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Department of Mechanical Engineering, Iowa State University
1
Performance of a Compression-Ignition
Engine Using Direct-Injection of Liquid
Ammonia/DME Mixture
Song-Charng Kong
Matthias Veltman, Christopher Gross
Department of Mechanical Engineering
Iowa State University
Acknowledgements:
Iowa Energy Center;
Norm Olson, Kevin Nordmeyer
Department of Mechanical Engineering, Iowa State University 2
Background
• Motivation
• Ammonia (NH3) combustion does not generate CO2
• Hydrogen carrier, renewable, etc.
• Challenges
• Ammonia is very difficult to ignite
• Octane number ~ 130
• Autoignition T ~ 651 ºC (gasoline: 440 ºC; diesel: 225 ºC)
• Ammonia flame temperature is lower than diesel flame T
• Ammonia emissions can be harmful
• Potential high NOx emissions due to fuel-bound nitrogen
• Gas phase at atmospheric pressure; Erosive to some materials
• Low energy content (~40% of that of diesel fuel per unit mass)
Department of Mechanical Engineering, Iowa State University 3
Thermodynamics/Chemistry
• Stoichiometric chemical reaction
3 2 2 2 20.75 ( 3.76 ) 1.5 3.32NH O N H O N
Fuel Molecule Boiling
Point (°C) (Air/Fuel)s
Latent
Heat
(kJ/kg)
Energy
Content
(MJ/kg-fuel)
Energy Content
(MJ/kg-
stoichiometric
mixture)
Methanol CH3OH 64.7 6.435 1203 20 2.6900
Ethanol C2H5OH 78.4 8.953 850 26.9 2.7027
Gasoline C7H17 --- 15.291 310 44 2.5781
Diesel C14.4H24.9 --- 14.3217 230 42.38 2.7660
Ammonia NH3 –33.5 6.0456 1371 18.6103 2.6414
Department of Mechanical Engineering, Iowa State University 4
Approach #1
• Introduce ammonia to the intake manifold
• Create premixed ammonia/air mixture in the cylinder
• Inject diesel fuel to initiate combustion
• Without modifying the existing injection system
Diesel ignition
Induce NH3
combustion
Burn out
premixed NH3
Department of Mechanical Engineering, Iowa State University 5
Engine Setup
• John Deere (4 cylinder, 4.5 liter)
• Operated at various load and speed conditions
• Vapor ammonia introduced into the intake duct – after turbo,
before manifold
Induction
point
Liquid NH3 tank
Fuel line
Fuel line
Department of Mechanical Engineering, Iowa State University 6
Test Results – Constant NH3 Flow Rate
• Engine torque increases suddenly once ammonia is
inducted
0
100
200
300
400
500
-80
-60
-40
-20
0
20
40
0 20 40 60 80 100 120
1800rpm Engine Torque
Engin
e T
orq
ue
(ft-lb)
Energ
y b
y N
H3 (%
)
Engine Load (%)
Diesel baseline
Diesel+ NH3
Energy replacement
by NH3
0
100
200
300
400
500
-50
0
50
0 20 40 60 80 100 120
1400rpm Engine Torque
Engin
e T
orq
ue
(ft-lb)
Energ
y b
y N
H3 (%
)
Engine Load (%)
Diesel baseline
Diesel+ NH3
Energy replacement
by NH3
Department of Mechanical Engineering, Iowa State University
• Fixed at specific diesel fueling, adjusted NH3 flow
rate to maintain constant torque
• Can achieve 5% diesel / 95% NH3 energy ratio
0
5
10
15
20
25
30
35
40
45
0 20 40 60 80 100
Power Contribution from Diesel Fuel (%)
Po
we
r (k
W)
Diesel Only
NH3 + Diesel
Contribution
from NH3
0
5
10
15
20
25
30
35
40
45
0 20 40 60 80 100
Power Contribution from Diesel Fuel (%)
Po
we
r (k
W)
Diesel Only
NH3 + Diesel
Contribution
from NH3
7
Test Results – Constant Torque
from
NH3
diesel
Department of Mechanical Engineering, Iowa State University
0
500
1000
1500
2000
2500
3000
3500
0 20 40 60 80 100
Power Contribution from Diesel Fuel (%)
NH
3 (
pp
mV
)
8
NH3 Exhaust Concentrations
• Concentrations vary depending on NH3 fueling rate
• Further study is required to reduce NH3 emissions.
High NH3
fueling
Low NH3
fueling 20
30
40
50
60
70
80
90
100
0 20 40 60 80 100
Constant Engine Torque
Ma
ss C
on
ve
rsio
n E
ffic
ien
cy (
%)
Diesel Load (%)
Ammonia combustion
efficiency
Department of Mechanical Engineering, Iowa State University
Approach #2
• Use direct liquid fuel injection
• Confine combustion mixture near the center
• To reduce exhaust ammonia emissions
• Ignition source – dimethyl ether (CH3-O-CH3)
• Mixture of DME and NH3
• Fuel mixing and storage at high pressure
• New fuel injection system – without fuel return
• Injection pump, injector, electronic control
9
Fuel injector
Department of Mechanical Engineering, Iowa State University
Engine Setup
• Yanmar diesel engine (L70V, 320 c.c.)
• Rated power at 6.26 hp at 3480 rpm
• Develop new fuel injection and engine control systems
• Bosch GDI type injector (up to 200 bar injection pressure)
Department of Mechanical Engineering, Iowa State University
Setup
• Mixing and storage of ammonia/DME at high pressure
• Exhaust emissions measurements
• Horiba MEXA-7100DEGR (CO2, CO, O2, HC)
• Horiba 1170NX (NOx, NH3)
• AVL Smoke Meter (PM)
Fuel mixing system
Emissions analyzers
Department of Mechanical Engineering, Iowa State University
Operating Conditions
12
Operating map using original diesel injection system
Department of Mechanical Engineering, Iowa State University
Test Results
• Baseline operation using 100% DME
• Explore operating range before using NH3/DME mixture
• For each operating point, various start-of-injection timings
were tested
• Provide flexibility for future optimization
13
SOI= –25 ~ 5 BTDC SOI= –30 ~ 0 ATDC
SOI= –35 ~ 20
BTDC
SOI= –30 ~ 20 BTDC
SOI= –30 ~ 20 BTDC
Department of Mechanical Engineering, Iowa State University
100% DME
• Mode 7 (2548 rpm) emissions
14
0
0.002
0.004
0.006
0.008
0.01
0
100
200
300
400
500
-30 -25 -20 -15 -10 -5 0
100% DME
Soo
t (F
SN
)
NO
x (p
pm
)
SOI (ATDC)
Soot - Smoke number
NOx
0
500
1000
1500
2000
-30 -25 -20 -15 -10 -5 0
100% DME
CO
& H
C (
pp
m)
SOI (ATDC)
CO
HC
Department of Mechanical Engineering, Iowa State University
Effects of Ammonia Combustion (Mode 7)
• 100%DME vs. 20%NH3/80%DME
• Soot remains at low level
• NOx increases due to fuel-bound nitrogen
15
0
0.002
0.004
0.006
0.008
0.01
-30 -25 -20 -15 -10 -5 0
Mode 7 (2548 rpm)
Soo
t (F
SN
)
SOI (ATDC)
100%DME
20%NH3/80%DME
0
100
200
300
400
500
600
700
800
-30 -25 -20 -15 -10 -5 0
Mode 7 (2548 rpm)
NO
x (
pp
m)
SOI (ATDC)
100%DME
20%NH3/80%DME
Department of Mechanical Engineering, Iowa State University
Effects of Ammonia Combustion (Mode 7)
• 100%DME vs. 20%NH3/80%DME
• Lower combustion temperature of ammonia causes more CO
and HC emissions
• Implication to fuel efficiency
16
0
500
1000
1500
2000
2500
3000
3500
4000
-30 -25 -20 -15 -10 -5 0
Mode 7 (2548 rpm)
CO
(p
pm
)
SOI (ATDC)
100%DME
20%NH3/80%DME
0
100
200
300
400
500
600
-30 -25 -20 -15 -10 -5 0
Mode 7 (2548 rpm)
HC
(pp
m)
SOI (ATDC)
100%DME
20%NH3/80%DME
Department of Mechanical Engineering, Iowa State University
Effects of Ammonia Combustion (Mode 21)
• Comparable combustion and fuel efficiency at this
lower speed
17
0
0.005
0.01
0.015
0.02
-35 -30 -25 -20 -15 -10 -5 0 5
Mode 21 (2200 rpm)
So
ot
(FS
N)
SOI (ATDC)
100%DME
20%NH3/80%DME
0
100
200
300
400
500
600
-35 -30 -25 -20 -15 -10 -5 0 5
Model 21 (2200 rpm)
NO
x (
ppm
)
SOI (ATDC)
100%DME
20%NH3/80%DME0
500
1000
1500
2000
2500
0
500
1000
1500
2000
2500
-35 -30 -25 -20 -15 -10 -5 0 5
Model 21 (2200 rpm)
100%DME
20%NH3
DME-HC
20%NH3
CO
& H
C (
pp
m)
SOI (ATDC)
CO
HC
Department of Mechanical Engineering, Iowa State University
Effects of Ammonia Combustion
• Exhaust ammonia emissions much lower than Approach#1
• Direct injection strategy benefits exhaust ammonia
emissions
18
0
50
100
150
200
250
300
350
400
-40 -35 -30 -25 -20 -15 -10 -5 0
NH3 Emissions (20%NH3/80%DME)
NH
3 (
pp
m)
SOI (ATDC)
Mode 7 (2548 rpm, low)
Mode 20
(2200 rpm, medium)
Mode 21 (2200 rpm, low)
Department of Mechanical Engineering, Iowa State University
Alternate Injection Strategy
• To extend the operating range
• Proposed strategies
• Double fuel injections
• Offer flexibilities in fuel delivery
• Used in industry for emissions and noise
reduction
• New fuel injector
• Original: single hole
• Alternate: eight holes – help with air
utilization
19
x % (100–x) %
pilot main
Department of Mechanical Engineering, Iowa State University
Double Injection, 100% DME
• Current system modified for using double injections
• Engine operations possible using double injections
• Comparable fuel efficiency and emissions
• Results based on Mode 7 (2548 rpm)
• Pilot SOI= –45 ~ –35 ATDC
• Pilot quantity=30% of total fuel
• Main SOI= –10 ATDC
• Exploring other conditions
• Varying the three injection variables
• Other operating points
20
0
0.002
0.004
0.006
0.008
0.01
300
350
400
450
500
550
600
-50 -45 -40 -35 -30
Double Injections (Mode 7)
So
ot
(FS
N)
NO
x (p
pm
)
Pilot SOI (ATDC)
Soot - Smoke number
NOx
Department of Mechanical Engineering, Iowa State University
Multi-Hole Injector
• Change from single hole to 8 holes
• Higher exhaust NOx – may imply higher combustion
temperature to sustain higher load operation
• Exploring combination of using 8-hole injector in
combination with double injections
21
0
0.005
0.01
0.015
0.02
0.025
-30 -25 -20 -15 -10 -5 0
Mode 7 (2548 rpm)
Soo
t (F
SN
)
SOI (ATDC)
Single hole
8 holes
0
100
200
300
400
500
600
-30 -25 -20 -15 -10 -5 0
Mode 7 (2548 rpm)
NO
x (
pp
m)
SOI (ATDC)
Single hole
8 holes
Department of Mechanical Engineering, Iowa State University 22
Summary
• Demonstrated ammonia combustion in diesel engines
• Port induction of ammonia coupled with direct-injection
diesel fuel
• Exhaust ammonia level at “thousands of ppm” under the
conditions studied
• Direct injection of ammonia/DME
• Exhaust ammonia level at “hundreds of ppm” under the
conditions studied
• Exploring optimal injection strategies for ammonia combustion
• Perspectives – effects of engine size
• Challenges for small engine: more heat loss, higher engine speed
required, lower fuel injection pressure
• Large engine will favor ammonia combustion