Re: Don't buy GAS {slightly rocco related}

[Dan <dan@angband.org>]

On Wed, Apr 14, 1999 at 07:15:09AM -0700, Mark Mages wrote:

> Mass Transit - electrical (subway) or  Hydrogen
> powered - some cities already have hydrogen powered
> busses, the only emission they give off is in the form
> of distilled water... 

That is completely false.  I worked as an R&D engineer in a company that
sold alternative fuel vehicle equipment, mostly for regional trucking and
transit systems, and have had plenty of experience in the
aerospace combustion lab here at GA Tech. H2-Air combustion results in
rather high combustion temperatures, which causes the N2 in the air to
dissociate and recombine with oxygen to form nitrous oxide compounds,
which are prime contributors to both smog and acid rain. The primary NOx
compound in exhaust is NO, N2O and NO2 concentrations are several orders
of magnitude smaller.

For example, I ran a quick simulation of combustion in a 8.5:1 compression
ratio engine with the intake air being 300 K, which is pretty much ambient
temperature. I considered the combustion to occur at constant volume,
which gives a fairly close approximation to an actual temperature.  Both
cases assumed a stoichiometry of 1, most cars run slightly richer for
stability reasons.  I didn't have time to assemble a model for gasoline,
which is a blend of several hydrocarbons, so I used isooctane, which is
the primary component.

The isooctane/air reaction reached a maximum temperature of 2863 K, and
resulted in .00865 mols of NO per mol of intake air.

The H2/air reaction reached a max of 3055 K, and resulted in .00915 mols
of NO per mol of intake air, a 6% increase over NO emmissions from the
gasoline engine.

> saw some news clip with a mayor
> drinking a glass of the bus' exhaust :)

You could most likely do that with a regular gasoline engine's exhaust
too. H2O is the primary exhaust gas component of any combustion process.
In the above gas engine, it is 13% by volume of the total of everything
coming out the tailpipe (N2 is 72%, CO2 is 10%, CO is 2.5%, O2 is .9%, NO
is .9%, rest is various trace products) 


> And on another note - I know the rocco is a
> "performance" vehicle, but has anyone looked into
> natural gas conversions for any vehicle?  

Well, aside from our actual money-making business of selling both
conversions and OEM LNG systems, we also did several technology
demonstration projects.  We converted several vehicles for
Lockheed-Martin, the Department of Energy, and recently finished a project
to convert a BMW 316 to LNG (It's like a 318ti but with only 2 seats and a
1.6L engine.) Additonally, we converted 2 of our company cars to run on
LNG, a beat up old Chevy dually pickup and a Ford Aerostar minivan. 

That being said, I wouldn't rush out to convert your car. First off, NG
runs best in engines with a compression ratio of around 15, to take
advantage of NG's higher anti-knock index. While bi-fuel vehicles do work
(all of tech. demonstrations were bi-fuel), they're not too efficient. 

Next, you need to understand the difference between CNG and LNG.

CNG is nautral gas that is stored at room temperature in a high pressure
tank.  LNG is nautral gas that is compressed and cooled, so that it
condenses, and can be stored in it's much more compact liquid phase.
However, it needs to be kept at cryogenic temperature. This is done by
keeping it at a low pressure in a vaccum insulated container. Imagine a
big pressurized thermos bottle. 

Each system has advantages and disadvantages.

CNG: Advantages:
low pressure distribution system already installed, all you need is a
compressor to have a gas station at home. Some gas stations in large
cities sell it. Tank is relatively simple & cheap.

Disadvantages: Tank needs to be filled to high pressures, around 3000 PSI.
Could be more dangerous in an accident. Fill times are slow, maybe 15 mins
at a gas station, overnight with a compressor. Low range, probably a
little more than the most advanced electric cars. 

LNG: Advantages:
High range, our BMW had nearly 1000 miles on a single tank. Quick fill,
our BMW (16 gal. tank) took less than a minute and a half to fill. Tank is
low pressure, normally 70 PSI, could be up to 230 PSI. Tank is double
walled, so it's safer in an accident. The insulation on these tanks is
incredible. We fire tested one at a fire department training grounds
(Filled with liquid nitrogen instead of LNG, just in case), and it sat in
an intense fire for 6 hours without failing.

Disadvantages:
Availibility. There are 2 public LNG fueling stations (maybe 3 now, I'm
currently out of the loop) LNG makes the most sense if you have a fleet of
trucks that all come back to the same "home base" each night, for example
package delivery, taxis, sanitation trucks (i got to drive one. neat!),
etc. That way you can afford to have your own fueling station. The other
problem is the cost of the system. In addition to the cost of the
engine-management stuff, which is exactly the same as the CNG system, you
need a heat exchanger to vaporize the LNG and the insulated tank.

Dan


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