ICE-13 — The Ignition System

ASSUMPTION — This lesson covers the spark-ignition system in general terms; specific energy/voltage values are not given.

In this lesson you will learn:

• The system’s components
• The importance of ignition timing
• The spark energy concept

1. What the System Does

The ignition system produces a high-voltage spark at the plug to ignite the compressed mixture at the right moment.

FACT — The ignition coil steps up low voltage (12V) to the high voltage needed for the spark; the arc across the plug electrodes ignites the mixture. The ECU controls timing.

2. Ignition Timing (Advance)

FACT — Combustion is not instantaneous; the flame needs time to propagate. So the spark fires before TDC so peak pressure occurs just after TDC. Too much advance causes knock; too little causes efficiency loss.

3. Spark Energy and Dwell

• Dwell — the coil’s energy-charging time.
• Spark energy — must be enough for reliable ignition.

FACT — Lean mixtures and high cylinder pressure are harder to ignite and may need higher spark energy; modern systems adapt to engine state.

4. Knock Relationship

FACT — The ECU retards spark based on the knock sensor signal to suppress knock (closed-loop knock control, ICE-27).

5. Summary

• Coil steps voltage up; plug makes the spark.
• Advance sets combustion efficiency and knock risk.
• Spark energy and dwell ensure reliable ignition.

6. Sources

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

Next Lesson

• ICE-14 — Common Rail: the diesel high-pressure injection system.