Free Piston range extender

[motorlad]

I have just read an interesting thread on using a wankel engine as a range extender on this forum. Yes, the wankel is being seriously looked at, and developed, for range extender duties. It promises to perform more efficiently at this role than a conventional piston engine with a crankshaft. That is good news as cars are moving towards EVs with range extenders to alleviate range anxiety. The following is what I have gleened directly from people involved in this field, and that is that it may be more fuel efficient to run an EV with an efficient range extender than charge batteries from the electricity grid. Having the electric driving traction motors disconnected from the generating engine makes all this work efficiently allowing the generator to run at its most efficient constant speed and load independently of the demands of the driving electric motors. That means the on-board battery only needs to be big enough to be used as a buffer rather than the prime storage of on-board energy. Larger battery sets may be insisted upon to reduce emissions in cities, by running more on zero emissions for most of running time.

It is argued that this is also the case for piston engines with crankshafts, and that is true, however, the wankel's small size and weight with very smooth running and predicted greater efficiency at this role may preclude conventional piston engines.

As many manufacturers and research establishments are looking into small highly efficient range extenders, different approaches have been looked at. The two-stroke OPOC engine, backed by Bill Gates, looks to be a good range extender and is making it to production in China as a general purpose generator. But it still has a heavy bulky crankshaft, so it is just an modernised and greatly improved opposed piston design.

The problem with engines is that there are great inefficiencies to get "turning motion" in order to turn a generator. To make electricity turning motion is not needed. A piston moving up and down with coils in it is all that is needed. Working back from this then a crankshaft is not needed. The engine and generator can be combined into one compact efficient unit.

Toyota are developing a piston range extending generator with no crankshaft. The free piston moves up and down with coils in the piston and cylinder lining to produce electricity. The piston is a top hat and "W" shaped affair. Think of a large can of beans with small can on top with coils around the large can. There is no crankshaft with an air spring returning the piston. It is also a two stroke design using computer controlled hydraulic exhaust poppet valves with no camshaft. The intake is via cylinder ports, like a diesel two-stroke. The unit is small and light and returned on the first run 42% efficiency about 9 months ago. Toyota hope to reach over 50%, when a conventional powertrain in a vehicle only returns about 20% efficiency this is a great advance in such a small mechanically simple unit. Over 50% efficiency in producing electricity is greater than the 40% efficiency (depending on where you live) of electricity from a power station to socket in the home.

A good explanation:
http://www.greencarcongress.com/2014/04/20140422-f...

A video animation of the engine:
https://www.youtube.com/watch?v=QUbBqSu9Hdc&fe...

An opposed free piston version being developed by the German Equivalent of NASA. This has the electrical coils separate from the driving pistons.
https://www.youtube.com/watch?v=yV09wMXTSIc&fe...

The free piston engine is readily scalable upwards, as is also the wankel, to use in large trucks, buses, trains and ships. For the likes of ferries with electrically driven propellers giving independent control of each prop is a great advantage in manoeuvring.

Expect EVs with buffer batteries, using ultracapacitors for brake kinetic reclaim energy, and physically small free piston range extenders or wankel engines as the generators. Expect them to be mainstream well within 10 years. I would bet the the free piston unit over the wankel to be the eventual unit of choice. Some are predicting this will be the last internal combustion engine development before the units eventually are fully superseded.

Edited by motorlad on Monday 12th January 10:47

[motorlad]

Max_Torque said:

(The issue with ICE's is that ~70% of your fuel energy is wasted as low level heat)

Correct, well about 80% really. It can be about 30% if the engine is running on constant load and speed. If I recall rightly, the maximum was just under 50% in a constant speed, constant load ships' diesel, with no losses from the camshaft as it used hydraulic valves. Pumping losses, friction losses and down the exhaust pipe are the losses. Not enough energy is used to create turning motion so it ends up as heat. Look at a gas condensing boiler. The products of combustion just after the flame are very hot. The design of the heat exchanger is so efficient that you can put your hand on the exhaust so much heat is transferred into the circulating the water.

This brings us to the Stirling engine which uses an oil type of continuous burn burner used in an oil boiler. Have a free piston Stirling and they can be used in large vehicles. Stirling are too big for smaller vehicles to be used a generators. Free piston Stirlings are used in cogen boilers/electricity generators. The efficiency of Stirlings rises when the cold section is very cold creating a large differential to the hot section. Experiments on running a compressor to cool that section have raised the efficiency. Stirlings work well in cold climates. NASA did some very successful work with Stirlings in autos in the 1970/80s.

I fail to see what some think I am supposed to be spamming.

Yes, hello to all.

Edited by motorlad on Monday 12th January 10:09

[motorlad]

GavinPearson said:

The wankel engine would only be able to be used for a very limited amount of a drive cycle, because it has a fundamental emissions problem. It does package well though.
The OPOC engine is bulky. Fine for generating electricity for houses, less so for cars.
There is a great deal of claim making in this industry but oftentimes the claims are not realised, I.e. don't believe everything you read.

R&D has cleaned up wankel emissions and running at a constant speed the emissions improve greatly. True as a range extender the wankel will be part time engine. The OPOC is not as bulky as you think. It is long and thin. Claim making in engines is ongoing, however we are moving up a level in autos, not just penny pinching as it was before, with EVs, batteries and range extenders. The Free piston generator looks good and it is proven technology. I doubt Bill Gates would invest in an engine which he thought would not meet expectations and fail. OPOC are not after investment cash. The OPOC is the lesser of the two others, the free piston and wankel.

[motorlad]

AER said:

None of these technologies represent a huge leap forward in capability or cost reduction. They are tinkering on the edges of conventional technology and adding a bunch of risk to boot. The conventional reciprocating piston engine has the first mover advantage by a hundred years, which includes a huge knowledge base and supplier infrastructure. If you add on the licence and royalty fees these guys will want, the ideas are dead in the water.

Hello, I am not sure what you mean by cost reduction. If in manufacturing then there is no crankshaft and conrods. I am unaware of the risks involved you mention considering the application. They are clearly a leap in efficiency in the intended constant speed application, to what we have now. I do not see the current pistons/crank engine having any advantage as it is about on the last legs of its lifespan. The free piston engine I believe is licence free.

As long as they work and the efficiencies are much higher, I cannot see a major barrier.

[motorlad]

AER said:

There is no clear leap in efficiency. To suggest so is to demonstrate your ignorance of combustion engines.

Cut out the insults please. There is always one isn't there Here is a massive leap in efficiency if you read what I wrote. On first run Toyota got ~42%, on their "first" run, which is way above what a piston/crank engine can deliver, then the total simplicity and very small packaging of the setup making it ideal for auto use. R&D will improve on that. The only complexity is the hydraulically activated poppet valves, which is not new. A piston/crank engine can only dream of that efficiency and packaging. Crankshafts, high pressure oil pumps, con-rods and all, cost and add great bulk and weight. Eliminating all that alone is a massive saving.

Over 20 years ago Toyota went alone in developing its hybrid setup. Toyota pulled back on technology as the original model was to have ultracapacitors not a battery setup. The Prius has been around for 18 years now. The detractors were all like you, very negative and unable to see the advantages wanting to keep the status quo.

The KSPG (Pierburg) engine is still a piston crank setup with the inherent inefficiencies that brings. They have done a good job in the packaging of the generator. Lotus have also made a dedicated range extending 3 cyl piston/crank engine which is to be produced in Spain. These are all ready when other makers turn to full series-hybrids setups. The BMW 2 cyl motorbike engine in the i3 used a range extender is rather a cobbled together affair only to get you home slowly. Only legislation will force manufactures to move, as the auto industry is famous for wanting to keep the status quo.

The way ahead is all looking to be EVs with range extenders with electric motor traction and only the departure from the current piston/crank setup will make it work properly in giving full range and speed with depleted batteries. Judging by the Toyota free piston efficiencies, banks of batteries could be replaced by ultracapacitors as only a small buffer may be needed. The like of London with its congestion charging, which is free to EVs and hybrids (but not diesel hybrids), may dictate the size of the energy buffer, as they ultimately want zero emissions in the city centre.

stevieturbo said:

Smaller less moving parts etc etc, surely if they were solely to generate electricity that can only be a good thing ?

Rather than using a gas spring to compress, or two pistons travelling towards each other.

Why dont they use the opposing pistons combustion to compress the other sides

Stevie, I thought of that myself when first looking at the German opposed piston generator. Like the back pressure of the shot in an AK47 gun is used to load the next bullet, the back pressure of a piston can return another piston back up a cylinder. Or join the two back ends of the pistons in an opposed piston setup so they both acts on each other ensuring they both go back up the cylinders. It must be worth looking into.

Edited by motorlad on Monday 12th January 10:53

[motorlad]

stevieturbo said:

Using the Prius to justify anything is pushing it though...it's terrible in every respect.

The Prius, as I mentioned, is now 18 years old. It was quite advanced for its time. It is now outdated to the likes of the Volt and BMW i3, but give it respect as it was the first of the current crop of hybrids which set the scene which the auto industry followed.

I have driven quite a few and I love driving them. They do take off from stop on the batteries most of the time. The engine will sometime come in at odd revs as the management system calls in the engine to generate electricity. A company in the USA called Calcars, did conversions to add a lager battery bank and a plug to charge from the grid. The battery bay is large and only a small part is used, Calcars just filled it. The car could run about 30 miles on a full charge. The car was transformed by just a larger battery bank and mains plug. It was almost a DIY installation. Toyota initially refused to fit mains charging plugs to the Prius so as not to give the impression it was held back by charging.

The Prius around town can get 65mpg, the mpg rises on long fast trips, the opposite of conventional cars. The car was designed to cut down kerbside emissions in Japan and does that handsomely. The engine is off when the car is stopped. The emissions are low otherwise it would not be exempt from the London congestion charge.

Toyota are now looking at the BMW i3 setup of electric only traction motors with a superior range extender. The Toyota free piston range extender looks like it could be also an after market slot in.

Gas turbine generators are used in some buses.
http://en.wikipedia.org/wiki/Environmental_Perform...

Edited by motorlad on Monday 12th January 14:02

[motorlad]

AER said:

It's not an insult unless you want it to be. Every post you add makes it a clearer point of fact, however.

It is insulting for sure, even 996TT02 pulled you up on it. You are a know-it-all, unsure of yourself so start insulting at the first step and repeating the insults. Intelligent people do not have your attitude. You cannot get your head around anything new or any deviation from the status quo. You are not worth engaging with as you add zero. You probably make your living from regrinding crankshafts.

Write to Toyota and tell them they haven't got a clue.

[motorlad]

Max_Torque said:

The day that battery technology improves by approx another 30 to 50%, is the day that ALL internal combustion engine energy converters become obsolete.

That is stating the obvious. We all know the IC engine has little time left. We know that battery and ultracapacitor technology is improving like wildfire. Look at battery advances. It was not so long ago mobile phone batteries were like bricks. Look at them now, they can run small computers all day. A smart phone battery on just a cell phone that only does phone calls will last for weeks. Look at power tool batteries! An SDS drill can drill a largish hole through a brick wall on one battery charge. Great for men up ladders.

Japan has introduced battery powered urban trains, that take a small top-up charge at each station stop, and a full charge at the terminus. This is viewed to massively reduce costs by eliminating full line electrification. Bombardier in the UK is doing battery train trials. The view is to use mains electricity from overhead wires or a 3rd rail at each station to accelerate the train from halt, and the batteries take it along to the next station. The DfT is looking very closely in order to use these battery trains to extend underground urban rail networks like London, Liverpool, Newcastle and Glasgow onto low passenger usage unelectrified track; high passenger usage justifies full line electrification. They will not allow diesel engines and their fuel tanks into underground stations and tunnels.

The point is that batteries are now small and hold a big charge. Battery and ultracapacitor R&D is big and newer superior batteries with much faster charging are in the pipeline for sure. If the advancements continues at the rate of the past 15-20 years EVs will be the norm in 15 years time. Most autos sold in the developed world will be EVs.

Any range extender is viewed to be an interim measure for sure, as all are expecting batteries and/or fuel cells to greatly improve over the next decade. But the likes of Toyota and Mazda can also use these small auto generators as small luggable generators in no-auto applications (note Toyota are talking about one cylinder free piston units which can be doubled up for larger vehicles; just add another genny). Mazda has muttered about using wankels for luggable usages to keep production numbers up. The free piston and wankel designs are small and light, just what is needed for these applications. So, their investment will not be wasted by pouring millions into IC/genny R&D. When the auto industry sheds these range extending IC units and moves over to full EV there is always a market for these small generators, so R&D money is not wasted.

Edited by motorlad on Tuesday 13th January 11:32

[motorlad]

AER said:

Well, that's a great ad hominem. Normally people resort to such methods when their arguments have failed.

Some resort to insults when they are insecure and have failed arguments.

I am not arguing with you. Toyota on the first run got 42% and are confident of getting far more. Please do not bring up nonsense like the K series or large heavy diesel engines. Toyota's range extender is very small and light and can fit in a spare wheel well.

Read Max's and my posts again. You never got much of it.

Charging infrastructure will improve as EVs are introduced. I don't think anyone would be so foolish as to think it will stay static. Also, as EVs become more common, petroleum fuel distribution will tail down to the point it will be difficult to obtain roadside fuel, meaning large trucks will become EVs. The price of petroleum fuel will rise. Even ships may be hybrids with dockside charged battery banks and physically small range extenders. Large diesel engines take up valuable cargo/passenger space. Ship can be clad in solar panels.

AER said:

EVs will shine and 100 mile ranges will be a problem only in peoples heads rather than reality.

You got that right

Edited by motorlad on Tuesday 13th January 11:38

[motorlad]

amstrange1 said:

Clearly in something with poor EV-only range the ICE efficiency becomes more important, but in the i3 where the APU is a "limp-home" device, why burden the project with huge development costs to recover by re-inventing the wheel in the pursuit of every last drop of efficiency?

The i3's range extender is a cobbled together joke, it limps the car home. It is an old piston/crank motorbike engine. The Chevy Volt's range extender engine is an off-the-shelf motor not designed for such applications and is not fully suitable for the task in hand. Toyota and Mazda are looking at dedicated designs for specific applications; producing only electricity for range extending EV's.

Your attitude is not to advance and make do. I find this attitude and view too typical of the modern British. You are not alone. Most of the posts here are wanting to keep hopelessly inefficient 19th century technology going, shunning and sneering new developments. The British are a race that catapulted the word forward in technology at one time. Pretty sad really.

stevieturbo said:

Batteries are improving ???

Your Smart phone is a small palm sized computer. Look at the batteries we had 15 years ago. If you want only an old type cell "phone" to have a lasting battery, one is available. The battery can last for about a week or more.

Edited by motorlad on Tuesday 13th January 11:40

[motorlad]

Max_Torque said:

LOL, now we are into the realms of fantasy! Ships clad in "solar panels"?

You should really read the points put across which is not difficult rather than trying to mock advancement and be funny. 19,000 containers on one ship to Hull? Now that is funny. There is only about two in the world that size and they cannot get into Hull. Solar panels on ships can easily run the ship's ancillaries, using the batteries as a buffer.

Motorcycle engines with crankshafts will not have the efficiencies of a small free piston genny. Please keep up It looks like piston engines with cranks, hopelessly inefficient Victorian technology, will disappear. You may need a career change.

stevieturbo said:

Why dont they use the opposing pistons combustion to compress the other sides ?

Stevie, This is one way to return opposed pistons.
http://www.unimodengines.com/technical.html

Two levers and the gas is remote from the pistons in a shock absorber. The electrical coils can be in this remote cylinder. The levers can have stops to prevent pistons from crashing into each other or the ends of the cylinders.

What no one has noticed is that power is generated, via the electrical coils, on the downstroke "AND" the upstroke of the piston in the Toyota and Germany's "NASA" free piston generator engines. In a piston/crankshaft engine energy is only generated on every other one of the downstrokes in a 4-stroke cycle and only on the downstroke of a two-stroke cycle. Efficiency has to be greater.

amstrange1 said:

When we tried to buy one, the Lotus/Fagor engine wasn't available given its largely unvalidated status at the time. The inverter used with the system would be kindest to describe as motorsport-focussed, and was a long way behind some of the competition in terms of meeting accepted automotive standards.

Interesting. If you do not mind me asking, what were you wanting to do with this small light range extender?

Edited by motorlad on Tuesday 13th January 20:02

[motorlad]

amstrange1 said:

motorlad said:

The i3's range extender is a cobbled together joke, it limps the car home. It is an old piston/crank motorbike engine.

Scooter engine actually... Pedantry aside, it's reliable, proven technology -

It does not do the job and is antiquated technology.

amstrange1 said:

It's not about living in the dark ages, most of the OEMs have pretty innovative (and/or odd!) stuff happening behind closed doors

A pity we have not seen it and doubt we ever will.

Edited by motorlad on Tuesday 13th January 20:10

[motorlad]

Max_Torque said:

motorlad said:

Solar panels on ships can easily run the ship's ancillaries, using the batteries as a buffer.

You can put solar panels on the roof of your car, and charge the battery whilst it's parked,

Which is nowhere near the surface are that a ship offers. Please try. Please.
Your job is on the line. Once again you may need a career change.

Max_Torque said:

What everyone has noticed is that unfortunately you have no idea what you're talking about.

You deal with hopelessly inefficient, antiquated Victorian technology. Not only that you are a know-it-all who knows nothing. You cannot absorb simple points. When you are cornered, which is easy to do, you insult. If you know anything about propulsion you make a reasoned argument, however you cannot. You struggle even with simple concepts. You are a very negative person. Get yourself sorted.

You have little of electric generation.

Edited by motorlad on Wednesday 14th January 00:26

[motorlad]

Max_Torque said:

(The biggest frictional loss in any engine is the piston rings sliding again the bores under gas loading, something "Free piston" engines do nothing about).

A two-stroke free piston does not have the dead pumping loses of piston/crank arrangements. Anyone who knows about engines will tell you that. And power is generated on both strokes of the piston in Toyota's free piston engine. You cannot understand something so simple.

Get out the business. Have you tried delivering milk?

Edited by motorlad on Wednesday 14th January 00:44

[motorlad]

AER said:

motorlad said:

AER said:

Well, that's a great ad hominem. Normally people resort to such methods when their arguments have failed.

Some resort to insults when they are insecure and have failed arguments.

Indeed! It seems you're a past master at this.

You started the insults because you know little.

I am not arguing with you. Toyota on the first run got 42% and are confident of getting far more. The "first run" is bks is it. Prey tell. Now do make things up as you usually do.

You have been involved in running several prototype antiquated Victorian technology engines. No more.

I know exactly what power ships consume. Believe me.

Edited by motorlad on Wednesday 14th January 00:43

[motorlad]

AER said:

motorlad said:

two-stroke free piston does not have the dead pumping loses of piston/crank arrangements. Anyone who knows about engines will tell you that. And power is generated on both strokes of the piston in Toyota's free piston engine. You cannot understand something so simple.

Clearly power cannot be generated on both strokes of the two-stroke cycle even with the Toyota free piston engine magic applied.

But it is. When the piston returns it creates electrical power. That is obvious. Of course, the gas spring will absorb some energy but will throw the piston back up producing electrical power. No exploded fuel throws the piston back up, it is all from the energy released in the one combustion chamber at one end (in the Toyota engine). In a 4-stroke cycle in the antiquated technology you adore, three out of the four strokes are a complete drag adding to the hopeless efficiency.

Rectification is not a nightmare as free piston Stirlings do just this and are available on the market.

AER said:

Is this an insult or a recommendation?

Recommendation. You must be impressed by my English. Thank you.

Auntieroll said:

English teacher, his/her posts sound more like an English student!

Another one impressed. Thank you.

I clearly value modern engineering over "antiquated Victorian" engineering for sure. Not to see that the current piston/crank engines are an anachronism does display poor knowledge and ignorance. Please keep up with current events as you may have to change careers.

Thinking just slightly out of the box is something which is beyond some. That is sad.

Max_Torque said:

motorlad said:

Anyone who knows about engines will tell you that.

It is extremely clear that you know nothing about engines unfortunately.

Your lack of basic conceptual engineering thought I find amazing, especially from people who say they work in the business. That is sad.

Edited by motorlad on Wednesday 14th January 16:43

Edited by motorlad on Wednesday 14th January 16:45

[motorlad]

"The most difficult subjects can be explained to the most slow-witted man if he has not formed any idea of them already; but the simplest thing cannot be made clear to the most intelligent man if he is firmly persuaded that he knows already, without a shadow of doubt, what is laid before him."
-- Leo Tolstoy