My favorite fuel cells burn hydrogen-rich hydrocarbon fuels, like methane (natural gas) instead of pure hydrogen. Methane is far more energy dense, and costs far less than hydrogen per energy content. The US has plenty of methane and has pipelines that distribute it to every city and town. It’s a low CO2 fuel, and we can lower the CO2 impact further by mixing in hydrogen to get hythane. Elon Musk has called hydrogen- powered fuel cells “fool cells”, methane-powered fuel cells look a lot less foolish. They easily compete with his batteries and with gasoline. Besides, Musk has chosen methane as the fuel for his proposed starship to Mars.
Solid oxide fuel cells, SOFCs, can use methane directly without any pre-reformer. They operate at 800°C or so. At these temperatures, methane reacts with water (steam) within the fuel cell to form hydrogen by the reaction, CH4 + H2O –> 3H2 + CO. The hydrogen, and to a lesser extent the CO is oxidized in the fuel cell to create electricity,, but the methane is not 100% consumed, generally. Unused methane, CO, and some hydrogen exits a solid oxide fuel cell along with the products of combustion, CO2 and water.
Several researchers have looked for ways to recycle this waste fuel to capture the energy value. Six years ago, I patented a membrane method to extract the waste fuel and recycle it, see a description here. I now see this method as too complex, and have applied for a patent on a simpler version, shown below as Figure 1. As before the main work is done by a membrane but here I dispense with the water gas shift reactor, and many of the heat exchangers of the previous approach.
Simple way to improve fuel use in a high temperature fuel cell, using just a membrane.
The fuel cell system of Fig. 1 operates at somewhat elevated pressure, 2 atm or more. It is expected that the majority of the exhaust going to the membrane will be CO2 and water. Most of this will pass through the membrane and will exhaust to the air. The rest is mixed with fresh methane and recycles to the fuel cell. Despite the pressure of the fuel cell, very a little energy is needed for recirculation since the methane does not go through the membrane. The result is a light, simple, and energy efficient process. If you are interested, please contact me at REB Research. Or you can purchase the silicone membrane module here. Alternately, see here for flux information and other applications.
A hydrogen molecule consists of two protons held together by a covalent bond. One way to think of such bonds is to imagine that there is only one electron is directly involved as shown below. The bonding electron only spends 1/7 of its time between the protons, making the bond, the other 6/7 of the time the electron shields the two protons by 3/7 e– each, reducing the effective charge of each proton to 4/7e+.
We see that the two shielded protons will repel each other with the force of FR = Ke (16/49 e2 /r2) where e is the charge of an electron or proton, r is the distance between the protons (r = 0.74Å = 0.74×10-10m), and Ke is Coulomb’s electrical constant, Ke ≈ 8.988×109 N⋅m2⋅C−2. The attractive force is calculated similarly, as each proton attracts the central electron by FA = – Ke (4/49) e2/ (r/2)2. The forces are seen to be in balance, the net force is zero.
It is because of quantum mechanics, that the bond is the length that it is. If the atoms were to move closer than r = 0.74Å, the central electron would be confined to less space and would get more energy, causing it to spend less time between the two protons. With less of an electron between them, FR would be greater than FA and the protons would repel. If the atoms moved further apart than 0.74Å, a greater fraction of the electron would move to the center, FA would increase, and the atoms would attract. This is a fairly pleasant way to understand why the hydrogen side of all hydrogen covalent bonds are the same length. It’s also a nice introduction to muon-catalyzed cold fusion.
Most fusion takes place only at high temperatures, at 100 million °C in a TOKAMAK Fusion reactor, or at about 15 million °C in the high pressure interior of the sun. Muon catalyzed fusion creates the equivalent of a much higher pressure, so that fusion occurs at room temperature. The trick to muon catalyzed fusion is to replace one of the electrons with a muon, an unstable, heavy electron particle discovered in 1936. The muon, designated µ-, behaves just like an electron but it has about 207 times the mass. As a result when it replaces an electron in hydrogen, it forms form a covalent bond that is about 1/207th the length of a normal bond. This is the equivalent of extreme pressure. At this closer distance, hydrogen nuclei fuse even at room temperature.
In normal hydrogen, the nuclei are just protons. When they fuse, one of them becomes a neutron. You get a deuteron (a proton-neutron pair), plus an anti electron and 1.44 MeV of energy after the anti-electron has annihilated (for more on antimatter see here). The muon is released most of the time, and can catalyze many more fusion reactions. See figure at right.
While 1.44MeV per reaction is a lot by ordinary standards — roughly one million times more energy than is released per atom when hydrogen is burnt — it’s very little compared to the energy it takes to make a muon. Making a muon takes a minimum of 1000 MeV, and more typically 4000 MeV using current technology. You need to get a lot more energy per muon if this process is to be useful.
You get quite a lot more energy when a muon catalyzes deuterium fusion or deuterium- fusion. With these reactions, you get 3.3 to 4 MeV worth of energy per fusion, and the muon will be ejected with enough force to support about eight D-D fusions before it decays or sticks to a helium atom. That’s better than before, but still not enough to justify the cost of making the muon.
The next reactions to consider are D-T fusion and Li-D fusion. Tritium is an even heavier isotope of hydrogen. It undergoes muon catalyzed fusion with deuterium via the reaction, D+T –> 4He +n +17.6 MeV. Because of the higher energy of the reaction, the muons are even less likely to stick to a helium atom, and you get about 100 fusions per muon. 100 x 17.6 MeV = 1.76 GeV, barely break-even for the high energy cost to make the muon, but there is no reason to stop there. You can use the high energy fusion neutrons to catalyze LiD fusion. For example, 2LiD +n –> 34He + T + D +n producing 19.9 MeV and a tritium atom.
With this additional 19.9 MeV per DT fusion, the system can start to produce usable energy for sale. It is also important that tritium is made in the process. You need tritium for the fusion reactions, and there are not many other supplies. The spare neutron is interesting too. It can be used to make additional tritium or for other purposes. It’s a direction I’d like to explore further. I worked on making tritium for my PhD, and in my opinion, this sort of hybrid operation is the most attractive route to clean nuclear fusion power.
Electric vehicles work well for short trips between places where you can charge with cheap electricity. Typically that’s trips from home to a nearby place of work, and to local shopping malls and theaters with low-cost charge spots. If you drive this way, you’ll pay about 3.2¢/mile for home electricity, instead of about 17¢/mile for gasoline transport (e.g. 24 mpg with $4/gallon gas). Using an EV also saves on oil changes, transmission, air filters, belts, etc., and a lot of general complexity. Battery prices are still high, but much lower than they were even a few years ago.
The 10 kW Aquarius Engine is remarkably small and light, about 10kg (22 lb).
EVs are less attractive for long trips, especially in the cold. Your battery must provide the heat, as there is no waste heat from the engine. Expect to have to recharge every 200 -250 miles, or perhaps twice in the middle of a long trip. Each charge will take a half-hour or more, and fast charging on the road isn’t low cost. Expect to pay about 15¢/mile, nearly as much as for gasoline. See my full comparison of the economics here.
One obvious solution is to have two cars: a short commuter and an EV. Another solution is a hybrid. The Toyota’s Prius and the Chevy Volt were cutting edge in their day, but people don’t seem to want them. These older hybrids provided quick fill-ups, essentially infinite range, and about double the gas milage of a standard automobile, 30-45 mpg. The problem is you have even more complexity and maintenance than with even a gas automobile.
Aquarius liner engine as a range extender
I recently saw a small, simple, super-efficient (they say) gas engine called Aquarius. It provides 9.5 kW electric output and weighs only 22 lbs (10 kg), see picture above. A Tesla S uses about 16 kW during highway driving, implying that this engine will more than double the highway range of a Tesla S at minimal extra weight and complexity. It also removes the fear of being stranded on the highway, far from the nearest charge-station.
The energy efficiency is 34%, far higher than that for normal automobile engines, but fairly typical of floating piston linear engines. The high efficiency of these engines is partly due to the lack of tapper valves, risers, crank-shaft, and partially due to the fact that the engine always runs at its maximum power. This is very close to the maximum efficiency point. Most car engines are over sized (200 hp or so) and thus must run at a small fraction of their maximum power. This hurts the efficiency, as I discuss here. The Aquarius Engine makes electricity by the back-forth motion of its aligner rods moving past magnetic stator coils. Slots in the piston rod and in the side of the cylinder operate as sliding valves, like in a steam engine. First versions of the Aquarius Engine ran on hydrogen, but the inventors claim it can also run on gasoline, and presumably hythane, my favorite fuel, a mix of hydrogen and natural gas.
At the moment shown, slit valves in the piston rod are open to both cylinder chambers. The explosion at left will vent to the exhaust at left and out the manifold at top. The sliding valve is currently sending fresh air into the cylinder at right, but will soon send it into both cylinders to help scavenge exhaust and provide for the next cycle; engine speed and impression are determined by the mass of the piston.
A video is available to show the basic operation (see it here). The drawing at right is from that video, modified by me. Air is drawn into the engine through a sliding valve at the middle of the cylinder. The valve opens and closes depending on where the piston is. At the instant shown in the picture, the valve is open to the right. Air enters that chambered is likely exiting through slits in the hollow piston rod. It leaves through the manifold t the top, pushing exhaust along with it. When the piston will have moved enough, both the slits and the intake will close. The continued piston motion (inertially driven) will compress the air for firing. After firing, the piston will move left, generating electricity, and eventually opening the slit-valve in the piston to allow the exhaust to leave. When it moves a little further the intake will open.
The use of side-opening exhaust valves is a novelty of the “Skinner UniFlow” double-acting, piston steam engines, seen on the Badger steamship on Lake Michigan. It’s one of my favorite steam engine designs. Normally you want a piston that is much thicker than the one in the drawing. This option is mentioned in the patent, but not shown in the drawing.
Aquarius is not the only company with a free-piston range extender. Toyota built a free-piston extender of similar power and weight; it was more complex but got higher efficiency. It has variable compression though, and looks like a polluter. (the same problems might affect the Aquarius) They dropped the project in 2014. Deutsch Aerospace has a two headed version that’s more powerful, but long and heavier: 56kg and 35kW. Lotus has a crank-piston engine, also 56kg, 35kW; it’s more complex and may have service life issues, but it’s compact and relatively light, and it probably won’t pollute. Finally, Mazda is thinking of bringing back its Wankel rotary engine as a range extender. Any of these might win in the marketplace, but I like the Aquarius engine for its combination of light weight, compact size, and simplicity.
This is not to say that Aquarius motors is a good investment. Aquarius automotive went public on the Toronto exchange in December, 2021, AQUA.TA. The company has no profits to date, and the only chance of them making a profit resides in them getting a good licensing deal from an established company. The major car companies have shown no interest so far, though they clearly need something like this. Their plug in hybrids currently use standard-size, 4 stroke engines: 110-150 kW, 100-150 kg, complex, and low efficiency. Consumers have not been impressed. Tesla autos could benefit from this engine, but Musk shows no interest either.
Robert Buxbaum May 5, 2022. I have no stock in Aquarius motors, nor have I received any benefits from them, or any auto company.
There are two ASTM-approved methods for measuring the gas permeability of a material. The equipment is very similar, and REB Research makes equipment for either. In one of these methods (described in detail here) you measure the rate of pressure rise in a small volume.This method is ideal for high permeation rate materials. It’s fast, reliable, and as a bonus, allows you to infer diffusivity and solubility as well, based on the permeation and breakthrough time.
Exploded view of the permeation cell.
For slower permeation materials, I’ve found you are better off with the other method: using a flow of sampling gas (helium typically, though argon can be used as well) and a gas-sampling gas chromatograph. We sell the cells for this, though not the gas chromatograph. For my own work, I use helium as the carrier gas and sampling gas, along with a GC with a 1 cc sampling loop (a coil of stainless steel tube), and an automatic, gas-operated valve, called a sampling valve. I use a VECO ionization detector since it provides the greatest sensitivity differentiating hydrogen from helium.
When doing an experiment, the permeate gas is put into the upper chamber. That’s typically hydrogen for my experiments. The sampling gas (helium in my setup) is made to flow past the lower chamber at a fixed, flow rate, 20 sccm or less. The sampling gas then flows to the sampling loop of the GC, and from there up the hood. Every 20 minutes or so, the sampling valve switches, sending the sampling gas directly out the hood. When the valve switches, the carrier gas (helium) now passes through the sampling loop on its way to the column. This sends the 1 cc of sample directly to the GC column as a single “injection”. The GC column separates the various gases in the sample and determines the components and the concentration of each. From the helium flow rate, and the argon concentration in it, I determine the permeation rate and, from that, the permeability of the material.
As an example, let’s assume that the sample gas flow is 20 sccm, as in the diagram above, and that the GC determines the H2 concentration to be 1 ppm. The permeation rate is thus 20 x 10-6 std cc/minute, or 3.33 x 10-7 std cc/s. The permeability is now calculated from the permeation area (12.56 cm2 for the cells I make), from the material thickness, and from the upstream pressure. Typically, one measures the thickness in cm, and the pressure in cm of Hg so that 1 atm is 76cm Hg. The result is that permeability is determined in a unit called barrer. Continuing the example above, if the upstream hydrogen is 15 psig, that’s 2 atmospheres absolute or or 152 cm Hg. Lets say that the material is a polymer of thickness is 0.3 cm; we thus conclude that the permeability is 0.524 x 10-10 scc/cm/s/cm2/cmHg = 0.524 barrer.
This method is capable of measuring permeabilities lower than the previous method, easily lower than 1 barrer, because the results are not fogged by small air leaks or degassing from the membrane material. Leaks of oxygen, and nitrogen show up on the GC output as peaks that are distinct from the permeate peak, hydrogen or whatever you’re studying as a permeate gas. Another plus of this method is that you can measure the permeability of multiple gas species simultaneously, a useful feature when evaluating gas separation polymers. If this type of approach seems attractive, you can build a cell like this yourself, or buy one from us. Send us an email to reb@rebresearch.com/blog/, or give us a call at 248-545-0155.
Platinum catalysts can be very effective at removing hydrogen from air. Platinum promotes the irreversible reaction of hydrogen with oxygen to make water: H2 + 1/2 O2 –> H2O, a reaction that can take off, at great rates, even at temperatures well below freezing. In the 1800s, when platinum was cheap, platinum powder was used to light town-gas, gas street lamps. In those days, street lamps were not fueled by methane, ‘natural gas’, but by ‘town gas’, a mix of hydrogen and carbon monoxide and many impurities like H2S. It was made by reacting coal and steam in a gas plant, and it is a testament to the catalytic power of Pt that it could light this town gas. These impurities are catalytic poisons. When exposed to any catalyst, including platinum, the catalyst looses it’s power to. This is especially true at low temperatures where product water condenses, and this too poisons the catalytic surface.
Nowadays, platinum is expensive and platinum catalysts are no longer made of Pt powder, but rather by coating a thin layer of Pt metal on a high surface area substrate like alumina, ceria, or activated carbon. At higher temperatures, this distribution of Pt improves the reaction rate per gram Pt. Unfortunately, at low temperatures, the substrate seems to be part of the poisoning problem. I think I’ve found a partial way around it though.
My company, REB Research, sells Pt catalysts for hydrogen removal use down to about 0°C, 32°F. For those needing lower temperature hydrogen removal, we offer a palladium-hydrocarbon getter that continues to work down to -30°C and works both in air and in the absence of air. It’s pretty good, but poisons more readily than Pt does when exposed to H2S. For years, I had wanted to develop a version of the platinum catalyst that works well down to -30°C or so, and ideally that worked both in air and without air. I got to do some of this development work during the COVID downtime year.
My current approach is to add a small amount of teflon and other hydrophobic materials. My theory is that normal Pt catalysts form water so readily that the water coats the catalytic surface and substrate pores, choking the catalyst from contact with oxygen or hydrogen. My thought of why our Pd-organic works better than Pt is that it’s part because Pd is a slower water former, and in part because the organic compounds prevent water condensation. If so, teflon + Pt should be more active than uncoated Pt catalyst. And it is so.
where is molar volume. The substance-specific constants and can be understood as an attraction force between molecules and a molecular volume respectively. Alternately, they can be calculated from the critical temperature and pressure as
Now, I’m going to assume that the effect of a hydrophobic surface near the Pt is to reduce the effective value of a. This is to say that water molecules still attract as before, but there are fewer water molecules around. I’ll assume that b remains the same. Thus the ratio of Tc and Pc remains the same but the values drop by a factor of related to the decrease in water density. If we imagine the use of enough teflon to decrease he number of water molecules by 60%, that would be enough to reduce the critical temperature by 60%. That is, from 647 K (374 °C) to 359 K, or -14°C. This might be enough to allow Pt catalysts to be used for H2 removal from the gas within a nuclear wast casket. I’m into nuclear, both because of its clean power density and its space density. As for nuclear waste, you need these caskets.
I’ve begun to test of my theory by making hydrogen removal catalyst that use both platinum and palladium along with unsaturated hydrocarbons. I find it works far better than the palladium-hydrocarbon getter, at least at room temperature. I find it works well even when the catalyst is completely soaked in water, but the real experiments are yet to come — how does this work in the cold. Originally I planned to use a freezer for these tests, but I now have a better method: wait for winter and use God’s giant freezer.
It’s been a while since I did an assessment of hydrogen and batteries for automobile propulsion, and while some basics have not changed, the price and durability of batteries has improved, the price of gasoline has doubled, and the first commercial fuel cell cars have appeared in the USA. The net result (see details below) is that I find the cost of ownership for a gasoline and a battery car is now about the same, depending on usage and location, and that hydrogen, while still more pricey, is close to being a practical option.
EV Chargers. They look so much cooler than gasoline hoses, and the price per mile is about the same.
Lithium battery costs are now about $150/kwh. That’s $10,000 for a 70 kWh battery. That’s about 1/5 the price of a Tesla Model 3. The reliability that Tesla claims is 200,000 miles or more, but that’s with slow charging. For mostly fast charging, Car and Driver’s expectation is 120,000 miles. That’s just about the average life-span of a car these days.
The cost of the battery and possible replacement adds to the cost of the vehicle, but electricity is far cheaper than gasoline, per mile. The price of gasoline has doubled to, currently, $3.50 per gallon. A typical car will get about 24 mpg, and that means a current operation cost of 14.6¢/mile. That’s about $1,460/year for someone who drives 10,000 miles per year. I’ll add about $150 for oil and filter changes, and figure that operating a gas-powered car engine costs about $1,610 per year.
If you charge at home, your electricity costs, on average, 14¢/kWh. This is a bargain compared to gasoline since electricity is made from coal and nuclear, mostly, and is subsidized while gasoline is taxed. At level 2 charging stations, where most people charge, electricity costs about 50¢/kWh. This is three times the cost of home electricity, but it still translates to only about $32 for a fill-up that take 3 hours. According to “Inside EVs”, in moderate temperatures, a Tesla Model 3 uses 14.59 kWh/100 km with range-efficient driving. This translates to 11.7¢ per mile, or $1170/year, assuming 10,000 miles of moderate temperature driving. If you live in moderate climates: Californian, Texas or Florida, an electric car is cheaper to operate than a gasoline car. In cold weather gasoline power still makes sense since a battery-electric car uses battery power for heat, while a gasoline powered car uses waste heat from the engine.
Battery cars are still somewhat of more expensive than the equivalent gasoline car, but not that much. In a sense you can add $400/year for the extra cost of the Tesla above, but that just raises the effective operating cost to about $1,570/year, about the same as for the gasoline car. On the other hand, many folks drive less than 50 miles per day and can charge at home each night. This saves most of the electric cost. In sum, I find that EVs have hit a tipping point, and Tesla lead the way.
Now to consider hydrogen. When most people think hydrogen, they think H2 fuel, and a PEM fuel cell car. The problem here is that hydrogen is expensive, and PEM FCs aren’t particularly efficient. Hydrogen costs about $10/kg at a typical fueling station and, with PEM, that 1 kg of hydrogen takes you only about 25 miles. The net result is that the combination hydrogen + PEM results in a driving cost of about 40¢/mile, or about three times the price of gasoline. But Toyota has proposed two better options. The fist is a PEM hybrid, the hydrogen Prius. It’s for the commuter who drives less than about 40 miles per day. It has a 10kWh battery, far cheaper than the Tesla above, but enough for the daily commute. He or she would use charge at home at night, and use hydrogen fuel only when going on longer trips. If there are few long trips, you come out way ahead.
Toyota 2021 Mirai, hydrogen powered vehicle
Toyota also claims to have a hydrogen powered Corolla or debut in 2023. This car will have a standard engine, and I would expect (hope) will drive also — preferably — on hythane, a mix of hydrogen and methane. Hythane is much cheaper per volume, and more energy dense, see my analysis. While Toyota has not said that their Corolla would run on hythane, it is supposed to have an internal combustion engine, and that suggests that hythane will work in it.
A more advanced option for Toyota or any other car/truck manufacturer would be to design to use solid oxide fuel cells, SOFCs, either with hydrogen or hythane. SOFCs are significantly more efficient than PEM, and they are capable of burning hythane, and to some extent natural gas too. Hythane is not particularly available, but it could be. Any station that currently sells natural gas could sell hythane. As for delivery to the station, natural gas lines already exist underground, and the station would just blend in hydrogen, produced at the station by electrolysis, or delivered. Hythane can also be made locally from sewer gas methane, and wind-power hydrogen. Yet another SOFC option is to start with natural gas and convert some of the natural gas to hydrogen on-board using left-over heat from the SOFC. I’ve a patent for this process.
Speaking of supply network, I should mention the brown outs we’ve been having in Detroit. Electric cars are part of the stress to the electric grid, but I believe that, with intelligent charging (and discharging) the concern is more than manageable. The driver who goes 10,000 miles per year only adds about 2,350 kWh/year of extra electric demand. This is a small fraction of the demand of a typical home, 12,154 kWh/year.It’s manageable. Then again, hythane adds no demand to the electric grid and the charge time is quicker — virtually instantaneous.
Branson’s Virgin Space Ship (VSS) Unity was cheered as a revolutionary milestone today (July 10) after taking Branson, three friends and two pilots on a three minute ride to the edge of space, an altitude of 53.5 miles or 283,000 feet. I’d like to put that achievement into contest, both with previous space planes, like the Concorde and X-15 (the 1960s space plane), and also in context with the offerings of Elon Musk’s Space-X and Bezos’s, Blue Horizon.
To start with, the VSS Unity launched from a sub-sonic mother ship, as the X-15 had before it. This saves a lot in fuel weight and safety equipment, but it makes scale up problematic. In this case, the mother-ship was named Eve. Unity launched from Eve at 46,000 feet, about 9 miles up, and at Mach 0.5; it took Eve nearly 90 minutes to get to altitude and position. It was only after separation, that Unity began a one minute, 3 G rocket burn that brought it to its top speed, Mach 3, at about 16 miles up. What followed was a 3 minute, unpowered glide to 53.5 miles and down. Everyone seems to have enjoyed the three minutes of weightlessness, and it should be remembered that there is a lot of difference between Mach 3 and orbital speed, Mach 31. Also there is a lot of difference between a sub-orbital and orbital.
Concorde SST landing in Farnborough.
By comparison, consider the Concorde SSTs that first flew in 1976. It reached about 2/3 the speed of Unity, Mach 2.1, but carried 120 commercial passengers. It took off from the ground and maintained this speed for 4500 miles, going from London to Houston in 4.5 hours. While the Concorde only reached an altitude of 60,000 feet, it is far more impressive going at Mach 2.1 for 4.5 hours than going at Mach 3 for three minutes. And there is a lot of difference between 120 passengers and 4. There is also the advantage of taking off from the ground. A three minute ride in a space plane should not require a 90 minute ascent on a mother ship.
X-15 landing, 1962.
Next consider the X-15 rocket plane of the 1960s. This was a test platform devoted to engine and maneuverability tests; it turns out that maneuverability is very difficult. The X-15 hit a maximum altitude of 354,200 ft, 67 miles, and a maximum speed of Mach 6.72, or 4520 mph. That’s significantly higher than Branson’s VSS, and double the maximum speed. As an aside, the X-15 project involved the development of a new nickel alloy that I use today, Inconel X-750. I use this as a support for my hydrogen membranes. If any new materials were developed for VSS, none were mentioned.
The Air Force’s X-37B Orbital Test Vehicle at Kennedy Space Center, May 7, 2017.
Continuing with the history of NASA’s X-program, we move to the X-41, a air-breathing scramjet of the 1980s and 90s. It reached 95,000 feet, and a maximum speed of Mach 9.64. That’s about three times as fast as Virgin’s VSS. The current X-plane is called X-37B, it is a rocket-plane like the X-15 and VSS, but faster and maneuverable at high speed and altitude. It’s the heart of Trump’s new, US Space force. In several tests over the past 5 years, it has hit orbital speed, 17,426 mph, Mach 31, and orbital altitudes, about 100 miles, after being launched by a Atlas V or a Falcon 9 booster. The details are classified. Apparently it has maneuverability. While the X-37B is unmanned, a larger, manned version, is being built, the X-37C. It is supposed to carry as many as six.
Reaching orbital speed or Mach 31 implies roughly 100 times as much kinetic energy per mass as reaching the Mach 3.1 of Virgin’s VSS. In this sense, the space shuttle, and the current X-plane are 100 times more impressive than Virgin’s VSS. There is also a lot to be said for maneuverability and for a longer flight duration– more than a few minutes. Not that I require Branson to beat NASA’s current offerings, but I anyone claiming cutting edge genius and visionary status should at least beat NASA’s offerings of the 1960s, and the Concorde planes of 1976.
Bezos’s Blue Origin, and the New Shepard launcher.
And that bring’s us to the current batch of non-governmental, space cadets. Elon Musk stands out to me as a head above the rest, at least. Eight years ago, his Grasshopper rocket premiered the first practical, example of vertical take off and landing booster. Today, his Falcon 9 boosters send packages into earth orbit, and beyond, launching Israel’s moon project, as one example. That implies speeds of Mach 31 and higher, at least at the payload. It’s impressive, even compared to X-37, very impressive.
Bezos’ offering, the Blue Origin Shepherd, seems to me like a poor imitation of the SpaceX Falcon. Like Falcon, it’s a reusable, vertical takeoff and landing platform, that launches directly from earth, and like Falcon it carries a usable payload, but it only reaches speeds of Mach 3 and altitudes about 65 miles. Besides, the capsule lands by way of parachutes, not using wings like the space shuttle, or the X-37B, and there is no reusable booster like Falcon. Blue Origin started carrying payloads only in 2019, five yers after SpaceX. There is nothing here that’s cutting edge, IMHO, and I don’t imagine it will be cheaper either.
Branson has something that the other rocket men do not have, quite: a compelling look: personal marketing, a personal story, and a political slant that the press loves and I find hypocritical and hokey. The press, and our politicians, managed to present this flight as more than an energy wasting, joy ride for rich folks. Instead, this is accepted as Branson’s personal fight against climate change. Presented this way, it should qualify as a tax-dodge. I don’t see it getting folks to stop polluting and commit to small cars, but the press is impressed, or claims to be. The powers have committed themselves to this type of Tartuffe, and the press goes along. You’d think that, before giving Branson public adoration for his technology or environmentalism, he should have cutting technology and have been required to save energy, or pollute less. At least beat the specs of the X-15. Just my opinion.
I month ago, I wrote to endorse hythane, a mix of natural gas (methane) and 20-40% hydrogen. This mix is ideal for mobile use in solid oxide fuel cell vehicles, and not bad with normal IC engines. I’d now like to write about the advantages of an on-broad hydrogen generator to allow adjustable composition fuel mixes.
A problem you may have noticed with normal car engines is that a high hp engine will get lower miles per gallon, especially when you’re driving slow. That seems very strange; why should a bigger engine use more gas than a dinky engine, and why should you get lower mpg when you drive slow. The drag force on a vehicle is proportional to speed squared. You’d expect better milage at low speeds– something that textbooks claim you will see, counter to experience.
Behind these two problems are issues of fuel combustion range and pollution. You can solve both issues with hydrogen. With normal gasoline or Diesel engines, you get more or less the same amount of air per engine rotation at all rpm speeds, but the amount of air is much higher for big engines. There is a relatively small range of fuel-air mixes that will burn, and an even smaller range that will burn at low pollution. You have to add at least the minimal fuel per rotation to allow the engine to fire. For most driving that’s the amount the carburetor delivers. Because of gearing, your rpm is about the same at all speeds, you use almost the same rate of fuel at all speeds, with more fuel used in big engines. A gas engine can run lean, but normally speaking it doesn’t run at all any leaner than about 1.6 times the stoichiometric air-to-fuel mix. This is called a lambda of 1.6. Adding hydrogen extends the possible lambda range, as shown below for a natural gas – fired engine.
Engine efficiency when fueled with natural gas plus hydrogen as a function of hydrogen amount and lambda, the ratio of air to stoichiometric air.
The more hydrogen in the mix the wider the range, and the less pollution generally. Pure hydrogen burns at ten times stoichiometric air, a lambda of ten. There is no measurable pollution there, because there is no carbon to form CO, and temperature is so low that you don’t form NOx. But the energy output per rotation is low (there is not much energy in a volume of hydrogen) and hydrogen is more expensive than gasoline or natural gas on an energy basis. Using just a little hydrogen to run an engine at low load may make sense, but the ideal mix of hydrogen and ng fuel will change depending on engine load. At high load, you probably want to use no hydrogen in the mix.
As it happens virtually all of most people’s driving is at low load. The only time when you use the full horse-power is when you accelerate on a highway. An ideal operation for a methane-fueled car would add hydrogen to the carburetor intake at about 1/10 stoichiometric when the car idles, turning down the hydrogen mix as the load increases. REB Research makes hydrogen generators based on methanol reforming, but we’ve yet to fit one to a car. Other people have shown that adding hydrogen does improve mpg.
Carburetor Image from a course “Farm Power”. See link here. Adding hydrogen means you could use less gas.
Adding hydrogen plus excess air means there is less pollution. There is virtually no CO at idle because there is virtually no carbon, and even at load because combustion is more efficient. The extra air means that combustion is cooler, and thus you get no NOx or unburned HCs, even without a catalytic converter. Hydrogen is found to improve combustion speed and extent. A month ago, I’d applied for a grant to develop a hydrogen generator particularly suited to methane engines. Sorry to say, the DoT rejected my proposal.
Some years ago I wrote a largely negative review of Brown’s gas, but the COVID crisis in India makes me want to reconsider. Browns gas can provide a simple source of oxygen for those who are in need. First, an explanation, Browns gas is a two-to-one mix of hydrogen and oxygen; it’s what you get when you do electrolysis of water without any internal separator. Any source of DC electricity will do, e.g. the alternator of a car or a trickle charger of the sort folks buy for their car batteries, and almost any electrode will do too (I’d suggest stainless steel). You can generate pressure just by restricting flow from the electrolysis vessel, and it can be a reasonable source of small-scale oxygen or hydrogen. The reaction is:
H2O –> H2 + 1/2 O2.
The problem with Brown’s gas is that it is explosive, more explosive than hydrogen itself, so you have to handle it with care; avoid sparks until you separate the H2 from the O2. Even the unseparated mix has found some uses, e.g. as a welding gas, or for putting in cars to avoid misfires, increase milage, and decrease pollution. I think that methanol reforming is a better source of automotive hydrogen: hydrogen is a lot safer than this hydrogen-oxygen mix.
Browns gas to oxygen for those who need it.
The mix is a lot less dangerous if you separate the oxygen from the hydrogen with a membrane, as I show in the figure. at right. If you do this it’s a reasonable wy to make oxygen for patients who need oxygen. The electrolysis cell can be a sealed bottle with water and the electrodes; add a flow restriction as shown to create the hydrogen pressure that drives the separation. The power can be an automotive trickle charger. You can get this sort of membranes from REB Research, here and many other suppliers. REB provide consulting services if you like.
In a pinch, you don’t even need the membrane, by the way. You can rely on your lungs to make the separation. A warning, though, the mix is dangerous. Avoid all sparks. Also, don’t put salt into the water. You can can put in some baking soda or lye to speed the electrolysis, but If you put salt in, you’ll find you don’t make oxygen, but will instead make chlorine. And chlorine is deadly. If you’re not sure, smell the gas. If it smells acrid, don’t use it. This is the chlorine-forming reaction.
2NaCl + 2 H2O –> H2 + Cl2 + 2NaOH
Ideally you should vent the hydrogen stream out the window, but for short term, emergency use, the hydrogen can be vented into your home. Don’t do this if anyone smokes (not that anyone should smoke about someone on oxygen). This is a semi-patentable design, but I’m giving it away; not everything that can be patented should be.
Fuel cells are highly efficient and hardly polluting. They have a long history of use in space, and as a power source for submarines. They are beginning to appear powering city buses and intercity trains, at least in Europe, but not so much in the US or Canada. The business case for fuel cells is that they provide clean electric power to the train or bus, without the need for overhead wires. Avoiding wires helps make up for the high cost of hydrogen as a fuel. The reluctance to switch to fuel cells is the US is due to the longer distances that must be covered. The very low volumetric energy density of hydrogen means you need many filling stations with hydrogen fuel cells, and many fill ups per trip.
Energy density CNG, hydrogen, hythane.
On a mass-basis, hydrogen is energy dense, with 1 kg providing the same energy as 2-3 kg of gasoline. The problem with hydrogen (aside from the cost) is that its mass density is very low, less than 50g/liter, even at high pressure. This is terribly un-dense on a volume basis. It would take 20 liters of high pressure hydrogen (about 5 gallons) to take a car or bus as far as with one gallon of gasoline. Even with a huge tank of high pressure hydrogen, 150 gallons or so, a cross country trip would require some 12 fill ups, one every 250 miles, and this is an annoyance, besides being an infrastructure problem.
Then there is cost. In California, hydrogen costs far more than gasoline, between $12 and $15 per kg. That’s ten times as expensive as gasoline on a weight basis and 4 times as expensive on an energy basis. What’s needed is a cheaper, more energy-dense version of hydrogen, ideally one that can be used in both fuel cells and IC engines, and the version I’d like to suggest is hythane, a mix of methane (natural gas) and 20-30% hydrogen.
Hythane dispenser
Hythane has about 3 times the volumetric energy density of hydrogen, and about 1/3 the price. It makes less CO and CO2 pollution because there is far less carbon. On an energy basis, hythane costs just slightly more than gasoline, and requires less infrastructure. Natural gas is cheap and available, delivered by pipeline, without the need for hydrogen delivery trucks. Because hythane has about three times the volumetric energy density of hydrogen, the tank described above, that would give a 250 mile ride with hydrogen, would give 750 miles with hythane. This means a lot fewer fueling stations are needed, and a lot fewer forced stops. As a bonus, hythane can be used in (some) IC engines as well as in fuel cells.
Hydrogen for hythane-automotive use can be made on site, by electrolysis of water. Because there is relatively little hydrogen in the mix, only 25% by volume, or 8% on an energy basis, there is relatively little burden on the electric grid, and fueling will be a lot faster than with battery chargers. Hythane is already in use in buses in China and Canada. These are normal combustion buses but hythane works even better — more efficiently — with fuel cells (solid oxide fuel cells) and thus hythane provides a path to efficiency and greater fuel cell use.
Hythane bus, Montreal.
Natural gas does not work as well in fuel cells; it requires a pre-reformer to make some H2, and even then tends to coke. To be used in most fuel cells, the methane has to be converted, at lest partially into hydrogen and this takes heat energy and water.
CH4 + H2O + energy –> 3H2 + CO
Reforming is a lot easier with hythane; it can be done within the fuel cell. Within a SOFC, the hydrogen combustion, H2 + 1/2 O2 –> H2O, provides heat and water that helps feed the reforming reaction and helps prevent coking. Long term, fuel cells will likely dominate the energy future, but for now it’s nice to have a fuel that will work well in normal IC engines too.
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