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

[Boosted LS1]

What a very strange first posting, a 'hello' would have been a good start. Is this an advert or promo posting?

[TerzoNeil]

spam

[Transiter]

MX5.

[hacksaw]

Frozen sausages?

[anonymous-user]

The "inefficiency" in an internal combustion engine is NOT the turning of uppy downy into twisty turny.......

Free piston generators have been used for years on space craft, and in fact, where heavily patent protected until recently.


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

[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

[GavinPearson]

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.

[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.

[AER]

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.

[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.

[stevieturbo]

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 ?

I guess like a flat 2cyl engine would be, just with no crankshaft ?

But is the engine itself really any cleaner or efficient at producing electricity than conventional stuff ?

[AER]

motorlad said:

Hello, I am not sure what you mean by cost reduction. If in manufacturing then there is no crankshaft and conrods.

The crankshaft and conrods, whilst looking like relatively expensive parts, are still pretty cheap to make, or at least the industry has learned to make them cost-effectively.

motorlad said:

I am unaware of the risks involved you mention considering the application.

I'm sure you are unaware of the risks. This is the problem because the end user/OEM will also be unaware of the risks but will realize that they do exist and this will make them cautious in adopting the technology.

motorlad said:

They are clearly a leap in efficiency in the intended constant speed application

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

motorlad said:

The free piston engine I believe is licence free.

Noone promotes this kind of technology unless they a) can sell it to you more-or-less off-the-shelf, or b) want to fleece you for licence and royalty fees and leave you with the steaming turd to figure out how to monetize. Most "new engine technology" providers fall into category "b". Even some in category "a" haven't had much success in selling their wares - Pierburg's range extender seems to be an example of this, at least from what I can make out.

motorlad said:

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

So, if their efficiency isn't "much higher" and they turn out to be just like ordinary ICEs, but with novel and untried features, would this be a barrier? I think so.

[996TT02]

AER said:

motorlad said:

They are clearly a leap in efficiency in the intended constant speed application

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

I take it Toyota are also ignorant? It's all well and good countering an argument, but you need to back it up.

"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."

Please do so and contribute something interesting to this discussion. Seriously.

[AER]

42% thermal efficiency* is about 199g/kWh which is pretty much the best BSFC point of the VW 1.9 PD and earlier derivatives. This is nothing close to a "clear leap in efficiency" although it is quite good for only 10kW of power. Of course this was using (effectively) active radical combustion which has been played about with by many people for many years and has only been seen in the wild in some Honda motorcycles in the late '90s and nothing since.

So, the industry has been here for at least 20 years with their reciprocating engines. So, where was that great leap forward again, Chairman Mao?

(* all the other numbers quoted are just pipe dreams...)

Edited by AER on Monday 12th January 09:34

[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

[AER]

motorlad said:

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 of the setup. R&D will improve on that. The only complexity is the hydraulically activated poppet valves, which is not new. A piston/crack engine can only dream of that. Crankshafts, high pressure oil pumps, con-rods and all, cost and add great bulk and weight. Eliminating all that alone is a massive saving.

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

If you read my last post, you'd see that 42% thermal efficiency isn't anything new. In fact most diesel engines will easily achieve this on a test bench with no exhaust, no aftertreatment and no inlet silencing. In fact, you could probably make many gasoline engines run at 42% if you don't bother with emissions control. Even the humble K-series achieves nearly 34% when running stoichiometric! With some work, you'll pretty quickly get it to 42% at a single test point. A more appropriate design will probably get a little further, but when the gloves (regulatory constraints) are off, conventional technology can do some impressive stuff on the fuel consumption front!

Now, back to your free piston engine. Where did the power come from to operate the valves? If you think this happens for free, you're opening yourself up to more accusations of cluelessness. And, pray tell, how will R&D improve the thermal efficiency? Combustion engines are a very well understood science and any efficiency improvement will come from optimizing their useage profile (which is exactly what the hybrid drivetrain does - you won't get me being negative about this technology from an efficiency standpoint, by the way!) The peak thermal efficiency of combustion engines hasn't really changed much in decades, perhaps half a century!

[stevieturbo]

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

Any I've seen when driving about, the engine has always been running.

Seems a total waste creating massive pollution and energy waste claiming to build a clean car...when it always has its petrol engine running when driving about anyway !

I guess electric and hybrids have come a long way, but they really do have a massive way to go yet.
But finding a new more efficient or cleaner power source seems to be essential for powering any electric type vehicle.

Whatever happened gas turbine type generators ?

[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.