4 Conclusion and recommendations for further work
4.2 Recommendations for further work
Experimental measurements of temperature and NOx concentrations at different
premixing ratios should be carried out. Results from experiments could help verifying the results from the simulations of the swirl burner. If the simulations appear to be
inaccurate, measures to improve the model should be made. These measures could for instance be to improve the boundary conditions (to import velocity, temperature profiles etc.), to model the swirl burner in 3D or to change turbulence and reaction models. Also, a LIF measurement of the temperature could help investigate if the increase in the NOx
emissions when partial premixing is implemented is because of a larger high temperature area in the combustion chamber.
A larger number of simulations or experiments at different air-fuel ratios should also be carried out, especially around ratios between 2 and 3.5. More simulations could give answer to if the local minimum in this range is lower than the one found in this thesis.
If an up scaled version of the swirl burner is used, there is possible to apply both propane and methane as fuel. This will give an interesting comparison of the differences between the fuels, which was not possible when using the 20 kW swirl burner.
Appendix A Calculations
A.1 Calculations of new nozzle area with varying partial premixing
Based on pressure measurements, the fuel injected into the oxidizer is found to be distributed with 35% upstream and 65% downstream of the swirl generator [3]. This distribution proved difficult to simulate in FLUENT and problems with air seeping into the gas tube occurred (See Figure 17 in chapter 3.3.1). The nozzle upstream of the swirl generator was therefore removed and only the downstream nozzle is included in the constant velocity calculations.
Figure 28: Illustration of fuel distribution in the burner
The original nozzle velocity was calculated with the following equation:
fuel
v Velocity in nozzle upstream the swirl generator
mfuel Fuel pipe mass flow
ρfuel density of the fuel
Anozzle Area of the nozzles
By setting the velocity in the nozzle constant and then rearranging equation (4-1), the new nozzle area with a different fuel-air mass flow can be found:
Where ρmix can be found by applying equation (4-3):
Swirl
1
1 1
mix
fuel air
fuel air
mf mf
ρ
ρ ρ
=⎛ ⎞
⎜ + ⎟
⎜ ⎟
⎝ ⎠
(4-3)
Where mfi is the mass fraction of fuel and air.
Appendix B Some results from the simulations
B.1 Contours with premixed air-fuel ratio equal to 0
Figure 29: Contours of temperature [˚C], 10 kW @ 3% O2 with mair mfuel =0
Figure 30: Contours of OH mole fraction, 10 kW @ 3% O2 with mair mfuel =0
Figure 31: Contours of zero-axial velocities [m/s], 10 kW @ 3% O2 with mair mfuel =0
B.2 Contours with premixed air-fuel ratio equal to 0.5
Figure 32: Contours of temperature [˚C], 10 kW @ 3% O2 with mair mfuel =0.5
Figure 33: Contours of OH mole fraction, 10 kW @ 3% O2 with mair mfuel =0.5
Figure 34: Contours of zero-axial velocities [m/s], 10 kW @ 3% O2 with mair mfuel =0.5
B.3 Contours with premixed air-fuel ratio equal to 1
Figure 35: Contours of temperature [˚C], 10 kW @ 3% O2 with mair mfuel =1
Figure 36: Contours of OH mole fraction, 10 kW @ 3% O2 with mair mfuel =1
Figure 37: Contours of zero-axial velocities [m/s], 10 kW @ 3% O2 with mair mfuel =1
B.4 Contours with premixed air-fuel ratio equal to 1.5
Figure 38: Contours of temperature [˚C], 10 kW @ 3% O2 with mair mfuel =1.5
Figure 39: Contours of OH mole fraction, 10 kW @ 3% O2 with mair mfuel =1.5
Figure 40: Contours of zero-axial velocities [m/s], 10 kW @ 3% O2 with mair mfuel =1.5
B.5 Contours with premixed air-fuel ratio equal to 2
Figure 41: Contours of temperature [˚C], 10 kW @ 3% O2 with mair mfuel =2
Figure 42: Contours of OH mole fraction, 10 kW @ 3% O2 with mair mfuel =2
Figure 43: Contours of zero-axial velocities [m/s], 10 kW @ 3% O2 with mair mfuel =2 B.6 Contours with premixed air-fuel ratio equal to 3
Figure 44: Contours of temperature [˚C], 10 kW @ 3% O2 with mair mfuel =3
Figure 45: Contours of OH mole fraction, 10 kW @ 3% O2 with mair mfuel =3
Figure 46: Contours of zero-axial velocities [m/s], 10 kW @ 3% O2 with mair mfuel =3
B.7 Contours with premixed air-fuel ratio equal to 3.5
Figure 47: Contours of temperature [˚C], 10 kW @ 3% O2 with mair mfuel =3.5
Figure 48: Contours of OH mole fraction, 10 kW @ 3% O2 with mair mfuel =3.5
Figure 49: Contours of zero-axial velocities [m/s], 10 kW @ 3% O2 with mair mfuel =3.5
B.8 Contours with premixed air-fuel ratio equal to 4
Figure 50: Contours of temperature [˚C], 10 kW @ 3% O2 with mair mfuel =4
Figure 51: Contours of OH mole fraction, 10 kW @ 3% O2 with mair mfuel =4
Figure 52: Contours of zero-axial velocities [m/s], 10 kW @ 3% O2 with mair mfuel =4
B.9 Comparison of HCN concentration at different air-fuel ratios
Figure 53: Contours of HCN mole fraction for air-fuel ratios of: a) 0; b) 0,5; c) 1; d) 1,5; e) 2; f) 3; g) 3,5; h) 4
a) b)
c) d)
e) f)
g) h)
Appendix C Pictures of the 20 kW swirl burner
Figure 54: The swirl generator [3]
Figure 55: a) The gas tube without the burner tube and the combustion chamber b) The burner without the combustion chamber
a) b)
Figure 56: The combustion chamber
chimney
Water tube
Appendix D Enclosed DVD
The enclosed DVD contains the following:
• The GRIMECH 3.0 formation mechanism [26]
• Excel sheet with an overview of the geometry of the 20 kW swirl burner
• Excel sheet with the results from the simulations
• GAMBIT and FLUENT files for all of the different air-fuel ratios
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