As i've explained before to someone else who did the same thing not so long ago.
Petrol and diesel both come from crude oil and are not much different - petrol hydrocarbon chains are shorter, however EN590 standard does not say that the shorter chains can't be present in fuel sold as "diesel" - it actually allows somewhere around 5-10% to be the shorter "petrol" chains.
In very simple words - pump diesel contains petrol
This is all for a very simple reason, separating everything perfectly would take a lot of energy and make the whole thing cost prohibitive (for example - kerosene (heating oil) is a mix somewhere between pure petrol and diesel and it costs less than 30p/liter - it is also used as rocket fuel RP-1 where it is refined few more times to be a very precise mix of different hydrocarbons and no other contaminants, but it then costs £1/liter)
The reasons why petrol is damaging to diesel engines are actually very simple - longer hydrocarbons are good at lubricating things (engine oil is just a very long hydrocarbon), and engine designers used this property all throughout the engine, when you end up with high % content of the shorter hydrocarbons that are not very good at lubricating things - that's when problems start - high pressure fuel pump and injectors will not like it (low pressure lift pump is same both for diesel and petrol models).
Last edited by jacekowski; 31-05-15 at 20:24.