Download Soot measurements in rich-premixed/diffusion flames using Laser

Development of a predictive method to
analyze the effect of sustainable gases on soot
Soot measurements in rich-premixed/diffusion flames using Laser Induced Incandescence (LII)
Research performed at DNV GL Gas Consultancy & Services Groningen
Pieter Visser, Martijn van Essen, Sander Gersen & Howard Levinsky Contact: [email protected]
Measurement results
Equivalence ratio at
30 ppb soot [-]
Introduction
18
•
The diminishing natural gas reserves, increasing diversity of supply and desire to introduce sustainable gases have
resulted in an increasing trend towards the use of “new” gases in the Netherlands.
•
It was observed that the soot fraction increased with the
primary equivalence ratio (Figure 4)
•
These gases may have different tendencies to soot than traditionally distributed gases.
•
Figure 3 shows that the soot fraction measured at a
constant equivalence ratio for methane and the binary
hydrocarbon mixtures scales with the propane equivalent
number.

Consequences: Soot formation due to new gases in end user equipment may cause soot deposition resulting in clogging
and safety issues, while in equipment dependent on soot, soot formation may diminish.
Goal: Development of a model that predicts soot formation in new gases.
1
•
LII signal[a.u.]
•
Soot particles are heated to 4000K using laser pulses
(λ=1064nm) the subsequent emission (incandescence
signal) is a measure for the soot concentration (soot
volume fraction).
Gating and optical filters are used to reduce
interferences (e.g. C2 emission and PAH fluorescence).
The peak of the LII signal is proportional to the
average soot particle diameter (dp) and the number of
soot particles (Np) as follows:
0.8
LII signal
0.6
Laser pulse
Gating
0.4
0.2
0
0
LII signal ~Np·dp3
200
400
Time [ns]
Figure 1: Example of LII signal decay and gating
Soot fraction [ppb]
Laser Induced Incandescence
•
The addition of inert gases and hydrogen to methane
reduces the soot fraction in the flame. In contrast, higher
hydrocarbons have the opposite effect.
•
120
100
60
40
20
0
• The measurements were performed at the highest soot fraction in the flame by positioning the burner on the vertical
axis. The overall reproducibility of the measurements was better than 10%.
Partly premixed
diffusion flame
Power meter
Diaphragm
Lens
Burner
Nd:YAG
Foto
diode
Glass beads
laser
Attenuator
Filter
PC
ICCD
camera
Air
Air
Fuel
Figure 2: Experimental setup LII (left) and the experimental burner (right)
10
15
Equivalence ratio [-]
14
12
10
8
6
4
0
5
10
Propane equivalent number[-]
•
For mixtures of propane in methane the addition of
inert gases decreases the soot fraction at a constant
equivalence ratio (Figure 4).
•
The addition of approximately 5% hydrogen to
mixtures with a fixed propane fraction in methane
decreases the soot fraction while a small increase is
observed upon the addition of approximately 10% and
20% hydrogen. This effect deviates from the addition
of hydrogen to methane. The influence of hydrogen on
soot formation is a topic of study in literature and is at
present poorly understood.
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Figure 4: Measured soot fractions in diffusion flames of 3- and 4component mixtures as function of the equivalence ratio
Model
A statistical model is developed to characterize gases for their soot tendencies. This model predicts the equivalence ratio at
which a soot fraction of 30 ppb is expected (here ϕ30ppb). Both the binary and multi-component mixtures have been used as
input for the model. Based on a linear fit of the soot fraction versus the equivalence ratio for each mixture the measured
ϕ30ppb is determined. An excellent agreement was found between the measurements and the model as shown in Figure 5.
Predicted ϕ at 30 ppb
soot [-]
• The flame height was kept constant for each individual gas mixture during the LII measurements while varying the
equivalence ratios.
5
16
20
Conclusion
y = 0.9691x + 0.3219
R² = 0.9691
15
• A model was developed to determine the soot tendency
of gases with different compositions.
10
• The model can be used to characterize gaseous fuels for
soot formation.
5
0
5
10
15
Measured ϕ at 30 ppb soot [-]
Figure 5: Predicted versus the measured values of ϕ30ppb
15
Figure 3: Equivalence ratio at a soot fraction of 30 ppb as a function
of the propane equivalent number for different hydrocarbons
pseudo ELG 6.6% C3 & 12.8% N2
4.7% C2 & 4.9% C3
9.4% C3H8
9.3% C3 & 10.9% H2
9.3% C3 & 20.7% CO2
80
Measurements and experimental setup
• A coflow diffusion burner was used to produce the partly premixed flames fueled with 2, 3 and 4 component mixtures of
C2H6, C3H8, C4H10, N2, CO2 and H2 in CH4.
CH4
pseudo DLG 0.9% CO2, 3.8% C3 & 14.0% N2
3.8% C2, 5.9% H2 & 11.0% N2
9.3% C3 & 5.3% H2
9.3% C3 & 20.8% H2
CH4
C2H6
C3H8
C4H10
20