The diesel fuel I bought recently has a darker color than I am used to seeing. I accidentally mixed gasoline with my diesel. Petrol is the fuel designed for spark-ignition internal combustion engines. Conventional petrol is a mixture of compounds, called hydrocarbons, derived from petroleum crude plus a small amount of a few additives to improve its stability, control deposit formation in engines, and modify other characteristics.
Spark knock is the sound of abnormal combustion.
When combustion in a spark-ignition internal combustion engine is initiated by a spark, the flame front should fan out from the spark plug and travel across the combustion chamber rapidly and smoothly. Knocking occurs because the octane of the petrol is below the antiknock requirement of the engine at that moment. Occasional light knocking won't harm an engine. Heavy or prolonged knocking can result in loss of power, overheating of parts in the cylinder and engine damage. Octane number is a measure of the antiknock quality of petrol - the ability of the petrol to resist knocking when it is burned in an engine.