ICE-28 — Pre-ignition

ASSUMPTION — This lesson covers pre-ignition conceptually; specific LSPI thresholds are not given.

In this lesson you will learn:

• Pre-ignition vs knock
• Its causes
• The LSPI concept

1. What Is Pre-ignition?

Pre-ignition is ignition of the mixture before the spark, by a hot surface (e.g., an overheated plug or carbon deposit).

FACT — Knock is end-gas auto-ignition during flame propagation; pre-ignition is combustion starting before the spark. Pre-ignition shifts combustion much earlier, creating severe pressure and heat loads.

2. Causes

FACT — Causes include a hot spark plug/exhaust valve, carbon deposits, a wrong heat-range plug, and overheated chamber surfaces acting as an ignition source.

3. LSPI (Low-Speed Pre-Ignition)

FACT — In small, high-boost (downsized) direct-injection engines, a pre-ignition-like event can occur at low speed/high load (LSPI). Its cause is complex (oil droplet/deposit related) with high damage risk; it is managed via calibration and fuel/oil formulation.

4. Relationship to Knock

INTERPRETATION — Pre-ignition can trigger knock, and together they can be highly destructive. Control strategies (advance, mixture, cooling) consider both.

5. Summary

• Pre-ignition is hot-surface ignition before the spark.
• It differs from knock; earlier and potentially more destructive.
• LSPI is a special risk in downsized GDI engines.

6. Sources

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

Next Lesson

• ICE-29 — Engine Cooling.