optimization of a turbocharger for high egr … more egr is used for nox reduction, turbine spends...
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Optimization of a turbocharger for high EGR applications
H. Sun, D. Hanna, Ford Motor Co. L. Hu, J. Zhang, Ming-Chia Lai, Wayne State Univ.
E. Krivitzky, C. Osborne, ConceptsNREC NETL Project Manager: Ralph Nine
DOE Contract: DE-FC26-07-NT43280
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Emission regulation: Heavy EGR needed for LTC pushes the operation points into less efficient or even surge area
Market competitiveness: Centrifugal compressor needs to have wide range for high horse power and better efficiency at low end for better fuel economy on customer driving cycles
Objectives: 2-3% fuel economy improvement on customer driving cycles and 15-20% extension of turbo operation range
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As more EGR is used for NOx reduction, turbine spends more time in low U/C area. Conventional turbine blade, optimized for low/none EGR applications 10-15 years ago, performs well at high U/C but not at low U/C. Therefore future diesel application requires that turbine should have high efficiency in low U/C areas.
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Turbine Efficiency vs. U/C
0.30.35
0.40.45
0.50.55
0.60.65
0.70.75
0.8
0.000 0.200 0.400 0.600 0.800 1.000
U/C
Turb
ine
Effic
ienc
y (%
)
60% open, high speed 40% open, high speed 40% open, low speed
Small nozzle opening reduces efficiency
Slow turbine speed further reduces efficiency
[ ]285.00 )(12 −−
=TpTC
UCU
π
High exp ratio reduces U/C
Conventional radial flow VGT has low efficiency at small nozzle open positions and low U/C. Heavy EGR, bigger turbo pushes part load turbine operation points into less efficiency areas
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Advanced compressor impeller
Mixed flow turbine
Optimized compressor diffuser and
volute
Advanced casing treatment
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CFD Simulation to optimize casing treatment design
Lean backward
Lean forward No casing treatment
Lean backward w/ wider slot
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0.64
0.66
0.68
0.70
0.72
0.74
0.76
0.78
0.80
0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00Mass flow(normalized)
Eff (t-t)
Adv comp tech
Conventional 2
Conventional 1
Simulation @ 120krpm (with volute)
2.4
2.5
2.6
2.7
2.8
2.9
3.0
3.1
3.2
3.3
3.4
0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00Mass flow(normalized)
Pr (t-t)
Adv comp tech
Conventional 2
Conventional 1
Optimization of casing treatment can extend flow range/surge margin without compromising efficiency
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Transient CFD simulation indicated that mixed flow turbine can effectively utilize exhaust energy, esp. at low U/C area
Turbine efficiencies, radial flow vs. mixed flow under stead state and transient conditions
68%
70%
72%
74%
76%
78%
80%
82%
84%
86%
0.50 0.52 0.54 0.56 0.58 0.60
U/C
Turbine efficiency
Mixed flow steady
Mixed flow pulsating
Radial flow pulsating
Radial turbine steady flow
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Mixed flow turbine has better flow capacity that may help downsizing
Mass flow of mixed flow turbine vs. radial flow turbine
1.34 1.36 1.38 1.4 1.42 1.44 1.46 1.48Pr(T-S)
M_p
aram
(m*s
qrt(T
0)/P
0)
radial turbine pulsatingradial turbine steadyMixed turbine pulsatingMixed turbine steady
4%Radial turbine pulsatingRadial turbine steady
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Major design changes: •Arbitrary surface compressor impeller blades to improve compressor efficiency at light load conditions; optimal casing treatment to improve efficiency at high load •Mixed flow turbine for better performance at high EGR (or low U/C) conditions
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Efficiency Improvement with Advanced Compressor (tested at two suppliers' flow benches )
0.560.580.600.620.640.660.680.700.720.740.760.780.80
0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2Mass Flow (normalized)
Effi
cien
cy (t
-t)
2010MY Prod Advanced Compressor
Advanced compressor with adv. casing treatment demonstrated better efficiency and wider operation range than a 2010MY production compressor that enables BSFC and performance improvement
Efficiency on customer driving cycle will impact FE, emission and transient response
Choke capacity extended 12%
Flow bench test of compressor
Surge margin enhanced
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The advanced turbo demonstrated better FE at light load conditions
The advanced turbo gained more BSFC advantages at lower NOx or higher EGR (thus low U/C) conditions
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Performances at full load conditions were improved as well
The mixed flow turbine gained better efficiency at low EGR or high U/C conditions
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• EGR based NOx control pushes operation points into less efficient area on compressor and turbine maps, which has to be addressed with advanced turbocharger technologies
• Optimal design of compressor impeller, combined with advanced casing treatment improved compressor efficiency over wide operation range
• Mixed flow turbine has demonstrated improved efficiency at low U/C area, which is relevant to high EGR applications and pulsating exhaust environment
• The engine dyno test has demonstrated BSFC improved 3-5% at light load and 3% improvement at full load with wider operation range due to design optimization on compressor impeller, advanced casing treatment and mixed flow turbine
Conclusions