Low-Emission, Fuel-Flexible Combustion of Liquid Fuels - Novel Combustion Concepts for Sustainable Energy Development - page 471

8 Concluding Remarks

We have investigated low-emission, fuel- fl exible combustion of liquid fuels using a

novel flow-blurring (FB) atomization technique. FB injector provides a simple

atomization method that can reduce CO and NO X emissions by a factor of 3

fl

5 when
compared to an AB injector. FB atomization method is inherently different than AB
process in that atomization mechanism is based on expansion of gas in two-phase
flow instead of shear between the fuel and air. FB atomizer produces water sprays
with smaller droplets and a narrower range of droplet sizes as compared to AB
atomizer. FB atomizer is capable of cleanly atomizing and combusting straight
vegetable oil (VO) with no fuel processing or preheating. FB atomizer operating
with VO produces lower emissions than AB atomizer operating with biodiesel,
meaning that transesteri

-

cation of VO to produce biodiesel is not necessary to
achieve clean combustion. An insulated combustion environment is necessary

to ensure proper thermal feedback in glycerol ames. FB combustor can be used to

atomize and combust glycerol in an insulated environment without any fuel mixing
or preheating. Suf

fl

cient residence time within hot environment is critical to com-
plete oxidation of glycerol. Although the FB injector was effective for fuel atom-
ization, the thermal feedback from the pure glycerol

flame was inadequate to fully
prevaporize the fuel and/or preheat the reactant mixture. Combining the glycerol
combustion with methane combustion was shown to effectively solve these issues,
resulting in wider operating limits while minimizing CO emissions. While co-

fl

ring

glycerol with methane, the methane flow can be split between combustion and

atomizing air lines to minimize emissions. Emissions were mostly formed near the
combustor wall, where large droplet migrated and burned in diffusion mode.
Subsequent work would delineate the coupling between thermal and

fl

flow aspects of
the system to ensure stable combustion of many different fuels in the same system.

fl

Acknowledgments Author would like to thank his former graduate students Pankaj Kolhe,
Heena Panchasara, Benjamin Simmons, and Lulin Jiang for their contributions to this research.
Financial support from the US Department of Energy, US Department of Education, and the
University of Alabama facilitated this research.

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fl

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