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The Fuel of the Future

What will your car run on in 2020 or 2030? What form of energy storage and transmission will allow intermittent energy sources, such as wind and solar, to be a viable input to the economy?

There’s a good chance, of course, that cars will still run on gasoline — its demise has been predicted early and often — but there are also lots of reasons that petroleum will not be a sound basis for a rapidly-expanding economy. We’ll want to save the hydrocarbons as a feedstock to our nanofactories…

Why not batteries? For cars, in particular, batteries are heavy but they are also inefficient. You lose a lot of energy by storing it in a battery and taking it out again. Almost certainly, nanotech will allow us to build lighter, more efficient batteries, or their equivalent, such as ultracapacitors. But that comes with a major drawback: the higher the energy density of a closed-cycle battery, and the more quickly you can charge it, the more quickly it can release its energy. In simple terms, a really good battery would be a bomb.

The answer to both weight and safety concerns is an air-breathing battery. Only storing one of the two reagents saves weight, and means that the potential energy isn’t in the battery, but in the battery and a large volume of air.

The answer has always been hydrogen. (I assume hydrogen in Nanofuture, for example.) Hydrogen is very light. It’s fairly safe — since it’s lighter than air, a leak dissipates rather than forming an explosive mixture. It can be generated from water by electrolysis and used in fuel cells with decent efficiency (about twice that of internal combustion engines). It seems likely that nanotech will give us ways to separate and recombine hydrogen that produce a very high-efficiency energy-storage cycle.

But there are some drawbacks: hydrogen is bulky, though light, and it needs to be stored at very low temperatures. It’s a real pain to deal with, and that means it’s expensive to deal with. Storage and transportation quadruple the cost of hydrogen as a fuel (see the bottom of the last page here).

Turns out the best way to deal with hydrogen is to use some highly hydrogen-bearing compound, such as methane. This is in wide use as a fuel, in the form of natural gas. (Alternative forms are the alcohols, such as methanol and ethanol). But we are still stuck with that carbon, and not only does it produce CO2 emissions but intermediate products such as CO tend to poison present-day fuel cells.

ammonia

An often-overlooked alternative is (anhydrous) ammonia, NH3. Because it’s a polar molecule, it’s easier to liquefy than methane (-33C as opposed to -162C). A liter of ammonia contains more hydrogen than a liter of hydrogen. It’s easy to crack into hydrogen and nitrogen — nitrogen can be emitted without worry since it is already 78% of the atmosphere. You could burn ammonia in a big, powerful, fuel cell, or even a big, powerful internal combustion engine, indoors without the kind of problems you’d get with carbon-bearing fuels.

There’s a fairly easy path to using ammonia as a fuel. It’s already produced in major industrial quantity and there are thousands of miles of ammonia pipelines. It’s a good fuel for current-day fuel cells, and near-term nanotech is likely to improve the catalysts for all parts of the cycle.

8 Responses to “The Fuel of the Future”

  1. Says:

    Not sure I entirely agree. Synthesizing octane should be pretty efficient, and octane has far higher power density than methane, pure hydrogen, or ammonia. Why not run octane + atmospheric oxygen in nanomechanical direct power generators? The cell does something quite similar in the krebs cycle of course.

  2. Says:

    Ammonia is a dangerous (deadly) chemical in high concentrations from the MSDS:

    “Anhydrous ammonia gas or liquid is very corrosive to body tissues, reacting with body moisture on contact.

    The odour threshold for ammonia is on average 17 PPM although the range of sensitivity ranges from 0.7 PPM to 50 PPM for acclimatized individuals. Generally, concentrations of up to 25 PPM are tolerated although unpleasant and pungent. Above this concentration, irritation of the eyes, nose and throat may begin. The extent of irritation increases with increasing ammonia concentration.

    Eye and throat irritation is more pronounced between 100 and 400 PPM. Above 400 PPM, skin irritation is noticeable and immediate throat irritation and coughing will result. NIOSH has established 500 PPM as the concentration immediately dangerous to life and health (IDLH), which is defined as the concentration above which self-rescue may be difficult or impossible due to physiological effects. At concentrations between 1000 and 2500 PPM increasing chest tightness, brochospasm and severe eye and skin irritation will result. Delayed effects such as chemical pneumonitis and pulmonary edema may develop several hours after exposure. At concentrations above 2500 PPM, laryngeal spasm may occur resulting in rapid asphyxia. Effects may be more pronounced at lower concentrations in children, the elderly, and persons with impaired lung function.”

    The PPE needed

    Respiratory Protection:
    Use a NIOSH approved chemical cartridge respirator with full facepiece for ammonia concentrations up to 300 PPM. Use a positive pressure (pressure demand) SCBA for concentrations above 300 PPM, for emergency response, or for entry into unknown concentrations.

    Eye Protection:
    Contact lenses should not be worn when handling anhydrous ammonia. Use chemical goggles and a face shield or full facepiece air purifying or air supplied respirator.

    Skin Proection:
    Where chemical contact is unlikely, wear butyl rubber, nitrile, or polyvinyl chloride boots, gloves, rain jacket and pants.

    The short answer is anhydrous ammonia is too dangerous of a chemical for daily use by non trained individuals.

    As far as energy storage technology what about diamond or graphene springs?

  3. Says:

    Actually I should correct my statement above. It should read “Ammonia is a deadly chemical at fairly low concentrations. (2,500 PPM is 0.25%)”

    Note* , Ammonia has to be treated with a lot of respect. It is a potentially deadly chemical, (NOT even close to being the most deadly chemical) but it should only be handeled by people with the proper equipment AND training.

    jim moore

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  6. J. Storrs Hall Says:

    Nanosprings (and flywheels) fall under the problem with batteries — all the potential energy is right there in the device, so at useful energy densities it’s a potential bomb.

    Ammonia vs octane: I wouldn’t reccommend breathing either :-) … ammonia has the advantage of being very unpleasant in very small doses, meaning people would be more careful with it. A reasonable distribution system would never expose it to open air…

    It’s lighter than air, and thus would dissipate quickly in the case of a spill, and is non-flammable, a remarkable property for a fuel!

    Liquid ammonia has about half the volumetric energy as octane, but given an efficient fuel cell you’d get the same usable energy out of it as you do now with gasoline in an IC engine.

  7. Says:

    Lots of non-technical responses here. I’ve laid hands on a working ammonia powered engine, but nano-springs? Are they charged with di-lithium crystals or a zero point generator? Maybe they’re downscale and using a Moray Valve?

  8. Says:

    “but nano-springs? Are they charged with di-lithium crystals or a zero point generator? Maybe they’re downscale and using a Moray Valve?”

    No Mr Snarky, you are wrong, like all springs, nano spings are energized by streching them (or compressing them).

    And as far as laying your hands on them, you have been playing with a loosely joined, amorphous network of nanosprings most of your life its called rubber. With better selection of raw material (say graphene) and much better organization you should be able to store a great deal of energy (but still less than most chemical fuels)

    jim moore

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