The present invention provides a process for preparing acetylene and synthesis gas by partial oxidation of hydrocarbons with oxygen, by first separately preheating the starting gases comprising a hydrocarbon-containing stream and an oxygen-containing stream and then mixing them in a mixing zone and, after they have flowed through the burner block, reacting them in the firing space and then cooling the products rapidly, wherein the surface on the firing space side of the burner block is covered with a purge gas stream and this purge gas stream is introduced through the burner block by means of several bores, where the averaged ratio of effective surface area of the burner block to number of these bores in the burner block for the purge gas stream is within a range from 5 to 100 cm2.