Why can't gasoline be used in a diesel engine?

The correct answer is that gasoline will start to burn long before the piston reaches the top of the stroke. This phenomenon is due to the differing combustion processes between gasoline and diesel engines. Diesel engines operate on the principle of compression ignition, where air is compressed to such a high degree that it ignites the diesel fuel injected into it; this requires a much higher compression ratio. In contrast, gasoline ignites at a much lower compression ratio and would pre-ignite or detonate in a diesel engine before the piston reaches the optimal point in its stroke.

If gasoline were used in a diesel engine, the engine could experience knocking or pinging, which can lead to severe engine damage. The combustion timing would be out of sync, causing excessive heat and pressure that the diesel engine components are not designed to withstand. Understanding these fundamentals of engine design is crucial for diagnosing and preventing potential problems in automotive applications.