han shen's presentation

Turbulence and Combustion Research LaboratoryTurbulence and Combustion Research Laboratory

Han Shen

Department of Mechanical and Aerospace Engineering,

The Ohio State University,

Characterization of the Structure of Turbulent Nonpremixed Dimethyl Ether Jet Flames

Jeffrey A Sutton

Flames

Turbulence and Combustion Research Laboratory

Outline

Motivation

Comparisons of CH4- and DME flame structure using “Equivalent” flames

(1) Comparison at constant Reynolds number

(2) Comparison at constant Damköhler number

Comparison between Direct Numerical Simulation (DNS) and Experiments of DME Flames

Conclusions and Recommendations for Future Work

Jeffrey A Sutton

you will want to make a comment (orally) that you will explain the motivation for the development of "equivalent" CH4 and DME flames

Jeffrey A Sutton

Han,It is not gramatically correct to say " same Reynolds number comparison"You need to say that you will discuss the cases at constant Reynolds number and constant Damkohler number


Motivation

Dimethyl ether (DME) is a promising alternative to diesel fuel in compression-ignition engines

DME results in high thermal efficiencies and favorable ignition properties due to its high cetane number

DME can result in cleaner engine operation – decrease in particulate formation, nitrogen/sulfur oxides, and CO

Little is known about the fundamental DME combustion processes, especially turbulence-chemistry interaction (TCI)


Motivation (Cont.)

DME is important in terms of “fundamental” research as well

Detailed studies (large data sets) exist for simple fuels (e.g., hydrogen and methane)

Larger and more complex fuel molecules are desired targets

Experimentally, DME is chemically manageable, produces relatively low soot, and has sufficient vapor pressure to facilitate well-defined canonical turbulent flame experiments

Chemically it is the simplest ether; kinetic models are manageable (< 500 reactions for “full” mechanism)


Direct Comparisons of CH4- and DME-based Flame Structure


Current DME-based flames are formulated to directly compare to well-characterized “DLR” (CH4/H2/N2) flames, which are target cases in TNF workshop

Flame Configurations

Fuel Mole Fractions

Flame XCH4 XDME XH2 XN2 ReD xs Tad (K)a % Reblowout U (m/s) Da

DLR A 0.221 - 0.332 0.447 15200 0.167 2122 65% 38.8 0.0619

DLR B 0.221 - 0.332 0.447 22800 0.167 2122 97% 58.3 0.0412

DME A - 0.221 0.332 0.447 15200 0.169 2199 47% 27.6 0.0899

DME B - 0.221 0.332 0.447 22800 0.169 2199 71% 41.4 0.0599

DME C - 0.221 0.332 0.447 31050 0.169 2199 97% 56.3 0.0440

a corresponds to f = 1 conditions

DLR B DME B

Fuel issues from a 0.8-cm diameter tube into a 0.3 m/s annular (30 cm x 30 cm) co-flow (same facility across fuels).

Reynolds numbers, Damköhler number, and stoichiometric mixture fraction (xs) are matched across flames of different fuels.


Previous Work

Laminar flame calculations showed rapid DME pyrolysis and significant increases in CO, CH2O and other oxygenated hydrocarbons for DME flames

CH2O PLIF imaging: signal much higher in DME flames; mean CH2O profiles peak in low temperature regions for DME flames (800-1000 K) and near peak temperature for DLR flames; CH2O is more actively consumed in low temperature regions for DME flames.

CH2O CH2O

Mie Mie

x/d = 5

x/d = 10

x/d = 20

DLR A DME A

0 3000PLIF Signal (arb. Units)

x200 x 1

40 mm


Experimental Setup - OH PLIF

OH PLIF was performed with 2 mJ/pulse, exciting the A-X (1,0) transition near 283 nm.

OH PLIF was performed with 2.0 mJ/pulse, exciting the A-X (1,0) transition near 283 nm.

OH emission from the A-X(1, 1), (0, 0) and B-X (0, 1) bands between 306 nm and 320 nm was detected by a lens-coupled ICCD camera system

Field-of-view was 42 mm x 56 mm; ICCD gate was 100 ns


Data Processing

OH PLIF images were acquired at axial position of x/d = 7, 10, 20, 30, 40, and 60;

Statistical analysis performed only on images at x/d=7, 10, and 20

800 OH PLIF images taken at each location to determine mean and RMS fluctuations

Topographical flame characteristics were extracted: (1) OH layer curvature, (2) OH layer thickness, (3) OH layer orientation, (4) OH layer surface area, (5) “flame holes”, which were determined as a local discontinuity in the OH layer


Example OH PLIF Imaging(Constant Reynolds Number)

DLR B DME B

Re = 22800

x/d = 60

x/d = 40

x/d = 30

x/d = 20

x/d = 10

42 mm

Similar OH PLIF signal levels in both sets of flames

DLR flame appears more wrinkled with higher probability of local flame extinction (e.g., OH holes)

OH layers in DME flame are more “laminar like, while OH layers are highly strained and segmented in DLR flame

At equivalent Reynolds number, DME flames appear less affected by turbulence

DLR B DME B


Example OH PLIF Imaging(Constant Damköhler Number)

Similar OH PLIF signal levels in all sets of flames

DME C flames appear more wrinkled than the DME B flame, but not as wrinkled nor as contorted as the DLR B flames

x/d=20

x/d=10

x/d=7

DLR BRe=22800Da=0.041

At equivalent Damköhler numbers, DME flames appear less affected by turbulence

DME BRe=22800Da=0.059

DME CRe=31050Da=0.044

Jeffrey A Sutton

Ok - this was confusing at first sight. You need a label to denote both the Re and Da numbers. You need to explicitly state (when speaking) that the images in the left hand column are the DLR flames at Re = 22,800; the images in the middle column are the DME flames at the same Reynolds number and the images in the right column are the DME flames at an equivalent Da number as the DLR images in the left column


Mean and RMS Profiles(Constant Reynolds Number)

DME flames have higher peak mean intensity of OH

DLR flames show broader mean OH profiles

DLR flames have higher relative RMS fluctuations

For flame set A, results between the DLR and DME flames are similar. Results suggest that at the upstream positions (where strain is highest and TCI is most vigorous), DME flames are more robust; at downstream locations (strain is decreased), results are similar

0 0.25 0.5 0.75 1 1.25 1.5

x/d=7

DLR BDME B

Average OH Profile

0 0.25 0.5 0.75 1 1.25 1.5

x/d=7

DLR BDME B

RMS OH Profile

0 0.25 0.5 0.75 1 1.25 1.5

Sig

nal

Inte

nsit

y i

n a

bs.

un

it

x/d=10

DLR BDME B

0 0.25 0.5 0.75 1 1.25 1.5

Sig

nal

Inte

nsit

y i

n a

bs.

un

it

x/d=10

DLR BDME B

-40 -20 0 20 40 0 0.25 0.5 0.75 1 1.25 1.5

Radial Position (mm)

x/d=20

DLR BDME B

-40 -20 0 20 40 0 0.25 0.5 0.75 1 1.25 1.5


x/d=20

DLR BDME B

Jeffrey A Sutton

you will have to carefully explain the normalization such that it is clear that the DLR flames have higher RMS fluctuations. It is not clear from these figures.

Jeffrey A Sutton

Has "TCI" been defined anywhere.if not, make sure you say it orally.


Mean and RMS Profiles(Constant Damköhler Number)

0 0.25 0.5 0.75 1 1.25 1.5

x/d=7

DLR BDME C

Average OH Profile

0 0.25 0.5 0.75 1 1.25 1.5

x/d=7

DLR BDME C

RMS OH Profile

0 0.25 0.5 0.75 1 1.25 1.5

Sig

nal

In

ten

sity

in

ab

s. u

nit

x/d=10

DLR BDME C

0 0.25 0.5 0.75 1 1.25 1.5

Sig

nal

In

ten

sity

in

ab

s. u

nit

x/d=10

DLR BDME C

-40 -20 0 20 40 0 0.25 0.5 0.75 1 1.25 1.5


x/d=20

DLR BDME C

-40 -20 0 20 40 0 0.25 0.5 0.75 1 1.25 1.5


x/d=20

DLR BDME C

DLR B peak OH intensity is approximately 75% of the mean OH intensity of DME C at all axial locations

Relative RMS fluctuation of DLR B flames is ~ 80% of that of the DME C flames at all axial locations

DLR B flames show broader RMS OH profiles

Unlike the previous comparisons within flame set A and flame set B at a constant Reynolds number, the relative mean peak and RMS OH intensity between DLR and DME flames is independent of axial position


Mean and RMS Profiles(Constant Damköhler Number)

Mean OH intensity of DLR A increases relative to that of DME B flame with increasing axial position

Mean OH intensity profile is not broader for DLR A flame in comparison to DME B flame

RMS profiles are almost identical

0 0.25 0.5 0.75 1 1.25 1.5

x/d=7

DLR ADME B

Average OH Profile

0 0.25 0.5 0.75 1 1.25 1.5

x/d=7

DLR ADME B

RMS OH Profile

0 0.25 0.5 0.75 1 1.25 1.5

Sig

nal

Inte

nsit

y i

n a

bs.

un

it

x/d=10

DLR ADME B

0 0.25 0.5 0.75 1 1.25 1.5

Sig

nal

Inte

nsit

y i

n a

bs.

un

it

x/d=10

DLR ADME B

-40 -20 0 20 40 0 0.25 0.5 0.75 1 1.25 1.5


x/d=20

DLR ADME B

-40 -20 0 20 40 0 0.25 0.5 0.75 1 1.25 1.5


x/d=20

DLR ADME B


OH Layer Thickness(Constant Reynolds Number)

For the Re = 15,200 cases, the median of the distribution is ~ 0.4 mm for the DLR flame and ~ 0.6 mm for the DME flame

DLR flames exhibit a higher probability of thin OH layers (<0.4 mm) and a slower decaying exponential tail to the PDF

Indicates large influence of flow turbulence on the OH layer structure in the DLR flames

“thin” OH layers indicate the presence of larger eddies which “stretch” (and thin) the layers

thick OH layers indicates the interaction of smaller eddies which “thicken” the layers

Results are qualitatively similar for the “B” flames

0 0.05 0.1 0.15 0.2

Pro

bab

ility

x/d=7

DLR ADME A

0 0.05 0.1 0.15 0.2

Pro

bab

ility

x/d=10

DLR ADME A

0 1 2 3 40 0.05 0.1 0.15 0.2

Thickness/Lamniar Flame Thickness

Pro

bab

ility

x/d=20

DLR ADME A

0 0.05 0.1 0.15 0.2

Pro

bab

ility

x/d=7

DLR BDME B

0 0.05 0.1 0.15 0.2

Pro

bab

ility

x/d=10

DLR BDME B

0 1 2 3 40 0.05 0.1 0.15 0.2


Pro

bab

ility

x/d=20

DLR BDME B

0 0.05 0.1 0.15 0.2

Prob

abili

ty

x/d=7

DLR BDME C

0 0.05 0.1 0.15 0.2

Prob

abili

ty

x/d=10

DLR BDME C

0 1 2 3 40 0.05 0.1 0.15 0.2


Prob

abili

ty

x/d=20

DLR BDME C

Jeffrey A Sutton

original text was too much for bullet points.It needs to be "short" pieces of information. You can expound verbally


OH Layer Thickness(Constant Damköhler Number)

DLR A flames still appear to display a slightly slower decaying tail to the pdf indicating larger probability of thicker OH layers.

DLR B and DME C flames show similar behavior with no obvious differences

0 0.05 0.1 0.15 0.2

Pro

babi

lity

x/d=7

DLR ADME B

0 0.05 0.1 0.15 0.2

Pro

babi

lity

x/d=10

DLR ADME B

0 1 2 3 40 0.05 0.1 0.15 0.2


Pro

babi

lity

x/d=20

DLR ADME B

0 0.05 0.1 0.15 0.2

Pro

babi

lity

x/d=7

DLR BDME C

0 0.05 0.1 0.15 0.2

Pro

babi

lity

x/d=10

DLR BDME C

0 1 2 3 40 0.05 0.1 0.15 0.2

Thickness/Lamniar Flame ThicknessP

roba

bilit

y

x/d=20

DLR BDME C

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=7

DLR BDME C

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=10

DLR BDME C

0 1 2 3 40 0.05 0.1 0.15 0.2


Pro

bab

ilit

y

x/d=20

DLR BDME C

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=7

DLR BDME C

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=10

DLR BDME C

0 1 2 3 40 0.05 0.1 0.15 0.2


Pro

bab

ilit

y

x/d=20

DLR BDME C


OH Layer Curvature(Constant Reynolds Number)

DME flame A has a higher probability of small absolute curvatures (near zero) and a narrower distribution of curvature

DME flame B is qualitatively similar

Near-zero curvature is consistent with a laminar flame; that is, OH layers oriented parallel to axial flow

Similar to instantaneous images, the DME flames are statistically more “laminar like” as compared to the DLR flames for a given Reynolds number.

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=7

DLR ADME A

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=10

DLR ADME A

0 1 2 3 40 0.1 0.2 0.3 0.4

Curvature (1/mm)

Pro

bab

ilit

y

x/d=20

DLR ADME A

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=7

DLR BDME B

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=10

DLR BDME B

0 1 2 3 40 0.1 0.2 0.3 0.4

Curvature (1/mm)

Pro

bab

ilit

y

x/d=20

DLR BDME B

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=7

DLR BDME C

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=10

DLR BDME C

0 1 2 3 40 0.1 0.2 0.3 0.4

Curvature (1/mm)

Pro

bab

ilit

y

x/d=20

DLR BDME C


OH Layer Curvature(Constant Damköhler Number)

Constant Damköhler number conditions show little difference between DLR and DME flames

At the upstream axial positions of x/D = 7 and x/D = 10, DME flames exhibit less curvature

The less wrinkled or more “laminar-like” nature of the DME flames appears to support the notion that DME flames are less affected by the local turbulent flow field.

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=7

DLR BDME C

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=10

DLR BDME C

0 1 2 3 40 0.1 0.2 0.3 0.4

Curvature (1/mm)

Pro

bab

ilit

y

x/d=20

DLR BDME C

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=7

DLR BDME C

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=10

DLR BDME C

0 1 2 3 40 0.1 0.2 0.3 0.4

Curvature (1/mm)P

rob

abil

ity

x/d=20

DLR BDME C

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=7

DLR ADME B

0 0.1 0.2 0.3 0.4

Pro

bab

ilit

y

x/d=10

DLR ADME B

0 1 2 3 40 0.1 0.2 0.3 0.4

Curvature (1/mm)

Pro

bab

ilit

y

x/d=20

DLR ADME B

Jeffrey A Sutton

I don't see this at all??????


OH Layer Orientation(Constant Reynolds Number)

Centered at 90 degrees (parallel to the flow direction)

DME A has a narrower distribution around 90 degrees, especially at the upstream axial locations of x/d=7 and 10

At x/d=20, DLR A and DME A are similar

B case is qualitatively similar to A case

At x/d=20, DLR B and DME B are almost identical

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=7

DLR ADME A

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=10

DLR ADME A

0 50 100 150 2000 0.05 0.1 0.15 0.2

Orientation (degree)

Pro

bab

ilit

y

x/d=20

DLR ADME A

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=7

DLR BDME B

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=10

DLR BDME B

0 50 100 150 2000 0.05 0.1 0.15 0.2


Pro

bab

ilit

y

x/d=20

DLR BDME B


OH Layer Orientation(Constant Damköhler Number)

Centered at 90 degrees (parallel to the flow direction)

DME has a narrower distribution around 90 degrees at x/d=7 but differs less compared to equivalent Reynolds number cases

At x/d=10 and 20, DLR and DME flames are very similar

Consistent with the mean and RMS profiles

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=7

DLR BDME C

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=10

DLR BDME C

0 50 100 150 2000 0.05 0.1 0.15 0.2

Orientation (degree)P

rob

abil

ity

x/d=20

DLR BDME C

0 0.05 0.1 0.15 0.2

Pro

bab

ility

x/d=7

DLR ADME B

0 0.05 0.1 0.15 0.2

Pro

bab

ility

x/d=10

DLR ADME B

0 50 100 150 2000 0.05 0.1 0.15 0.2


Pro

bab

ility

x/d=20

DLR ADME B

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=7

DLR BDME C

0 0.05 0.1 0.15 0.2

Pro

bab

ilit

y

x/d=10

DLR BDME C

0 50 100 150 2000 0.05 0.1 0.15 0.2

Orientation (degree)P

rob

abil

ity

x/d=20

DLR BDME C


OH Layer Surface Area(Constant Reynolds Number)

DME A flame exhibits a narrower distribution at x/d=7

Further downstream, DLR A flame peaks at a larger surface area with a slower decaying tail

Same pattern is observed in B cases

Consistent with the previous results for OH layer thickness and OH layer curvature

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=7

DLR BDME B

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=10

DLR BDME B

0 100 200 3000 0.05

0.1 0.15

Surface Area (mm2)

Pro

bab

ilit

y

x/d=20

DLR BDME B

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=7

DLR ADME A

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=10

DLR ADME A

0 100 200 3000 0.05

0.1 0.15

Surface Area (mm2)

Pro

bab

ilit

y

x/d=20

DLR ADME A

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=7

DLR BDME B

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=10

DLR BDME B

0 100 200 3000 0.05

0.1 0.15

Surface Area (mm2)

Pro

bab

ilit

y

x/d=20

DLR BDME B

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=7

DLR BDME B

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=10

DLR BDME B

0 100 200 3000 0.05

0.1 0.15

Surface Area (mm2)

Pro

bab

ilit

y

x/d=20

DLR BDME B


OH Layer Surface Area(Constant Damköhler Number)

No obvious differences

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=7

DLR ADME B

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=10

DLR ADME B

0 100 200 3000 0.05

0.1 0.15

Surface Area (mm2)

Pro

bab

ilit

y

x/d=20

DLR ADME B

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=7

DLR BDME C

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=10

DLR BDME C

0 100 200 3000 0.05

0.1 0.15

Surface Area (mm2)

Pro

bab

ilit

y

x/d=20

DLR BDME C

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=7

DLR BDME B

0 0.05

0.1 0.15

Pro

bab

ilit

y

x/d=10

DLR BDME B

0 100 200 3000 0.05

0.1 0.15

Surface Area (mm2)

Pro

bab

ilit

y

x/d=20

DLR BDME B


OH Layer Holes(Constant Reynolds Number)

For DME flame A, there is little probability of observing a OH discontinuity at x/d = 7 and 10; average “holes”/image ~2 for DLR flame A.

For “A” flames there is an increasing probability of finding an OH layer hole with increasing axial distance; rate increases significantly for DLR flame A.

For DLR B flame, the distribution of holes remains constant for increasing axial position; for DME B, the number increases with increasing axial position

0 0.25 0.5 0.75 1

x/d=7

Pro

bab

ilit

y

DLR A

0 0.25 0.5 0.75 1

x/d=7

Pro

bab

ilit

y

DME A

0 0.25 0.5 0.75 1

x/d=10

Pro

bab

ilit

y

0 0.25 0.5 0.75 1

x/d=10P

rob

ab

ilit

y

0 5 100 0.25 0.5 0.75 1

x/d=20

Pro

bab

ilit

y

Number of Holes per Picture 0 5 10

0 0.25 0.5 0.75 1

x/d=20

Pro

bab

ilit

y

Number of Holes per Picture

0 0.25 0.5 0.75 1

x/d=7

Pro

bab

ilit

y

DLR B

0 0.25 0.5 0.75 1

x/d=7

Pro

bab

ilit

y

DME B

0 0.25 0.5 0.75 1

x/d=10

Pro

bab

ilit

y

0 0.25 0.5 0.75 1

x/d=10

Pro

bab

ilit

y

0 5 100 0.25 0.5 0.75 1

x/d=20

Pro

bab

ilit

y


0 0.25 0.5 0.75 1

x/d=20

Pro

bab

ilit

y



OH Layer Holes(Constant Damköhler Number)

At equivalent Damköhler numbers, DME flames differ significantly as compared to DLR flames despite the similarities in all previously-examined parameters

The most probable number of OH layer holes of DME C is between 1 and 2 per image, while it is between 4 and 5 for DLR B flames

DME C has increasing number of OH layer holes with increasing downstream position

0 0.25 0.5 0.75 1

x/d=7

Pro

bab

ilit

y

DLR A

0 0.25 0.5 0.75 1

x/d=7

Pro

bab

ilit

y

DME A

0 0.25 0.5 0.75 1

x/d=10

Pro

bab

ilit

y

0 0.25 0.5 0.75 1

x/d=10

Pro

bab

ilit

y

0 5 100 0.25 0.5 0.75 1

x/d=20

Pro

bab

ilit

y


0 0.25 0.5 0.75 1

x/d=20

Pro

bab

ilit

y


0 0.25 0.5 0.75 1

x/d=7

Pro

bab

ilit

y

DLR B

0 0.25 0.5 0.75 1

x/d=7

Pro

bab

ilit

y

DME B

0 0.25 0.5 0.75 1

x/d=10

Pro

bab

ilit

y

0 0.25 0.5 0.75 1

x/d=10P

rob

ab

ilit

y

0 5 100 0.25 0.5 0.75 1

x/d=20

Pro

bab

ilit

y


0 0.25 0.5 0.75 1

x/d=20

Pro

bab

ilit

y


0 0.25 0.5 0.75 1

x/d=7

Pro

bab

ilit

y

DLR B

0 0.25 0.5 0.75 1

x/d=7

Pro

bab

ilit

y

DME C

0 0.25 0.5 0.75 1

x/d=10

Pro

bab

ilit

y

0 0.25 0.5 0.75 1

x/d=10

Pro

bab

ilit

y

0 5 100 0.25 0.5 0.75 1

x/d=20

Pro

bab

ilit

y


0 0.25 0.5 0.75 1

x/d=20

Pro

bab

ilit

y



Comparison between Direct Numerical Simulation and Experiments of DME Flames


Numerical and Experimental Flame Characteristics

The work is a research collaboration with Sandia National Laboratories

The goals is to achieve understanding of DME combustion at near-extinction conditions

The DNS configuration is a 3D, non-premixed, temporally-evolving slot jet flame

The experiment is a spatially-evolving, axisymmetric jet flame

The fuel (12% DME, 18% H2 and 70% N2) and oxidizer streams (31% O2 and 69% N2) are matched between DNS and experiment

Parameter DNS Expt

Jet Reynolds number, Rejet 13050 13050

Jet Width, H (mm) 2.3 N/A

Hydraulic diameter, D (mm) 4.1 3.43

Jet Velocity, ΔU (m/s) 98 57

Fuel core width, HZ (mm) 3.6 N/A

Pressure, P (atm) 1.0 1.0

Damkohler number, Da 0.08 0.074

Stoichiometric mixture fraction, Zst 0.375 0.375

Unburnt temperature, Tu (K) 450 298

Burnt temperature, Tb (K) 2380 2299

Extinction dissipation rate, Χq (s-1) 1950 1210


Parametric Study of Nozzle Geometry

DDNS is the hydraulic dynamic used in the DNS studies, ν is the kinematic viscosity of the fuel, and T is the temperature of the fuel

13600

Vary tube thickness to find the optimized tube design

Tube inner diameter is 3.43 mm with a wall thickness of 3.05 mm

Achieved equivalent Re and Da

Jeffrey A Sutton

Han,You will need to explain very carefully that the target is to match fuel/oxidizer compositions (stoichiometric mixture fraction); Reynolds number, and Damkohler number. This leaves you one variable to play with - geometry - which in our case is the nozzle diameter.


Simultaneous OH and CH2O PLIF Experiment Layout


Instantaneous realizations of simultaneous OH/CH2O measurements

OH exists within high-temperature, “burning” regions

CH2O exists in low-temperature regions

The OH/CH2O region is a good surrogate for peak heat release rate

The spatial locations were chosen to correspond to the three phases identified in the DNS, i.e. burning, partially-extinguished and reigniting.

Qualitatively, these locations compare well with representative realizations from the DNS


Joint PDF of OH and CH2O

Two species that play a key role in the extinction re-ignition process are OH and CH2O

Both joint PDFs exhibit the same functional form, i.e. there exists a strong anti-correlation between OH and CH2O

OH is located primarily in burning regions, CH2O is found primarily in non-burning regions


PDF of Alignment Index of CH2O and OH

Alignment index:

PDF peaks at −1 at all time instances in the DNS and spatial locations in the experiment, indicating that the gradients of OH and CH2O are opposed.


Conclusions I

Statistical descriptions of the OH layer thickness, OH layer curvature, OH layer orientation, OH layer surface area, and OH layer “holes” showed differences in the flame structure between the DLR and DME flames

At the constant Reynolds numbers

o The CH4-based DLR flames displayed higher probability of both thinner and thicker OH layer distribution, presumably due to higher levels of interaction with local turbulent flowfield

o DLR flames display higher probability of larger curvature, surface area, OH layer orientation and number of OH layer holes per image

o DME-based flames appear to be less affected by local turbulence than DLR flames


Conclusions II

At the constant Damköhler numbers

o The DME and DLR flames exhibit very similar statistics in terms of OH layer thickness, OH layer curvature, OH layer orientation, and OH layer surface area

o The DME flames displayed much less discontinuation and individual OH layer breaks than DLR flames even at near-extinction condition

o The exact reason for the DME flames exhibiting more robustness (in terms of local extinction) is not known, but presumably is due to rich low-temperature chemistry and/or accelerated re-ignition processes in the DME flames as compared to the methane-based DLR flames.


Conclusions III and Future Work

Simultaneous OH and CH2O imaging displayed similar extinction and re-ignition phenomena as observed in the DNS

Joint statistics of OH and CH2O exhibit a strong anti-correlation

Probability density function (PDF) of the alignment index peaked at -1 at all time (DNS) and spatial (experiments) instances, indicating that the gradients of OH and CH2O are opposed.

OH and CH2O PLIF images overlap only in very small spatial regions, presumably demarcating the regions between fuel oxidation and primary heat release.

Future work includes simultaneous OH PLIF, CH2O PLIF and velocity measurements via PIV to investigate relationship between the local turbulent flow field (vorticity and strain rate) and the DME flame chemistry


Acknowledgements

Acknowledgment is made to the Donors of the American Chemical Society Petroleum Research Fund for support of this research as well as the Combustion Energy Frontier Research Center funded by the US department of Energy, Office of Science.

han shen's presentation

Documents

dme flame structure

dme flames ch2o plif

dme based flame structure

dlr flames ch2o

rapid dme pyrolysis

high cetane number dme

equivalent flames

flames of different