Misfueling scenario: If diesel fuel is used in a conventional petrol (spark-ignition) engine, what will happen?

Introduction / Context:
Using the wrong fuel type undermines the ignition method and spray/volatility characteristics for which an engine is designed. Petrol engines require a volatile, high-octane fuel that forms a combustible mixture and ignites by spark at the right timing, whereas diesel fuel is less volatile and intended for compression ignition with injection.

Given Data / Assumptions:

• Conventional SI petrol engine with spark ignition and either carburetion or port injection.
• Diesel fuel substituted for petrol in the tank.
• No hardware changes (no high-pressure injection or glow assistance).

Concept / Approach:
Diesel has lower volatility and higher auto-ignition tendency at high temperature but resists forming a proper combustible vapor mixture at typical SI intake conditions. The spark may fail to ignite large droplets; plugs foul with unburned fuel; the engine may cough briefly and stall. Pre-ignition or “explosion” is highly unlikely under these conditions; the usual outcome is failure to start or poor running followed by stalling.

Step-by-Step Solution:

Verification / Alternative check:
Workshop experience confirms petrol engines misfueled with diesel typically do not start or stall quickly due to plug fouling and lack of proper vaporization/ignition.

Why Other Options Are Wrong:

• Run more efficiently / at high speed: Opposite of observed behavior.
• Explode: Unfounded; diesel in an SI engine lowers, not raises, knock risk during attempted operation.

Common Pitfalls:
Confusing misfueling cases (diesel in petrol vs. petrol in diesel). Petrol in a diesel can cause severe knock-like noise and damage; diesel in a petrol mainly causes no-start/poor running.

Final Answer:
not run