Recuperated Brayton Cycle Engine Using a

Screw Compressor and ExpanderPI: Jim Kesseli, Tech Lead:Chad Everbeck, Tom Wolf

• 40% LHV to electric

conversion efficiency

• 80% overall cogeneration

efficiency

• 80,000 hour product life.

• CARB-compliancy

Project Goal

Fed. funding: $2.4M

Length 36 mo.

• Current component test support electric conversion efficiency 37% LHV

• Met CARB emissions

• Working toward full bread-board test this summer

Current Technical Status

A miniature Brayton Cycle ‘Gas Turbine’

‣ Traditional radial and axial

turbomachinery suffers

significant efficiency limitations.

‣ Screws dominate the air moving

industry in flow class appropriate

for <10 kWe Brayton cycle

engine.

‣ Both are ‘rotary’ engines with

non-contacting rotary machinery,

demonstrating exceptional

longevity and maturity.

1

Turbomachinery for 1 kWe gas turbine ?

1 kWe: Screw compressor (34mm)

& expander diameter (52mm)

Brayton has designed 1 and 2 kWe power

modules – building 2 kWe for early trials

2

- Non-contacting dry screw

compressor & expander

- Custom-conventional

compressor

- Ceramic expander

- Large recuperator

- Brayton proprietary

- In-house pilot

manufacturing

- Combustor – low risk scale of

CARB-compliant design

General Product Characteristics

Validating and qualifying the principal components

through rigorous performance and life testing

3

- Compressor efficiency testing

- Isolated three mechanical loss

mechanisms in both

compressor and expander:

1. Bearing test rig

2. Windage; measured

3. Gear mesh; measured

- In previous quarters:

- Tested ceramic expander –

proved thermal shock

tolerance at 1110℃.

- Met combustor emission

standards.

Compressor

and

mechanical

loss test rigs

Compressor Test & Model Validation: 2 kWe Rotary Screw Brayton

4

65

67

69

71

73

75

77

79

81

83

85

87

30 40 50 60 70 80 90 100

Isen

trop

ic E

ffic

ienc

y (%

)

Rotor Clearance (um)

Analysis modelTest data, run 1Test data, run 2Test data, run 3

Near-term GENSET goal

Target efficiencyηengine = 40%

Manufacturing limit = Machining tolerances

Rotordynamic deflections Shaft bending Thermal growth Σ

Analytical modelDATA

Recuperator Performance

‣ Recuperator production, performance test and life test.

– Built full scale 2 kWe recuperator

– Achieved 96.4% effectiveness at design conditions.

• Derived and managed external heat losses.

– Subjected heat exchanger cells to accelerated life testing: creep and fatigue

– Conducted in-house manufacturing process trials to refine production plan.

5

In-house Development of Proprietary Near-

zero CTE Ceramic for Expander

Key Technology/IP

Details on Envisioned Product Offering

Metric Program Target Current Status Envisioned Product

offering

Device Application Residential CHP Residential CHP Residential CHP

w/ black-start & off-

grid operation

Power (kWe) 1 1.9 (design target) 2

Fuel-to elec. eff. (%) 40 34% ±3 pct 38%

System cost* ($) 2,500 2,900 2,900

O&M cost ($/kWh) ≤0.005 NA 0.005 to 0.01

Capacity factor (%) 99.9 NA 99.9

System Life (years) ≥10 NA >10

System Noise (dB(A)

at 3 feet away)

≤55 <55

System Mass (kg) ≤150 120 +/-20 100 +/- 10

* excluding 30% mark-up for commercial price

Current Challenges

Programmatic Challenges

• Specialized ceramic production costs and schedule

• Breadboard engine test schedule

Technical Challenges

• Component heat losses

• Bearing losses

Business Challenges

• CHP heat capture and economics

• Simple payback > 3 years for most US regions

• Finding next stage investor

Tech-to-Market Strategy

• Approach to market

• Brayton GENSETS shows potential in all key categories to succeed in µ-CHP +

• Roughly twice the efficiency of best available technology (>35% LHV)

• CARB emissions

• Near zero maintenance for 10 years continuous duty

• Factory cost < $1500/kWe

• Alternative Markets: µ-CHP + back-up power, remote power in developing countries

• Where do you fit in the supply chain?

• Component manufacturer?

• Engine / generator manufacturer?

• System manufacturer?

• Pathway to success: partnerships, capital requirements over 4 year commercialization

venture.

• Approach to manufacture• Capital equipment plan: <$5M to achieve cost targets

• Demand-flow manufacturing meshes well with other OEM lines

Desirable Partnerships

Desirable partnerships (one or more of the

following profiles could be leveraged to advance

our product)

• Appliance manufacturer; for refined production

experience and channel to residential market

• Screw compressor manufacturer: Leverage capital

equipment

• Heat exchanger manufacturer; Leverage capital

equipment

• Emergency generator installer; for channel to market and

experience with utility interface permitting