RE: [Vo]:Stirling engine used as a reactor
From: Roarty, Francis X * I think one of the little sterling [Stirling] models would make an interesting reactor platform where the Ni foam or skeletal cat is captive at the bottom of the cylinder and the hydrogen gas is sealed inside like the Papp engine – a sort of hybrid between only using exotic gases like Papp and the present Rossi or Mills device using pressurized gas with Ni powder or skeletal cat. Something like this, but not exactly - has been under discussion for a while in another context. It could possibly work with Ni-H as well, since the “trigger” temperature is achieved by gas compression during normal operation. This could work in what is known as the “double alpha” design, which has four pistons and forms what is essentially a complete loop. The single alpha configuration, nor the beta or gamma, probably would not work well, since the Carnot spread is narrow. In fact, this is close to what Papp should have done. As Fran will appreciate, the alpha design can provide what is high gas flow through Casimir cavities, when properly implemented. To the extent that the “T-effect” (excess heat from Ni-H) depends on cavity containment (even if that containment is only the first step in a two or three step thermal process) then this double alpha Stirling could be a preferred implementation over any other. If he was not a con-man from the start, then Papp’s design would have benefited from rudimentary knowledge of the thermodynamics of heat engines– leading many to suspect outright fraud. Since he used no effective external heat sink at all, in the sense that his pistons were sealed - his engine could never have been very reliable. I suspect that it did work, barely, despite the idiotic design, but for what is a completely different rationale than what Papp thought was going on… Oh well, another nutty inventor bites the dust. Figure 12.23 on the page below shows (almost) the proper type of Stirling engine component arrangement that I am talking about - the double alpha– which is the image with four double acting pistons (which would need to be connect mechanically on a single crankshaft but remain thermally isolated). The nickel - in the form of nickel sponge could serve as the four “regenerators” aka “recuperators” and any one of the four cylinders can serve as the heat sink. IOW - only one cylinder, the most forward-facing one in the car, needs to be water cooled using a radiator, as in the typical ICE - and the other three get progressively hotter in operation (with proper plumbing which is not shown) and those three would need to be made of ceramic or cermet to tolerate the heat. http://www.powerfromthesun.net/Book/chapter12/chapter12.html Jones
Re: [Vo]:Stirling engine used as a reactor
Interesting idea. Maybe when we master the ignition condition we could do something like a family explosion engine, based Piston technology. I can anticipate the 2 mode of ignition : - self ignition by pressure and temperature, like diesel - triggered ignition by catalyser (RF, manetic field, chemical injection, local temperature), like otto engine however the speed of the cycle might be much slower that diesel/otto IC engine (few turns per minutes) anyway maybe future LENr reactors will be very difefrents from now... should tell defkalion and rossi 8-) 2012/2/6 Roarty, Francis X francis.x.roa...@lmco.com I think one of the little sterling models would make an interesting reactor platform where the Ni foam or skeletal cat is captive at the bottom of the cylinder and the hydrogen gas is sealed inside like the Papp engine – a sort of hybrid between only using exotic gases like Papp and the present Rossi or Mills device using pressurized gas with Ni powder or skeletal cat. The shaft of the sterling engine would be externally driven to vary the pressure and then measure the temp variation of the cooling system. Fran
Re: [Vo]:Stirling engine used as a reactor
I am something of an expert in heat engines, I've worked in IC engine development, Brayton development, have built (for fun) Rankine cycle engines, and even an engine that ran on the expansion and contraction of solid metal. I've also been involved in the development of hydrogen working fluid stirling engines, and while they might look attractive there are big problems: -Very expensive and heavy ($1000/kW, 5-10kg/kW for kinematic engines (ie with crankshaft), $3000/kW, 20-30kg/kW for free piston engines that don't require external hydrogen seals) -Don't scale well to large sizes - as bigger means must run slower to keep gas flow losses the same. -Work best at much higher pressures than suitable for LENR (from what we know of Rossi) ie 150bar vs 25bar. Lower pressures mean much bigger heavier and less efficient engines. -Cannot have any powder or other detritus mixed in with the hydrogen working fluid - as it will quickly abrasively destroy your seals regenerators and coolers. -Seals for kinematic designs are unreliable and only last for a few 1000 hours at best. I don't think that stirling will be competitive with rankine or brayton cycles in terms of overall size, weight and cost for LENR applications. On 6 February 2012 17:35, Alain Sepeda alain.sep...@gmail.com wrote: Interesting idea. Maybe when we master the ignition condition we could do something like a family explosion engine, based Piston technology. I can anticipate the 2 mode of ignition : - self ignition by pressure and temperature, like diesel - triggered ignition by catalyser (RF, manetic field, chemical injection, local temperature), like otto engine however the speed of the cycle might be much slower that diesel/otto IC engine (few turns per minutes) anyway maybe future LENr reactors will be very difefrents from now... should tell defkalion and rossi 8-) 2012/2/6 Roarty, Francis X francis.x.roa...@lmco.com I think one of the little sterling models would make an interesting reactor platform where the Ni foam or skeletal cat is captive at the bottom of the cylinder and the hydrogen gas is sealed inside like the Papp engine – a sort of hybrid between only using exotic gases like Papp and the present Rossi or Mills device using pressurized gas with Ni powder or skeletal cat. The shaft of the sterling engine would be externally driven to vary the pressure and then measure the temp variation of the cooling system. Fran
RE: [Vo]:Stirling engine used as a reactor
From: Robert Lynn I've also been involved in the development of hydrogen working fluid stirling engines, and while they might look attractive there are big problems: -Very expensive and heavy ($1000/kW, 5-10kg/kW for kinematic engines (ie with crankshaft) That conclusion may be premature and short sighted, given the advantages. The high cost to date for Solar Stirling seems to more of a issue of mass production (lack thereof). Certainly, it can cost 10 to 100 times more to produce engines one-off or low volume now, compared to the typical automotive, robotically enhanced, engine production line. However, I see no ultimate impediment to this for the Stirling concept - once there is demand for millions per year. That kind of demand would be guaranteed if mated to a Ni-H heat source. The Solar 4-95 Stirling engine developed by United Stirling of Sweden, was as an outgrowth of an automotive engine development program - and is expensive due to low volume and the need for exceptional lifetime in operation, far more than any car. But they would not have gotten into it if there was a systemic problem that could not be overcome with higher demand and better engineering. IOW all of the negativity seems to be a short-horizon issue that can be resolved simply by high demand and a few workarounds. Except for hydrogen seals and the nickel, the cost of a converted ICE should be in the range of standard auto engines (if and when mass production is guaranteed). The easiest solution to the sealing problem (the workaround) is to live with it in the sense of providing only the simplest solution - the best O-rings, etc and then to utilize makeup H2 from onboard electrolysis. Only one liter of H2/min (or less) should be adequate for makeup of seal leakage in a 50 kW engine operating as a genset for a Prius style battery pack using standard sealing techniques for hydrogen. That amount of H2 used as a makeup would be parasitic for about 200 watts from the genset and is of no risk as a slow leak, due to the extraordinary mobility of H2. IOW this workaround solution is de minimis in terms of net value of an installed engine which does not demand fossil fuel. Moreover - it sounds like just the kind of objection that the OPEC petro-lobby would dream-up to thwart Stirling development at this critical stage. Jones
RE: [Vo]:Stirling engine used as a reactor
At the very core of my suggestion I was only trying to find an economical way to drive a piston back and forth to provide a very rapid and large change in gas pressure. Perhaps a magnetic linkage to a piston like a water pump for a fish tank would avoid the costly seals and then route the gas via metal tubing to a standard reactor. Although current researchers already utilize pressurized gas to coarsely control their reactors I am convinced that they underestimate the full potential of this mechanism for dynamic control of the reaction. An oscillating piston with controllable frequency and possibly pressure shunts to shape a pressure pulse with variable width and repetition frequency to drive the gases through the changes in NI geometry. I think a reaction that is being constantly cycled on and off is less likely to self destruct and will be easier to extract energy from then a constantly engaged but throttled back reaction. VR Fran From: Jones Beene [mailto:jone...@pacbell.net] Sent: Monday, February 06, 2012 1:51 PM To: vortex-l@eskimo.com Subject: EXTERNAL: RE: [Vo]:Stirling engine used as a reactor From: Robert Lynn I've also been involved in the development of hydrogen working fluid stirling engines, and while they might look attractive there are big problems: -Very expensive and heavy ($1000/kW, 5-10kg/kW for kinematic engines (ie with crankshaft) That conclusion may be premature and short sighted, given the advantages. The high cost to date for Solar Stirling seems to more of a issue of mass production (lack thereof). Certainly, it can cost 10 to 100 times more to produce engines one-off or low volume now, compared to the typical automotive, robotically enhanced, engine production line. However, I see no ultimate impediment to this for the Stirling concept - once there is demand for millions per year. That kind of demand would be guaranteed if mated to a Ni-H heat source. The Solar 4-95 Stirling engine developed by United Stirling of Sweden, was as an outgrowth of an automotive engine development program - and is expensive due to low volume and the need for exceptional lifetime in operation, far more than any car. But they would not have gotten into it if there was a systemic problem that could not be overcome with higher demand and better engineering. IOW all of the negativity seems to be a short-horizon issue that can be resolved simply by high demand and a few workarounds. Except for hydrogen seals and the nickel, the cost of a converted ICE should be in the range of standard auto engines (if and when mass production is guaranteed). The easiest solution to the sealing problem (the workaround) is to live with it in the sense of providing only the simplest solution - the best O-rings, etc and then to utilize makeup H2 from onboard electrolysis. Only one liter of H2/min (or less) should be adequate for makeup of seal leakage in a 50 kW engine operating as a genset for a Prius style battery pack using standard sealing techniques for hydrogen. That amount of H2 used as a makeup would be parasitic for about 200 watts from the genset and is of no risk as a slow leak, due to the extraordinary mobility of H2. IOW this workaround solution is de minimis in terms of net value of an installed engine which does not demand fossil fuel. Moreover - it sounds like just the kind of objection that the OPEC petro-lobby would dream-up to thwart Stirling development at this critical stage. Jones
Re: [Vo]:Stirling engine used as a reactor
If you have a few hundred million $ to put into stirling development then by all means have a go and see what you can do, but almost no-one who has actual experience of Stirling engines and their problems (and I know a fair number) would put their own money into developing them for automotive LENR. Phillips spent something like 1-2 billion over 30 years, NASA probably half that, GE, SES, STM, GE, USAB, Kockums, Sunpower, Stirling Biopower, Infinia, Microgen and lots of other smaller players have all also managed to each spend 10's - 100's of millions without every managing to create a product that was even half way to being commercially viable, primarily due to high manufacturing costs, but also intractable seal reliability issues. The Philips (then USAB then Kockums) 4-95 engine you talk of never had exceptional lifetime - at best it would only operate for 2-4000 hours only before the seals failed (though often failed earlier), though that is not something it is easy to learn through reading the literature - for some insight into these issues read the 1980s MOD I and MOD II reports from NASA. For comparison IC car engines typically manage 4000 hours or more, truck engines 10's of thousands of hours. The 4-95 (a Rinia/Siemens type 4 cylinder kinematic Stirling) is in fact the engine that was further developed and productionised by recently bankrupted SES. They were talking of making 50,000 of them at one point, but their manufacturing costs were still in the $15-20k range, and that is after they had demounted and centralised all of the expensive hydrogen re-compression and storage to reduce their unit cost (these systems add a lot of cost to any hydrogen stirling engine). Infinia's 3kW free piston engine is in the $10k range, but uses Helium not hydrogen. Optimistic estimates for mass production of the NASA 30kW (60kW peak, but very short life at power) automotive MOD I and MOD II engine developed during the 1980s typically ranged around the $5k mark, but would be far more expensive now due to inflation and greatly increased nickel and cobalt prices - as the SES experience attests. In large scale mass production the cost of a product generally comes down to a multiple of 2-4 times the material costs, the problem is that unlike cars for big and heavy Stirling engines large quantities of those materials are very expensive and difficult to work nickel and cobalt superalloys, and for free piston engines lots of expensive permanent magnets are also required. In terms of specific components the regenerators are extremely expensive ($1k) to make being formed out of sintered stacks of 100's of layers of 50µm stainless steel wire mesh. The heaters are a nightmare to make being 100's of superalloy tubes that typically can't be welded so must be vacuum braised together at high temps all with zero leaks. The coolers comprise 1000's of 1mm tubes brazed into large parallel flow heat exchangers, and all of these must be assembled in casings with zero porosity, in extremely clean conditions with seals that will reliably seal against leakage of high pressure hydrogen. All of these components must also withstand temperature extremes between -40 and +80°C in dirty, corrosive, high vibration environments for 10-20 years while never releasing hydrogen in a dangerous manner when in a confined space like a garage, and somehow also not creating excessive dangers when involved in a crash. As for recirculating hydrogen from leaking conrod seals, that is done anyway, but separating the oil out is difficult, and you need to oil cool and lubricate those pumping leningrader (PL) conrod seals so the bigger problem is that as the seals leak they also transport oil into the engine from the crankcase, leading to blocking of regenerators and carbon particles destroying the seals. So take an (optimistic) $10k 30kW 200kg Stirling + generator + very large radiators (need much cooler temps than IC engines) to the already heavy and expensive $5-10k electric powertrain and you can perhaps begin to see why stirling is such a non-starter for vehicles compared to: Rankine turbine generator + condenser that weighs perhaps 100kg (turbine and generator are smaller as operate at much higher speeds) and costs probably $3-5k when mass produced. Recuperated Brayton (like capstone C30) that weighs 100kg and costs about $5-10k when mass produced. On 6 February 2012 18:50, Jones Beene jone...@pacbell.net wrote: *From:* Robert Lynn ** ** I've also been involved in the development of hydrogen working fluid stirling engines, and while they might look attractive there are big problems: -Very expensive and heavy ($1000/kW, 5-10kg/kW for kinematic engines (ie with crankshaft) ** ** That conclusion may be premature and short sighted, given the advantages.* *** ** ** The high cost to date for Solar Stirling seems to more of a issue of mass production (lack thereof). Certainly, it can cost 10 to 100 times more to
Re: [Vo]:Stirling engine used as a reactor
Now forgetting about stirling... So you clearly thing that with today's technology, using a turbine is a realistic solution for a serial hybrid vehicle ? what is the minimum realistic power of a turbine, at 400C, at 600C ? is 10-15kW mechanic reasonable? which effciency ? is 50kW mechanic reasonable... which efficiency ? will organic rankine turbine have any interest à 400C ? 600C? for cooling faster? note that about the problem I see two tracks for hope : - when the car goes fast, it consume much heat, but air flow can be used to cool quickly... if going slower, need less power... could even use a fan... - second if thermal evacuation is a problem, maybe on could design the car to be a good radiator does it seems reasonable ? 2012/2/6 Robert Lynn robert.gulliver.l...@gmail.com So take an (optimistic) $10k 30kW 200kg Stirling + generator + very large radiators (need much cooler temps than IC engines) to the already heavy and expensive $5-10k electric powertrain and you can perhaps begin to see why stirling is such a non-starter for vehicles compared to: Rankine turbine generator + condenser that weighs perhaps 100kg (turbine and generator are smaller as operate at much higher speeds) and costs probably $3-5k when mass produced. Recuperated Brayton (like capstone C30) that weighs 100kg and costs about $5-10k when mass produced.
RE: [Vo]:Stirling engine used as a reactor
From: Robert Lynn * * If you have a few hundred million $ to put into Stirling development then by all means have a go and see what you can do, but almost no-one who has actual experience of Stirling engines and their problems (and I know a fair number) would put their own money into developing them for automotive LENR. Of course it makes no sense to use a Stirling for fossil-fuel powered automotive, given the sunk cost in the ICE - and NONE of these companies you mention presently believe that LENR can provide low cost heat. So you are conflating two distinct issues that do not mix well. Once you get over that hurdle - that LENR is valid, then the Stirling makes a lot of sense, compared to other alternatives like steam - but not to be implemented by aerospace companies, whose cost structure is not competitive with the automotive arena by a wide margin. No one can disagree with you that the Stirling make little economic sense to use with fossil fuel, but we can all agree that this fact is irrelevant to anything related to LENR, other than that it represents an added risk, when most companies want to avoid risk, and especially when LENR is not proved. Even with solar, where the Stirling has not worked out yet -that is due to greed and mismanagement more than anything else, combined with a massive drop in PV pricing. Stirling Energy Systems (SES) filed for bankruptcy after failing to obtain financing for massive projects that were boondoggles to begin with. This is part of the same Solyndra, SpectraWatt and Evergreen scams, where billions of taxpayer dollars was wasted by entrepreneurs, most of them former DoE staff - who came out smelling like a rose. The absurdly high cost of manufacturing of the SES engines were actually the crux of the problem that was never adequately addressed by competitive bidding. They expected DoE to step in bail them out, and for once this did not happen. The Stirling technology is valid, and the Chinese will once again seize our missed opportunity and optimized the Stirling for solar - and maybe for LENR as well - by producing those same $20,000 reciprocating engines for less than the $5,000 that should have been our goal to begin with. All these technical issues are solvable, but you have to desperately want to solve them; and China is in that position, since they have little oil. whereas the USA and even GB are only moderately committed, due to having just the right amount of oil (to maximize incomes of oil barons and politicians) - and also by having well-placed technology manipulators - who would love nothing more than to see LENR and a Stirling implementation of it be delayed as long as possible. Jones
Re: [Vo]:Stirling engine used as a reactor
OK Ignore the fuel price. In work that has been done on exhaust heat recovery (where the heat is effectively free and temps 4-600 degrees C) for trucks and cars Rankine is popular (eg BMW with steam), and Brayton too (many trucks and ships use turbocompounding, recovering power from the turbine of a turbocharger, F1 will as well from next year), but I have never seen anyone try to use Stirling. If you just look at the weight of a hybrid car LENR engine; stirling vs rankine vs brayton turbine the stirling is by far the heaviest, has the lowest operating speed (so bigger generator, belt or gearbox required), has a large number of high tolerance components, is made from high cost materials, has known issues with reliability, needs very large radiators, and needs a system for re-compressing leaked hydrogen. Which do you think will end up being cheapest to put in a car? I couldn't pick between Brayton and Rankine: Brayton (recuperated or not) probably has lower efficiency (10-20%), with lower density working fluid for heat transfer meaning large heat exchangers with large pressure differentials (ie big and heavy), very high bearing speeds a hassle, but no condenser required. Rankine, small, light, dense high pressure working fluid = compact boiler and engine (turbine or reciprocating), good efficiency (15-25%), but likely a large condenser. But what I am very sure of is that it won't be Stirling, even if it can manage 35% efficiency, it simple misses on too many other cost, weight and size factors. On 6 February 2012 22:39, Jones Beene jone...@pacbell.net wrote: *From:* Robert Lynn **Ø ** **Ø **If you have a few hundred million $ to put into Stirling development then by all means have a go and see what you can do, but almost no-one who has actual experience of Stirling engines and their problems (and I know a fair number) would put their own money into developing them for automotive LENR. ** ** Of course it makes no sense to use a Stirling for fossil-fuel powered automotive, given the sunk cost in the ICE - and NONE of these companies you mention presently believe that LENR can provide low cost heat. So you are conflating two distinct issues that do not mix well. ** ** Once you get over that hurdle – that LENR is valid, then the Stirling makes a lot of sense, compared to other alternatives like steam - but not to be implemented by aerospace companies, whose cost structure is not competitive with the automotive arena by a wide margin. ** ** No one can disagree with you that the Stirling make little economic sense to use with fossil fuel, but we can all agree that this fact is irrelevant to anything related to LENR, other than that it represents an added risk, when most companies want to avoid risk, and especially when LENR is not proved. ** ** Even with solar, where the Stirling has not worked out yet –that is due to greed and mismanagement more than anything else, combined with a massive drop in PV pricing. Stirling Energy Systems (SES) filed for bankruptcy after failing to obtain financing for massive projects that were boondoggles to begin with. This is part of the same Solyndra, SpectraWatt and Evergreen scams, where billions of taxpayer dollars was wasted by “entrepreneurs”, most of them former DoE staff - who came out smelling like a rose. ** ** The absurdly high cost of manufacturing of the SES engines were actually the crux of the problem that was never adequately addressed by competitive bidding. They expected DoE to step in bail them out, and for once this did not happen. ** ** The Stirling technology is valid, and the Chinese will once again seize our missed opportunity and optimized the Stirling for solar – and maybe for LENR as well - by producing those same $20,000 reciprocating engines for less than the $5,000 that should have been our goal to begin with. ** ** All these technical issues are solvable, but you have to desperately want to solve them; and China is in that position, since they have little oil… whereas the USA and even GB are only moderately committed, due to having just the right amount of oil (to maximize incomes of oil barons and politicians) - and also by having well-placed technology manipulators - who would love nothing more than to see LENR and a Stirling implementation of it be delayed as long as possible. ** ** Jones ** **
Re: [Vo]:Stirling engine used as a reactor
Capstone started out developing recuperated turbines for hybrid cars in the late 80's (NoMac), I think they were originally aiming for about 25kW and 30kg (old SAE paper), but that crept up (weight especially) over time, and I believe their C30 weigh more like 100kg with 30kW output at 26% efficiency now. 30kW is ideal for a mid-sized hybrid car - as it allow you to drive indefinitely on a flat road at 120km/hr Capstone C30 achieves about 26% efficiency with the extra gas flow and higher specific heat of burnt fuel going through the turbine as well as relatively low pressure losses through the combustor and relatively high combustion temperatures of 800+ deg C. Brayton and Recuperated Brayton turbines are extremely sensitive to combustion temp and pressure losses so if the peak temp drops to 500-600deg C and you have significant pressure losses in heating the air going through the combustor as well as reduced turbine mass flow and specific heat compared to compressor flow then I expect the overall efficiency to drop to probably below 20% for recuperated and probably only 10-13% for unrecuperated (like Bladeon). Though these are only guesses, and you can compensate for lower efficiency with bigger heavier and more expensive recuperators and hot end heat exchanger to get higher temps, there will be an economic ideal for a cheap heat source like LENR. On 6 February 2012 22:30, Alain Sepeda alain.sep...@gmail.com wrote: Now forgetting about stirling... So you clearly thing that with today's technology, using a turbine is a realistic solution for a serial hybrid vehicle ? what is the minimum realistic power of a turbine, at 400C, at 600C ? is 10-15kW mechanic reasonable? which effciency ? is 50kW mechanic reasonable... which efficiency ? will organic rankine turbine have any interest à 400C ? 600C? for cooling faster? note that about the problem I see two tracks for hope : - when the car goes fast, it consume much heat, but air flow can be used to cool quickly... if going slower, need less power... could even use a fan... - second if thermal evacuation is a problem, maybe on could design the car to be a good radiator does it seems reasonable ? 2012/2/6 Robert Lynn robert.gulliver.l...@gmail.com So take an (optimistic) $10k 30kW 200kg Stirling + generator + very large radiators (need much cooler temps than IC engines) to the already heavy and expensive $5-10k electric powertrain and you can perhaps begin to see why stirling is such a non-starter for vehicles compared to: Rankine turbine generator + condenser that weighs perhaps 100kg (turbine and generator are smaller as operate at much higher speeds) and costs probably $3-5k when mass produced. Recuperated Brayton (like capstone C30) that weighs 100kg and costs about $5-10k when mass produced.
Re: [Vo]:Stirling engine used as a reactor
It will interesting to see what the future has to offer regarding automobile powering. Maybe the Stirling design is a non starter for the first generation of vehicles, but may come on strong later. My crystal ball is cloudy at the moment, but I usually expect to see the simplest solution to be the one that gets the race started. I wonder if a small turbine drive for each wheel that is centrally controlled might be the solution. Each power unit could then be quite small and easy to handle in manufacturing. All wheel drive of this type should be an excellent sales feature as well. We need to think out of the box as much as possible as we ponder the overall system design. What would the vort think of having a GPS system on board that is sent data about the traffic flow at the current location? The vehicle thus throttles back the LENR device to have the power required for the existing conditions. Perhaps in this manner there would not be a major problem with dumping excess heat. Of course a hydraulic or steam powered fan could be used for the heat dumping at stops. Or consider a steam storage tank that is sized to store the carefully metered amount of steam required for the traffic and immediate needs. I think that the total traffic system might be utilized as we proceed with these new products to make them perform much better than existing concepts. Dave -Original Message- From: Robert Lynn robert.gulliver.l...@gmail.com To: vortex-l vortex-l@eskimo.com Sent: Mon, Feb 6, 2012 7:56 pm Subject: Re: [Vo]:Stirling engine used as a reactor OK Ignore the fuel price. In work that has been done on exhaust heat recovery (where the heat is effectively free and temps 4-600 degrees C) for trucks and cars Rankine is popular (eg BMW with steam), and Brayton too (many trucks and ships use turbocompounding, recovering power from the turbine of a turbocharger, F1 will as well from next year), but I have never seen anyone try to use Stirling. If you just look at the weight of a hybrid car LENR engine; stirling vs rankine vs brayton turbine the stirling is by far the heaviest, has the lowest operating speed (so bigger generator, belt or gearbox required), has a large number of high tolerance components, is made from high cost materials, has known issues with reliability, needs very large radiators, and needs a system for re-compressing leaked hydrogen. Which do you think will end up being cheapest to put in a car? I couldn't pick between Brayton and Rankine: Brayton (recuperated or not) probably has lower efficiency (10-20%), with lower density working fluid for heat transfer meaning large heat exchangers with large pressure differentials (ie big and heavy), very high bearing speeds a hassle, but no condenser required. Rankine, small, light, dense high pressure working fluid = compact boiler and engine (turbine or reciprocating), good efficiency (15-25%), but likely a large condenser. But what I am very sure of is that it won't be Stirling, even if it can manage 35% efficiency, it simple misses on too many other cost, weight and size factors.
