The normal flame is from the dirt, but it doesnt light very easily, abit like diesel realy and nitro fuel has nearly no flash point compared to somthing like petrol
Only burns when heated or in gas form
Off topic -
!!!DO NOT TRY THIS AT HOME!!!
My uncle demonstrated that he could drop a lit match into petrol (just a tad on the floor) and that it wouldnt explode , It worked The only thing with petrol is that the fumes light