"Pistonless Engine" Used To Generate Electricity

[Sionyn]

thermodynamics efficiency aside this is a very cool step forward

[blerb]
"Now auto engineers are working to refine combustion power as part of cars that are increasingly electrified, including plug-in hybrids. Toyota's new 'Free Piston Engine Linear Generator' (or FPEG) shows us one potential way. Linear engines eliminate the rotating crankshaft of conventional engines in favor of a single chamber, in which a piston moves forward and backward"

http://www.greencarreports.com/news/1091794_toyota-describes-combustion-engine-that-generates-electricity-directly

[ludzinc]

"Pistonless Engine"

... in which a piston moves forward and backward"

 

[scientist]

More like "crankshaftless."

[Phaedrus]

"Pistonless Engine"

... in which a piston moves forward and backward"

 

Yeah, "pistonless" doesn't show up in the article at all.

[johansen]

wouldn't it make sense, given that it's a two stroke, that it be a two cylinder inline engine?

it would be interesting to see such an engine run away..

[harnon]

The boxer layout should be better for two cylinders (with no crankshaft) as by running them opposed the shaking inputs can cancel each other out.

I can't imagine why you'd ever want to run a single piston - it seems like it would be a rough ride and you may as well ride your bike for all the power you get

[tom66]

Why doesn't it generate power on the reverse stroke - is that an animation error?

[Wytnucls]

I don't think so. Back-EMF would probably be too strong for the trapped gas acting as a spring for the return stroke.

[vk6zgo]

Of course,the original posting was misnamed,but pistonless engines have been producing electricity for many years--Steam turbines,Gas turbines,etc.

"Free piston" engines have been around forever,but they normally  use the exhaust gases to drive a turbine.
Direct electricity generation?---maybe,but I'm not holding my breath!

[BennyBoy]

wouldn't it make sense, given that it's a two stroke, that it be a two cylinder inline engine?

No.

[calexanian]

I hear there is a bridge in Brooklyn for sale. 

[johansen]

wouldn't it make sense, given that it's a two stroke, that it be a two cylinder inline engine?

No.

please explain why.

I don't think so. Back-EMF would probably be too strong for the trapped gas acting as a spring for the return stroke.

do you know what back emf is?

if you pull too much energy out on the combustion stroke, there won't be enough energy to compress the gas, because the piston won't even make it all the way down the pipe.
if you don't pull enough out, you slam the piston into the bottom of the gas cylinder.
if the gas spring is over sized, then you can pull energy out both on the combustion stroke and the compression stroke, which is how i would build it.


2 cycles is great for proof of concept but if a two stroke engine could pass the emission standards, we wouldn't need hybrids.

[SeanB]

2 cycle with fuel injection, using oil free ceramic linings and ceramic pistons have been demonstrated. Only issue is the bore wear is not conducive to long life. They also have issues with seals and cooling the piston effectively.

A lot of large marine diesels are 2 stroke though, using a massive supercharger to pump the air into the cylinder, and have a large valve overlap to scavenge the combustion chamber effectively. Low emissions and twice the power of a 4 stroke engine in the same space. Of course top RPM is in the range where you can still see the valving open and count revolutions by hand.

[calexanian]

I am not going to hold my breath on this one.... Internal Combustion is still rather inefficient. Driving a emag coil directly may remove some of the other losses, but it is still not going to get any better with most of the energy leaving as heat out the exhaust! I still place my bet on the High Beta Fusion system Lockheed skunk works is building as the way to go in the future for clean energy production. That has all the sexieness.. High energy particle physics, plasma dynamics, magnetic focusing, small footprint, cheap plentiful fuel, no carbon emissions, and just a high cool factor. Just one the size of a truck trailer could replace a whole power plant!

[G7PSK]

Free piston engines have been used in compressors and water pumps since the 1920,s at least. There used to be a reservoir near Manchester I think that had a truly piston-less engine/pump that ran on gas and used water as the working medium in the cylinder.

[Hypernova]

Instead of air spring on one end why not another combustion chamber? I would imagine that the spring would become a limitation on the engine's cycle rate.

[harnon]

Toyota say two of these small engines will sustain 75MPH driving in a small or mid sized car. Obviously that will improve with development as time goes on, but even now it would make a great hybrid Yaris or Auris.

I calculate for a Toyota Prius about 11kW to maintain velocity at this speed due to air resistance alone. Typically above 50mph aero drag is greater than rolling resistance so yeah 20kW would likely be sufficient at this speed. The problem is you have to supply enough power to get to 75mph so you would need either a big hill or be a very patient person

Instead of air spring on one end why not another combustion chamber? I would imagine that the spring would become a limitation on the engine's cycle rate.

I can think of two possible issues. Firstly the double piston is likely to be quite long. To prevent this buckling or bending excessively then you'd need it to be quite chunky, and the excess mass would reduce efficiency. Secondly this would be an unbalanced engine as each piston would fire at different times in opposite directions. This can make for an uncomfortable ride or cause damage / failure of components.

A quick look on the SAE journal database to find the thermal efficiency of free piston engines shows people have been making these generators since the 90s! (SAE technical paper 1999-01-0619 looks interesting if you happen to have access) Using hydrogen and compression ignition a thermodynamic efficiency around 55% is possible, compared with peak efficiency around 40% on modern diesel/petrol engines.

So I know next to nothing about this... but Wikipedia leads me to believe the amount of electricity generated will rely on Maxwell's equation(s?) and the Lorentz Force? Does this mean that higher velocity will result in a larger dB/dt and hence more power being generated?

[electr_peter]

Such form of combustion engine and electric motor/generator integration is very promising. This leads to better use of space and material in vehicle plus load of additional functions:

• Crankshaft is eliminated
• Starter motor is not required to start engine
• Additional electric generator is not required (*)
• Any number of such engine modules could combine one engine block (**) or be operated at one time. Thus engine cooling and exhaust systems can be smaller in partial usage cases.
• There may be some advantages for engine combustion/efficiency/emissions
• Concept is well suited for hybrid cars

(*) - due to elimination of fixed linkage to wheels or gears from piston engine, some form of generator is required. However, electricity can be generated by electric motors during braking.
(**) - multiple engine blocks can be used in high performance cars.

[ajb]

Instead of air spring on one end why not another combustion chamber? I would imagine that the spring would become a limitation on the engine's cycle rate.

Perhaps, but if you're using this as part of a hybrid system with energy storage, you don't ever need to vary the engine's cycle rate; you simply turn it on when you need it and turn it off when you don't.  That's one of the benefits of series hybrids: because there's no mechanical coupling between the engine and the wheels you don't need to match the engine RPM to wheel RPM and the engine can always run at peak efficiency (or not run at all). 

On the other hand, as the engine temperature increases the gas spring pressure will naturally increase as well, so presumably the engine controller will need to adjust the quantity of fuel injected per cycle to control piston travel.  Notice those notches along the side of the cylinder--part of a linear encoder, I wonder?

[harnon]

   There may be some advantages for engine combustion/efficiency/emissions

For the CI versions in the SAE papers above NO was greatly reduced, but HC and CO increased due to lower combustion temperature.  I'm not sure about the SI version Toyota have designed as I don't see many technical details in the article.

EDIT: A link to a 1999 PhD thesis explaining some of the science.

[ConKbot]

For series hybrids/range extended hybrids, I dont see why gas-turbines arent used more.  Automotive turbochargers last plenty long with minimal service.  Add a combustor between the compressor and turbine, and in the exhaust stream, put a power turbine geared down as needed to run a generator.  Turbines arent good with rapid changes in speed and would be more happy turning on, running upto one speed, and sitting there for a while.   Perfectly suited for a range extended electric/volt-ish vehicle. No need for the engine to run at anything other than 100%  Its a mature technology (See gas turbine electric plants)  and obviously more efficient than diesel piston engines, hence why its preferred for big turbines.   Throw some R+D and scale of economy at it to make vehicle size ones commercially viable.  No need for wobbly pistons or other arm-wavy mechanical things. 

[electr_peter]

For series hybrids/range extended hybrids, I dont see why gas-turbines arent used more.  Automotive turbochargers last plenty long with minimal service.  Add a combustor between the compressor and turbine, and in the exhaust stream, put a power turbine geared down as needed to run a generator.  Turbines arent good with rapid changes in speed and would be more happy turning on, running upto one speed, and sitting there for a while.   Perfectly suited for a range extended electric/volt-ish vehicle. No need for the engine to run at anything other than 100%  Its a mature technology (See gas turbine electric plants)  and obviously more efficient than diesel piston engines, hence why its preferred for big turbines.   Throw some R+D and scale of economy at it to make vehicle size ones commercially viable.  No need for wobbly pistons or other arm-wavy mechanical things. 

I agree that there is potential for turbines in hybrids (investment is made into small turbine generators http://www.imeche.org/news/engineering/british-firm-wins-funding-for-micro-gas-turbine-car-engines)
Main advantage of of jet powered generators are power per weight ratio (main reason to use jet engines in air planes).
However, there are many problems to be solved. Low weight is an advantage, but that weight can accommodate more total volume (inlet, outlet, heat/noise isolation) than conventional solution.
Jet powered turbine generators are a bit more complicated than you describe - they have many moving parts, more than equivalent piston engines in case of more powerful units (part count increases because of compressor/turbine construction). Small jet engines use monolithic shafts of high precision, high quality bearings, oil and cooling systems - reliability issue comes to mind.
Also, precision and custom parts quickly adds up in cost. Big part of appeal for hybrid car is it running cost and price.

IFRC, British engineers constructed small jet turbine for Jaguar(10-20 years back), but it was not implemented at that time.

[Neverther]

You need to run turbines at their maximum rated load as they are most efficent there.
Abrams likes to drink a lot of fuel (factor the lower air density in deserts in). Leopard with similar power output use less fuel.

There is turbo compund which is used to run the exhaust power back into crankshaft, but that has no use in consumer applications as the efficency boost is rather small when compared to the cost.

When we are going to see high pressure heat engines back in action 

[scientist]

Jet engines are loud, high maintenance, and expensive; plus, the rotor blades have to be made of a specific nickel alloy which is neither robust nor cheap. Have you ever wondered why only Jay Leno owns a turbine powered car?

JP-1 is also hard to find and expensive compared to gasoline.

[G7PSK]

Turbine blades can be made from ceramics and small turbines can have the blade sets made as one unit, the problem is silencing them, no one wants the sound of Concorde going down the high street, big power plants have the space for large silencing structures which cars do not have, generating turbines also run the exhaust through a boiler plant to make steam which greatly improves efficiency again something you cant do on a car scale. You don't need JP 1 to run a gas turbine any combustible material will do, they have even been run on straw for experimental purposes, heating kerosene,diesel or petrol would be fine aviation fuel is expensive due to the requirements of having zero water content to prevent high altitude freezing not a requirement at ground level.