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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.