Why do unsaturated carbon compounds produce a sooty flame and saturated carbon compounds produce a clean flame?

 unsaturated carbon compunds burns with sooty flame because . in that cobustion reaction heat is very less to burn out all the carbons  ex take gas stove it gives tremendous heat which can burn all carbon compound it burns  blue in colour which means saturated c-compound  .  but in candle it burns in very less heat which is not capabel to burnout all the carbon properly and it burns yellow in colour which is unsaturated 

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