about 0.3' cloth dipped in diesel will burn petrol it self will burn the gasses too i dont know if non flammable is the correct term theres inflamable flamable & non flam
Diesel is less combustible (i.e. flammable), therefore less hazardous if spilled. But it does burn in a diesel engine, where it's ignited by high pressure rather than a spark as in a petrol engine. They're both hydro-carbons, formed as the name suggests from hydrogen and carbon.
If i remember chemistry at school correctly then petrol and diesel are produced at different stages of the the refining process for crude oil. This gives them different properties as mentioned previously. I believe petrol(naptha fraction) is produced earlier in the process than diesel and as such it is less volatile (ie more likely to combust).