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A Comparison of Combustion Promoters for Ammonia and Two Ways to Run Engines on Ammonia as the Only Fuel Shawn Grannell, Casey Stack and Donald Gillespie GSG

A Comparison of Combustion Promoters for Ammonia€¦ · A Comparison of Combustion Promoters for Ammonia and Two Ways to Run Engines on Ammonia as the Only Fuel Shawn Grannell, Casey

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A Comparison of Combustion Promoters for Ammonia and

Two Ways to Run Engines on Ammonia as the Only Fuel

Shawn Grannell, Casey Stack and Donald Gillespie

GSG

Summary of Ammonia Engine Progress

•Hydrocarbons, Hydrogen & Oxygen as Combustion Promoters for Ammonia

•Summary of Operating Maps•Ammonia/Oxygen Test Engine Results •Ammonia Flame Cracker•Conclusion

Combustion of 0.79N2 + 0.21O2 + 0.28NH3

•Works only for special cases, for example WOT, 12:1, 1000 RPM, warmed up when ammonia is burned with air.•Cold Start? Not reliable on ammonia/air mixture. •Can’t idle on ammonia/air mixture.•Can use gasoline promote ammonia combustion and this is dual fuel. •But for ammonia as the only fuel, and air as the only oxidizer:

–Combustion Promoter from air = Oxygen!–Combustion Promoter from ammonia = Hydrogen!

Ammonia/Hydrogen Rough Limit.Or: Crack all ammonia to H2 and burn the H2 with air!

Gasoline/Air, H2/Air, and O2/NH3 Mixtures are Combustion Promoters for Additional NH3/Air.

•(0.79 N2 + 0.21 O2) + 0.024b C6H11 + 0.28(1-b) NH3 ⇒(0.93 – 0.14b) N2 + (0.42 – 0.288b) H2O + 0.144b CO2

Combustion Promoter is Gasoline/Air

•(0.79 N2 + 0.21 O2) + 0.42b H2 + 0.28(1-b) NH3 ⇒(0.93 – 0.14b) N2 + 0.42 H2O

Combustion Promoter is Hydrogen/Air

•(1-b)(0.79 N2 + 0.21 O2) + 0.21b O2 + 0.28 NH3 ⇒(0.93 – 0.79b) N2 + 0.42 H2O

Combustion Promoter is Oxygen/Ammonia

0

200

400

600

800

1000

0 600 1200 1800 2400 3000

Total Spec. Fuel Input J/L

Spec

. Hyd

roge

n In

put J

/L

100% Hydrogen8:110:112:1

Rough Limit at 1600 RPM for Hydrogen

Idle

2

2.5

3

3.5

4

4.5

5

150 175 200 225 250 275

Spec. H2 Input (J/L)

CO

V(IM

EPn)

(%) N

ear I

dle

8CR

10CR

12CR

14CR

16CR

Rough Limit is determined by Combustion Promoter input at COV(IMEP) = 3% at light loadHydrogen can be obtained by cracking Ammonia!

100

150

200

250

300

8 9 10 11 12 13 14 15 16

Compression Ratio

Spec

. H2

Inpu

t Nea

r Idl

e (J

/L)

WOT

2

2.5

3

3.5

4

4.5

5

300 350 400 450 500 550

Spec. O2 Input (J/L)

CO

V(IM

EPn)

(%) N

ear I

dle

8CR

10CR

12CR

14CR

16CR

Oxygen curve is generated by COV(IMEP) crossings at 3%

Rough Limit Comb. Promoter Input at 12:1, 1600 RPM: •Hydrogen/Air ~200 J/L •Oxygen/Ammonia ~400 J/L•Gasoline/Air, ~600 J/L•Methane/Air ~800J/L

Oxygen is a Combustion Promoter Obtained from Air!

O2 Rough Limit at 1600 RPM and ~ Idle

0100200300400500600700800900

1000

6 8 10 12 14 16 18

Compression Ratio

Spec

ific

Prom

oter

Inpu

t J/L

Methane Rough LimitGasoline Rough LimitO2 Rough LimitH2 Rough Limit

Operating Maps for 1600 RPM, 12:1 Rough Limit

0

600

1200

1800

2400

3000

3600

0 600 1200 1800 2400 3000 3600

Total Specific Fuel Input (Joules/Liter)

Com

pone

nt In

put

(Jou

les/

Lite

r)

AirAmmoniaHydrogen

0

600

1200

1800

2400

3000

3600

0 600 1200 1800 2400 3000 3600

Total Specific Fuel Input (Joules/Liter)

Com

pone

nt In

put

(Jou

les/

Lite

r)AirAmmoniaGasoline

0

600

1200

1800

2400

3000

3600

0 600 1200 1800 2400 3000 3600

Total Specific Fuel Input (Joules/Liter)

Com

pone

nt In

put

(Jou

les/

Lite

r)

AmmoniaAirOxygen

At Stoichiometric, the Chemical Equivalence Relationships are: •Air = Gasoline + Ammonia•Air = Hydrogen + Ammonia•Ammonia = Air + Oxygen

Idle Idle WOTWOT

WOTIdle

Small Test Engine for NH3/O2

•Constant Oxygen Fraction for air+O2 portions:•(1 - X)N2 + (X)O2 + (4X/3)NH3 ⇒

(1 – X/3)N2 + (2X)H2O•X = 0.21 (21%) for Air

•Compression Ratio ~ 6:1•3600 RPM•Fixed Spark Timing ~ 20 deg BTC•COLD-START CAPABLE!

(Easier than gasoline!)•Operates without Ammonia Cracker.

Air Pinhole with Fine Adjustment for Stoich.

Intake PlenumOxygen

Sensor

Oxygen Inlet with Pinhole

Ammonia Inlet with Pinhole

Small Test Engine Results for NH3/O2

80

100

120

140

160

0 100 200 300 400 500 600 700 800 900 1000 1100 1200

Power (Watts)

Out

put V

olta

ge GasNH3 + 29.2% O2NH3 + 30.1% O2NH3 + 30.9% O2NH3 + 31.9% O2NH3 + 33.1% O2NH3 + 34.6% O2

When the Oxygen Fraction of the Air/O2 portions is 33%, Engine has Same WOT Power as for Gasoline!

Spark Adv. ~ 20 degrees Not MBT?

O2 > Rough Limit ->Wastes O2

0102030405060708090

100

0 600 1200 1800 2400 3000

Total Spec. Fuel Input (J/L)

% O

2 in

Air

Rough Limit

Knock Limit33% Test Engine

Idle

WOTO2 < Rough Limit -> Runs Rough

0

600

1200

1800

2400

3000

0 600 1200 1800 2400 3000

Specific NH3 Input (J/L)

O2

Inpu

t (J/

L)

Rough LimitKnock Limit33% Test Engine

O2 > Rough Lim.O2 < Rough Lim.

WOT

Same Engine now with Ammonia Flame Cracker

•0.79N2 + 0.21O2 + 0.42H2 + 0.4-0.6(Inert Gases) ⇒Nitrogen and Water from Engine Combustion

•Operates without Oxygen Separator.•Additional Inert Intake Gases Buffer Against Knock and Backfire, and limit NOx emissions.

•COLD-START CAPABLE!•VERY LITTLE OR NO NH3 ENTERS THE ENGINE!

Air Pinhole with Fine Adjustment for Stoich.

NH3Line

H2 Line into Engine

Air/NH3pinhole mixer for Cracker

Ammonia Cracker

“Zero”Regulator

Ammonia Cracker Output

How the Ammonia Flame Cracker works•Ideal Cracker Combustion:: 0.79N2 + 0.21O2 + 0.28φNH3 ⇒

0.42H2O + (0.79 + 0.14φ)N2 + 0.42(φ - 1)H2

•Gas is heat exchanged to expend less energy bringing NH3 up to cracking temperature and to cool H2 product. •Heat released by combustion is absorbed by cracking. •Filament resistively heated to start, then turned OFF during normal operation.•Very high effective flame speeds ≥ 30-40 meters/sec.

Air/NH3 InletH2 Exit

Filament

Filament Assembly and Terminal Port

FilamentInsulation

Heat Exchange Tube is Silicon Carbide

H2 Exit Air/NH3Inlet

Mostly Non-Catalytic Reactions in Bulk Gas.

Flame initiation on Filament.

Ammonia Flame Cracker Analysis

Gas Temperature in Filament Inlet Region is Initial Temperature before Reactions Start

Ammonia Cracker Ammonia Cracker

High NH3Content

Very Little NH3Mostly H2

0

200

400

600

800

1000

1200

1400

1 2 3 4 5 6 7 8Ammonia/Air Equivalence Ratio

Gas

Tem

pera

ture

in F

ilam

ent

Inle

t Reg

ion

(Cel

sius

)

Threshold for Full CrackingMeasured Cracker PerformanceIdeal Performance Limit

Ammonia Flame Cracker Theoretical Operating Limit

Gas Temperature in Filament Inlet Region is Initial Temperature before Reactions Start

Post-Reaction Temperature

0200400600800

100012001400

0 20 40 60 80 100 120 140

Heat per Mole NH3 (kJ)

Tem

pera

ture

(Cel

sius

)

NH3 Fully Cracked

NH3 Cracking begins.

Gas Temperature in Filament Inlet Region might be 1000 C, For Example.

ε6.64

6.66

6.68

6.70

6.72

800 900 1000 1100 1200 1300

Reaction Temperature (Celsius)

Equ

ival

ence

Rat

io fo

r Ze

ro T

empe

ratu

re R

ise

Cracking Range. Varies with Throughput Rate.

•If ε → 0, then Reactions are balanced for Zero Temperature Rise. •Worst Case Theoretical Maximum Full-Cracking Equiv. Ratio = 6.66

Conclusions•CH4 (800J/L), Gasoline (600J/L), O2 (400J/L), and H2(200J/L) are useful Combustion Promoters for NH3.•Engines can work on 100% Ammonia without cracker when Oxygen is used, and Cold-Start is as Easy as for Gasoline.•Ammonia Flame Cracking can be used to run on NH3/H2Rough Limit OR 100% Hydrogen. Easy Cold-Start, and the Cracker can be run so that the Engine sees only trace quantities of Ammonia, or none at all. •Theoretical Performance Limit of Ammonia Flame Cracker with Zero Losses: Full Cracking at Equivalence Ratio = 6.66, Product containing ~52% H2 by volume, and NH3-to-H2 Thermal Conversion Efficiency = 97.3%, on an LHV energy basis.