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

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

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.

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

Advanced compressor impeller

Mixed flow turbine

Optimized compressor diffuser and

volute

Advanced casing treatment

CFD Simulation to optimize casing treatment design

Lean backward

Lean forward No casing treatment

Lean backward w/ wider slot

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

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

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

10

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

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

12

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

13

Performances at full load conditions were improved as well

The mixed flow turbine gained better efficiency at low EGR or high U/C conditions

14

• 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