4. Conclusions
The present study is focused primarily upon the combustion
characteristics of small alkanes on noble metal surfaces in pre-mixed
homogeneous-heterogeneous hybrid systems. The homogeneous-heterogeneous
combustion characteristics small alkanes on noble metal surfaces are
investigated to gain a greater understanding of the mechanisms of flame
stabilization and to gain new insights into how to design pre-mixed
combustors with improved stability and robustness. The essential factors
for design considerations are determined with improved combustion
characteristics and flame stability. The primary mechanisms responsible
for the loss of flame stability are discussed. The major conclusions are
summarized as follows:
- The combustion effluent is characterized by high thermal energy and
typically by low nitrogen oxides content.
- Precise tuning of the combustion process is needed to establish a
balance between stable combustion and low emissions.
- Simply changing the combustor geometry to maintain near-stoichiometric
ratios will not avoid nitrogen oxides formation.
- The catalytic reactor oxidizes substantially all of the ingested fuel
and produces thermal energy.
- Adiabatic combustion systems, from a practical standpoint, have
relatively low heat losses, thus substantially all of the heat
released from the combustion zone of such systems appears in the
effluent gases as thermal energy for producing power.
- Catalytic oxidation has the disadvantage that the physical reaction
surface which must be supplied for complete oxidation of the fuel
increases exponentially with decreasing combustor inlet temperatures,
which greatly increases the cost of the combustor and complicates the
overall design.
- The operating temperature is determined by the theoretical adiabatic
flame temperature of the fuel-air admixture passed to the combustor
and thus is dependent on the initial temperature of the air as well as
the amount of fuel contained therein.
- The temperature of the catalyst zone is controlled by adjusting the
composition and initial temperature of the fuel-air admixture as well
as the uniformity of the mixture.