Inventor creates 100 mile to the gallon engine using 200-year-old Stirling technology 

Posted: June 20, 2016 by oldbrew in innovation

Stirling engine model  [image credit: Wikipedia]

Stirling engine model [image credit: Wikipedia]

Daily Mail Online reports on a new twist to the Stirling engine concept. Will the motor industry be overjoyed? Possibly not.

For thrifty motorists, squeezing an extra few miles out of each gallon of fuel can become an obsession. But some have been striving for a semi-mythical goal of achieving 100 miles per gallon of fuel from their vehicles.

Now an inventor in Texas claims to have built an engine that can reach this efficient milestone – using a design that is more than 200 years old.

Josh MacDowell, combined a Stirling engine – first created by a clergyman in Scotland 200 years ago – with thermopile technology that converts heat energy into electricity.

Mr MacDowell, from San Antonia, Texas, is currently testing his invention in a Hybrid electric car, allowing it to drive at highway speeds without the need for recharging.

He believes the engine would also be capable of letting an SUV achieve 100 miles to the gallon. He is now hoping to patent his design.

Internal combustion engines currently used in cars only use 14 per cent of the energy they produce, but Stirling’s engine design can use almost 50 per cent, making them much more efficient.

Speaking to KHOU, Mr MacDowell said: ‘I imagine in 20 years the only place you will see an internal combustion engine is on a Harley-Davidson motorcycle because people like the way they sound.’

Mr MacDowell’s concept has received scientific backing by researchers at Texas A&M University.
Dr Mirley Balasubramanya, a mathematical physicist at Texas A&M University, said: ‘This is a wonderful idea, why didn’t someone else think of this?’

Full report: Inventor creates 100 mile to the gallon engine using 200-year-old Stirling technology | Daily Mail Online

KHOU TV news report and interview here.

  1. tallbloke says:

    Warming up time is an obstacle to automobile applications of Stirling engines. People want to jump in and go. I’d certainly consider a 5 minute wait acceptable for the economy on offer though.

  2. Graeme No.3 says:

    Carnot’s principle applies to a Stirling engine, so a 700℃ hot zone is required for around 45% efficiency. Using some of the waste heat via a thermopile would add about 9% extra (at most).
    So he is really getting about twice the efficiency (at best) of a modern diesel.
    I suspect there are a few patents that he should watch out for, e.g. Ford. Which makes one wonder why Ford haven’t used this approach.
    He might do better to try using a Stirling motor in a hybrid type.

  3. oldbrew says:

    Graeme No.3 says: ‘He might do better to try using a Stirling motor in a hybrid type.’

    That’s what he is doing.

    ‘Trying to describe just how significant this invention could be, Mr MacDowell said his design is to the Hybrid industry, what Diesel-electric locomotives were to steam engines.’

    Read more:

    ‘His next plan, is to use his current engine in an SUV, starting on the east coast of the US, and driving to California – a journey around 2000 miles long.’

  4. Stephen Richards says:


    That will be better than the current several hours wait for battery cars. Some graudiad twats took a fast charging Tesla down to west france and thought it was brilliant. It only took 3 days and 2 hotel stays

  5. A C Osborn says:

    When I worked for Fords I made a suggestion in their Suggestion Scheme to use thermopiles to extract energy from the Exhuast System to cut down on the Alternator & battery sizes to increase economy.That was long before Hybrids were thought about. It was totally ignored even though it was shown that a truck Diesel engine could produce about 1kW of electricity using the same technique.
    I believe nothing ever came of that either.

    I wish him every success.
    Does anyone on here remember the Australian Gvang Steam powered sports car, it had a beautiful body.
    Anyone remember the Sarich orbital engine, based on the Wankel, it died due to technical issues?
    Anyone remember the British Torotrak CVT transmission, it is still going?

  6. Stephen Richards says:

    Anyone remember the British Torotrak CVT transmission, it is still going

    Certainly CVT is still going. In fact, its very prevalent. Nissan use in their auto and so do several other companies

  7. Stirling engines are VERY large for the power that they develop. They are inherently slow engines so large capacity is required for a required power level.

    Large modern diesel engines easily achieve peak efficiency of around 50%. They’ve been quite good since the 1930’s. Junkers Jumo 205 aviation diesel engines got in excess of 40%.

    In smaller turbo-diesels, Audi’s V6 2.5-litre exceeded 42% efficiency in 1990 matched closely by BMW’s 2-litre in 2007.

  8. A C Osborn asked: “the Sarich orbital engine, based on the Wankel, it died due to technical issues?”

    [I think that I can talk freely about this, having last worked on the engineering in 1979 and last contracted to the company in 1999.]

    A myriad of technical issues. It wasn’t based on the Wankel. Its piston orbited, without rotation, around the centre of the crank.

    There are fundamental mechanical limitations in terms of efficiency in that layout. Engines proportioned large enough for a car (in terms of swept volume and revs) struggled to achieve autonomous rotation. Most of the engine studies were with the test engines driven by an electric motor.

    The layout works much better as an air pump.

    As in the Wankel, the sliding seals were always problematic.

    The struggle to achieve efficient operation led to the company pursuing pneumatically-forced fuel injection and it was serendipity more than planning that resulted (in the summer of 78/79) in the discovery of air-assisted fuel injection with high-pressure air shearing the liquid fuel through the injector nozzle.

  9. oldbrew says:

    With a hybrid vehicle, the electric motor could power it while the Stirling engine warms up.

    If it’s a series hybrid the engine is used solely to charge the battery.

  10. oldbrew says:

    The Stirling engine in question IS a range extender and he has the US patent.

    It runs on any fuel: petrol, diesel, natural gas etc. The key to the fuel economy is that it operates at fixed rpm regardless of vehicle speed, because the battery powers the wheels.

    TV news report and interview here:

  11. tallbloke says:

    Bernd: Stirling engines are VERY large for the power that they develop. They are inherently slow engines

    That used to be true when they relied on a connecting rod and seals to transfer power. However, the advent of using them for electricity generation eliminates the need for those so totally sealed units with high fluid pressure has made them a lot more efficient and lighter.

    What surprises me from the description of this new design is that it generates electricity from thermopiles converting heat, rather than induction from the piston motion. Maybe you could do both simultaneously (don’t see why not).

  12. oldbrew says:

    Toyota Prius also has a version of the CVT transmission.

    ‘Once you learn to use the powertrain’s torque and to gently squeeze the throttle, the petrol/electric Toyota Prius can become strangely satisfying to drive.’ (19 May 2016)

  13. Graeme No.3 says:

    There was a breakthrough a few years ago on thermo-electric conversion when efficiency jumped from 8% to 17%. It was promptly whipped under wraps by GM and the US Navy. From memory worked at around 400℃.
    I assumed that he was using this as an add-on to boost efficiency of fuel use.
    Re the Stirling engine, it may be large but isn’t that heavy and with electric motors (no gear box, transmission) that would help overall economy.

    Oh well, bang goes my thought of using a Stirling & lithium batteries in a hybrid (as per Chevy Volt), which I have occasionally mulled over for about a year. Another one for the waste paper bin.

  14. Petrossa says:

    as is with every ‘breakthrough’ in battery design, so it is with this idea: when it’s to good to be true it isn’t

  15. oldbrew says:

    Let’s see if it gets from coast to coast USA on one [sealed] tank of ‘gas’ as proposed by the inventor.

    Not sure if any new battery tech is involved. The Stirling engine is a range extender i.e. it just charges the batteries.

    Jaguar had a fairly similar concept except they had a gas turbine instead of a Stirling engine. It turned out to be too expensive IIRC.

  16. catweazle666 says:

    I’m not impressed.

    How about 180 m.p.g from a 350cc BSA motor cycle?

  17. Free piston engine can have minimal parts and be employed as both a hot gas (for thermopile) as well as linear generator. As a two-stroke (e.g. Stelzer) it’s very light and compact. Toyota were working on a similar 4-stroke version; with obviously more complexity.

    Here’s a toy version:

    If the objective is to move air, then a free piston engine is the way to go. Such engines have been used in large compressors; at least those yielding large amounts of pressurised air, for about a century. All they need is fuel and air and beyond the free piston assembly/assemblies, have only a few moving parts like valves. i.e. no large moving mechanical parts.

    Moving hot exhaust air over thermopiles isn’t a problem. However, high combustion temperatures for efficient operation in lean-burn necessarily produce NOx emissions; emissions that are tightly regulated.

  18. oldmanK says:

    Interesting, but other considerations tell another story.

    For many years I raced around, and carried everything, in cars with engines all under 1000cc. There was little traffic to speak of. Today we crawl in jammed roads with the equivalent of troop carriers with engines mostly about 2ltr, to ferry kids to school.

    Fashion and perception sells, efficiency no.

  19. oldbrew says:

    They don’t make them like the 2CV any more: cardboard wings, deckchair seats, umbrella handle gearstick etc.

    ‘Noted automotive author L. J. K. Setright described the 2CV as “the most intelligent application of minimalism ever to succeed as a car”, calling it a car of “remorseless rationality”.’