Will MHD generators replace ICE?

[Moreno]

What do you think about perspectives of MHD generators to replace ICE in series hybrids as a range extender? May it ultimately happen?

[Frank]

Only if efficiency, weight and cost are better than alternatives.  Best I can tell, ICE is best now and fuel cells next if cost and weight come down.

 

Hadn't heard of MHD: https://en.wikipedia.org/wiki/Magnetohydrodynamic_generator#Generator_efficiency

 

Edited December 16, 2017 by Frank

[Moreno]

30 minutes ago, Frank said:

Only if efficiency, weight and cost are better than alternatives.  Best I can tell, ICE is best now and fuel cells next if cost and weight come down.

 

Hadn't heard of MHD: https://en.wikipedia.org/wiki/Magnetohydrodynamic_generator#Generator_efficiency

 

In my understanding power to weight ratio of MHD generator is much better than ICE/fuel cells. What is about cost? Is it too high? This one work assumes MHD generators can reach 60-65% efficiencies ultimately. Carnot efficiency at 1.500 C suppose to be around 80% and 90% at 3000 C hot sink and 300 C exhaust temperature.

http://veprints.unica.it/616/1/PhD_Roberto_Pintus.pdf

Edited December 16, 2017 by Moreno

[Frank]

MHD is interesting and I'll look into it more, but for this application, it looks like conversion of fossil fuel to laser energy would be inefficient.  Nuclear reactors - too heavy (among other issues).  Brayton cycle needs a regenerator and heat exchangers are always heavy - why turbines tend to weight more than ICE.  Take these as hints/pointers for what to look for as show stoppers, I'm just responding from memory of the research I did for that same application.

Come to think of it, in the ICE category, free-piston engine (or similar integrated generator/engine) generators are coming soon.

 

[Moreno]

23 minutes ago, Frank said:

MHD is interesting and I'll look into it more, but for this application, it looks like conversion of fossil fuel to laser energy would be inefficient.  Nuclear reactors - too heavy (among other issues).  Brayton cycle needs a regenerator and heat exchangers are always heavy - why turbines tend to weight more than ICE.  Take these as hints/pointers for what to look for as show stoppers, I'm just responding from memory of the research I did for that same application.

Come to think of it, in the ICE category, free-piston engine (or similar integrated generator/engine) generators are coming soon.

 

Free piston engines aren't bad, but coming late. I guess there have to be plenty of problems too. What do you mean under: "converting fossil fuel to laser energy"? Where did you take it from? I'm not sure MHD generator has to be based on Bryton cycle and requires regenerators. Better it would be a one stage cycle with relatively "cool" exhaust.

[Frank]

I glanced at the link you posted which has efficiency at 70% conflicting with wiki's (presumably more recent than 1987) 22%.  The link has MHD as the receiving end of a laser transmission system for power transmission which was one way of efficiently producing plasma (that's interesting).  Other ways are to use heat from nuclear to create liquid metal (LMMHD) and there is mention of brayton cycle or rankine cycle.  Maybe I didn't read it right?

Let's go the other way, maybe you can explain further how MHD would be used with fossil fuel - create a plasma flow somehow, but how is the plasma energy recovered once it passes the MHD generator?

 

[Moreno]

32 minutes ago, Frank said:

I glanced at the link you posted which has efficiency at 70% conflicting with wiki's (presumably more recent than 1987) 22%.  The link has MHD as the receiving end of a laser transmission system for power transmission which was one way of efficiently producing plasma (that's interesting).  Other ways are to use heat from nuclear to create liquid metal (LMMHD) and there is mention of brayton cycle or rankine cycle.  Maybe I didn't read it right?

Let's go the other way, maybe you can explain further how MHD would be used with fossil fuel - create a plasma flow somehow, but how is the plasma energy recovered once it passes the MHD generator?

 

1) Probably it wasn't a correct link.

2) Probably we would need to ionize exhaust components somehow. For example, use electric discharges, lasers, electron beam or rf waves of certain frequencies to get relatively "cold" plasma at 2000-2500 C. If we would succeed to ionize 1/1000 of exhaust atoms it would be regarded as a relatively well conducting plasma.

The key is to make it well conducting at nearly any temperature and we would need some external impact for this. 

[Frank]

Still seems more efficient to run a magnet pushed by a piston through a coil of wire or convert fuel directly to electricity through a fuel cell.  Maybe this would make an efficient power take-off for jet engines?

 

[Moreno]

5 minutes ago, Frank said:

Still seems more efficient to run a magnet pushed by a piston through a coil of wire or convert fuel directly to electricity through a fuel cell.  Maybe this would make an efficient power take-off for jet engines?

 

MHD gen. doesn't need a lubrication system in comparison to free piston and hence no oil filter or oil changes, no friction looses. It may not need cooling system as well, if made of tungsten or ceramics. Hence no radiator, no cooling energy looses. No moving parts. No noise or vibration. I'm not sure what efficiency fuel cells can reach, if they use methanol, gasoline or other hydrocarbon fuel. Perhaps not higher than 20%? And definitely they are bulkier, more fragile and expensive.

[Frank]

It helps to have the right link...   I guess I responded too fast and got the wrong link.

If figure 1.8 of http://veprints.unica.it/616/1/PhD_Roberto_Pintus.pdf is representative, I think the heat exchangers will make this too bulky and heavy for automotive applications.  If someone figures out a way around that, it would be better.  The 90% efficiency upper bound is enticing.

Vibration in ICE can be cancelled and oil changes are infrequent because there is no side force on the pistons in the free-piston style engines.  I'm hoping fossil fuels won't be needed in the future for automotive use because of better battery technology.

 

[Moreno]

11 hours ago, Frank said:

If figure 1.8 of http://veprints.unica.it/616/1/PhD_Roberto_Pintus.pdf is representative, I think the heat exchangers will make this too bulky and heavy for automotive applications.  If someone figures out a way around that, it would be better.  The 90% efficiency upper bound is enticing.

Vibration in ICE can be cancelled and oil changes are infrequent because there is no side force on the pistons in the free-piston style engines.  I'm hoping fossil fuels won't be needed in the future for automotive use because of better battery technology.

 

1) Heat exchangers indicate hot exhaust and therefore poor plasma conductivity at relatively moderate temperatures. Those are older designs, definitely some ways around it have to be found. Some ways to obtain "cold plasma". 

2) I afraid you will need to wait for a long time. For now no researchers do even envision electrically rechargeable batteries which could closely compete with fossil fuels in energy density. Therefore range extenders will be topical in the nearest 50 years at least.

[Moreno]

I have a question to a specialists in MHD generation. There exist some claims that degree of interaction between flowing molecules (gases) and ions on one hand and flowing molecules (gases) and electrons on other hand is vastly different. Therefore movement of ions in a gas flow will occur much faster than movement of free electrons. If this is correct then why we need to use a strong magnets to separate ions and electrons in MHD generator? If speed of the ions and electrons movement in the same gas flow is vastly different then doesn't charge separation suppose to occur by itself just due to a gas flow? Shouldn't majority of electrons concentrate at the beginning of the duct while many more ions at the end? Then only thing we need to generate current is to put an electrode at the beginning of the duct and another one at the end and let electrons flow from the inside of the duct through the external load to the end of the duct and recombine with ions there? And no need for a magnets.

[Ken Fabian]

What do the proposed MHD devices use as fuel/energy? The Wikipedia description fails to say where the energy required is coming from; they must be powered with something. I admit I don't really understand how these are expected to work as automobile "engines".

In any case I think it is not ICE vehicles that it must prove significantly better than; MHD will struggle to compete with battery electric - which, for all the well known limitations, appears well capable of delivering enough range for most practical purposes, with fast charge stations becoming common enough and fast enough that long trips are not being found to be problematic. Everyday commuter use charging is mostly a matter of plugging in when garaged, saving time, not adding to it - and added up, most ICE vehicle users spend more time refueling than EV users spend waiting at charge stations.

 300 - 500 km range is common (not far short of range with many ICE cars) and over 600 km (390 miles) is already commercially available; any significant improvements in battery energy density (and I think we will see improvements) will extend that.

I think the range "problem" for EV's, like the related battery energy density issue, is getting overstated. 

It does seem likely that most Tesla EV's will manage more than 500,000 miles/800,000km with reduced but still useful range without battery replacement - longer than we could expect an ICE drive train to last. Tesla is claiming improved batteries are being developed - not greater range if I understand it, but longer life, up to 1,000,000 miles/1,600,000 km.

Any competing technology has a high - and continually rising - bar to get over.

Edited March 2, 2020 by Ken Fabian

[Moreno]

10 hours ago, Ken Fabian said:

1) What do the proposed MHD devices use as fuel/energy? The Wikipedia description fails to say where the energy required is coming from; they must be powered with something. 2) I admit I don't really understand how these are expected to work as automobile "engines".

3) In any case I think it is not ICE vehicles that it must prove significantly better than; MHD will struggle to compete with battery electric - which, for all the well known limitations, appears well capable of delivering enough range for most practical purposes, with fast charge stations becoming common enough and fast enough that long trips are not being found to be problematic. Everyday commuter use charging is mostly a matter of plugging in when garaged, saving time, not adding to it - and added up, most ICE vehicle users spend more time refueling than EV users spend waiting at charge stations.

 300 - 500 km range is common (not far short of range with many ICE cars) and over 600 km (390 miles) is already commercially available; any significant improvements in battery energy density (and I think we will see improvements) will extend that.

I think the range "problem" for EV's, like the related battery energy density issue, is getting overstated. 

It does seem likely that most Tesla EV's will manage more than 500,000 miles/800,000km with reduced but still useful range without battery replacement - longer than we could expect an ICE drive train to last. Tesla is claiming improved batteries are being developed - not greater range if I understand it, but longer life, up to 1,000,000 miles/1,600,000 km.

Any competing technology has a high - and continually rising - bar to get over.

1) I think MHD's can be flexi-fuel. They can work on hydrogen, methane, perhaps LPG or even gasoline or ethanol. 

2) You take it too literally. It could work as a generator and charge a battery. Then run an electric motor. A system could be similar to what is used in Chevy Volt. But MHD could be even more compact than ICE generator and have higher efficiency for the absence of moving parts, liquid cooling and lubricating systems.

3) I think a reasonable person has to look at plug-in's together with EV's in the nearest 50 years. What is the price and weight of a Li-ion battery that allows to drive Tesla for 500 km? Perhaps not all people want or can afford it? Plug-in's on other hand give a small range anxiety and allow to ride on electricity 90-95% of time. 

Edited March 2, 2020 by Moreno

[Ken Fabian]

@Moreno With EV's nudging 5% of new passenger vehicle sales - and the strongest growing section of the market - they are well ahead of MHD powered vehicles at 0%. This would not be the case if battery powered vehicles did not work satisfactorily now - and they will almost certainly work even better and be cheaper in 10 years time, let alone 50.

Battery technology is still improving and does not need to approach the energy densities of hydrocarbon fuels to work more than well enough. EV's also complement growing levels of Renewable Energy very well and are likely to become fully integrated into home energy systems as well as electricity grids;  a single connected EV can be backup power to a home but a million connected EV's can be backup power for a city. Just responsive, smart scheduling of charging makes them a means of load levelling for stability for electricity networks.

If it is to be zero emissions MHD needs fuels that are zero emissions - renewable Hydrogen or bio-ethanol? Synthetic fuels made with RE? Higher efficiencies for fossil fuel use has serious limits with respect to emissions reductions - it can be a transitional option but is not a solution. I'm not convinced bio-ethanol is going to be a significant fuel replacement and Hydrogen (if/when MHD beats fuel cells, that are also subject to continuing improvement) as transport fuel is struggling to gain traction.

Our transport technology choices cannot be independent of the need to reduce emissions - and that requirement is running on a shorter time frame than 50 years.

[Moreno]

7 hours ago, Ken Fabian said:

This would not be the case if battery powered vehicles did not work satisfactorily now - and they will almost certainly work even better and be cheaper in 10 years time, let alone 50.

 

Cheaper in 10 years - unlikely. They will struggle to do it in 50. Plug-in's consume 5-10% of what regular non-hybrids do. I think it could be sufficient emission cut measure in the nearest 100 years even if they will run on fossil fuels. But there suppose to be enough ethanol or bio-methane to power them all.

Edited March 3, 2020 by Moreno

[Moreno]

Possibly plug-in technology is not exactly there yet. Chevy Volt is capable to run just 85 km on electricity at best. I'm looking at the plug-in's with 200 km electric-only range. Definitely they will need to release some much cheaper and energy dense batteries than Li-ion to make them affordable. Possibly zinc-air or sodium-sulfur?

Edited March 3, 2020 by Moreno

[swansont]

On 3/3/2020 at 6:13 AM, Moreno said:

Possibly plug-in technology is not exactly there yet. Chevy Volt is capable to run just 85 km on electricity at best. I'm looking at the plug-in's with 200 km electric-only range. Definitely they will need to release some much cheaper and energy dense batteries than Li-ion to make them affordable. Possibly zinc-air or sodium-sulfur?

The Volt is a hybrid, so it’s not optimized for longer range electri-only. But there are cars that are

https://en.wikipedia.org/wiki/List_of_modern_production_plug-in_electric_vehicles

[Moreno]

1 hour ago, swansont said:

The Volt is a hybrid, so it’s not optimized for longer range electri-only. But there are cars that are

https://en.wikipedia.org/wiki/List_of_modern_production_plug-in_electric_vehicles

Still Chevy Volt does have the longest claimed range on this list among PHEVs. The rest (with longer electric range) are BEVs or fully electric. BEV stands for Battery Electric Vehicle. Typically they have no hybrid capability. I don't expect that majority of customers will choose all-electric in the nearest decades.

Edited March 4, 2020 by Moreno

[swansont]

1 hour ago, Moreno said:

Still Chevy Volt does have the longest claimed range on this list among PHEVs. The rest (with longer electric range) are BEVs or fully electric. BEV stands for Battery Electric Vehicle. Typically they have no hybrid capability. I don't expect that majority of customers will choose all-electric in the nearest decades.

Yes, that’s the point - you don’t maximize the electric capacity for a hybrid. But you framed this as plug-in technology. BEVs are plug-in technology 

[Moreno]

2 hours ago, swansont said:

Yes, that’s the point - you don’t maximize the electric capacity for a hybrid. But you framed this as plug-in technology. BEVs are plug-in technology 

Sorry if I'm wrong but the term "plug-in" is commonly reserved for hybrids only. In contrast to all-electric BEVs. I used it accordingly to tradition. Currently the longest electric range among plug-in hybrids on the wide market is 85 km. But I suggested in the future it may increase to 200 km. In this case plug-in hybrids may be able to run 95% of total time on electricity. And still will relieve the drivers from range anxiety and necessity to charge them fast. 

Edited March 4, 2020 by Moreno

[swansont]

2 hours ago, Moreno said:

Sorry if I'm wrong but the term "plug-in" is commonly reserved for hybrids only. In contrast to all-electric BEVs. I used it accordingly to tradition. 

The article I linked to disagrees, as well as the sources cited within. Plug-in means you can plug it in.

 

[Ken Fabian]

GM just committed 20 billion USD to new battery electric vehicles, including a joint battery plant with LG Chem. They hope to bring down battery costs with reduced Cobalt/reduced cost chemistry in pouch cells. They intend to build battery electric vehicles with plug in (level 2 240V?) charging as well as Fast Charging. They are talking "could be" 400+ mile range.

 

Whoever invents seriously better batteries will become rich beyond all imagination and there is a lot of active R&D.

 

[Moreno]

Also MHD could be used on the power plants or for generation in remote areas where is no wires. Portable generation.

Quote

They hope to bring down battery costs with reduced Cobalt/reduced cost chemistry in pouch cells.

I have doubts they will bring them down much. All kind of Li-ion are quite expensive. Even contra, some manufacturers are planning switch to solid-state Li-ion or monolith-crystal cathode (like Elon Musk) in the future, what doesn't look cheap at all.

Edited March 5, 2020 by Moreno

[Moreno]

Can someone explain how MHD can work on electrolyte solutions similar to a salt water? If there is no free electrons but only positive and negative ions than what runs through the external circuit to generate power?