COMPARISON OF
AMMONIA / GASOLINE AND
AMMONIA / ETHANOL MIXTURES
Rakesh Leeladhar
Shawn Grannell
Stanislav Bohac
Dennis Assanis
Mechanical Engineering Dept.
University Of Michigan
Background and Motivation
z
z
z
z
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We wish to use ammonia as a primary transportation
fuel.
Ammonia works well at high engine loads but a
combustion promoter is needed at lower loads.
Gasoline has previously been shown to be a good
combustion promoter.
What about ethanol? Ethanol can be grown locally, can
be carbon neutral, etc…
It would be very difficult or impossible to produce enough
ethanol to displace all of the gasoline that we use. But
we could produce enough to use it as a combustion
promoter.
But is ethanol a good ammonia combustion promoter?
Overview
Experimental Engine
z Comparison of Ethanol and Gasoline
Characteristics
z Ethanol/Ammonia Fuel Mix
z Comparison of Gasoline/Ammonia and
Ethanol/Ammonia Fuel Mix Maps
z Comparison of Rough and Knock Limits
z Comparison of Thermal Efficiency
z Conclusions
z
Comparison of Ethanol Gasoline Properties
Properties
Gasoline
E85
RON
92
101
Density (g/cm3)
Heat of combustion (MJ/kg)
Latent heat of vaporization (KJ/kg)
0.74
42.4
420
0.79
32.6
845
Stoichiometric Air Fuel Ratio
14.3
9.0
Characteristics of Ethanol
Ethanol has a high antiknock quality due to
its high octane number.
z Ethanol has a high latent heat of
vaporization.
z
z Advantage:
Decreases the compressed gas
temperature during the compression stroke.
z Disadvantage: Property influencing cold start
ability.
Experimental Investigations
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Roughness Limit
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¾
¾
¾
¾
Knock Limit
¾
¾
There are various methods to determine the cycle to
cycle variability which determines the vehicle drivability.
Pressure related parameters, burn rate related
parameters, flame front position parameters.
Pressure related quantities are the easiest and the
efficient way to determine the cycle to cycle variability.
The IMEPn derived from the pressure data is expressed
as Rough Limit= COV(IMEPn) = σimep/IMEPn×100
The maximum gasoline fraction used to avoid knock
Efficiency
¾
It is the ratio maximum work output to input.
Cooperative Fuel Research Engine (CFR)
83.4 mm bore diameter, 114.3 mm stroke, 625 cc swept volume displacement
Effect of Compression Ratio & Load on
Combustion Promoter Input at Roughness Limit
Rough Limit Map(E85)
100
80
60
40
20
0
L H V b a s is E 8 5
In p u t (% )
L H V G a s o in e
In p u t( % )
Rough Limit Map(Gasoline)
8:1 COV~3%
10:1 COV~3%
12:1 COV~3%
0
500
1000
1500
Total Specific Fuel Input (J/l)
2000
100
80
60
40
20
0
8:1 COV~3%
10:1 COV~3%
12:1 COV~3%
14:1 COV~4%
0
500
1000
1500
Total Specific Fuel Input (J/l)
¾The fraction of required promoter input decreases drastically as load is
increased.
¾The required promoter input (%) is the same for both gasoline and
ethanol mixtures at the roughness limit.
2000
Compressed Promoter Density @ Spark (kJ/l)
Promoter Density at Spark at Rough Limit
4.5
8:1, Gasoline/NH3
4
10:1, Gasoline/NH3
3.5
8:1, E85/NH3
10:1, E85/NH3
3
2.5
2
1.5
1
0.5
0
0
0.5
1
1.5
2
2.5
3
3.5
Compressed NH3 Density @ Spark (kJ/l)
4
4.5
Promoter Density at Spark at Rough Limit
E85
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
0.0
8:1, COV ~3%
10:1, COV ~3%
12:1, COV ~3%
Compressed E85 Density @ Spark
(kJ/l)
Compressed Gasoline Density @
Spark (kJ/l)
Gasoline
4.5
8:1, COV ~3%
4.0
10:1, COV ~3%
3.5
12:1, COV ~3%
14:1, COV ~4%
3.0
2.5
2.0
1.5
1.0
0.5
0.0
0
1
2
3
4
5
6
7
Compressed NH3 Density @ Spark (kJ/l)
8
0
1
2
3
4
5
6
7
Compressed NH3 Density @ Spark (kJ/l)
The promoter input (%) decreases as
compressed NH3 density at spark increases.
8
Promoter Density at Spark at Rough Limit
8:1 and 10:1, E85/NH3
8:1 and 10:1, Gasoline/NH3
2.5
P r o m o te r D e n s ity @
S p a r k (k J /l)
G a s o lin e D e n s ity @
S p a r k (k J /l)
2.5
1000 RPM
2
1300 RPM
1600 RPM
1.5
y = -0.113x + 1.363
1
2
3
4
5
6
7
1600 RPM
1
y = -0.2258x + 1.5712
0.5
0
0
1300 RPM
1.5
1
0.5
1000 RPM
2
8
0
0
NH 3 Density @ Spark (kJ/l)
1
2
3
4
5
6
NH 3 Density @ Spark (kJ/l)
Minimum gasoline requirement at spark= 1.36
Minimum E85 requirement at spark=1.57
Both the fuels require almost the same energy/volume at the spark!!
7
8
Promoter Density at Spark at Rough Limit
Promoter Density @ Spark (kJ/l)
8:1 and 10:1, Gasoline/NH3 and E85/NH3
2.5
1000 RPM
2
1300 RPM
1.5
1600 RPM
1
0.5
y = -0.1512x + 1.4252
0
0
1
2
3
4
5
NH3 Density @ Spark (kJ/l)
6
7
8
Is Ammonia a Good Fuel ?
800
Specific Promoter Input (J/l)
700
600
500
400
E85/NH3 8:1 1000 RPM
300
E85/NH3 8:1 1300 RPM
E85/NH3 8:1 1600 RPM
200
Gas/NH3 8:1 1000 RPM
Gas/NH3 8:1 1300 RPM
100
Gas/NH3 8:1 1600 RPM
0
0
1000
2000
3000
4000
Total Specific Fuel Input (J/l)
¾ The required promoter input decreases slightly as load is
increased., showing that ammonia as a fuel having a slighter
positive or neutral effect when used with both gasoline and ethanol
at the rough limit.
Promoter Input, 10:1, All Speeds
Specific Promoter Input (J/l)
700
600
500
400
E85/NH3 10:1 1000 RP M
300
E85/NH3 10:1 1300 RP M
E85/NH3 10:1 1600 RP M
Gas/NH3 10:1 1000 RP M
Gas/NH3 10:1 1300 RP M
200
100
Gas/NH3 10:1 1600 RP M
0
0
500
1000
1500
2000
2500
Total Spe cific Fue l Input (J/l)
3000
3500
How Does Promoter Input Vary with Speed?
Specific Promoter Input @ NH3 cut-in point
(J/L)
800
700
600
8:1 E85
10:1 E85
12:1 E85
14:1 E85
8:1 gas
10:1 gas
12:1 gas
500
400
900 1000 1100 1200 1300 1400 1500 1600 1700
Speed
Knock Limit LHV Basis (% Promoter)
Knock Limit
100
90
80
70
60
50
40
30
20
10
0
8:1 E85/NH35
10:1 E85/NH3
12:1 E85/NH3
14:1 E85/NH3
8:1 Gasoline/NH3
10:1 Gasoline/NH3
12:1 Gasoline/NH3
14:1 Gasoline/NH3
0
500
1000
1500
2000
Total Spe cific Fue l Input (Joule s /Lite r)
2500
Knock and Rough Limit Crossover –
Gasoline
100
LHV Basis (%Gasoline)
8:1
90
10:1
80
12:1
70
14:1
16:1
60
50
40
30
20
10
0
0
500
1000
1500
2000
2500
3000
3500
4000
Total Specific Fuel Input (Joules/Liter)
¾
%Gasoline decreases as total fuel input increases.
¾
At some point there is a crossover between roughness
limited minimum gasoline fraction and knock limited
maximum gasoline fraction. The crossover occurs at 12:1
Compression Ratio.
LHV basis % E85
Knock and Rough Limit Crossover
– E85
100
90
80
70
60
50
40
30
20
10
0
Rough Limit E85
8:1 Knock Limit
E85
10:1 Knock
Lim it E85
12:1 Knock
Limit E85
14:1 Knock
Limit E85
0
500
1000 1500 2000 2500 3000
Tota l Spe cific Fue l Input (J/l)
3500
The Crossover occurs at 13.5:1 Compression Ratio.
4000
Thermal Efficiency At Rough Limit
E85
40
35
30
25
20
15
10
5
0
8:1
10:1
12:1
0
200
400
IMEPn
600
800
N e t In d ic a t e d T h e r m a l% ,A ll
speeds
N e t In d ic a te d
T h e rm a l% ,A ll s p e e d s
Gasoline
40
35
30
25
20
15
10
5
0
8:1
10:1
12:1
0
100
200
300
400
IMEPn
500
600
700
Summary of Ethanol/NH3 Combustion
put into figure…Fuel Mix Sweep at
1600 RPM, 10:1
and IMEPn ~ 550 kPa.
100
90
80
Spark Advance(deg)
70
Ignition Delay(deg)
60
50
Burn
Duration(degrees)
40
Net Indicated
Thermal%
30
COV(IMEPn)%
20
10
0
0
20
40
60
80
100
120
Conclusions
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The knock and rough limit crossover occurs at
~13.5:1 for E85 and ~12:1 for gasoline.
E85/NH3 has higher knock limit and allows for a
higher maximum compression ratio and thermal
efficiency.
Gasoline/NH3 has a lower roughness limit and allows
for a slightly more fuel mixture flexibility.
The roughness limited promoter fraction is found to
be almost the same for both (Ethanol &Gasoline)
when used with Ammonia as the primary fuel.
The fuel blend does not change much with speed.
E85 is an attractive combustion promoter, like
gasoline, when used with ammonia as the primary
fuel.
Acknowledgement
Dennis Assanis , Chair, Dept. of Mechanical
Engineering, University of Michigan
Stani Bohac, Research Scientist, Dept. of
Mechanical Engineering, University of
Michigan
Shawn Grannell, Doctoral Student,
University of Michigan