Internal Combustion Engine GroupInternal Combustion Engine Group
OH and NO distributions in combusting diesel sprays
13 June 2006
Romain Demory
Outline
• IntroductionDiesel combustion and nitrogen oxides
• Laser-Induced FluorescenceValidity and limitations
• Results and DiscussionFlame development and nitric oxide formation
• Conclusions
IntroductionIntroduction
Aim: Identify the conditions leading to the formation of NO in combusting diesel sprays
(1) Characterise the combustion in time and space
(2) Acquire spatially and temporally precise distributions of NO
-1
0
1
2
3
4
5
6
7
-180 -120 -60 0 60 120 180
1350
1400
1450
1500
1550
1600
1650
-200 -150 -100 -50 0 50 100 150 200
Instrumented engine Videos of the spray/flame
Combustion marker: OH-LIF
: NO-LIF
2/15
Laser-Induced Fluorescence Correction ModelLaser-Induced Fluorescence Correction Model
),(),()(
21221
2112 TpQWPA
ATpgBTfNIS
iBNOlaserLIF
3/15
1) Population (Boltzmann) distribution
2) Broadening and shift
3) Collisional Quenching
temperature dependent
overlap integral is rather constant over the range of pressure and temperature
can be evaluated if local temperature and molar fractions of colliding species are know
Laser-Induced Fluorescence Correction ModelLaser-Induced Fluorescence Correction Model
4) Model
180°
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
-12.00 -10.00 -8.00 -6.00 -4.00 -2.00 0.00 2.00
time [°c.a. aTDC]
he
at r
ele
ase
ra
te [
MP
a.m
³.s-
1]
total heat release rate pre-mixed mixing-controlled
1) Pre-mixed volume
2) Mixing-controlled volume
Integration of the heat release rate in time gives a local temperature
Combustion is scaled on heat release rate to obtain local χCO2
χH2O χO2
8/15
Laser-Induced Fluorescence Correction ModelLaser-Induced Fluorescence Correction Model
5) Model results
Temperature evolution
Stern-Vollmer (yield) factor Boltzmann (population) factor
1.9 ms 2.3 ms 2.8 ms 3.3 ms 4.0 ms
9/15
Results and discussionResults and discussion
Raw OH-LIF results Laser attenuation is visible (brighter on left side)
All images are for the same timing, different cycles
Injection of 30 mm³ of fuel in a quiescent air at 630 K and 5 MPa
Injection pressure: 100 MPa
OH is found in the flame front
The flame front is heavily rippled and unevenly thick
Even in a quiescent air environment, the spray development and evaporation leads to a rippled diffusion flame
10/15
Results and discussionResults and discussion
1.25 1.5 1.75 2 2.5 3.5 4 4.5 5 5.5 6
OH
flame
NO
3
OH (simulation)
time
[ms aSOI]
laser sheet height
Injection pressure: 100 MPa
Injected volume: 30 mm³
In-cylinder presssure: 5 MPa
In-cylinder temperature: 630 K
Summary
11/15
Results and discussionResults and discussion
-0.1
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1.1
1 2 3 4 5 6 7 8 9 10 11
time [ms aSOI]
aver
age
fluor
esce
nce
/ lu
min
osity
[a.
u.]
-0.1
0
0.1
0.2
0.3
0.4
1 2 3 4 5 6 7 8 9 10 11
heat
rel
ease
rat
e [M
J/s]
NO-LIF signal OH-LIF signal Flame luminosity Heat release rate
injection pressure: 100 MPainjected volume: 30 mm³
in-cylinder pressure: 5 MPain-cylinder temperature: 630 K
Summary
13/15
Conclusion
Pre-mixed phase:•Very short and mostly invisible to the optical techniques employed •The heat release rate remains the best indicator of the beginning of the combustion chemistry
Mixing-controlled phase:•Varying but sometimes very early start of the diffusion flame•Part of the “pre-mixed spike” in the heat release rate could be attributed to the diffusion flame. Whereas the flame front is rather stable downstream of the evaporation zone, the combustion near the tip of the spray is more chaotic and becomes increasingly richer, possibly leading to high concentrations of soot in the late part of the combustion.
Nitric oxide formation:•No fluorescence detected from the pre-mixed combustion (too rich or/and too short) as reported by Dec (1998)•NO distributions moved downstream as the diffusion flame developed, no structured pattern was detected during the stabilised diffusion flame (can be partially explained by the Stern-Vollmer factor and the Boltzmann distribution)
14/15
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