Fractionation columns separate oil into basically molecule sizes, obviuslywith some degree of overlap. This generally means the more carbon atoms ithe string, or ring, the higher the boiling point of that component.
In addition refineries also 'crack' the longer chains into shorter, more volatile componets. It all depends on the type of feed and what fractions are desired at the output.
Higher RMM (Relative Molecular Mass) components tend to have lubricatig properties (think engine oil, here). Kerosene/paraffin fractions have little lubricity (petrol about nil), so these should c not be usedvwhere lubricity is required (diesel injection pumps and diesel injectors).
It is well known that a diesel engie with some kerosene will burn cleaner than the heavier fraction. It is ilegal to do so, of course, but MOT emissions failures have returned with kero in the filter, and passed.
Petrol in diesel clearly reduces the lubricity and may damage the close tolerance pumping and injection components. In addition, diesel fuel containing petrol will burn much closer to the injector tip and potentially overheat and damage it. Expensive job, having nozzles repaced! I would not like to leave more than about 5% contamination for long. 10% tops. The higher the injection pressure, the worse the problem gets, so common
r
ail diesels are more susceptible to damage.
There is also the issue of sulphur content of these fuels. Low sulphur means low lubricity, hence some older engines may be incompatible with modern low sulphur fuel, needing an additive to avoid damage to the injection equipment. DERV is defiitely low sulphur these days.
A much more interesting topic than Darwin awards, where blow lamps are concerned.