CHAPTER FOUR
4. RESEARCH METHODOLOGY AND DESIGN
4.1. Part One: Philosophical perspectives
4.1.4 Methods of data collection
4.1.4.4 Statistical analysis of quantitative data
Reacting spray results
5.3 Effect of biodiesel blend on droplets
Reacting spray results shows rather similar profiles as Jet-A1 at the radii between x = 0 and x = 10 mm, but slightly lower SMD values than pure PME. The effect of fuel physical properties on spray characteristic is perpetuated in the comparison of droplet concentration and volume flux profiles as shown in Fig. 5.29c and 5.29d respectively. The droplet density profiles show a lower droplet concentration for the biodiesel blend by a factor of 2 compared to PME. Similarly, the volume flux profiles show a lower value for the biodiesel blend by a factor of 3 compared to PME. The spray characteristics of the blended fuels show the expected trend of profiles that fall in between the two parent fuels, although the linearity of the droplet characteristic in relation to the percentage of blend is not evident.
0 30 60 90
0 0.01 0.02 0.03 0.04 0.05
Axial velocity (ms-1) (a) x=7 mm, y=20 mm, Jet-A1
0 6 12 18 24
0 0.06 0.12 0.18 0.24 0.3
D10 (μm) (b) x=7 mm, y=20 mm, Jet-A1
0 10 20 30 40 50
-30 0 30 60 90 120
Axial velocity (ms-1)
D10 (μm)
(c) x=7 mm, y=20 mm, Jet-A1
0 30 60 90
0 0.015 0.03 0.045
Axial velocity (ms-1) (d) x=7 mm, y=20 mm, B50
0 6 12 18 24
0 0.06 0.12 0.18 0.24 0.3
D10 (μm) (e) x=7 mm, y=20 mm, B50
0 10 20 30 40 50
-30 0 30 60 90 120
Axial velocity (ms-1)
D10 (μm) (f) x=7 mm, y=20 mm, B50
0 40 80 120
0 0.01 0.02 0.03 0.04
Axial velocity (ms-1) (g) x=7 mm, y=20 mm, PME
0 6 12 18 24
0 0.05 0.1 0.15 0.2
D10 (μm) (h) x=7 mm, y=20 mm, PME
0 10 20 30 40 50
-30 0 30 60 90 120
Mean velocity (ms-1)
D10 (μm)
(i) x=7 mm, y=20 mm, PME
Figure 5.30: Distribution of the droplet (a,d,g) axial velocity (b,e,h) SMD and (c,f,i) droplet size-velocity correlation for Jet-A1, 50 % PME/Jet-A1 and PME swirl flame at spatial location of downstream y = 20 mm and radial position of x = 7 mm under the same power output condition.
Reacting spray results The droplet distribution and trajectories at the location of y = 20 mm downstream and radial position of x = 7 mm in the spray flame was investigated. The droplet distributions of velocity, size and the drop velocity-size correlation of PME, Jet-A1 and 50 % PME/Jet-Jet-A1 under the same power output of 6 kW are shown in Fig.
5.30. In general, the droplet velocity distributions for all fuels considered are rather similar, with a normal distribution of droplet velocity that spans between 0-80 m/s.
The droplet SMD distribution is also similar between the three fuels, although Jet-A1 exhibits a lower PDF peak due to the lower droplet counts. This is evident in the drop velocity-size correlations, where in spite of the relatively similar drop distributions, the number of drops of Jet-A1 is lowest. The presence of large droplets is significantly reduced compared to PME and biodiesel blend. The lower droplet concentration of A1 compared to other heavier fuels has been shown in Fig. 5.25a. This is because Jet-A1 is relatively more volatile and evaporates faster than PME.
5.3.2 Blend of 50% RME/Diesel
Comparison of the droplet characteristics of 50 % RME blend with the unblended fuels under the same power output condition is shown in Fig. 5.31. The droplet velocity and SMD profiles of the 50 % RME/diesel blend are almost identical to the profiles of diesel and RME as shown in Fig. 5.31a and 5.31b. The indistinguishable droplet size and velocity profiles are not surprising considering the almost identical physical properties between RME and diesel. This concurs with the trend shown in the non-reacting spray investigations where the blend of biodiesel with baseline fuels also exhibits similar profiles as the unblended fuels (section 5.1.3). The droplet concentration and volume flux profiles of the biodiesel blend closely resembles the diesel profiles, indicating the spray droplet characteristic of 50 % RME/diesel blend under the reacting flame is almost similar to diesel fuel. This highlights the compatibility of biodiesel in the burner employing a plain-jet airblast atomizer, in which the nozzle is less dependant on the fuel properties compared to a pressure atomizer.
Reacting spray results
0 5 10 15 20
0 20 40 60 80
Axial velocity (m/s)
Radial position (mm)
(a) 100% Diesel
100% RME 50% RME/Diesel
0 5 10 15 20
0 8 16 24 32
SMD (μm)
Radial position (mm)
(b) 100% Diesel
100% RME 50% RME/Diesel
0 5 10 15 20
0 3000 6000 9000 12000
Droplets density (#/cm2/s)
Radial position (mm)
(c) 100% Diesel
100% RME 50% RME/Diesel
0 5 10 15 20
0 4 8 12 16x 10-3
Volume flux (cm3 /cm2 /s)
Radial position (mm)
(d) 100% Diesel
100% RME 50% RME/Diesel
Figure 5.31: Comparison of the droplet (a) velocity, (b) SMD, (c) number density and (d) volume flux profiles between diesel, 50 % RME/diesel and RME under the same power output at the axial location of y = 15 mm from burner exit.
The droplet distribution and trajectories at the spatial position of y = 15 mm downstream of burner outlet and radius x = 5 mm for RME, 50% RME/diesel and diesel are shown in Fig. 5.32. This spatial location within the spray flame corresponds to the peak velocity at the radial profile of y = 15 mm. Comparison of the droplet velocity and size shows almost identical drop distributions between the fuels, highlighting the similarity of the droplet transport behaviour between diesel, RME and the 50 % RME/diesel/blend within the spray flame. The result also shows that the minor differences in that physical property between biodiesel and diesel fuel are not reflected in the flame. Hence, for a gas turbine combustor that employs the present
Reacting spray results plain-jet airblast atomizer, the spray characteristics of biodiesel closely resembles diesel fuel.
0 50 100 150
0 0.006 0.012 0.018 0.024 0.03
Axial velocity (ms-1) (a) x=5 mm, y=15 mm, Diesel
0 6 12 18 24
0 0.05 0.1 0.15 0.2 0.25
D10 (μm)
(b) x=5 mm, y=15 mm, Diesel
0 10 20 30 40 50
0 40 80 120
Axial velocity (ms-1)
D10 (μm)
(c) x=5 mm, y=15 mm, Diesel
0 50 100 150
0 0.007 0.014 0.021 0.028 0.035
Axial velocity (ms-1) (d) x=5 mm, y=15 mm, RD50
0 6 12 18 24
0 0.05 0.1 0.15 0.2 0.25
D10 (μm) (e) x=5 mm, y=15 mm, RD50
0 10 20 30 40 50
0 40 80 120
Axial velocity (ms-1)
D10 (μm)
(f) x=5 mm, y=15 mm, RD50
0 50 100 150
0 0.007 0.014 0.021 0.028 0.035
Axial velocity (ms-1) (g) x=5 mm, y=15 mm, RME
0 6 12 18 24
0 0.05 0.1 0.15 0.2 0.25
D10 (μm) (h) x=5 mm, y=15 mm, RME
0 10 20 30 40 50
0 40 80 120
Axial velocity (ms-1)
D10 (μm)
(i) x=5 mm, y=15 mm, RME
Figure 5.32: Distribution of the droplet (a,d,g) axial velocity (b,e,h) SMD and (c,f,i) droplet size-velocity correlation for (a) diesel, (b) 50% RME/diesel and (c) RME swirl flame at axial position of y = 15 mm and radial position of x = 5 mm under the same power output condition.
Conclusion