Introductory presentation of new optimized Stirling engine topology dubbed a delta Stirling configuration. It is described as a lunar reactor power conversion system but can also be used for terrestrial concentrating solar power generation.

1. Delta Stirling Engine for Space
and Terrestrial Power Needs
Introducing a New Free-Piston Stirling (FPS) Concept
Expected to Create a Paradigm Shift in Stirling
Machine Applications
Advanced Power Systems for Deep Space Exploration
Maury White
August 30, 2022

2. Presentation Overview
• Categories of Stirling Engines
• Introducing the Delta Stirling Engine
• Conceptual Design of 1-MW Modular Central Receiver for Utility or Lunar Solar Power with
Phase-Change Salt Thermal Energy Storage (TES)
• Delta Engine Projected Performance
• Potential 24-kW Delta Engine Prototype Demonstration
• Hardware Successes that Validate Delta Concept
• FPS Timeline that led to Delta Stirling Concept
8/4/22 Stirling Innovations LLC 2

3. Two Basic Types of Stirling Engines
• Kinematic engines, with piston and displacer motions, and phase angles, dictated by mechanical
linkages have existed since the first patent in 1816
• Kinematic engines have inherent life and reliability limitations as a result of crankcase oil vapors
leaking past piston and/or rod seals that make them unsuitable for space power
• Free-piston Stirling (FPS) engines were first conceived in the 1960s and have received far fewer
development resources than kinematic engines
• FPS engines have demonstrated very long maintenance-free operation: three Infinia engines at NASA
GRC continue with >15-year world records for dynamic machines
• FPS engines are mechanically simple with a low parts count but resonant disparities between piston
and displacer require intense design and analysis sophistication
8/4/22 Stirling Innovations LLC 3

4. Stirling Engine Classifications
• Stirling engines are classified as alpha, beta, or gamma depending on piston and displacer
configurations
• Kinematic engines are built in all configurations with single-acting or double-acting alpha options –
kinematic linkages impose stable stroke and phase angle by brute force
• Traditional FPS engines are limited to beta and gamma configurations: they use one or two heavily
damped power piston(s) and a very lightly damped displacer, all of which operate as resonant
spring/mass/damper modules
• FPS engines are controlled by limiting voltage at the alternator terminals to reduce longer naturally
resonant stroke
• The challenge is to have both the displacer and power piston, which are only coupled by a pressure
wave, operate at full stroke and with the proper phase angle and reasonable stability
8/4/22 Stirling Innovations LLC 4

5. Introducing the Delta Stirling Engine
• The delta Stirling engine is a unique 3-cylinder FPS topology in a double acting alpha (DAA)
configuration
• Innovative DAA FPS functionality has been demonstrated with parallel piston axes using convoluted
heat exchangers that limited performance
• The delta configuration places the piston axes in a plane on the sides of an equilateral triangle which
enables optimal heat exchanger topology
• Combines FPS life and reliability with near-kinematic operational stability
• Three identical resonant pistons; no displacer complexity or stability issues
• Stirling cycle efficiency is increased
• No typical vibration or oscillation; circular motion of system is canceled by coupling two engines
• Cost is reduced by at least a factor of two relative to other FPS or kinematic Stirling machines
• Eliminates at least two closed-end pressure vessels
• Eliminates displacers and other costly components
• Cylindrical inline heat exchangers eliminate precision concentric annuli and complex manifolding
8/4/22 Stirling Innovations LLC 5

6. Delta Stirling Engine Concept Design
• The delta engine layout shown uses a 4-kW
Qnergy alternator/piston assembly modified to
add a second piston
• The cooler/regenerator HX couples directly
with the compression piston
• The hot cap on the expansion piston is used
on all alpha engines
• The heater HX is designed to accommodate
thermal expansion
• One issue for a prototype is to resolve
potential piston leakage biasing
8/4/22 Stirling Innovations LLC 6
Delta Stirling Engine Conceptual Design

7. Delta Stirling Generator Concept
• Side elevation of two coupled and fully
balanced delta engines is shown with NaK pool
boiler for lab simulation of fission heat
• Upper and lower heater heads are aligned to
receive Na vapor from a single duct
• Output is easily varied with high efficiency
down to below 25% of full power
• Delta configuration is virtually identical for
space and terrestrial applications
• Direct burner is also terrestrial option
8/4/22 Stirling Innovations LLC 7
Balanced Delta Stirling Overall View

8. 1-MW Solar TES Delta Stirling Concept
• Top view of conceptual design for 1-MW mini-central
receiver solar power/TES tank
• Uses hermetically sealed tank with NaF/NaCl phase-
change salt thermal energy storage (TES)
• 15 hours of TES enables 1-MW output 24/7 all year at
most latitudes in 22’ diameter by 18’ high tank
• Straightforward hybrid heating during extended cloudy
conditions
• Totally passive except for EM pump to return liquid Na or
other heat transfer fluid to tower receiver
• 22 balanced 48-kW delta engines on top of tank are
heated by Na vapor ducts that interface with the internal
Na vapor near the top of the tank
• Similar approach could cover 2-week night on the Moon
8/4/22 Stirling Innovations LLC 8
1-MW Delta Stirling/TES System

9. Projected Delta Engine Performance
• Sage is the gold standard of Stirling
thermodynamic design and analysis
• Sage and Stirling expert Barry Penswick analyzed
delta engines using Qnergy 4-kW and 8-kW 60 Hz
alternator specifications
• Case 2A: Optimized piston and regenerator
diameters varied widely
• Case 2S1: Constrained piston and regenerator
diameters to be equal
• Case 2S1 is preferred for production simplicity
and lower risk despite lower efficiency
• Part load efficiency is outstanding
• Efficiency improves at lower frequencies
• >40% efficiency possible if needed
8/4/22 Stirling Innovations LLC 9
0.280
0.300
0.320
0.340
0.360
0.380
0.400
100
105
110
115
120
125
130
50 55 60 65 70
Eff
and
Pm/100
(bar)
Component
Common
Diameter
(mm) Operating Frequency (Hz)
Dr
Eff
Pm/100
0.000
0.050
0.100
0.150
0.200
0.250
0.300
0.350
0.400
3 4 5 6 7 8 9 10 11 12 13 14
Engine
Efficiency
Piston Amplitude (mm)
2A Eff
2S1 Eff

10. Potential Delta Stirling Engine Demo
• The delta Stirling engine is practical from tens of watts to >100 kW
• Leveraging Qnergy production capability for 24-kW prototype is the preferred approach
• Qnergy has commercial 4-kW and 8-kW linear alternators available that produce 12-kW or 24-kW
delta engines at 60 Hz (10-kW or 20-kW at 50 Hz)
• Fully balanced 24-kW or 48-kW (20-kW or 40-kW at 50 Hz) configurations have many advantages
• This robust capacity can be demonstrated for a cost comparable to a much smaller engine with a
costly new linear alternator/piston development
• Prototype delta engine operation will establish performance envelope and resolve potential issues such
as piston biasing mitigation
• Preferred laboratory prototype heat source is electric immersion heaters in pool boiler to enable precise
heat input measurements
8/4/22 Stirling Innovations LLC 10

11. Infinia Engine Example
• Radioisotope Stirling Generator (RSG) Engines
• About 25 FPS TDC engines were built for NASA-GRC/DOE
program
• Four engines were designated for endurance testing
• All have operated at GRC since about 2007 with no maintenance
or performance degradation
• One endurance test engine was destructively evaluated at
105,616 hours (12 years)
• Some internal oxidation from early operation when
atmospheric oxygen permeated o-rings before recognition of
need for inert cover gas around o-rings but no failure mode
identified
• Three continue on test with more than 15 years of operation
• Photo shows single TDC on endurance test after
companion of balanced pair shut down for evaluation
8/4/22 Stirling Innovations LLC 11
TDC Engine at NASA-GRC

12. Infinia Engine Example
• Solar Dish Stirling Systems
• More than 100 early 3.5-kW FPS dish engines
were installed in various venues
• 429 Fourth generation dish engines (1.5-MW) were
installed at the Tooele Army Depot in 2013
• Installation was a technical success but cost
overruns led to Chapter 11 bankruptcy
• Qnergy acquired Infinia assets including Ogden
production facility from bankruptcy
8/4/22 Stirling Innovations LLC 12
About one-third of the 1.5-MW solar
dish engine installation at the Tooele
Army Depot near Salt Lake City

13. Qnergy Engine Examples
• Hundreds of Qnergy FPS Generators have accrued
millions of trouble-free hours in often harsh field
conditions
• PowerGen© FPS generators from 600W to 5650W
serve a wide range of remote power needs
• Compressed Air Pneumatic systems dramatically
reduce methane emissions on gas pipelines while
providing electric power and dry instrument air
• Qnergy engineering and production facilities stand
ready to support delta Stirling engine prototype
development
8/4/22 Stirling Innovations LLC 13
Qnergy PowerGen and CAP Units

14. AMSC Cryocooler Example
• AMSC-West in Richland, Washington
developed and manufactures the best
performing cryocoolers available to support
AMSC Navy ship HTS degaussing systems
• Lifts 300-W at 50K with world-class efficiency
• Installation of first AMSC HTS degaussing
system is underway on LPD 28, the USS
Fort Lauderdale, using 23 cryocoolers
• AMSC will support delta cryocooler
development projects
8/4/22 Stirling Innovations LLC 14
LPD 28 Under Construction in Dry Dock

15. Legacy FPS Timeline for Delta Stirling
• Stirling Innovations LLC founder Maury White and the delta Stirling machine concept
have a direct FPS continuity from 1962 to the present
• 1962-1964 Was protégé of Ted Finkelstein who originally conceived FPS concept at AI
• 1966-1978 Worked with Bill Martini on FPS engines at DWDL
• 1978-1985 Managed FPS group at UW
• 1985-2013 Principal founder of STC/Infinia and served as President and CTO
• 2013-2017 Worked at Qnergy in remote R&D group
• 2017-2021 Worked at AMSC in cryocooler R&D group
• 2021-Present Founder and President of Stirling Innovations LLC
8/4/22 Stirling Innovations LLC 15
Stirling
Innovations
Atomics
International
McDonnell
Douglas
University of
Washington STC/Infinia Qnergy
AMSC
1962-64 1966-78 1978-85 1985-2013 2013-17
2017-21
2021-
Present

16. Thank you for your attention
Maury White
President and CTO
Stirling Innovations LLC
8509 Clara
Pasco WA 99301
509-531-5900
maury.white@stirlinginnovations.com