Xin Q. Diesel Engine System Design
Подождите немного. Документ загружается.
952 Diesel engine system design
© Woodhead Publishing Limited, 2011
15.7 Estimate on compressor pressure ratio and peak cylinder
pressure at different EGR rate and power rating.
Heavy-duty diesel engine simulation at 2300 rpm,
A/F ratio = 22, engine compression ratio = 17.5
200 hp
250 hp
300 hp
350 hp
200 hp
250 hp
300 hp
350 hp
15 20 25 30 35 40 45 50 55
EGR rate (%)
15 20 25 30 35 40 45 50 55
EGR rate (%)
Overall compressor pressure ratio
8
7
6
5
4
3
2
1
Peak cylinder pressure (psi, absolute)
5500
5000
4500
4000
3500
3000
2500
2000
1500
1000
220 bar
200 bar
Diesel-Xin-15.indd 952 5/5/11 12:07:07 PM
953Diesel engine system specification and subsystem interaction
© Woodhead Publishing Limited, 2011
15.3.5 Critical mode design – peak torque
The peak torque condition has the maximum mean effective pressure, and
is prone to compressor surge (especially at high altitude) due to the low
engine air ow rate and the relatively high boost pressure. It is also usually
the most difcult mode to drive EGR due to insufcient engine delta P. The
minimum ow restriction of the EGR circuit (with EGR valve fully open,
with or without a check valve) and the minimum required turbine area are
often determined based on the EGR-driving requirement at peak torque,
although the lower speeds at full load also need to be checked to ensure the
minimum turbine area is acceptable. In fact, strictly speaking, the minimum
required turbine area should be determined at the most demanding operating
mode in terms of a combination of the requirements of EGR driving, air–fuel
ratio and engine torque, rather than simply ‘peak torque’. In some vehicle
applications, the peak torque or a medium speed between the peak torque and
rated power may produce the maximum engine outlet coolant temperature.
In that speed–load region, although the coolant heat rejection is lower than
that at the rated power, the coolant ow rate is relatively low so that the
engine coolant temperature may reach the highest value.
15.3.6 Critical mode design – part load and other modes
At part load, it is important to check pumping loss, fuel economy, the EGR
driving capability with the selected turbocharger, and the capability to control
15.8 Engine fundamental trade-offs at a fixed speed and power.
1300 1350 1400 1450 1500 1550 1600 1650 1700
Exhaust manifold gas temperature (°F)
Peak cylinder pressure (psia)
2700
2600
2500
2400
2300
2200
2100
2000
1900
1800
With heat
release rate B
SOC = –6°
SOC = –6°
SOC = 0°
SOC = 0°
Direction of friction reduction or
any other efficiency improvement
Higher
power
SOC advance direction
SOC = –12°
Heat release rate A
Heat release rate B
With heat
release rate A
SOC = –12°
EGR increases
0° 90°
0.02
0.01
0.00
Crank angle
Diesel-Xin-15.indd 953 5/5/11 12:07:07 PM
954 Diesel engine system design
© Woodhead Publishing Limited, 2011
the air or cooling system in order to raise the turbine outlet exhaust temperature
for aftertreatment thermal management such as DPF regeneration.
15.4 Subsystem interaction and optimization
15.4.1 Types of sensitivity analysis
In the sensitivity analysis by parametric sweeping or optimization, there are
generally three types of simulation as follows:
1. Type A: Simulation at fully xed emissions constraints (i.e., NO
x
and
soot) to compare BSFC and hardware cost. The simulation results are
presented in the domain of the characteristic parameter of one subsystem
vs. the characteristic parameter of another subsystem. The values of
factors and responses are presented as contour maps in the domain.
2. Type B: Simulation at partially xed emissions constraints (e.g., xed
NO
x
or soot; or xed EGR rate or air–fuel ratio). The simulation results
are presented in the subsystem parameter domain similar to type A.
3. Type C: Simulation at variable emissions or at variable air–fuel ratio and
EGR rate. The simulated results are presented in the domain of ‘air–fuel
ratio vs. EGR rate’ that represents the capability of the air system.
Types A and B can be used to conveniently study the interaction between the
two subsystems plotted on the two axes of a map to facilitate the selection of
a system design point from the map. Type C is particularly useful when the
emissions recipe or design constraints are uncertain, and the required air or
EGR ows are moving targets. In type A analysis, the emissions constraints
can usually be approximated by one of the following methods: (1) a pair
of xed air–fuel ratio and EGR rate; (2) a pair of xed peak cylinder gas
temperature and air–fuel ratio; (3) a pair of xed peak cylinder gas temperature
and intake manifold oxygen mass fraction; or (4) a pair of xed NO
x
and soot
predicted by emissions models. Figure 15.9 illustrates an analysis process
to analyze subsystem interactions and optimize the system.
Figures 15.10–15.16 present simulation examples of type A analysis with
different subsystems plotted on the horizontal and vertical axes in each gure
to illustrate the subsystem interactions at approximately xed emissions.
These examples are produced by optimization with DoE emulators. The
BSFC of each point in the data domain has been minimized within the
factor range of the DoE subject to the optimization constraints. A hardware
design point (e.g., the white dot on the maps) can be selected based on the
best trade-offs between different subsystems supported by these sensitivity
contours maps.
Figures 15.17 and 15.18 illustrate type B analysis. Figures 15.19–15.21
illustrate type C analysis showing the sensitivity of engine performance to
Diesel-Xin-15.indd 954 5/5/11 12:07:07 PM
955Diesel engine system specification and subsystem interaction
© Woodhead Publishing Limited, 2011
the change in emissions target. A system design point can be selected based
on the best trade-offs between the tentative emissions target and the design
constraints from these analysis maps.
15.4.2 Subsystem interaction and optimization
In engine air system design, there are strong dependencies among the following
four parameters: exhaust restriction, EGR circuit ow restriction, turbine
effective area, and turbocharger efciency. In hardware selection at each
speed and load mode for a pair of target air–fuel ratio and EGR rate, when
the EGR valve is set fully open to minimize the engine delta P, the required
turbine area and turbocharger efciency are unambiguously determined (Table
4.1). But the reality is that the turbocharger efciency cannot reach all the
desirable values computed as such at all speeds and loads. At some modes,
if the actual turbocharger efciency is too low, the air–fuel ratio will become
System engineers receive air system requirements (intake manifold temperature, A/F,
EGR rate, fuel injection timing) from combustion emissions testing at minimum BSFC
System engineers conduct simulation types of A, B and C analyses to define air system
Type A: Study subsystem interaction at fixed NO
x
and soot target, and optimize
hardware requirements at critical speeds/loads. Sequence of selection: cooler
size, EGR circuit flow restriction, exhaust restriction, turbocharger. Determine
baseline values of DoE factors for Type C.
Type B: Simulate subsystem interaction between EGR circuit restriction, turbocharger
and exhaust restriction with fixed EGR rate and moving A/F ratio, or vice versa.
Type C: Simulate system performance and hardware requirements at moving
emissions targets to check sensitivity to A/F ratio and EGR rate changes.
Give the air system definition/requirements to suppliers (turbocharger, aftertreatment,
EGR cooler, EGR valve, charge air cooler) to let suppliers propose subsystem designs
Review suppliers’ proposals and coordinate the conflicts in subsystem requirements
Review revised proposals from suppliers. Check engine performance with real turbo
maps in engine cycle simulation for steady-state modes and transients. If the turbo is
acceptable, finalize all suppliers’ requirements and order hardware. If not, revise it.
15.9 Process of engine system design to optimize subsystem
interaction.
Diesel-Xin-15.indd 955 5/5/11 12:07:07 PM
956 Diesel engine system design
© Woodhead Publishing Limited, 2011
too low. In order to compensate for that, a smaller turbine area must be used
and the EGR valve must be correspondingly partially closed to accommodate
the increased engine delta P. On the other hand, if the actual turbocharger
Corrected turbine flow rate Lump EGR circuit flow coefficient
Overall turbine efficiencyOverall turbine efficiencyOverall turbine efficiency
Overall turbine efficiencyOverall turbine efficiencyOverall turbine efficiency
0.76
0.74
0.72
0.7
0.68
0.66
0.64
0.62
0.6
0.58
0.76
0.74
0.72
0.7
0.68
0.66
0.64
0.62
0.6
0.58
0.76
0.74
0.72
0.7
0.68
0.66
0.64
0.62
0.6
0.58
0.76
0.74
0.72
0.7
0.68
0.66
0.64
0.62
0.6
0.58
0.76
0.74
0.72
0.7
0.68
0.66
0.64
0.62
0.6
0.58
0.76
0.74
0.72
0.7
0.68
0.66
0.64
0.62
0.6
0.58
9800
9600
9400
9200
9000
1200
1000
800
600
400
0.7 0.72 0.74 0.76 0.78 0.8 0.82
Overall compressor efficiency
0.7 0.72 0.74 0.76 0.78 0.8 0.82
Overall compressor efficiency
0.7 0.72 0.74 0.76 0.78 0.8 0.82
Overall compressor efficiency
0.7 0.72 0.74 0.76 0.78 0.8 0.82
Overall compressor efficiency
0.7 0.72 0.74 0.76 0.78 0.8 0.82
Overall compressor efficiency
0.7 0.72 0.74 0.76 0.78 0.8 0.82
Overall compressor efficiency
Compressor outlet temperature (°F)
BSFC (lb/(hp.hr))
Engine coolant heat rejection (including
EGR cooler heat rejection) (Btu/min)
Engine delta P (mbar)
0.025
0.024
0.023
0.022
0.021
0.02
0.019
360
350
340
330
320
310
300
0.415
0.41
0.405
0.4
0.395
0.39
0.385
0.45
0.4
0.35
0.3
0.25
0.2
15.10 HD diesel subsystem interaction at rated power, type A1
analysis with fixed A/F ratio = 22 and EGR rate = 31%.
Diesel-Xin-15.indd 956 5/5/11 12:07:08 PM
957Diesel engine system specification and subsystem interaction
© Woodhead Publishing Limited, 2011
EGR cooler thermal effectivenessEGR cooler thermal effectivenessEGR cooler thermal effectiveness
EGR cooler thermal effectiveness
EGR cooler thermal effectiveness
EGR cooler thermal effectiveness
0.9
0.85
0.8
0.75
0.7
0.65
0.9
0.85
0.8
0.75
0.7
0.65
0.9
0.85
0.8
0.75
0.7
0.65
0.9
0.85
0.8
0.75
0.7
0.65
0.9
0.85
0.8
0.75
0.7
0.65
0.9
0.85
0.8
0.75
0.7
0.65
6
5.9
5.8
5.7
5.6
5.5
220
200
180
160
0.41
0.405
0.4
0.395
33
32.5
32
31.5
31
30.5
30
29.5
9300
9200
9100
9000
8900
950
900
850
800
750
Turbine effective area (cm
2
)
Intake manifold gas temperature
(°F)
Engine coolant heat rejection (including
EGR cooler heat rejection) (Btu/min)
EGR rate (%)
BSFC (lb/(hp.hr)) Engine delta P (mbar)
0.9 0.91 0.92 0.93 0.94
Charge air cooler thermal
effectiveness
0.9 0.91 0.92 0.93 0.94
Charge air cooler thermal
effectiveness
0.9 0.91 0.92 0.93 0.94
Charge air cooler thermal
effectiveness
0.9 0.91 0.92 0.93 0.94
Charge air cooler thermal
effectiveness
0.9 0.91 0.92 0.93 0.94
Charge air cooler thermal
effectiveness
0.9 0.91 0.92 0.93 0.94
Charge air cooler thermal
effectiveness
15.11 HD diesel subsystem interaction at rated power, type A2
analysis with fixed A/F ratio = 22 and peak cylinder temperature =
2429°F.
1 kW = 56.869 Btu/min
Diesel-Xin-15.indd 957 5/5/11 12:07:08 PM
958 Diesel engine system design
© Woodhead Publishing Limited, 2011
EGR cooler thermal effectivenessEGR cooler thermal effectivenessEGR cooler thermal effectiveness
EGR cooler thermal effectivenessEGR cooler thermal effectiveness
EGR cooler thermal effectiveness
0.9
0.85
0.8
0.75
0.7
0.65
0.9
0.85
0.8
0.75
0.7
0.65
0.9
0.85
0.8
0.75
0.7
0.65
0.9
0.85
0.8
0.75
0.7
0.65
0.9
0.85
0.8
0.75
0.7
0.65
0.9
0.85
0.8
0.75
0.7
0.65
6.1
6
5.9
5.8
5.7
5.6
5.5
33
32.5
32
31.5
31
30.5
30
29.5
0.41
0.405
0.4
0.395
9400
9300
9200
9100
9000
8900
8800
1200
1100
1000
900
800
700
0.51
0.5
0.49
0.48
Turbine effective area (cm
2
)
EGR rate (%)
BSFC (lb/(hp.hr)) Engine delta P (mbar)
Overall turbocharger efficiency
Engine coolant heat rejection (including
EGR cooler heat rejection) (Btu/min)
0.18 0.2 0.22 0.24 0.26 0.28
EGR circuit flow restriction coefficient
0.18 0.2 0.22 0.24 0.26 0.28
EGR circuit flow restriction coefficient
0.18 0.2 0.22 0.24 0.26 0.28
EGR circuit flow restriction coefficient
0.18 0.2 0.22 0.24 0.26 0.28
EGR circuit flow restriction coefficient
0.18 0.2 0.22 0.24 0.26 0.28
EGR circuit flow restriction coefficient
0.18 0.2 0.22 0.24 0.26 0.28
EGR circuit flow restriction coefficient
15.12 HD diesel subsystem interaction at rated power, type A3
analysis with fixed A/F ratio = 22 and peak cylinder temperature =
2429°F.
System
design point
Diesel-Xin-15.indd 958 5/5/11 12:07:09 PM
959Diesel engine system specification and subsystem interaction
© Woodhead Publishing Limited, 2011
Turbine effective area (cm
2
)
Peak cylinder pressure
(psi, absolute)
BSFC (lb/(hp.hr))
Engine coolant heat rejection (including
EGR cooler heat rejection) (Btu/min)
Engine delta P(mbar)
Lumped EGR circuit flow coefficient
Overall turbocharger efficiencyOverall turbocharger efficiencyOverall turbocharger efficiency
Overall turbocharger efficiencyOverall turbocharger efficiencyOverall turbocharger efficiency
0.56
0.54
0.52
0.5
0.48
0.46
0.44
0.56
0.54
0.52
0.5
0.48
0.46
0.44
0.56
0.54
0.52
0.5
0.48
0.46
0.44
0.56
0.54
0.52
0.5
0.48
0.46
0.44
0.56
0.54
0.52
0.5
0.48
0.46
0.44
0.56
0.54
0.52
0.5
0.48
0.46
0.44
4 6 8 10 12 14
Total exhaust restriction (inch Hg)
4 6 8 10 12 14
Total exhaust restriction (inch Hg)
4 6 8 10 12 14
Total exhaust restriction (inch Hg)
4 6 8 10 12 14
Total exhaust restriction (inch Hg)
4 6 8 10 12 14
Total exhaust restriction (inch Hg)
4 6 8 10 12 14
Total exhaust restriction (inch Hg)
6.5
6
5.5
2050
2000
1950
1900
0.415
0.41
0.405
0.4
0.395
0.39
0.385
0.7
0.6
0.5
0.4
0.3
0.2
10000
9800
9600
9400
9200
9000
1200
1000
800
600
400
200
EGR valve
closes
1 kW = 56.869 Btu/min
System
design point
15.13 HD diesel subsystem interaction at rated power, type A4
analysis with fixed A/F ratio = 22 and peak cylinder temperature =
2439°F.
efciency is too high, the air–fuel ratio will become too high. In order to
reduce the air–fuel ratio to prevent over-boosting, a larger turbine area or
wastegating must be used to slow down the compressor, and the engine delta
Diesel-Xin-15.indd 959 5/5/11 12:07:09 PM
960 Diesel engine system design
© Woodhead Publishing Limited, 2011
15.14 HD diesel subsystem interaction at rated power, type A5
analysis with fixed A/F ratio = 22 and peak cylinder temperature =
2439°F (exhaust restriction = 9.7 inch Hg, IMT = 150°F).
P may become insufcient to drive enough EGR even if the EGR valve is
set fully open. These effects are shown in Figs 15.19–15.21.
As for the interaction with aftertreatment, the exhaust restriction ow
Turbine effective area (cm
2
)
BSFC (lb/(hp.hr))
Engine delta P (mbar)
Turbine wastegate opening (mm)
Overall turbocharger efficiency
Overall turbocharger efficiency
Overall turbocharger efficiency
Overall turbocharger efficiencyOverall turbocharger efficiencyOverall turbocharger efficiency
0.56
0.54
0.52
0.5
0.48
0.46
0.56
0.54
0.52
0.5
0.48
0.46
0.56
0.54
0.52
0.5
0.48
0.46
0.56
0.54
0.52
0.5
0.48
0.46
0.56
0.54
0.52
0.5
0.48
0.46
0.56
0.54
0.52
0.5
0.48
0.46
0.415
0.41
0.405
0.4
0.395
0.39
10
8
6
4
2
0
6
5.5
5
4.5
1400
1200
1000
800
600
0.16 0.18 0.2 0.22 0.24 0.26 0.28
Lumped EGR circuit flow coefficient
0.16 0.18 0.2 0.22 0.24 0.26 0.28
Lumped EGR circuit flow coefficient
0.16 0.18 0.2 0.22 0.24 0.26 0.28
Lumped EGR circuit flow coefficient
0.16 0.18 0.2 0.22 0.24 0.26 0.28
Lumped EGR circuit flow coefficient
0.16 0.18 0.2 0.22 0.24 0.26 0.28
Lumped EGR circuit flow coefficient
0.16 0.18 0.2 0.22 0.24 0.26 0.28
Lumped EGR circuit flow coefficient
Overall turbine pressure ratio (total-to-static) Turbine power (kW)
40
39
38
37
36
35
3.1
3
2.9
2.8
2.7
2.6
2.5
2.4
Diesel-Xin-15.indd 960 5/5/11 12:07:09 PM
961Diesel engine system specification and subsystem interaction
© Woodhead Publishing Limited, 2011
coefcient for given aftertreatment hardware changes only when the DPF
soot load changes. When the exhaust restriction or the turbine outlet pressure
increases, the turbine pressure ratio and the air–fuel ratio decrease. To
15.15 HD diesel subsystem interaction at rated power, type A6
analysis with fixed A/F ratio = 22 and peak cylinder temperature
= 2439°F (EGR valve fully open).
Turbine wastegate opening (mm)
BSFC (lb/(hp.hr))
Engine delta P (mbar)
Exhaust restriction flow coefficient
Overall turbocharger efficiencyOverall turbocharger efficiencyOverall turbocharger efficiency
Overall turbocharger efficiencyOverall turbocharger efficiency
Overall turbocharger efficiency
0.56
0.55
0.54
0.53
0.52
0.51
0.5
0.49
0.48
0.47
0.56
0.55
0.54
0.53
0.52
0.51
0.5
0.49
0.48
0.47
0.56
0.55
0.54
0.53
0.52
0.51
0.5
0.49
0.48
0.47
0.56
0.55
0.54
0.53
0.52
0.51
0.5
0.49
0.48
0.47
0.56
0.55
0.54
0.53
0.52
0.51
0.5
0.49
0.48
0.47
0.56
0.55
0.54
0.53
0.52
0.51
0.5
0.49
0.48
0.47
0.396
0.3955
0.395
0.3945
0.394
0.3935
0.393
0.3925
0.24
0.23
0.22
0.21
0.20
0.19
0.18
0.17
10
8
6
4
2
0
690
680
670
660
650
640
5.2 5.4 5.6 5.8 6
Turbine effective area (cm
2
)
5.2 5.4 5.6 5.8 6
Turbine effective area (cm
2
)
5.2 5.4 5.6 5.8 6
Turbine effective area (cm
2
)
5.2 5.4 5.6 5.8 6
Turbine effective area (cm
2
)
5.2 5.4 5.6 5.8 6
Turbine effective area (cm
2
)
5.2 5.4 5.6 5.8 6
Turbine effective area (cm
2
)
Overall turbine pressure ratio (total-to-static) Turbine power (kW)
35.5
35
34.5
2.8
2.7
2.6
2.5
2.4
Diesel-Xin-15.indd 961 5/5/11 12:07:10 PM