OCR Text |
Show hertz are generated in the ring-shaped resonance chamber. The fuel flows out of the nozzle through the control tube and is atomized in the ultrasonic field. Because of the low outlet velocity of the fuel, good flame stability is achieved so that even fuel mixtures with high water content can be burned without quenching of the flame. The combustion air is led to the flame on the outside, around the nozzle, and is mixed with fuel in the high turbulence of the atomizing medium inside the ultrasonic field. This results in good final combustion with minimum of excess air. With the Jet-nozzle shown in Figure 2, a relatively long, slender flame is produced. The constant cross-sectional area of the fuel pipe is very advantageous in burning viscous fuels with solid particules, since it does not promote clogging or high pressure drop. The T-nozzle exhibits an additional deflection plate in front of the fuel outlet so that the fuel reaches the ultrasonic field radially. This design produces a bushy flame in the form of a tulip. In this case, the pressure drop and the probable problems of clogging as well as nozzle material erosion are much greater. Both nozzle types can also be provided with an additional pipe for added material flow as shown in Figure 3. This pipe is located concentrically between passages for fuel and atomizing medium which provides the possibility of feeding at the same time, different fuels with independently controlled inputs. Thus, for a fuel with poor ignition quality, an easily ignitable supplementary fuel can be added. Both fuels are atomized outside the nozzle, mixed and burned. Compared to burners with other atomizing methods, the ultrasonic burner exhibits several advantageous characteristics in the combustion of alternative fuels. The fuel viscosity can be five to eight times the maximum value of the other systems. The required fuel pressure and pressure drop are very low. When using the jet-nozzle, clogging and nozzle erosion do not occur, even if the fuel contains a significant amount of solids. The relatively high volume of gas required for the atomizing process can be regarded as a shortcoming. It amounts to approximately 25 to 3 0 % of fuel throughput by weight, and about five times the requirement of a typical conventional steam atomizing burner. Although this fact cannot be discarded, the loss can be compensated for by the better combustion it provides. 16-5 |