Enhancement of Reaction and

Stability of Ammonia Flames using

Hydrogen Addition and Swirling Flows

Akihiro Hayakawa, Akinori Ichikawa, Yoshiyuki Arakawa,

Taku Kudo and Hideaki Kobayashi

Institute of Fluid Science, Tohoku University, Japan

2015 NH3 Fuel Conference, Argonne National Laboratory, IL, USA

September 22, 2015

Outline

1. Background and objectives

2. Reaction enhancement by the hydrogen addition

– Experimental evaluation of laminar burning velocity of ammonia/hydrogen/air flames at the high pressures

3. Stabilization enhancement by a swirling flow

– Stabilization limit of ammonia/air premixed flame on a gas turbine-like combustor

4. Conclusions1

Background• Ammonia(NH3) as a hydrogen-energy carrier

– New manufacturing process using alternative fuels and high efficiency conversion to hydrogen

• Features of ammonia– High hydrogen capability (hydrogen mass density: approx. 18 wt%)

– Storage and transportation are easy because ammonia liquidizes approx. at 8.5 atm in the room temperature.

– Infrastructures for ammonia manufacturing and distribution have already been established.

NH3

NH3

Ammonia production

from renewable energy Transportation and storage Direct combustion2

Application of NH3 as a fuel

Ammonia combustion = Carbon-free combustion

4NH3 + 3O2 → 2N2 + 6H2O

Issues of the ammonia combustion

Improvement of lower combustion intensity (Lower burning velocity, narrower flammable range etc.).

Large amount of NOx should be formed because NH3 includes N atom.

火炎に垂直方向の座標

NO濃度

温度

発熱速度

火炎に垂直方向の座標

NO濃度

温度

発熱速度

Structure of HC flame Structure of NH3 flame

Thermal NO Fuel NO

Fundamental characteristics of ammonia flames should be clarified.

NOHRR

Distance Distance

TT

HRR

NO

3

Recent studies NO formation/reduction mechanism[1]

Fundamental flame characteristics is being studied.

4

Laminar burning velocity of ammonia/air flames[2]

[1] A. Hayakawa et al., Mechanical Engineering Journal, Vol. 2, No. 14-00402. 2015.

[2] A. Hayakawa et al., Fuel, Vol. 159, pp. 98-106, 2015.

0.1 0.2 0.30

500

1000

1500

Pressure, P (MPa)

Mole

fra

cti

on o

f N

O (

ppm

)

Simulation

Equilibrium

Experiment

= 1.0

O2 = 16

0.7 0.8 0.9 1.0 1.1 1.2 1.30

2

4

6

8

10

(-)

SL (

cm

/s)

0.1

0.3

0.5

Pi (MPa)

Ammonia/air

0.6 0.8 1.0 1.2 1.40

500

1000

1500

Equivalence ratio, (-)

Mole

fra

cti

on o

f N

O (

ppm

)

Simulation

Equilibrium

Experiment

P = 0.1 MPa

O2 = 16

14 mm

NO decreases with the increase in equivalence ratio and mixture pressure.

Maximum value of laminar burning velocity of ammonia/air flame is about 7 cm/s, and is about 1/5 of methane/air

flame.

0.3 MPa

Spherically propagating

ammonia/air flame

Burner stabilized

ammonia/air flame

10

0 m

m

Flame enhancement

5

[3]S. Frigo and Gentili, Int. J. of Hydrogen Energy 38 2013: 1607-1615, [4] Lee et al. Int. J. Hydrogen

energy 35 2010; 11332-11341, [5] Kumar and Meyer. Fuel 108 2013;166-176, [6] Li et al. Int. J. Energy

Research 38 2014; 214-1223.

Actual combustor:High speed combustionHigh pressure combustion

for a high combustion load

Enhancement of the ammonia flame:• Reaction enhancement by the hydrogen addition

Higher combustion intensity, production from ammonia and carbon free Frigo and Gentili[3]: Hydrogen added ammonia is adopted to SI

engine. Laminar burning velocities of ammonia/hydrogen/air flame were

clarified by Lee et al.[4], Kumar et al.[5] and Li et al.[6]. • All experiments were performed at the atmospheric pressure.

• Stabilization enhancement by a swirling flow

Swirling flow is adopted in an actual gas turbine combustor to increase the flame stability. There is no study of ammonia flame on a swirl combustor.

Objective of this study

To achieve flame enhancement of ammonia flame:

– Reaction enhancement of ammonia by the hydrogen addition

– Stability enhancement by a swirling flow.

• Experimental investigation of laminar burning velocity of ammonia/hydrogen/air premixed flames using a constant volume combustion chamber up to 0.5 MPa.

• Flame stabilization limit of ammonia/air premixed flame on a gas turbine like swirl combustor.

Objective

6

7

Reaction enhancement by hydrogen addition

Detail:

A. Ichikawa, A. Hayakawa, Y. Kitagawa, K.D.K.A. Somarathne, T. Kudo and H.

Kobayashi, Laminar burning velocity and Markstein length of ammonia/hydrogen/air

premixed flames at elevated pressures, International Journal of Hydrogen Energy, Vol. 40,

pp. 9570-9578, 2015

• Experimental evaluation of laminar burning velocity and Markstein length

• Comparison between experimental and numerical results

Topic 1

Experimental setup

8

HiCORDER

CDI circuit

High speed camera

Lamp

Air

NH3

Valve

Pressure indicator

Pressure sensor (P1)

Vacuum pump

To atmosphere

Pulse circuit

PinholeSchlieren stop

Switch

Convex lens

Optical windowPressure sensor (P2)

Spark electrode

Trigger pulse

To atmosphere

Combustion chamber

H2

Experimental setup

Hydrogen ratio in fuel

𝑥H2 =

H2H2 + NH3

[X]：Mole fraction of X

• Volume： approx. 23 L• Observation windows： 60 mm• Diameter of the electrodes： 1.5 mm• Distance of the electrodes： 2 mm• Electrostatic energy： 0.28 - 2.8 J

• Mixture：NH3/H2/air• Initial temperature： 298 K• Initial mixture pressure, Pi：

0.1, 0.3, 0.5 MPa• Equivalence ratio, ： 1.0

(stoichiometry)• xH2 : 0 - 1.0

Constant volume combustion chamber

60 mm

High-speed schlieren images

9

xH2 = 0.2

5000 fps

xH2 = 0.6

10000 fps

Pi = 0.5 MPa

Observation of flames

10

t = 6.0 ms 18.0 ms 30.0 ms 42.0 ms

14.0 ms 22.5 ms 31.5 ms5.5 ms

7.4 ms 11.8 ms 16.2 ms3.0 ms

3.3 ms 5.3 ms 7.2 ms1.4 ms

rsch ≈ 5 mm 10 mm 15 mm 20 mm

xH2 = 0.1

0.2

0.4

0.6

7.4 ms 11.8 ms 16.2 ms3.0 ms

rsch ≈ 5 mm 10 mm 15 mm 20 mm

Pi = 0.1 MPa

0.3 MPa

0.5 MPa

5 ms 8.4 ms 12 ms1.8 ms

3.4 ms 5.6 ms 7.8 ms1.2 ms

Effects of hydrogen addition Effects of pressure

xH2 = 0.4Pi = 0.5 MPa

Flame propagation speed increases with xH2.

Flame front wrinkling can be observed at high xH2.

Flame propagation speed decreases with Pi.

)1(d

d

t

rS sch

N

)2(d

d2

d

d1

t

r

rt

A

A

sch

sch

)3( bNS LSS

Analysis of spherical flames

rsch

rb

ru

SN : Stretched flame speed

ru: Unburned mixture density

rb: Burned gas density

rsch: Flame radius, t: time, : Flame stretch rate

A: Flame front area ( = 4prsch2)

SS: Unstretched flame peed

SL: Unstretched laminar burning velocity

Lb: Burned gas Markstein length11

)4( Su

bL SS

r

r

Flame stretch rate, Str

etc

he

d f

lam

e s

pe

ed

,S

N

Lb < 0

Lb > 0

Time

SS(extrapolated

value as 0)

Slope: － Lb

Unstretched laminar burning velocity, SL

SL (xH2)

SL (xH2 = 0)＝ exp ( α・xH2 ) (5)a = 3.46

a = 3.64

a = 3.25

As hydrogen ratio increases, SL

increases linearly on semilog graph. (The vertical axis is shown as log scale.)

a : constant

• The values of a are about 3.5 at all initial mixture pressures.

• It can be presumed that the effects of pressure on hydrogen addition is small.

1

10

100

1000

SL

(cm

/s)

0 0.2 0.4 0.6 0.8 1.0xH2 (-)

[4] Lee et al. Int. J. Hydrogen energy 35 2010;11332-11341 , [5] Kumar and

Meyer. Fuel 108 2013;166-176, [6] Li et al. Int. J. Energy Research 38

2014;1214-1223, [7] Smallbone et al. J. Thermal. Sci. Technol 1 2006;31-41

[4]

[7]

[5]

[6]

12

xH2

Pi

Comparison of SL with numerical values

1

10

100

1000

-0.2 0 0.2 0.4 0.6 0.8 1 1.2

0.1 MPaLee et al.SmallboneKumarLi et al.TianMillerLindstedtKonnovGRI

xH2

(-)

SL (

cm/s

)

1.0

Experiment (Present study)

Experiment (Lee et al. [14])

Experiment (Smallbone et al. [28])

Experiment (Kumar and Meyer [13])Experiment (Li et al. [17])

Simulation (Tian et al. [9])Simulation (Miller et al. [11])Simulation (Lindstedt et al. [12])

Simulation (Konnov [10])

Simulation (GRI-Mech 3.0 [28])

Ammonia-Hydrogen

P

i = 0.1 MPa

1

10

100

1000

-0.2 0 0.2 0.4 0.6 0.8 1 1.2

0.5 MPaTianMillarLindstedtKonnovGRI

xH2

(-)

SL (

cm/s

)

1.0

Ammonia-Hydrogen

P

i = 0.5 MPa

Experiment (Present study) Simulation (Tian et al. [9])Simulation (Miller et al. [11])

Simulation (Lindstedt et al. [12])Simulation (Konnov [10])

Simulation (GRI-Mech 3.0 [28])

Pi = 0.1 MPa Pi = 0.5 MPa

Mechanism Year Species Reactions

Tian et al. 2009 84 703

Miller et al. 1983 23 98

Konnov 2009 129 1231

GRI-Mech 3.0 2000 53 325

Lindstedt et al. 1994 21 95

Further improvement of reaction mechanism is required. 13

[4]

[5]

[6]

[7]

)

)

)

)

)

c

cc

c

)

)

)

)

)

Markstein length, Lb

xH2 (-

)

Negative Lb is good for turbulent

combustion because local burning velocity is increased by flame stretch.

• As initial mixture pressure increases, Lb at xH2 = 0 decreases

to around 0.• Lb changed non-monotonically with

the increase in hydrogen ratio.

0 0.2 0.4 0.6 0.8 1.0-0.1

0

0.1

0.2

0.3

0.4

0.5

Lb

(cm

)

xH2 (-)

Markstein length, Lb : Sensitivity of

laminar burning velocity to flame stretch

Lb < 0 : Burning velocity increasesLb > 0 : Burning velocity decreases

for positive stretched flames.

14

Non-monotonic change in Lb cannot be explained from view point of effective Lewis number, Leeff.

0.2 0.4 0.6 0.8 1.00.4

0.6

0.8

1.0

1.2

1.4

0

Le

eff (

-)

xH2 (-)

Ammonia-Hydrogen

Pi = 0.1 MPa

xH2

Pi

Conclusions

• Laminar burning velocity of the ammonia/hydrogen/air premixed flame exponentially increases with the increase in the hydrogen ratio.

• Laminar burning velocity decreases as the initial mixture pressure increases.

• Markstein length varies non-monotonically with the hydrogen ratio.

This study is supported by Council for Science, Technology and Innovation (CSTI), Cross-

ministerial Strategic Innovation Promotion Program (SIP), "Energy carrier" (Funding agency:

the Japan Science and Technology Agency (JST)). 22

• Please refer the proceedings below:

Reaction enhancement by the hydrogen addition

Stability enhancement by the swirling flow

Reference:

Y. Arakawa, A. Hayakawa, K.D.K.A. Somarathne, T. Kudo and H. Kobayashi, Flame

characteristics of ammonia and methane flames in a swirl combustor, Proceedings of 12th

International Conference on Flow Dynamics (12th ICFD), Sendai, Japan, October 27 - 29,

2015.