[ RadSafe ] Liquid nitrogen as vehicle "fuel" (was: "Another recent article")

[Ernesto Faillace]

If liquid nitrogen were a practical alternative to battery storage and/or
combustible fuels, you'd think someone would have thought of this a long
time ago...  If it sounds too good to be true, it probably is.

Here's one reason why:
*Energy density of liquid nitrogen*

*Any process that relies on a phase-change of a substance will have much
lower **energy densities*
<http://en.wikipedia.org/wiki/Energy_density>*than processes involving
a chemical reaction in a substance, which in turn
have lower energy densities than nuclear reactions*. Liquid nitrogen as an
energy store has a low energy density. Liquid hydrocarbon fuels by
comparison have a high energy density. A high energy density makes the
logistics of transport and storage more convenient. Convenience is an
important factor in consumer acceptance. The convenient storage of
petroleum fuels combined with its low cost has led to an unrivaled success.
In addition, a petroleum fuel is a primary energy
source<http://en.wikipedia.org/wiki/Primary_energy_source>,
not just an energy storage and transport medium.

The energy density — derived from nitrogen's isobaric heat of vaporization
and specific heat in gaseous state — that can be realised from liquid
nitrogen at atmospheric pressure and zero degrees Celsius ambient
temperature is about 97 watt-hours per kilogram (W-hr/kg). This compares
with 100-250 W-hr/kg for a lithium-ion
battery<http://en.wikipedia.org/wiki/Lithium-ion_battery>and 3,000
W-hr/kg for a gasoline combustion
engine <http://en.wikipedia.org/wiki/Internal_combustion_engine> running at
28% thermal efficiency, 30 times the density of liquid nitrogen used at the
Carnot efficiency.[2]<http://en.wikipedia.org/wiki/Liquid_nitrogen_vehicle#cite_note-Knowlen-1>

For an isothermal expansion engine to have a range comparable to an
internal combustion engine, *a 350-litre (92 US gal) insulated onboard
storage vessel is
required.[2]<http://en.wikipedia.org/wiki/Liquid_nitrogen_vehicle#cite_note-Knowlen-1>
* A practical volume, but a noticeable increase over the typical 50-litre
(13 US gal) gasoline tank. The addition of more complex power cycles would
reduce this requirement and help enable frost free operation. However, no
commercially practical instances of liquid nitrogen use for vehicle
propulsion exist.
http://en.wikipedia.org/wiki/Liquid_nitrogen_vehicle#Energy_density_of_liquid_nitrogen
Much more practical (at today's relatively low natural gas prices) would be
to use methanol in existing or modified flex fuel vehicles (and this has
already been proven feasible).  About half the energy density of gasoline,
but better engine performance (higher "octane"), methanol has comparable
costs of production and distribution (at today's relatively high gasoline
costs), and no need to make substantial changes to motors, fuel tanks or
distribution networks.  It is usually blended at 85% methanol/15% gasoline
(M85) to prevent cold-start or vapor-lock issues.

For more, see http://en.wikipedia.org/wiki/Methanol_fuel

-- 
Ernesto Faillace, CHP

Date: Tue, 5 Jun 2012 15:02:33 -0700
From: "Brennan, Mike  (DOH)" <Mike.Brennan at DOH.WA.GOV>
Subject: Re: [ RadSafe ] Another recent article
To: "The International Radiation Protection (Health Physics)
       MailingList"    <radsafe at health.phys.iit.edu>
Message-ID:
       <37C41083D3480E4BBB478317773B845D07505EC7 at dohmxtum31.doh.wa.lcl>
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Hi Stan.
I haven't collected up any papers, though I've seen a couple over the
years.  The first time I was introduced to the idea was at a convention
where a University of Washington professor gave a presentation on some work
he was doing.  He was using a small automobile engine (old VW Bug, if I
recall), in which liquid nitrogen was squirted into the cylinders where it
vaporized and pushed the pistons.  He used the outside world as a heat
source, and the trick was keeping the engine warm enough.  Obviously there
are better designs possible for harvesting this energy.
Liquefied nitrogen has a much higher energy density than pressurized gas,
and is actually easier and safer to store (and much safer than gasoline or
electricity).  It is not as safe as water pumped to a height, but is much
more portable.
I am sure there are technical difficulties that were glossed over (but
nothing like the "if we get enough helium-3 fusion will be a snap!" crowd),
but really, what's not to like about liquid nitrogen?