t
TEMPERATURE COMBUSTION (LTC) ENGINES
J ld A C
g y ( )
THERMODYNAMIC ADVANTAGES OF LOW TEMPERATURE COMBUSTION (LTC) ENGINES
INCLUDING THE USE OF LOW HEAT REJECTION (LHR) CONCEPTSREJECTION (LHR) CONCEPTS
Jerald A. Caton Texas A&M University College Station, TX
for
Directions in Engine-Efficiency and Emissions Research (DEER)
2010 Conference
Detroit Marriott at the Renaissance Center
1
Detroit, MI 27 September 2010
( )
THERMODYNAMIC ADVANTAGES OF LOW TEMPERATURE COMBUSTION (LTC) ENGINESTEMPERATURE COMBUSTION (LTC) ENGINES
INCLUDING THE USE OF LOW HEAT REJECTION (LHR) CONCEPTS
• INTRODUCTION AND BACKGROUND
• DESCRIPTION OF THE CYCLE SIMULATION
• RESULTS AND DISCUSSION
9Engine and Operating Conditions9Engine and Operating Conditions
9Overall Results – Efficiencies
9Parametric Evaluations
9Nitric Oxide Results
• SUMMARY AND CONCLUSIONS
2
or
use
t t
INTRODUCTION AND BACKGROUND
• LTC engines have demonstrated low emissions and high efficiencies
These engines combinations of high CR high• These engines use combinations of high CR, high EGR, lean mixtures, fast burn rates, high boost and
other features • What is the contribution to the high efficiencies by each of these features? • What are the best combinations of these features? • Does including LHR concepts make sense?
Wh h not?Why or why not? • What does the second law say?
Wh i th i it i id i i ? 3
• What is the impact on nitric oxide emissions?
THERMODYNAMIC ENGINE CYCLE SIMULATION
Features/Considerations: 1. One common pressure 2. Three gas temperatures 3 Three volumes and masses
4
3. Three volumes and masses 4. Separate heat transfer
PROCEDURES FOR SOLUTIONS • ORDINARY DIFFERENTIAL EQUATIONS • NUMERICAL TECHNIQUES: EULERS• NUMERICAL TECHNIQUES: EULERS • INITIAL CONDITIONS: T1, p1, Residual Fraction • BOUNDARY CONDITIONS: INLET & EXHAUST • SPECIFY SUBMODEL PARAMETERS:
- Thermodynamic properties - Heat transfer coefficient - Fuel mass rates - Flow rate parameters
Nitric oxide kinetics - Nitric oxide kinetics - Other
5
6
SPECIFICATIONS FOR THE ENGINESPECIFICATIONS FOR THE ENGINE
PARAMETER VALUE Engine Automotive, V-8 Bore/Stroke 102/88 mm (4.0/3.5 in) Displacement 5.7 liter (350 in3) bmep 900 kPa Engine speed 2000 rpm C b i i iCombustion timing MBTMBT Geometric compression ratio from 8:1 to 20:1 Valve arrangement Valve arrangement OHV 2 valves/cylinderOHV, 2 valves/cylinder
t
= = = = =
Add f i ti l f hi
DESCRIPTION OF CASES -- STRATEGY –
Add features in a sequential fashion:
2 CR = 20 BD = 60o φ= 1 0 EGR = 0% T = 450 K 2 CR = 20; BD = 60o; φ= 1.0; EGR = 0%; Tw = 450 K 3 CR = 20; BD = 30o; φ= 1.0; EGR = 0%; Tw = 450 K 4 CR = 20; BD = 30o; φ= 0 7; EGR = 0%; T = 450 K 4 CR 20; BD 30o; φ 0.7; EGR 0%; Tw 450 K 5 CR = 20; BD = 30o; φ= 0.7; EGR = 50%; Tw = 450 K 6 CR = 20; BD = 30o; φ= 0.7; EGR = 50%; Tw = 550 K
7
6 CR 20; BD 30 ; φ 0.7; EGR 50%; Tw 550 K
CASECASE DESCRIPTION 1 CR = 8; BD = 60o; φ= 1.0; EGR = 0%; Tw = 450 K
RESULTSRESULTS � Thermal Efficiencies
� Cylinder Conditions
� Heat Transfer/Exhaust Energy
� Parameter Optimization
� Nitric Oxides� Nitric Oxides
� Low Heat Rejection (LHR) 8
Low Heat Rejection (LHR)
RESULTSRESULTS � Thermal Efficiencies
� Cylinder Conditions
� Heat Transfer/Exhaust Energy
� Parameter Optimization
� Nitric Oxides� Nitric Oxides
� Low Heat Rejection (LHR) 9
Low Heat Rejection (LHR)
THERMAL EFFICIENCIES ¾ Base Case
%)
50 bmep = 900 kPa
2000 rpm MBT Timing
Effic
ienc
y (% 45
Net Indicated Efficiency
Gross Indicated Efficiency
d an
d B
rake 40
Brake Efficiency
Indi
cate 35
SE = 20 30
o
0.7
R =
50%
l = 5
50 K
Efficiency
Case
1 2 3 4 5 6
30 BAS
CR
=
θ b =
φ =
0
EGR
T wal
l
10
THERMAL EFFICIENCIES 50
bmep = 900 kPa 2000 rpm
MBT Timing
¾ High compression ratio
ffici
ency
(%)
45
Net Indicated Efficiency
Gross Indicated Efficiency
and
Bra
ke E
40
y
Indi
cate
d
35
E 20 0 o 7 = 50
%
= 55
0 KBrake
Efficiency
Case
1 2 3 4 5 6
30 BAS
E
CR
=
θ b = 3
φ =
0.
EGR
=
T wal
l =
11
Case
Case
THERMAL EFFICIENCIES ¾ High compression ratio
¾ Short burn duration
)
50 bmep = 900 kPa
2000 rpm MBT Timing
Effic
ienc
y (% 45
Net Indicated Efficiency
Gross Indicated Efficiency
d an
d B
rake
E
40
Indi
cate
d
35
E = 20 30
o
0.7
R =
50%
= 55
0 KBrake
Efficiency
Case
1 2 3 4 5 6
30 BAS
E
CR
=
θ b =
3
φ =
0
EGR
T wal
l
12
¾ L i t
THERMAL EFFICIENCIES ¾ High compression ratio
¾ Short burn duration
)
50 bmep = 900 kPa
2000 rpm MBT Timing
¾ Lean mixture
Effic
ienc
y (%
)
45
Net Indicated Efficiency
Gross Indicated Efficiency
and
Bra
ke E
40
Brake
Indi
cate
d
35
E 20 30 o
.7 = 50
%
= 55
0 K
Brake Efficiency
Case
1 2 3 4 5 6
30 BAS
E
CR
=
θ b = 3
φ =
0.
EGR
T wal
l =
13
Case
¾ L i t
THERMAL EFFICIENCIES ¾ High compression ratio
¾ Short burn duration 50
bmep = 900 kPa 2000 rpm
MBT Timing ¾ Lean mixture
¾ High EGR
ffici
ency
(%)
45
g
Net Indicated Efficiency
Gross Indicated Efficiency
and
Bra
ke E
f
40
Efficiency
Indi
cate
d a
35
20 0 o 7 = 50
%
550
K
Brake Efficiency
1 2 3 4 5 6
30 BAS
E
CR
= 2
θ b = 3
0
φ =
0.7
EGR
=
T wal
l =
14
Case
Case
¾ L i t
w emp
THERMAL EFFICIENCIES ¾ High compression ratio
¾ Short burn duration
)
50 bmep = 900 kPa
2000 rpm MBT Timing
¾ Lean mixture
¾ High EGR
¾ High cylinder all t Effic
ienc
y (% 45
Net Indicated Efficiency
Gross Indicated Efficiency
¾ High cylinder wall temp
d an
d B
rake
E
40
Brake
Indi
cate
d
35
E = 20 30
o
0.7
R =
50%
= 55
0 K
Efficiency
Case
1 2 3 4 5 6
30 BAS
E
CR
=
θ b =
3
φ =
0
EGR
T wal
l
15
=
C 1
50
THERMAL EFFICIENCIES %
)
50 bmep = 900 kPa
2000 rpm MBT Timing
Pumping Losses
RESULTS Case 6:
ffici
ency
(% 45
Net Indicated Efficiency
Gross Indicated Efficiency Mechanical
Friction ηind,g = 49.5% η = 48 2%
nd B
rake
Ef
40
Efficiency
Brake Efficiency
ηind,n 48.2% ηbrk = 41.6%
ndic
ated
an
35
0% 0 K
Case 1: ηInd,g = 36.1%
In
30 BAS
E
CR
= 2
0
θ b = 3
0 o
φ =
0.7
EGR
= 5
0
T wal
l = 5
50
ηind,n = 35.6% ηbrk = 32.7%
16 Case
1 2 3 4 5 6
t
COMPARISON TO THE LITERATURE
Fuels Gasoline/Diesel Isooctane Inlet Pressure (kPa) 200 227 G i CR 16 1 20Geometric CR 16.1 20 EGR (%) 45.5 50 Equivalence Ratio 0.77 0.7 Speed (rpm) 1300 2000 RESULTS: IMEPNET (kPa) 1100 1047IMEPNET (kPa) 1100 1047 Net Ind Efficiency (%) 50 48.2 Peak Pressure (MPa) 12 13.9 Nitric Oxide (g/kW-h) 0.01 0
ITEM REFERENCE (Kokjohn et al.)
THIS WORK (Case 6)
Bore/Stroke (mm) 137/165 102/88Bore/Stroke (mm) 137/165 102/88
RESULTSRESULTS � Thermal Efficiencies
� Cylinder Conditions
� Heat Transfer/Exhaust Energy
� Parameter Optimization
� Nitric Oxides� Nitric Oxides
� Low Heat Rejection (LHR) 18
Low Heat Rejection (LHR)
15000
CYLINDER PRESSURES 15000
bmep = 900 kPa 2000 rpm
"MBT" Timing
Case = 6
Case = 5
a) 10000
ress
ure
(kPa
Case = 3
Case = 4
Pr
5000 Case = 2
Case = 1
19CRANK ANGLE
-90 -60 -30 0 30 60 90 0
CYLINDER TEMPERATURES
3000 bmep = 900 kPa
2000 rpm "MBT" Timing
C 2Case = 3
re (K
)
2000
2500
Case = 1
Case = 2
Case = 4
Tem
pera
tur
1500
Case = 6
One
-Zon
e
1000
Case = 5
500
20CRANK ANGLE
-90 -60 -30 0 30 60 90 0
RESULTSRESULTS � Thermal Efficiencies
� Cylinder Conditions
� Heat Transfer/Exhaust Energy
� Parameter Optimization
� Nitric Oxides� Nitric Oxides
� Low Heat Rejection (LHR) 21
Low Heat Rejection (LHR)
50
HEAT TRANSFER AND EXHAUST ENERGY
45
bmep = 900 kPa 2000 rpm
MBT Timing
Exhaust Energy (%)
ener
gy)
35
40 y
(% o
f fue
l e
30 Relative
Heat Transfer (%) Le2
3
Ener
gy
20
25
Higher CR
Shorter
Lean Burn High EGR 1
2
4
5
10
15
Shorter Burn
Duration
Higher Wall
Temp 6
22Net Indicated Efficiency (%)
35 40 45 50 10
Note: from Otto
n a
1.35
b 900 kP
Average “gamma” for Expansion Stroke ke
)
bmep = 900 kPa 2000 rpm
MBT Timing
5 Note: from simple “Otto”
nsio
n st
rok
1.30
5 6
simple cycle considerations –
a “0.01” increase of gamma results i about 1%
ama
(exp
an
3
4 results in about a 1% efficiency gain
This implies that about one-
Aver
age
Ga
1.25
1
2 half to two thirds of the efficiency increases are due to the increase of gamma.
1 20
23Net Indicated Efficiency (%)
35 40 45 50 1.20
RESULTSRESULTS � Thermal Efficiencies
� Cylinder Conditions
� Heat Transfer/Exhaust Energy
� Parameter Optimization
� Nitric Oxides� Nitric Oxides
� Low Heat Rejection (LHR) 24
Low Heat Rejection (LHR)
EFFECTS OF COMPRESSION RATIO
48
50 Case 6
(%) 44
46 Net Indicated Efficiency
l Effi
cien
cy
40
42 Case 6
Ther
mal
36
38
32
34 bmep = 900 kPa φ = 0.7, EGR = 50% 2000 rpm, θb = 30o
MBT Timing
Brake Efficiency
25Compression Ratio
0 5 10 15 20 25 30 30
g
EFFECTS OF BURN DURATION
48
50
C 6
(%)
46
Case 6
Net Indicated Efficiency l E
ffici
ency
42
44
C 6
Ther
ma
38
40
Case 6
Brake Efficiency
36 bmep = 900 kPa φ = 0.7, EGR = 50% 2000 rpm, cr = 20
MBT Timing
26Burn Duration, θb(oCA)
0 20 40 60 80 100 120 140 34
EFFECTS OF EGR
49
50
51
bmep = 900 kPa φ = 0.7, θb = 30o
2000 rpm, Twall = 550 K MBT Ti i 20
y (%
)
47
48
49 MBT Timing, cr = 20 Case 6
Net Indicated
al E
ffici
ency
45
46
Net Indicated Efficiency
Ther
m
43
44
40
41
42 Case 6 Brake
Efficiency
27EGR (%)
0 10 20 30 40 50 60 70 40
RESULTSRESULTS � Thermal Efficiencies
� Cylinder Conditions
� Heat Transfer/Exhaust Energy
� Parameter Optimization
� Nitric Oxides� Nitric Oxides
� Low Heat Rejection (LHR) 28
Low Heat Rejection (LHR)
NITRIC OXIDES FOR EACH CASE 2020
bmep = 900 kPa 2000 rpm
MBT Timing 1
3
kW-h
) 15
2
3
4
ic O
xide
(g/k
10 2
Nitr
i
5
35 40 45 50
0 5 6
29
Net Indicated Efficiency (%)
35 40 45 50
RESULTSRESULTS � Thermal Efficiencies
� Cylinder Conditions
� Heat Transfer/Exhaust Energy
� Parameter Optimization
� Nitric Oxides� Nitric Oxides
� Low Heat Rejection (LHR) 30
Low Heat Rejection (LHR)
LOW HEAT REJECTION (LHR)
%)
50 bmep = 900 kPa
2000 rpm MBT Timing
Pumping Losses
ffici
ency
(%
45
Net Indicated Efficiency
Gross Indicated Efficiency Mechanical
Friction
nd B
rake
Ef
40
Efficiency
Brake Efficiency
Indi
cate
d an
35
0%
50 K
0 K
I
30 BAS
E
CR
= 2
0
θ b = 3
0 o
φ =
0.7
EGR
= 5
0
T wal
l = 5
5
T wal
l = 8
80
31 Case
1 2 3 4 5 6 7
LOW HEAT REJECTION (LHR) 5555
bmep = 900 kPa 2000 rpm
MBT Timing LTC Engine
es (%
) 50
Net Indicated
e 6
LTC Engine
Cas
e 7
l Effi
cien
cie 45
Brake
Cas
e
Ther
ma 40
Conventional Engine Net Indicated
35 Brake
32Wall Temperature (K)
400 500 600 700 800 900 30
Oth C ditiOther Conditions
• Other operating conditions exhibit similar improvements
• For different “order” of features – same final result, but incremental gains slightly different
• For reduced heat transfer without higher wall temperatures, even higher gains are possible
33
thermal
d th i t d h i l f i ti i
CONCLUSIONS (1/2)CONCLUSIONS (1/2)
� High CR, high EGR, lean mixtures and other features can combine to yield ~50% net indicated thermal efficiencyefficiency
� Features of most importance: CR, EGR, lean mixtures
� The major reasons for the higher efficiencies include the lower heat transfer, the higher “gamma,” and the high CR
� To maintain load, higher cylinder pressures result
34
and the associated mechanical friction increases
c
CONCLUSIONS (2/2)CONCLUSIONS (2/2)
� The lower exhaust gas energy may cause the application of turbochargers to be problematic
� Low heat rejection (LHR) concepts are more compatible with LTC engines than with conventional enginesengines
� Predicted nitric oxides are “zero” for the LTC modes
� Exergy destruction during ombustion increases � Exergy destruction during combustion increases largely due to the lower temperatures – this is an acceptable trade-off for the higher efficiencies
35
36