The Status of  Double Acting Swash Plate Drive Stirling Engines (DA/SH)

(revised draft -- feedback appreciated, send to authors)


In this time of concern over the future availability and cost of power, the impact of global climate change and problems with noxious emissions it is important to that we explore all promising opportunities to reduce the US dependence on energy imports, and at the same time reduce emissions and costs.    A question then is - Why hasn’t serious consideration been give to the Double Acting Swash Plate Drive Stirling (da/sh) engine.  It can reduce fossil fuel use and emissions at a cost competitive or lower than other future power systems?   The da/sh engine can:


·        Produce electrical power at a cost competitive with utility power plants.


·        Double the miles per gallon of fuel over recent gasoline and diesel cars and trucks.


·        Reduce energy vulnerability by making it possible to use essentially any fuel or heat source.          


·        Reduce consumption of fossil fuel beyond that of first generation fuel cells.


·        Avoid the need to create new fuel delivery infrastructures.


·        Achieve environmental standards that are difficult for other thermal power systems.


·        Cost less to build and operate than other power systems.


·        Be available in volume before other advanced power initiatives.


The background these assertions is summarized in the attached papers:


1        Introduction to the Double Acting Swash Plate Drive Stirling Engines

2        Development of Double Acting Swash Plate Drive Stirling Engines

3        Applications for Double Acting Swash Plate Drive Stirling Engines

4        Operation of Double Acting Swash Plate Stirling Engines

While the information is presented from a U.S viewpoint, the benefits apply at least as well to other nations. The economic and technical feasibility of the da/sh engine has been established.  Its commercialization only requires effective, adequately funded engineering and development.

         Attached is also the resume of the author, Albert J. Sobey.


For further Information contact

Lennart Johansson at

Al Sobey at                  


                                                                              Additional information on which these papers are based can be made available on inquiry.

                                                                              Imperfections in formatting in this html version are the fault of Paul Werbos, not of the author(s).       



Introduction to the

Double Acting Swash Plate Drive Stirling Engines

March 2006


In this time of concern over the future availability and cost of power, global climate change and noxious emissions it is important that we seriously explore all promising opportunities to make effective use of US energy resources and reduce energy imports.    


There has been remarkable success in reducing the fuel use (and emissions) of internal combustion engines (spark and compression ignition) by improvements in controls and use of devices such as variable valve timing, superchargers, power on demand and after treatments such as catalytic converters and particulate traps.  Internal combustion piston engines are approaching their practical (and theoretical) limits of efficiency and emissions.   Attempts to extend their usefulness are time consuming and costly – in research and product cost.


Fuel cells (using hydrogen) are still decades away.  While many authorities believe that they will ultimately be technically and economically viable.   There still are serious technical (and cost) problems to resolve.


The Double Acting Swash plate type Stirling external Heat (da/sh) engines can meet many of the energy and environmental objectives, at a cost similar to existing engines while providing similar or superior performance.  The design of da/sh engines avoids many of the problems that have delayed earlier Stirling initiatives.   The da/sh engine can use conventional fuels (gasoline, diesel, methanol, ethanol) as well as other materials (wastes, low btu fuels) that are not now thought to be meaningful energy sources. 


Production da/sh engines can:

·        Produce electrical power systems at a cost competitive with utility power plants.

Total energy effeteness equal or superior to coal plants

Competitive costs at Sizes from 5->1.000 kW

·        Double the miles per gallon of fuel over recent automobiles and trucks.

Equal or superior fuel consumption to hybrids

·        Reduce energy supply vulnerability by using essentially any fuel or heat source.

Gasoline, Diesel, Naphtha, Ethanol,. Methanol, hydrogen, natural gas,

purpose grown and waste biomass as well as solar        

·        Reduce consumption of fossil fuel beyond that of first generation fuel cells   

Minimal energy consumed in fuel processing and distributions

·        Avoid the need to create new fuel delivery infrastructures

Can use or simplify the existing liquid fuel delivery and retail systems.

·        Achieve environmental standards that are difficult for other thermal power     

Meet regulated emissions with little or no after treatment

·        Cost less to build and operate than other power systems           

At comparable production volumes

·        Be available before other advanced power initiates.

Technical and economic feasibility established.

Commercialization only requires good engineering not basic research


The fact that da/sh engines have fewer than half the parts of modern gasoline engines will make it possible to build them at lower cost than comparable internal combustion engines (at similar production volumes).   Most of their components can be produced using the same processes now used in the manufacture of automobile engine components – thus reducing capital investment costs – and saving jobs.



The use of  constant process, ambient pressure, heat input systems makes it possible for da/sh engines to meet environmental standards that internal combustion engines can not meet economically (or at all in the case of noise).   With development da/sh engines may be able to meet 2007 environmental standards with an open tail pipe (no emission after treatments or mufflers)


The efficiency of the first test da/sh engines was in the 30-35% range (Btu in to shaft power out).  The first generation of upgraded JGT da/sh engines will be in the 40-45% range with the target efficiency of 50-55%.  These engines will be more efficient than practical diesel engines and above the target (set by US Dept of energy) for first generation Fuel Cells.   The ability of the da/sh engine to achieve these goals is well established by internal and independent studies (by NASA).


The da/sh engines can be designed for different levels of cost and reliability consistent with the intended application.  Stirling engines for electrical power will be designed for ten to twenty five years useful life with annual maintenance (Stirling engines, built in Sweden, have operated more than 25 years).   High speed da/sh engines can be designed for 200,000 miles life (4 to 6 thousand hours) for use in automobiles and light trucks (target 1,000,000 miles for heavy trucks).  


They can use fuels with a wide range of energy content and do not require control of cetane or octane content or energy content.   The simplification of fuel processing may permit an increase in the yield per barrel of crude oil.  They can use much lower Btu gas and are more tolerant of dirty fuels and air than internal combustion engines.  As more da/sh engines are deployed they will make gradual but significant reductions in fossil energy use, noxious emissions etc. 


da/sh engines can be available sooner than other improved power systems.   Serial production could start in 2 to 4 years for electrical power (after commitment of the needed resources).  Development (and demonstration) of vehicle propulsion engine will take longer.  Serial production could start in 4 to 7 years.  


They can provide significant social benefits.  They can reduce the economic and social costs of serious energy supply interruptions (accidents, vandalism or terrorism) more effectively than other power systems.     They can.  reduce the need for fossil fuels

First   By improving the efficiency of power generation (vehicle propulsion and electrical power generation and distribution). 


Second        By using combustible materials which are not now considered to be significant energy.

resources (agricultural, urban and indusial wastes etc)


The extent of their national energy and environmental benefits can be estimated from the size of the market for engines in the 2 kW to 1000 hp range.  Approximately thirty eight million gasoline and two million diesel engines were produced in the United States during 2005 by about thirty companies (about three times as many are produced overseas  - proportionately more diesel engines).  


The da/sh engines ability to use low grade or innovative energy resources (wastes, solar power, geothermal etc) is complementary with the need to use energy systems that will meet the needs of the growing global economy as economic fossil fuel resources are exhausted


The da/sh engines will have a long term future. .  They will make more efficient use of biomass and similar materials (urban and industrial wastes etc.) than other power plants.  They can produce power more effectively from solar, nuclear or geothermal heat than steam turbines or fuel cells.



The improved economics and performance the da/sh engines can provide have advantages for: 


Owners and Operators of Electrical Systems and Vehicles         

Once their cost and performance advantages are understood they should become the power systems of choice for base load or emergency electrical power systems and for most vehicles (5 kW to >1000 hp).Their ease of operation, performance and economics will be attractive to buyers


Government Energy and Environmental Regulators

          They will be able to meet future energy and environmental standards that will be difficult for internal combustion engines.  Once their low to negligible (nitrous oxide and particulate) emissions are understood their use may be, in effect, be mandated.


Engine and Vehicle Manufacturers

          They will provide competitive advantages in cost, performance and low cost over conventional internal combustion engines.  .  

Development of new engine sizes (5 kW to >500 hp) will take less time and cost less than equivalent internal combustion engines.


Energy Companies and Fuel Suppliers

          They will simplify the fuel slate and potentially increase the yield of useful fuel from a barrel of crude oil and extend the life of the resources.


The total market for da/sh engines may be larger than that of internal combustion engines.  . In 2005 approximately 38 million gasoline and 2 million diesel engines were produced in the US by about 30 manufactures.   In the order of twice that number was produced overseas


There are three primary reasons why the da/sh Stirling engine had not been commercialized.

First   Until recently internal combustion engines could meet energy and environmental standards economically.    The decision makers saw no pressing need for a new kind of engine.  Some engineers probably considered it a threat to their authority and knowledge.


Second        There have been many unsuccessful attempts to develop Stirling engines.  Public and private decision makers knew that the Philips Electronics rhombic drive Stirling engines were heavy, unreliable, and expensive - descriptors that do not apply to da/sh engines. Their slow power response was unacceptable for vehicles (and load following).  GM abandoned the rhombic drive concept in favor of the lower cost Wankel engine in the 1960’s.  Ford encountered similar problems.  In contrast Sweden also rejected the rhombic drive versions and in the process evaluated many innovative Stirling engine concepts.  They produced engines for submarines and for field power.  Other companies have encountered problems in attempting to adapt internal combustion engine technologies.  Stirling engines appear simple but design of effective engines requires understanding of Stirling technology.  Back engineering and cost reductions can  encounter problems from thing that are not obvious.


Third The efforts to develop commercially competitive da/sh engines have not been adequately funded. Initial investors had a limited view of its application and avoided developing the technologies for high risk opportunities.   Lennart Johansson has raised sufficient capital to confirm the engines technical and economic feasibility – but not to commercialize it.     This was accomplished at a fraction of the cost that would be required for a new gasoline or diesel engine.


The commercialization of da/sh engines does not require research breakthroughs – only adequately supported - good engineering and development.


Some of the advantages of the da/sh engine are summarized on the following table


Double Acting Swash plate Stirling Engine (da/sh) Based Power Systems

Advantages over Internal Combustion Power Systems Include:


Low Capital Costs                   

da/sh engine have fewer than half the parts of comparable gasoline or diesel engines.

An independent study found that da/sh engine based propulsion systems should cost less than

equivalent internal combustion systems at volumes over 50,000 per year


Low Operating Costs                        

Can use Low (or negative) cost fuels.  The potential for low maintenance costs has been demonstrated.


Fuel (or heat source) Flexibility          

          The da/sh engines can produce power from any source of heat (<700 to 1000 oC)

          They can use any liquid fuel (naphtha, ethanol, gasoline diesel) interchangeably, or any gaseous fuel (natural gas, hydrogen, 

                   land fill gas) interchangeably, as well as biomass, solar, combustible wastes, waste process heat etc. and solid



High Efficiency              

They will be as efficient as diesel engines - markedly superior at part load. 

The pre production engines are 30-35% efficient.  

The first production engines will be 40-45% efficient.   The target is 50-55% -


High Energy Effectiveness - Resource to Power     

The fuels for da/sh engines do not require control of octane, cetane or foreign material content thus reducing the

 cost of (and energy consumed in) fuel processing and distribution. 

They will provide more kilowatt hours or vehicle miles per unit original energy resource (oil, natural gas, coal, biomass

           etc.)  than other power systems (including first generation fuel cells).


Low Emissions     

The da/sh engine uses a constant process ambient pressure burner (or heat input system).  They can have very low

NOx, no measurable unburned hydrocarbons, CO, or particulates -    without after treatment

da/sh engines can meet some environmental standards (for emissions and noise) with an open tail pipe.


Rapid Response                                

Idle to full throttle 1/3 second using variable swash plate (no emission peak) and will start easily.


High Reliability     

150,00-200,000 miles for cars 1,000,000 + for trucks 25 to 50 years for electrical power, based on  

thousands of hours of operation in Sweden.   All loads (force and thermal) are sinusoidal - no shocks from

intermittent controlled explosions as with internal combustion engines.


Low Noise                               

Comparable to household appliances - Less than 58 db at nine feet.

Can be designed for near zero noise, heat and electronic signatures


Ease of Manufacture                          

The da/sh engine has no intake or exhaust valves, ignition only required for starting etc.

Most of the parts can be produced using similar manufacturing process to those used for automotive piston engines.


Competitive weight and volume                   

Similar volume to equivalent diesel existing engines (less when smaller transmissions are included). 

The existing engines (assuming 6000 rpm for propulsion) weight  2.5 lb/ hp. The target is 1.5 lb/hp



Volume production of da/sh engines only requires good well supported engineering – no research breakthroughs.

They can be available in volume within the time required to develop high efficiency, low emission internal

 combustion engines and much sooner than fuel cells 



Development of

Double Acting Swash Plate Drive Stirling Engines

March 2006


The concept of the Stirling (external heat) engine dates from the early 1800’s but the early “air cycle” engines was not cost or performance competitive with steam engines.   There was little serious interest until the manufacturing technologies improved and hydrogen and helium became available for the working fluid.   Within the last decade the Double Acting Swash plate Drive engine (da/sh) has reached the point where its technical and economic feasibility has been established.  


The availability of da/sh engines for electrical power generation and vehicle propulsion should benefit most companies and users in the power and vehicle communities.  Commercialization will require a much expanded effort – but is not dependent on technical or research “breakthroughs”. Given adequate resources da/sh engines can be available in volume about as soon as the next generation of internal combustion engines and much sooner than fuel cells.


The development of modern Stirling engines started in the 1940’s with the Philips Electronics Rhombic drive engine.  It was efficient and probably had low emissions but was complex, unreliable and had unacceptable (slow) power responsiveness.  General Motors had a license from Philips in the 1950s and 1960’s but was unable to resolve the problems inherent in the rhombic drive engines (later Ford encountered similar problems).  The most serious problem (from a propulsion standpoint) was their slow power transient characteristics (requiring changing the pressure of the working fluid - a slow and energy consuming process).   


The next major effort was that by United Stirling Company (Sweden) starting in the 1960’s. United Stirling obtained a license for the Philips Stirling technology in 1968.  It also found serious problems. Support was provided by FFV (the Swedish Defense Industry) to enable United Stirling to develop its own Stirling technologies.  After a multi year program (in which many technologies were evaluated) two Stirling engines were selected for production (one for submarines and one for field power).  Their experience confirms the Stirling engines potential for long lives and low maintenance costs.  

United Stirling Sweden was a joint venture of FFV and Kockums AB (a shipyard industry).


Some of the family of kinematic Stirling engines that United Stirling designed have been commercialized one (the V-160) by SOLO Kleinmotoren Gmbh a second (the 4-95) by Stirling Energy Systems Inc. as well as by Kockums (the 4-275).  Kockums installed Stirling engines in several submarines of the Royal Swedish Navy during the 1980s and continues its interest in this technology.  These engines are efficient, essentially noiseless and expensive.


Lennart Johansson managed the Unites Stirling Program (200 technical personnel for 20 years)


In 1977 Lennart Johansson was asked to come to the US to form Stirling Power Systems (a joint venture of Kokums and McDonnell Douglas).  When McDonnell Douglas with drew from that field Lennart Johansson created United Stirling/US.  He then merged that with Stirling Thermal Motors (STM). His objective was to develop engines that would be superior in performance and costs of gasoline and diesel engines building on Swedish technology.    (STM Inc. had been attempting to develop Philips engine concepts in the US).

In the process the rights to the 4-95 test engine were acquired by Stirling Energy Systems (SES) from McDonnell Douglas.  SES continues in business.  McDonnell Douglas is now owned by Boeing.

Lennart Johansson acquired the rights to the underlying technologies.


Three sizes of the Double Acting Swash plate drive external Heat (da/sh) engine were designed at STM Power Inc. two under Lennart Johanssons direction (including the 4-70 for hybrid drive, the 4-120 (25-30 kW) designed for use with land fill gas.  He provided the basic design of the 4-260 (55 - 60 kW) before creating


When STM’s Board decided to concentrate on production of da/sh engines for use with landfill gas (in 2003) Lennart Johansson created Johansson Global Technologies (JGT).    His objective was to create and expand the center of technical excellence for Stirling technologies (started when he headed STM).  JGT plans to increase the efficiency, reduce costs and develop heat input systems for a wide range of heat sources (combustible liquids and gases, solid fuels, waste industrial heat, solar power etc.).  Johansson Global Technologies has an agreement with STM to up grade engines it produces STM 4-260 (55kw) (and retain the intellectual rights) and to sell da/sh engine based power systems in Scandinavia.


Lennart Johansson has managed the development of the da/sh engine in the United States to the point where it is ready for commitment to commercialization.  In addition to his experience in engine development he understands how the da/sh (and other Stirling) engines can be improved. Commercialization of da/sh engines does not require basic research.   It does require good, well financed, engineering managed by people with an extensive knowledge of what can and what can not be done with Stirling engines.


We do not have adequate information to provide defense be estimates of how much the deployment of the da/sh engine will reduce energy dependence – with confidence.  It should be a significant improvement – a supplement to any other energy strategies.  Some insight can be gathered from the size of the internal combustion engine market.  In 2005 nearly 40 million internal combustion engines were built by US industry for a wide variety of markets. da/sh engines could replace gasoline and diesel engines in essentially all markets they now dominate as well as induce new markets. 


The next stages in the da/sh engines development will include:

·        Design and demonstration of a family of improvements that will increase the effectiveness of da/sh based power systems


·        Adapt the heat input systems to use non traditional fuels and reduce cost and weight.


·        Adapt the engine design to a range of potential applications - small and large power plants, commercial, personal and recreational vehicles etc.


·        Conduct demonstrations to confirm the performance and reliability of the new generation of da/sh engines for a range of competitive applications.


·        Initiate sales to the markets for producing power from traditional and non traditional fuels.


Assuming adequate resources the first generation of da/sh engines for distributed power should be available in two to three years.   It will take 4 to 6 years to complete development for propulsion and release them for use in vehicles.   Operational demonstration of the first generation of da/sh engines (coupled with reliability and performance experience in electrical power) are expected to be required to obtain the support of the automotive community


The relationships between the principal Stirling engines development organizations that lead to the design and development of the da/sh engine is shown on the following figure.


da/sh Stirling Family Tree


Not shown are the license Philips granted GM and Ford.  Both attempted to develop vehicle propulsion versions of the rhombic drive engines.

 There are two versions of the da/sh engine one with a fixed swash plate and one with a variable swash plate.  Only the variable swash plate version has the power response characteristics required for vehicle propulsion (or electrical load following). 

Other companies have worked on Stirling engine variations.  MTI designed and tested a free piston version under contract to the US Dept of Energy.  Approximately ten other companies have developed smaller engines for specialized applications.   If they become customers for JGT’s technical expertise it would accelerated the commercialization of this technology.

Applications for

Double Acting Swash Plate Drive Stirling Engines

October 2005


In theory da/sh engine could replace internal combustion engines in nearly every market they now dominate.   This could provide benefits for all sectors of the electrical and automotive communities.

Their use will reduce cost of ownership (purchase, operating, maintenance)

Manufacturers can use, or adapt, the same processes used to produce internal combustion engines.

They will reduce the costs of fuel producers and avoid major expenditures for new infrastructures.

They will make it easier to meet energy and environmental regulations

They can be adapted to a large number of applications 

They are easy to operate


da/sh engines can use essentially any source of heat provide (combustion of liquid, solid or gaseous fuel, waste process heat, solar energy).   Their total costs (purchase, fuel and maintenance) will be similar to or lower than competitive systems.  Their high efficiency, low emissions make it possible for da/sh engines to meet energy and environmental standards that other power systems find difficult.  Their low noise and vibration levels make it possible for to install da/sh engines in places where internal combustion engines are not acceptable


Public and Private decision makers need to know how competitive power systems compare in basic terms: (use of existing fuel resources, emissions, life, cost and performance)   The relative order of superiority provides more insight into their potential level of use than projecting if and how much candidate power systems will change the performance an existing product (i.e. a Chevrolet Impala or Lexus) 


The da/sh engine is divided into three sections which can be used in various combinations.  The heat input System, the power systems and the power output systems.  The same basic power section can be adapted for the two primary markets by changing the heat input systems, operating speeds, power output (generators or transmissions).   The differences will be driven by fuel arability, product performance requirements and trade offs between cost and design life. 

A third market - generating cryogenic temperatures and space cooling is not addressed in this paper.

Its advantages include higher efficiency, ease of control as well as elimination of the need for freon type working fluids.  Over 5,000 cryogenic systems developed by Philips are in use by air forces and hospitals to produce liquid oxygen and nitrogen.



The peak efficiency of existing da/sh engines is 30 to 35% (Btu in to shaft power out).  JGT plans to increase the efficiency to 40 to 45% in its first production engines (A NACA study confirmed that 50 to 55% is feasible).  This will require increasing cycle temperatures to approximately 1000 oC.  The high efficiency engines will use low cost high temperature materials and manufacturing technologies developed in cooperation with Oak Ridge National Laboratories and suppliers.


Future da/sh engines (55% efficiency) will be more efficient than practical internal combustion engines.   Da/sh engines only need a source of adequate heat (700 to 1000 oC).  Their fuel (or heat source) tolerance will simplify the process of producing and distributing liquid (and gaseous) fuels thus reducing the quantity of energy resources (natural gas, coal, petroleum etc.) required per unit power below that of internal combustion engines.


Extensive use of fuel cells that require 99.99+% pure hydrogen would substantially increase the consumption of natural gas (from which the hydrogen could be made) or require construction of additional electrical power plants (to produce hydrogen by electrolysis).



The capital and operating costs of the da/sh engine will be significantly lower than that of competitive internal combustion engines or fuel cells.   The first (low production) da/sh engines have a total cost advantage (acquisition and operating) over modified (spark equipped) diesel engines operating on dirty (landfill etc.) gases for stationary or distributed power applications.   They can use much lower btu gas and can tolerate variations in heat content and dirty atmospheres.


da/sh based distributed electrical power systems will operate for more than ten years between major overhauls and 8,000 hr. between routine maintenance.   The heat input systems can be designed to use any liquid fuel (interchangeably) any gaseous fuel (interchangeably) as well as solid fuels (purpose grown biomass, waste, - hazardous or negative value) solar energy and waste process heat. The 480 cc da/sh engine (four 120-cc cylinders) when optimized for long life produces 24 kW (45 hp) at 1800 rpm (peak efficiency).


da/sh solar hybrid systems can be designed to produce electrical power (in the Sun Belt) at a cost competitive with utility power plants.  Three demonstration Solar hybrid systems were installed in Arizona (two a utility, the third at a land fill gas site at an Indian reservation.).  One used natural gas night time and dark periods, the second used hydrogen generated during the day and the third used land fill gas. The engines were interchangeable. 


Several sizes of da/sh engines have been built 280 cc (15 kW), 480 cc (25 kW) and 1040 cc (55 kW).  Collectively they have accumulates over forty thousand operating hours.  The same 480 cc Stirling power section (that produces 25 kW electrical) when used for propulsion can produce 120 hp at 6,000 rpm (automotive life) for acceleration and hill climbing.  At typical road load power (steady state level) its most efficient power it will produce from 15 to 30 hp.   The 1040 cc engine could produce more than 250 hp - peak.   A 1500 cc engine could produce over 375 hp peak.   


Existing da/sh engines modified for propulsion (higher operating speeds) will weigh less than 2.5 lb. per hp (target is 1.5 lb. per hp).   da/sh engine for cars will be designed for more than 4,000 operating hours (heavy trucks for 20,000 hr.).  The automotive versions are comparable in size to internal combustion engines and have superior transient characteristics (ease of starting - acceleration idle to full power in 1/3 second with no emission spike).


The wide flat torque speed relationship of da/sh engines make it possible for da/sh engine base propulsion systems to use transmissions with half or fewer gears than comparable gasoline or diesel engines.   A class 8 truck with the 1500 cc da/sh engine will get slightly better acceleration and fuel economy with a manual four speed box compared to a ten speed box with a two speed rear end.   



da/sh engine based propulsion systems can be designed to operate on any liquid (or gaseous) fuel that will produce 700 to 1,000 oC.   They can use naphtha, ethanol, methanol, gasoline, diesel fuel and some unprocessed petroleum interchangeably.  The fuel tolerance of da/sh engines will permit simplification of the production and distribution of liquid fuels (they do not need high octane or cetane and will minimize the need for boutique fuels).   The use of da/sh engines (depending on market penetration) could make it possible to optimize refinery yields in terms of the energy content of the delivered fuel rather than control of cetane or octane etc. to produce a prescribed slate of gasoline and diesel fuel etc.


Because Stirling engines operate on temperature difference (heat input minus heat rejection) using the low temperature of liquefied fuels (or expansion of gaseous fuels) for cooling will increase their efficiency.  This can increase the efficiency.   They can recover part of the energy consumed in liquefaction of imported natural gas by generating electrical power during its re-gasification.   The efficiency of da/sh engines will increase as the ambient temperature increases.  The power output is independent of altitude (an attractive characteristic for trucks in mountainous areas – and perhaps for light aircraft or on board auxiliary power) 


There are eleven primary factors which decision makers should consider when comparing the relative energy performance of competitive power systems.  They include initial (purchase) costs, operating costs, engine (power system) efficiency, energy effectiveness (the percent of energy resources converted to power) the ability to meet regulated emission (and carbon dioxide generation) as well as noise.  Other criteria which differ with the applications include responsiveness (starting and power changes) weight and volume, reliability – and availability


In addressing the relative energy effectiveness of competitive power systems six major items should be considered. 

1                    The Application – whether for distributed power, electrical power back up etc. or in cars trucks and pleasure craft [1].        


2                    The development status of the power system


3                    The energy consumed in producing the fuel or energy source used.


4                    The energy consumed by the power system and auxiliary equipment.


5                    The difference in the efficiency of power system at a range of powers


6        The Uncertainty of delivered performance due to design objectives, manufacturing tolerances and differences in the processing and distribution (distance, mode etc) for fuel,


One way to screen competitive vehicle power systems is to compare the magnitude of the improvements (positive or negative) at two power conditions. 

·        First        Near  the most frequently used power  (i.e. road load)

·        Second   Near maximum. Power    


These power conditions (20 % or road load power and 85 % or acceleration and hill climbing power) account for the differences in engine efficiency with power.   This brackets the normal operating range of vehicle power plants

[1] On the Federal Urban driving cycle (FUDS) 73% of the time the power is at or below 20% of          maximum.  On the Federal Rural Driving Cycle (US06) 74% of the time power is at or below 35% of maximum


The relative energy benefits depend on the share of time spent at the different power levels (including idle and braking).  That in turn depends on the vehicle duty cycle whether a transit bus, intercity truck or car used primarily for urban or intercity driving.


The following table compares the fuel consumption of fourteen popular combinations of engines and fuels “well to wheels” and “tank to wheels” for the two power conditions.   It lists the percent of the original energy (oil, coal, natural gas, biomass etc.) delivered as useful power both - tank to wheels - and - well to wheels - and at two power levels terms of the percent of energy delivered to the wheels (or electrical grid) compared to a good gasoline internal combustion engine at the same condition


Tank to wheels consumption includes

The energy consumed in on board energy storage, (pressurizing tanks, charge-discharge loses for batteries) the efficiency of the engine (or fuel cells) power conditioning, transmissions and drive motors.

Well to wheels consumption includes

The above plus the energy consumed in producing (wells, farms or mines), collecting, transportation, processing (refining etc) , distributing (pipeline, railroad or truck) and storing the fuel at the refueling station (as a liquid or gas)


Comparison of Percent Power Delivered to Wheels

With 2006 Gasoline Piston Engines

Propulsion System Efficiency                 Total System Effectiveness

                                                                            Tank to Wheels                                 Well to Wheels

                                                            20% Power   85% power   20% Power   85% power


2005 Spark Ignition – Ethanol from corn +30% To -30%        +15% To - 25%        +300% To +35%          +300% To +45%

2005 Spark Ignition – Natural Gas               +50% To -20%        +35% To - 15%        +100% To -15%    +75% To -15%

2005 Compression Ignition - Diesel   - 20% To- 55%        - 30% To- 45%          - 25% To - 55%            - 02% To - 50%

First DA/SH engines  - Middle Distillate     - 50% To- 60%         - 05% To- 35%          - 45%To - 60%   - 02% To - 40%


Improved Spark Ignition – Ethanol from corn   - 05% To - 40%       - 05% To - 35%       +140% To +20% +260% To +20%

Improved Spark Ignition - Natural Gas       - 05% To - 40%        - 05% To - 35%         +05% To - 45%    + 05% To - 35%

Improved Compression Ignition – Diesel  - 45% To - 55%       - 70% To - 55%         - 35% To - 55% - 35% To - 60%

PEM Fuel Cell   Hydrogen from natural gas           - 45% To - 55%      +15% To - 20%       +200% To +20% +600% To +150%

PEM Fuel Cell   Methanol from natural gas        - 35% To - 55%      +45% To - 10%         +05% To +45% +140% To+30%

Future Fuel Cell         - Hydrogen from natural gas       - 70% To - 75%      - 40% To - 55%          +120% To - 25%     +300% To +45%

Future Fuel cell          - Methanol from natural gas        - 55 % To - 70%     - 15% To - 45%              - 55% To -  70%          - 08% To - 45

Future DA/SH ENGINE – any liquid fuel      - 70% To -75%       - 40% To - 50%          70% To - 80%     - 40% To - 60%


Average Efficiency of 2006 Spark Ignition Gasoline              09% 12% 15%     14% 19% 23 %      6%  9.6% 12. %      10%14.7%19% 

The most probable values for any combination of engine and fuel are near the average of the high and low values listed. 


The table is based on information from various sources, from engine developers, environmental advocates, energy and engine company economist’s etc. It is a summation of the highest and lowest of their suggestions (or where possible published data).  It is not based on a statistical analysis




The range show high % to low % (efficiency or effectiveness) is based on to the uncertainties in fuel processing and delivery as well as differences in power plant efficiencies etc.  The chart illustrates the difficulty in determining which of the candidate power systems will be most energy effective.  It is probable that several power systems will be continue to be used depending on application and fuel availability.

The assumptions and methodologies used  are available in separate reports


This table indicates that the first generation da/sh engines should provide nearly twice the miles per gallon of a gasoline engine at 20% power (50% to 60% more) and up to 40% more miles per gallon at 85% power.  The performance of first generation da/sh engines is similar to advanced diesel engines and Proton exchange membrane (PEM) fuel cells using methanol.   Well to wheels reductions in use of resources for first da/sh engines are similar.   Future da/sh Stirling engines (55% efficient) will provide from three to four times the miles per gallon of a gasoline engine (70 to 75% more) tank to wheel and about half that of gasoline engines (40 to 60%) considering well to wheels energy effectiveness.   


If accurate projection of a vehicles fuel economy (MPG) are required – the share of time at all applicable power conditions – defined by the duty cycle should be evaluated (including fuel use at idle and during accelerations).   The total benefits of competitive propulsion systems depend on the source of the fuel (biomass, coal etc.) and the objectives (reducing fossil fuel imports etc.)


The effectiveness of direct electrical and battery electrical propulsion systems have been addressed in other studies.   The uncertainty includes the fact that the efficiency of the utility power plant (average 30-35% best 50%) coupled with the distribution loses and the cost of batteries makes their energy effectiveness and cost uncompetitive with da/sh engines for most vehicle applications (depending on the source of energy for the electrical systems and cost of petroleum).  If zero emission range is mandated by law the combination of Stirling engines and thermal batteries will provide longer range than the best current batteries - for less cost.       

GM demonstrated a zero emission Stirling engine /  thermal battery vehicle in the 1960’s.


The poor energy effectiveness of biomass derived ethanol is primarily the result of the energy consumed in collecting and transporting the corn to central processing stations.    Up to three times the energy (in electricity) can be produced by burning the corn in a Stirling engine at a place adjacent to the place where it is grown  (burning the corn stover will further increase the useful power output).   Farmers in Sweden plan to use da/sh Stirling engines to produce electrical power from combustion of biomass (purpose grown or waste).   The local utility will provide (lease?) the engines and purchase the excess electrical power for distribution to other users.   Swedish energy authorities estimate that many farmers could double their cash income by this strategy. 


Table two summarizes the characteristics of the da/sh engine is to rank order them and thus provide a basis for assessing where the engine could be best used.


Qualitative Ranking of Attributes

Double Acting Swash Plate Drive Stirling Engines

Relative to Competitive Power Systems

Rankling 1 (poorest) 10 (best)

                             Compression      Spark                   Micro          PEM           DA/SH

                             Ignition                 Ignition                 Turbines              Cell             Stirling

Initial Cost           8 LOW          9 LOW             6 HIGH                   ? HIGH           10 LOW

Operating Cost             7 LOW          8 LOW            9 GOOD                 ? UNCERTAIN   10 LOW


Efficiency            8 LOW          6 LOW            5 LOW [1]               9 HIGH [2]                 10 HIGH

Energy Effectiveness  9 LOW           7 LOW            6 LOW                  ? POOR                          10 HIGH

Regulated Emissions  5 POOR (NOx)  6 POOR                     4 POOR                      ? LOW             9 LOW

CO2 Emissions             5 POOR                   4 POOR                     3 POOR                      ? UNCERTAIN [3]          10 LOW [4]

Noise                             6 HIGH           7 HIGH             4 HIGH                         ? UNCERTAIN   10 LOW


Responsiveness          9 GOOD                         9 GOOD                     5 SLOW                 ? UNCERTAIN   10 FAST  [5]

Weigh and Volume      7 GOOD                   9 GOOD                   10 LIGHT                 ? UNCERTAIN     9 GOOD

Reliability             8 GOOD                   7 LOWER                    9 GOOD                 ? UNCERTAIN   10 BEST

Availability           10 NOW                       10 NOW                    ? UNCERTAIN ? UNCERTAIN   ?                


                             [1] Micro turbines have poor off peak power efficiencies (In vehicles)

   The peak efficiency of combined cycle utility turbines is high (50 %+)

[2] Fuel Cells have the potential to be the most efficient

                             [3] Depends on how the hydrogen is produced and distributed

                             [4] Near zero if the da/sh engine uses biomass or wastes

                             [5] With a variable swash plate    


In theory, da/sh engines could replace spark and compression ignition engines (and micro turbines) as well as preempt the market for fuel cells in essentially many of their applications. For example:


·        Cities can produce electrical power from urban wastes at a cost competitive with other electrical generation technologies while reducing disposal costs.


·        Cities (or large buildings) with central or district heating systems can use the same heat producing boilers to provide the heat for da/sh Stirling engines thus reducing the cost of power generation


·        Farmers can reduce energy costs by using purpose grown biomass or agricultural wastes to meet their electrical and heat needs.   In Sweden the plan is to increase their income by selling any surplus to local utilities.


·        Da/sh engines provide a way for local utilities to create the capacity to meet incremental demands at low cost.   They can improve the total system reliability; reduce the dependence on electrical interconnecting grids and thus their liability in case of power failures due to weather, accidents, vandalism etc.


·        Home owners and small businesses can insure the reliability of their electrical power by using da/sh engines for base load and emergency power (and heat)


·        The fuel consumption of personal cars and commercial vehicles could be reduced to or below hybrid levels without the complications or costs of batteries and electric motors.


·        da/sh engine based propulsion systems for cars and trucks can achieve environmental standards that are difficult or impractical to meet with internal combustion engines.


·        Hybrid solar thermal systems can produce power at rates competitive with conventional utility power systems in areas with high incidence of solar energy


·        DA/SH engines can use unprocessed crude oil to power oil wells.    Electrical power can be produced at natural gas wells which have too low a yield or are too remote for conventional collection systems 


·        Low noise, high efficient auxiliary or propulsion power for yachts and recreational vehicles would be a unique high profile market



·        The da/sh engines power is independent of altitude an advantage for trucks and other vehicles in mountainous regions and may be attractive for light aircraft and auxiliary power.


·        Cost of operating construction equipment (earth movers, temporary electrical power generating systems etc.) can be reduced because of the da/sh engines tolerance of dirty atmospheres and their low noise.


·        The need to import fossil fuels (oil and natural gas) could be reduced significantly


·        Noxious and green house gas emissions can be reduced significantly


·        The vulnerability of the US to energy supply interruptions (natural, accidents, vandalism or terrorism) will be reduced as the use of da/sh engines increases. 


JGT recognizes the potential size and complexity of the market this represents.  da/sh engines could replace gasoline and diesel engines in essentially all markets they now dominate. In 2005 nearly 40 million internal combustion engines were built by US industry for a wide variety of markets .

Over 35 million gasoline engines

20    million less than 5 hp,

11.5 million 100 to 300 hp and

2.5   million over 300 hp.

Over 2.2 Million diesel engines

17,000                   under 50 hp

1.1 million    200 to 500 hp

11,500                   over 1,000 hp. 

Source Diesel Progress Magazine June 2005


The da/sh engine may take an increasing share of the growing markets in nations that lack effective electrical grid networks and are more dependent on hydrocarbon based fuels than the United States.


Not only would it be difficult to create a business to address all of these markets in a timely manner, it probably would not be allowed (antitrust).   In addition to building engines (and critical components) for selected markets JGT intends to license these technologies to companies that understand the markets and are qualified to adapt and/or manufacture the da/sh engines.    Cooperating with qualified companies will accelerate the deployment of da/sh engines – and provide income for JGT in markets where it would not otherwise be qualified.


The Photographs on the next page illustrate three applications where Stirling engines have been demonstrated.


1, A bank of 25 kW (4-120) da/sh engines that operated on land fill gas


2. Three demonstrated hybrid solar systems that operated on solar energy when available,

One used and natural gas, one used land fill gas and the third used hydrogen produced from excess power during the day.  The da/sh type engines were interchangeable


                      3, A Swedish Stirling powered bus demonstration  












Operation of Double Acting Swash Plate Stirling Engines

September 2005


Stirling engines operate in a very different manner from internal combustion engines. Instead of controlled intermittent explosions to drive a piston they produce power by creating a pressure differential across a piston.   The power is a function of the increased pressure (and temperature) of a captive working fluid (usually hydrogen) above a power piston and the decreased pressure (and temperature) below the piston.    The formula for efficiency is the same as the Carnot cycle the highest potential efficiency for thermal engines.

η   =  T max – T ambient        

                  T max


The basic operation is similar for all Stirling engines. Tmax is set by the temperature at the heat input system (combustion of fuel etc.).  Tambinent is determined by the effectiveness of the cooling system (heat rejected to the atmosphere etc.).


Double Acting Swash Plate Stirling (da/sh) engines consist of three major elements [1] an external heat system [2] a power section (or short block) where the power is produced and [3] a power output to an electrical motor, transmission etc.


 [1] The external heating systems (combustor and heater tubes) can be designed to use a variety of heat sources including combustion of any liquid fuel (interchangeably)- any gaseous fuel (interchangeably) solid wastes, solar energy, waste or stored heat etc.  The temperature of the hot section of the engine is held constant by control of the heat input (compensating for any differences in energy content of the fuel)


 [2] The short block produces the power (by the Stirling Cycle).  It contains four cylinders, four double acting pistons, the regenerators and the cooling system.  There is no direct contact between the heat source and the captive working fluid in the short block.  The power section needs no lubrication.


 [3] The power output can be through either a fixed or variable swash plate.














Double Acting Stirling Engine Cross Section


The four double acting pistons in da/sh engines have two functions.

First:         To produce power. 

Second:    To transfer the working fluid from the hot space above one piston to the cold space below an adjacent piston and back.  

There are four independent gas enclosures.  They connect the bottom (cold end) of one cylinder to the top (hot end) of an adjacent cylinder.  They are charged with high-pressure (2,200 psi) hydrogen that serves as a working fluid (helium and other gases can be used but reduce the performance).  The high temperature (expansion) spaces are maintained at the desired temperature by heat from the external heat input system.  The cold (compression) spaces are maintained at the desired (low) temperate by a liquid cooling system using conventional automotive radiators.    The gas being transferred from the cold to hot sections passes through three heat exchangers


1.     A heat exchanger adjacent to the expansion volume                    Heat Input   

2.     A regenerator located between the heater and the cooler    Heat storage         

3.            A cooler adjacent to the compression volume                   Heat rejection       


The four regenerators store heat during the compression cycle and release it during the expansion (power) cycle (thus conserve heat to increase efficiency).


The differential pressure across the piston provides the power.   It is a function of the difference in the temperature of gas at the top of one piston to that of the gas at the bottom of the adjacent piston (same gas enclosure).    Each of the four pistons is at a different point in the thermal cycle.  Power output of each piston is sinusoidal.   When combined by the swash plate the power out put is constant – electric motor like.   The power output is independent of altitude and advantages in the high mountains (or for aircraft).


The power output of a da/sh engine is almost linear with speed (at a fixed swash plate angle).  Changing the angle of the swash plate changes the stroke of the pistons thus the power output of the engine at a given speed.   Swash plate da/sh engines can accelerate from idle to maximum power in 1/3 second (faster than gasoline engines).


The Stirling engines require about one third larger radiators and a hydrogen replenishing system to compensate for the small hydrogen leakage.  This can be provided by electrolysis of a small quantity of water by purchased commercial hydrogen or by partial oxidation of the fuel etc.  (one gallon of water contains enough hydrogen to maintain the performance of a 25 kW engine for most of a year­).


The continuous process ambient pressure heat input systems (99.9+% complete combustion of liquid and gaseous fuels) provide exceptionally low NOx emissions.  Unburned hydrocarbons, CO, and particulate levels are not measurable.   Control of emissions is much easier in a constant process burner than in the intermittent combustion processes of an internal combustion piston engine.


The manufacturing processes used for piston engines can be used to produce most of the da/sh engine components.  No critical materials, catalysts or expensive manufacturing processes are required.  


Other Stirling engines are heavier and more complex.   Philips rhombic drive engines had two pistons in the same cylinder, a power piston and a transfer piston.   Power was changed by increasing or decreasing the working pressure, a slow inefficient process.  V -engines also have two cylinders (power and transfer) but in separate cylinders - one to move the working fluid from the hot to cold section - one to produce the power.    Most other concepts are not suitable for vehicle propulsion or load following applications.


 Albert (Al) Sobey




Allison – DIVISION GM                                                                           1945 - 1962

Flight Test Engineer                    Last Piston Engines (V-1710 in P-38, W-3460 in B-39) and first Jets (J-33 in F80 & F-92, J-35 in F-89)

Department Head               Turbine Engine Controls

Section Chief                      Rocket and Space Power Research

Solid and Liquid Rockets, Stirling Engines, Small Power Turbines

       GM Technical Center                                                                                             1962 -  1967

GM Research,                      Engineer In Charge – Transportation System Analysis                                                           Designed GM full scale aerodynamic wind tunnel

Chair -GM Corporate Vehicle Performance Assessment Committee

Transportation Technology Inc.                                                                       1967 - 1972           

President and Founder         Vehicle and Material handling licenses from GM.

Controlled Flxible Bus and St Louis Car. (TTI sold to Otis Elevator, Flxible sold to Rohr)

Booz Allen & Hamilton                                                                            1972 -1974          

Principal                  Transit and Rail Practices    - Introduced Articulated Buses to the US


GM Transportation Systems                                                                             1974 – 1980

Manager                   Divisional Planning and New Business Development

                                                Assessed future technical and business environments for personal

and commercial transportation – Sponsored Urban Energy Assessment

Organized assessment  teams(GM and outside) for Lean Machines, RoadRailers,

Railroad scheduling controls, Combined cycle turbines etc

GM Economic Staff                                                                                               1980 - 1987           

Sr. Director                        Energy and Advanced Product Economics 

                                                Provided Energy price and availability forecasts for GM Management

                                                Evaluated new product technical and economic feasibility

                                                            Assessed unrealized value of GM Technical developments

Initiated GM innovative power program (Fuel Cells)

Sponsored  The Energy Modeling Forum at Stanford University

                                                            Keystone Center workshops on economic impact of product liability

Member -          GM Corporate New Business Advisory Committee           


Albert Sobey and Associates                                                                            1987- Present

Provides professional services on energy, transportation and business strategies.

Clients have included:   GM, Exxon, Dow, Eaton, STM Power, Ricardo, US Dept. of Energy, US Army TACOM, California Energy Commission,

 California Dept. of Transportation, The United Nations, W.A Jones Foundation etc..


Created the energy propulsion panel – (merged in 1992 with the older energy economics panel)

Participants include:      Arco, Amoco, Aramco, BP, Chevron, Exxon, Mobil, Petro Venezuela, Shell, Sun, US Treasury, US Dept. of Energy, US Dept of Commerce, Center for Strategic and International Studies, Chrysler, Ford, GM, Ricardo etc.


                 Other             Chairman - ENTRAB Services,   Partner - Johansson Global Technologies                          


     Fellow of the                             Society of Automotive Engineers

            Member of the                          American Society of Mechanical Engineers

            Member of the                          National Association of Business Economics

Licensed Profession Engineer               Michigan, Colorado and Florida

Member - Supply and Demand Task Force          National Petroleum Council

Member - Heavy Engine Advisory Committee      US Department of Energy

Member of the Technical Advisory Board           Michigan Strategic Fund                                   

Member of the Board                            Michigan Product Development Corporation                  

Member of the Board                            Michigan Technology Council

Member of the Board                            Metropolitan Center for High Technology                       

Member of the Board                            Michigan Council for Economic Education         

Member of the Board                            Center for Cooperative Innovation

Trustee of the                            Detroit Science Center  


Education, Publications, Patents, Honors

            Bachelor of Mechanical Engineering Degree                   From General Motors Institute    1945

Honorary Doctors Degree                                       From Kettering University           1997


Over 100 Unclassified Papers                    On Engines, Fuel Systems, Urban Transportation, Railroad Technologies, Future Energy Technologies and Developments


Book                                                               Control of Aircraft and Missile Power Plants (Wiley 1962)


20 + Patents                                                  Turbine engines, rockets, engine controls, vehicle technology etc.