On the Formation of Nitrogen Oxides During the Combustion of ...

6 Summary and Conclusions
In times of depleting resources, processes involving the combustion of fossil
fuels have to be highly efficient. Moreover, it is essential to develop novel
combustion concepts that offer a high potential for improvement towards environmentally
neutral combustion engines and low exhaust gas emissions. Especially
in aero-engines, the NO x emissions are seen to have a large potential
for further reduction. In this respect, partial premixed combustion with a partial
degree of liquid fuel vaporization aims at combining the advantages of
lean premixed and nonpremixed combustion. The study at hand was undertaken
to help resolve the issue of a possible effect of partial droplet vaporization
on the overall NO x production under idealized conditions. Against this
background, the vaporization and combustion of single droplets and linear
droplet arrays were investigated by experiments as well as modeled and numerically
simulated.
The microgravity environment was utilized because it allows a detailed observation
of the most essential phenomena in droplet combustion without the
disturbance of natural convection. These experiments also provided a basis
for the validation of an advanced model on droplet combustion. Linear
droplet arrays of the hydrocarbon C 10 H 22 were burned without relative velocity
to the ambient gas. A sophisticated design and optimized control procedures
were used to guarantee representative gas samples from the experiment
runs and a reliable, subsequent gas analysis on the ground.
Numerical work was performed, studying the driving forces of NO x generation
in single droplet combustion based on a spherically symmetric 1D model.
Microgravity conditions were applied correspondingly and detailed kinetics
were used. Since none of the C 10 H 22 mechanisms considered contains NO x
chemistry by default, an approach for combining chemical kinetics was established,
and an energetically neutral ignition method was formulated within
the droplet combustion model proposed. It was essential to provide a manageable
combination of the fields of droplet vaporization, ignition, combus-
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