Environmental Engineering Reference
In-Depth Information
combustor prior to combustion. The operating pressure was one atmosphere. For
any of the numerical models, the volume consisted of more than one million
tetrahedral mesh cells.
The model boundary conditions are described in this section. For air inlet,
“
mass
fl
boundary condition was used with inlet turbulence intensity of 10 %,
mass fraction of O
2
of 0.233, and inlet temperature of 600 K. For fuel inlet,
flow inlet
”
“
mass
fl
boundary condition was used with inlet turbulence intensity of 10 %, the
mass fraction of CH
4
was set to 1, and the inlet temperature was set to 300 K. For
hot product gases to exit,
flow inlet
”
boundary condition was used, with zero-
gauge back pressure and 10 % turbulence intensity for back
“
pressure outlet
”
ow. For all the
numerical simulations, the resultant equivalence ratio was 0.8 with methane as the
fuel. For any numerical simulations, the conversion criterion was that the largest
residual was less than 10e
fl
field and
mixing behavior will deviate from the actual case; however, the trends are expected
to remain consistent as shown through velocity measurements compared to
numerical simulations in a previous study (Khalil and Gupta
2014a
), thus providing
an indication for the causes of pollutants emission behavior for the various cases
investigated here.
4. It is understood that the simulated
fl
ow
−
4 Results and Discussion
4.1 Injection Location
The experimental investigation was focused on examining different methods of fuel
introduction into the combustor to help develop an understanding of the mixing
process so as to enhance and accelerate the mixing and achieve adequate mixing
prior to ignition. The distributed combustion process requires that air and/or fuel be
mixed with the hot and chemically active gases from the combustion zone prior to
the mixture ignition for seeking distributed reactions. In this study, air preheats
were employed to simulate gas turbine combustion conditions with elevated inlet
combustion air temperatures. The experimental results are reported at equivalence
ratios of 0.8, 0.7, 0.6, and 0.5. These upper ends of equivalence ratios are higher
than that used in current engines and are used due to higher ef
ciency that can be
achieved at higher equivalence ratios. Emissions of NO and CO were recorded for
each arrangement at different equivalence ratios. Figures
4
and
5
show the emission
levels at different equivalence ratios with each arrangement.
The results obtained on NO emission indicate that coaxial injection provides
highest NO emission levels as compared to other fuel introduction methods. Sepa-
rate air and fuel introduction exhibited lower emission levels. The premixed com-
bustion mode
revealed the lowest emissions. For instance, at an equivalence
ratio of 0.6, coaxial injection provided emission levels of 21 PPM NO and 62 PPM
CO. Separate injection mode
“
PR
”
“
NP0
”
yielded emission levels of 14 PPM NO and 26
PPM CO. Case
“
NP1
”
yielded lower emissions at 10 PPM NO and 21 PPM CO.
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