Saturated hydrocarbons will generally give a clean flame but unsaturated sooty flame. Why?
Usually saturated hydrocarbons gives a clean flame while unsaturated carbon compounds gives a yellow sooty flame . However, limiting the supply of air results in incomplete combustion of even saturated hydrocarbons, giving a sooty flame. The gas/kerosene stove used at home has inlets for air so that a sufficiently oxygen-rich mixture is burnt to give a clean blue flame. If you observe the bottoms of cooking vessels getting blackened, it means that the air holes are blocked and fuel is getting wasted.