In internal combustion engine classification, petrol (gasoline) engines are commonly referred to by which ignition type based on the method of initiating combustion?

Introduction / Context:

Engines are categorized by how the combustible mixture is ignited. Petrol (gasoline) engines use an external spark, while diesel engines rely on compression heating of air followed by fuel injection. This terminology appears in textbooks, service manuals, and certification exams.

Given Data / Assumptions:

• Four-stroke and two-stroke petrol engines for automotive use.
• Conventional port- or direct-fuel injection.
• Ignition provided by spark plug and ignition system.

Concept / Approach:

Petrol engines operate on the spark ignition (S.I.) principle: a premixed air–fuel charge is ignited by an electrical discharge across the spark plug at near the end of the compression stroke. By contrast, diesel engines are compression ignition (C.I.) because fuel is injected into hot compressed air and ignites spontaneously without a spark.

Step-by-Step Solution:

Verification / Alternative check:

Service literature and SAE texts uniformly describe gasoline engines as spark ignition; diesel as compression ignition.

Why Other Options Are Wrong:

• Compression ignition: characteristic of diesel, not petrol.
• Steam engines: external combustion; not internal combustion.
• None of these / HCCI without spark: HCCI is experimental/limited; the standard petrol engine is S.I.

Common Pitfalls:

• Assuming direct-injected gasoline necessarily implies C.I.; GDI still uses spark ignition in mainstream applications.

Final Answer:

spark ignition (S.I.) engines