeds the fuel’s auto-ignition temperature; injected fuel self-ignites.

FACT — A diesel has no spark plug; ignition comes from compression heat, hence “compression ignition” (CI), with a much higher compression ratio than gasoline.

2. Differences from Gasoline

Feature	Gasoline	Diesel
Ignition	Spark	Compression heat
Mixture	Near stoichiometric	Always lean
Compression ratio	Low	High
Efficiency	Medium	High
Emissions	NOx-dominant	NOx + PM together

FACT — Because a diesel always runs lean, it cannot use a three-way catalyst; it uses EGR/SCR for NOx and a DPF for particulates.

3. Fuel Injection

Modern diesels use common rail: fuel is stored in a single high-pressure rail and delivered to each injector under electronic control, with multiple injections (pilot/main/post) to smooth combustion (ICE-14).

4. Turbo and Emissions Chain

• Turbo — standard for diesel power density (ICE-15).
• EGR — reduces NOx (ICE-19).
• DPF — traps particulates (ICE-23).
• SCR + AdBlue — reduces NOx (ICE-24).

INTERPRETATION — Diesel offers high efficiency and torque, but NOx/PM control requires a complex, costly aftertreatment chain — a key trade-off versus gasoline.

5. Summary

• Diesel is compression-ignited; no spark plug.
• Always lean; high efficiency and torque.
• Uses common rail + multiple injection.
• Emissions: EGR + DPF + SCR.

6. Sources

• Bosch, Diesel-Engine Management
• Heywood, Internal Combustion Engine Fundamentals

Next Lesson

• ICE-12 — Fuel Injection: comparing injection systems.