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Automation & Motion Control

Slideshow: Compressed Natural Gas Vehicles Picking Up Steam

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naperlou
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give me gas
naperlou   3/18/2014 11:22:05 AM
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Chuck, this is the way to go for users of larger vehicles.  As I have mentioned before, there is a large concrete contractor in the Chicago area that is converting all their vehicles to run on CNG.  A real opportunity to lower CO2 emissions and lower the use of oil is for governments, at all levels, to convert. In almost all cases, these groups refuel at their own fueling stations anyway.  Thus, the availability of fueling stations is not a problem.  It will also lower their costs in the long run. 

Another aspect of this is that the government purchases will create an industrial base for these vehicles.  Now that there are commercially available vehicles, the market for used vehicles will be opened up.  This seems like a no brainer. 

Charles Murray
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Re: give me gas
Charles Murray   3/18/2014 6:18:36 PM
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I agree, naperlou. Another advantage of CNG is the fact that, unlike batteries, it requires only engineering, not scientific discovery.

Wayne Eleazer
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Iron
Re: give me gas
Wayne Eleazer   3/19/2014 10:09:11 AM
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I did a study for NASA a few years ago on composite pressure vessels, and much of the available information was related to CNG use.

CNG powered vehicles clearly are the way to go for fleets, where an assured source of refueling is available.  Also, typically such larger vehicles can better accomodate the relatively large size and weight of CNG tanks.  With the best available current technology a CNG tank equal to 10 gal of gasoline is a few feet long, about 18 in in dia, and weighs 100 lb empty.

And contrary to what you would think, CNG tanks are markedly safer in an accident than are gasoline tanks.  There have even been instances in which a CNG tank leaked its contents, which ignited, inside a garage, and essentially no damage occured.  A gasoline leak probably would have destroyed the building.

But where CNG requires real care is in design, installation, and maintenance.  CNG tanks are very unforgiving to abuse, and while a wreck probably will not cause an immediate problem the aftermath may prove to be deadly.  A seemingly untouched CNG tank may react to damage some months later, and it usually does so during the refueling operation, when people are present very nearby.  Also, most CNG tanks have a specified service life, and woe be unto those who decide to ignore that limitation!

CNG is NOT suitable for shade tree mechanic work.

   

 

 

Turbineman
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Re: give me gas
Turbineman   3/19/2014 11:06:08 AM
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Wayne, what do you think the CNG tank service life would be - 100,000 miles or better or time constrained.  Wouldn't a steel tank last longer than composite?

If memory serves me, CNG has an octane rating of 138.  Wouldn't this require an engine modified to a higher compression ratio?  If so, a duel fuel engine would probably require premium gasoline.

Wayne Eleazer
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Iron
Re: give me gas
Wayne Eleazer   3/19/2014 12:17:32 PM
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CNG high pressure tanks are time constrained.  Usually the manufacturer prints the end of life date rigfht on it.  Vehicle mileage is not a factor, in an of itself.

However, they are also constrained by the environment they were in.  If it has a rough life, with corrosives and impacts from concrete blocks left in the road, it also has a short life - but you may not know how short until it is too late.  The average garage mechanic will be unable to make a proper evaluation.  Seemingly minor discoloration may indicate an impending catastrophy.  Once again, this argues for fleet use, where proper expertise can be applied.

Steel tanks very probably would not last as long as composite tanks due to corrosion.  In reality there are no all composite tanks in service.  They are steel or aluminum or plastic with an overwrap of composite material.  I believe the latest innovation is a metal or plastic liner, a composite overwrap and a glass fiber overwrap over that.  The liner prevents leaks, the composite provides strength and the glass fiber prevents corrosives form getting to the composite.

Titanium is probably the best liner material, due to its strength and corrosion resistance, but needless to say, it is rather pricy and mainly used only for aerospace applications.

GM once had a CNG powered pickup they marketed.  One truck's tank blew up in San Francisco; the truck had been used for collecting lead acid batteries for recycling and had been modified with an additional CNG tank mounted in the bed.  This led to battery acid leaking onto the original CNG tank below the bed, through the mounting holes for the added tank, and it failed when being refilled.

But then soon after that incident another GM truck blew up - and it had been used as a demo by a  gas company in the upper Midwest, led a fairly pampered life.  It also had the added tank in the bed. It may simply have been washed too often for the CNG tank to survive!  As a result GM pulled all those trucks off the street, bought them back.

A few years ago a CNG fleet van blew up in Pasadena.  There was no direct evidence of damage to the tank, but it was mounted under the vehicle floor and thus subject to road damage - and was nearing the end of its service life.

As for octane rating, I have never heard of a RON for CNG, but you need higher octane fuel to deal with higher compression engines, not the other way around.  Putting higher octane fuel in an IC engine will not make it produce more power, and the use of that fuel will not require a higher compression engine.           

bobjengr
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Platinum
CNG AND VEHICLES
bobjengr   3/19/2014 5:54:05 PM
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Excellent post Charles.  I think the following comment is worth its weight in gold:

The bi-fuel setup, which burns CNG and gasoline, will be available on almost all configurations of those trucks. Honda launched the 2014 Civic Natural Gas, which it calls the only factory-produced natural gas-powered vehicle from a major automaker.

Bi-fuel will provide a greater number of "lookers" if not buyers for CNG/gasoline systems. I think the planning here with these manufacturers is definitely on the money and marketable.  As you have discussed in previous posts, infrastructure will play a big role in consumer acceptance.   The bi-fuel "accommodation" will ameliorate any "panic" on the part of the buyer.

 The heating value of natural gas (methane) varies from about 900 to 1200 Btus/Cubic foot.  It depends upon the geographical area in which the natural gas originates.   One previous comment relative to octane rating was 138. That's definitely in the "ball park" with 130 being nominal.  I do think there may need to be slight modifications to the engine. (Not too sure about this one though.) Again, excellent post and thank you for keeping us informed. 

 

William K.
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Platinum
Re: give me gas
William K.   3/19/2014 5:55:41 PM
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Charles, the best of both worlds would be to run cars on liquid propane, which has a vapor pressure around 300PSI at normal temperatures. So the tanks can be much simpler to produce and a lot cheaper as well. Besides that, they are available almost everywhere. CVS sells them, even. And no new breakthroughs would be needed, since LP use is a quite mature technology. Plus, ythe tanks last many years. And when they do expire the inspection is simple and easy. CNG does take higer pressures, and far fewer are qualified to inspect the tanks. But the inspection is a lot like getting my oxygen and acetlyn tanks for my welding set inspected.

The simple fix against all of the raod hazards is to extend the trunk floor down and have them in a separate compartment, protected from the weather. Better yet, give them a coating that is salt proof.

Charles Murray
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Re: give me gas
Charles Murray   3/19/2014 7:51:06 PM
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CNG-capable engines generally have to have hardened intake and exhaust valves and valve seats, Turbineman. As for the higher octane rating (I had always thought it was around 120-125), I believe that is handled by the adjustments in the engine control module.

Charles Murray
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Re: CNG AND VEHICLES
Charles Murray   3/19/2014 8:00:02 PM
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I agree that bi-fuel is more appealing for many consumers, bobjengr. Chevy and Ford engineers always take pains to talk about the long driving ranges of their trucks, thanks to the bi-fuel setup.

Trenth
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Gold
Re: CNG AND VEHICLES
Trenth   3/19/2014 8:10:06 PM
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As long as the CNG comes form wastes this is a great option. Fracking is completely unsustainable as long as humans need fresh water.

Diesel from wastes seems like a better fuel, higher density, safer.

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