One of today's most important and challenging technological
problems is the development of advanced materials and processes
required to design and build a fleet of supersonic High Speed Civil
Transport (HSCT) airliners, a follow-up to the Concorde SST. The
innovative combustor designs required for HSCT engines will need
high-temperature materials with long-term environmental stability.
Higher combustor liner temperatures than today's engines and the
need for lightweight materials will require the use of advanced
ceramic-matrix composites (CMC's) in hot-section components. The
HSCT is just one example being used to demonstrate the need for
such materials. This thesis evaluates silicon carbide (SiC) as a
potential base material for HSCT and other similar applications.
Key issues are the environmental durability for the materials of
interest. One of the leading combustor design schemes leads to an
environment which will contain both oxidizing and reducing gas
mixtures. The concern is that these environments may affect the
stability of the silica (SiO2) scale on which SiC depends for
environmental protection. A unique High Pressure Burner Rig (HPBR)
was developed to simulate the combustor conditions of future gas
turbine engines, and a series of tests were conducted on
commercially available SiC material. These tests are intended as a
feasibility study for the use of these materials in applications
such as the HSCT. Linear weight loss and surface recession of the
SiC is observed as a result of SiO2 volatility for both fuel-lean
and fuel-rich gas mixtures. These observations are compared and
agree well with thermogravimetric analysis (TGA) experiments. A
strong Arrhenius-type temperature dependence exists. In addition,
the secondary dependencies of pressure and gas velocity are
defined. As a result, a model is developed to enable extrapolation
to points outside the experimental space of the burner rig, and in
particular, to potential gas turbine engine conditions.
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