Diesel engines do not use spark plugs. They rely on compression ignition and typically use glow plugs for warming the combustion chamber, not for igniting the fuel. So, the direct answer is: zero spark plugs in a diesel engine. Context and details:
- Spark plugs are used in gasoline/petrol engines to ignite the air-fuel mixture with a spark. In diesel engines, the fuel is injected into highly compressed hot air, igniting without a spark [web sources indicate this distinction; see related explanations and FAQs].
- Diesel engines commonly have one glow plug per cylinder to aid starting and cold-weather combustion, but these are glow plugs, not spark plugs. The typical configuration is one glow plug per cylinder, so a 4-cylinder diesel would have four glow plugs, a 6-cylinder diesel six glow plugs, etc.
- Some sources explicitly state that there are no spark plugs in diesel engines and that glow plugs replace their function for aiding cold starts and combustion.
If you’d like, I can tailor the answer to a specific diesel engine (make/model/year) to confirm the exact plug configuration.
