Multiple stage atomization of fuels for use in combustion applications

A three stage atomizer has been constructed consisting of airblast, swirl and effervescent stages allowing for more than one mode to contribute to the primary and secondary atomization of a single liquid jet. While the atomization mechanisms resulting from individual modes are fairly well understood, their combined usage to control the droplet size distribution is complex and has not been investigated in detail. A study of various combinations of air-blast, swirl and effervescence is conducted using phase Doppler anemometry and droplet imaging. This is done in order to quantify the effects on the resulting spray structure including the control of the droplet size to yield a desired range of equivalence ratios in combustion applications. Preliminary results for a non-reacting spray show that for a given atomizer geometry, the air-blast stage produces sprays with a D32 that typically ranges from 30 μm ∼ D32 ∼ 50 μm. The resulting size distribution depends heavily on the ratio of liquid to air mass flow-rate and to a lesser extent on the geometry of the liquid and air-blast nozzles. The effervescent mode produces sprays with a D32 < 30 μm such that a combination of the two modes allows for droplet size control. The swirling stage alters the spray structure significantly, allowing for simultaneous droplet size and cone angle control.