The Naval Nuclear Laboratory is operated for the U.S. Department of Energy by Bechtel Marine Propulsion Corporation,

a wholly owned subsidiary of Bechtel National, Inc.

Effect of Compressor Inlet Temperature

on Cycle Performance for a

Supercritical Carbon Dioxide Brayton Cycle

Jacqueline Lewis, Eric Clementoni, Tim Cox

Presentation Summary

• sCO2 Integrated System Test (IST) Overview

• IST System Control

• Test Configuration

• Compressor Inlet Pressure and Density Sensitivities

• Cycle Performance Sensitivities

• Compressor Performance

• Conclusions

2

IST Overview

• Simple recuperated Brayton cycle

• One variable speed turbine-compressor

• One constant speed turbine-generator

• Single recuperator

• Designed for 100 kWe at 570°F (299°C) and 75,000 rpm

• Intended to demonstrate operational control and performance characteristics during rapid transients between steady-state power levels

3

IST Physical Layout

4

IST Physical Layout

5

Normal System Control Overview

6

IHX

GenMot/

Gen

Pre

coo

ler

Recuperator

Load regulated to

maintain 60,000 rpm

shaft speed

No load

PI control

regulates

TC shaft

speed

TC speed

setpoint

function of

TG load

setpoint

T T C

Heater power controlled to maintain IHX outlet temperature setpoint

Precooler water flow controlled to maintain/adjust compressor

inlet temperature setpoint

Pressure not directly controlled but compressor inlet pressure is relatively

constant with fixed mass system

TC speed setpoint

via lookup table

Test Configurations

• Three test configurations

• Constant compressor speed (constant mass)

• Compressor recirculation valve maintains compressor speed

• Constant compressor recirculation valve position (constant mass)

• Compressor speed allowed to change with fixed system resistance

• Constant compressor inlet pressure

• Same as first test with mass adjustments to maintain pressure

• Evaluate performance over widest range of compressor inlet temperatures possible

• Limited by min/max power, compressor recirculation valve position, maintaining margin to critical point

7

Compressor Inlet Pressure Sensitivity

8

1150

1200

1250

1300

1350

1400

1450

86 88 90 92 94 96 98 100 102 104

Co

mp

ress

or

Inle

t P

ress

ure

(p

sia

)

Compressor Inlet Temperature (ᵒF)

Constant Compressor Speed

Constant Recirc Valve Position

Constant Compressor Inlet Pressure

Compressor Inlet Density Sensitivity

9

32

34

36

38

40

42

44

46

48

86 88 90 92 94 96 98 100 102 104

Co

mp

ress

or

Inle

t D

en

sity

(lb

m/f

t3)

Compressor Inlet Temperature (ᵒF)

Constant Compressor Speed

Constant Recirc Valve Position

Constant Compressor Inlet Pressure

System Power Output Sensitivity

10

0

5

10

15

20

25

30

35

40

45

86 88 90 92 94 96 98 100 102 104

Syst

em

Po

we

r O

utp

ut

(kW

)

Compressor Inlet Temperature (ᵒF)

Constant Compressor Speed

Constant Recirc Valve Position

Constant Compressor Inlet Pressure

Cycle Efficiency Sensitivity

11

0%

1%

2%

3%

4%

5%

6%

7%

8%

9%

86 88 90 92 94 96 98 100 102 104

Cyc

le E

ffic

ien

cy

Compressor Inlet Temperature (ᵒF)

Constant Compressor Speed

Constant Recirc Valve Position

Constant Compressor Inlet Pressure

Compressor Speed Sensitivity

12

40000

42000

44000

46000

48000

50000

52000

54000

56000

86 88 90 92 94 96 98 100 102 104

Co

mp

ress

or

Sp

ee

d (

rpm

)

Compressor Inlet Temperature (ᵒF)

Constant Compressor Speed

Constant Recirc Valve Position

Constant Compressor Inlet Pressure

Compressor Pressure Ratio Sensitivity

13

1.25

1.30

1.35

1.40

1.45

1.50

1.55

86 88 90 92 94 96 98 100 102 104

Co

mp

ress

or

Pre

ssu

re R

ati

o

Compressor Inlet Temperature (ᵒF)

Constant Compressor Speed

Constant Recirc Valve Position

Constant Compressor Inlet Pressure

Comparison of Compressor

Performance to Map Predictions

14

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

5

5.5

3 4 5 6 7 8 9 10 11 12 13 14 15

Co

rre

cte

d E

nth

alp

y R

ise

(B

tu/l

bm

)

Corrected Mass Flow (lbm/s)

Test Data - Constant Speed

Map Predictions - Constant Speed

Test Data - Constant Recirc Valve

Map Predictions - Constant Recirc Valve75,000 rpm

40,000 rpm

Design

Point

Conclusions

• IST has demonstrated stable performance over a range

of compressor inlet temperatures

• Widest range in temperatures for fixed compressor speed tests � as low as 88°F

• Widest range of power levels for fixed compressor recirculation valve position test

• Compressor performance continues to exceed map

predictions

• Consistent offset independent of compressor inlet temperature

• Sensitivities may be dependent upon scale of system

and specific components used

15