الفهرس 
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Abstract
Lean premixed flames could only stabilize over limited operating
conditions, therefore a good understanding of flame stabilization and
blowoff phenomena are of a great importance. This research work
investigated bluff body assisted-combustion with internal preheating of the
fuel-air mixture before entering the combustion zone. Ten hollow bluff
body shapes with different geometries were tested experimentally.
Examining the stabilization of lean premixed flames anchored to
hollow bluff bodies with internal preheat requires the investigation of
several interacting factors such as blockage ratios, geometrical attributes,
residence time inside and outside the bluff body, preheating, momentum
of downward reactive jet, and buoyancy of hot combustion gases.
Both the lean operation limit (i.e., equivalence ratio) and
stabilization limit (i.e., blowoff velocity) have proved to be significantly
affected by the reactive jet downward impingement onto the burner bottom
surface as well as the wake zone on the top of the bluff body.
Enlarging the turbulent impingement zone while keeping the
mixture exit as close as possible to the burner base hot surface pronounced
more intensive heat recirculation that is effectively associated with wider
stability limits of the flame. The resultant burning capacity becomes thus
correlated to the non-dimensional temperature differences namely the
preheated bluff body temperature ratio (BTR) and preheated mixture
temperature ratio (MTR).
Extending the bluff body outer contact surface while reducing the
interior residence time has been found to be more beneficial than extending
XVI
Studying Bluff Body-Assisted Combustion with Fuel-Air Mixture Internal Preheat
the bluff body outer surface while increasing the interior residence time. It
has also found that the enlargement in the bluff body surface is more
beneficial at the wake zone rather than at the early preheating zone since
the upstream displacement of the flame minimizes the contribution of the
wake zone to the enhancement of the flame stabilization.
In the current work, large magnitudes of blowoff velocities as high
as 179m/s and extensive reduction in the lean equivalence ratio limit down
to Ø = 0.42 were obtained.
While the maximum blowoff velocity was achieved via the
corrugated faceplate shape, the minimum lean operation limit was
achieved via the long-tapered sides shape. This is attributed to the
interactive effects of preheating and blockage ratio. In this respect, the
trapezoidal shape has larger interface with the mixture so as to cause more
effective preheating for achieving the minimum lean operation limit.
However, too large blockage ratio causes reduction in the effective gain of
the mixture velocity upstream of the bluff body such that less gain in the
burning capacity is pronounced.