cross section is achieved in the region where the vortex breaks down that is to say in the region of the return flow zone 6 in that the vortex flow imposes an angular velocity component on the fuel droplets produced by the oil nozzle the centrifugal force thereby produced drives the droplets of the liquid fuel 12 radially outwards however evaporation acts at the same time in the case under discussion the result of the interplay of centrifugal force and evaporation is that the inner walls of the partial conical bodies 1 2 are not wetted and that a very uniform fuel air mixture comes about in the region of the return flow zone 6 the ignition takes place at the peak of the return flow zone 6 it is not until this point that a stable flame front 7 can arise here there would be no fatal consequences of a kickback of the flame into the interior of the burner as is always to be feared in the case of known premixing sections where remedy is sought however against this with complicated flame retention baffles if the conditioned mixture 15 is preheated as is the case in the present example an accelerated comprehensive evaporation of the liquid fuel 12 arises as is explained in the description of fig1 before the point is reached at the outlet of the burner a at which the ignition of the mixture can take place the degree of evaporation is of course dependent upon the size of the burner a the drop.