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Old 05-13-2009, 06:27 AM   #1
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Join Date: May 2008
Posts: 7
What do you know about CNG

What experience is out there with the CNG busses. Are they engineered to run on NG or are they converted? Cna they be converted back to ???gasoline or diesel whichever they started life as. Curious if anyone has taken on one of these CNG powered busses.
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Old 05-13-2009, 08:11 AM   #2
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Join Date: Dec 2006
Location: downriver, detroit mi
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Re: What do you know about CNG

I have done some prototype dyno work on CNG conversions both diesel and gas, you will experience a much cleaner burning engine. the biggest downfall is fuel availability, their are more and more fleet vehicles that have their own fuel facilities turning to CNG. some of the local muncipalities, and cities are in the process of making the change. IIRC the new york state highway department had succesfully made the change with all of their trucks then someone had an accident that resulted in a fatality and that was the end of CNG until the end of the investigation.

gas engine conversions are mostly fuel and spark calibrations, also a change in valve material due to higher exhaust temps.

diesel engines use different heads with sparkplugs, addition of an ignition system and complete different fuel system, interestingly enough the modern electronic diesel management systems can support spark and fuel management with jst a programing change.

landfills and wastewater treatment plants have used large diesel engine conversions to burn off methane and generate electricity for many years.
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Old 05-18-2009, 03:02 AM   #3
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Join Date: May 2009
Location: Minneapolis, Minnesota
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Year: 2012
Coachwork: Need bus-as-home over RV
Chassis: still looking
Re: What do you know about CNG

Not much experience, just extensive alternative fuels reading and research.

They burn far cleaner, cheaper fuel than propane but less convenient because it doesn't store as nicely or easily in a tank. (less btu's of fuel for a given tank size/weight so less range) Fuel availability a serious problem "on the road", but easy "from the home" since many businesses or homes would have natural gas for heat already but it might require some kind of pressurization pump, it wouldn't be like plugging a hose in and filling your tank to 5000psi from the grid. Hence fine for fleet vehicles with known common routes they need to run and the cheaper fuel makes the additional infrastructure cost pay back over time.

The engines are similar to propane versions, different mixture and timing (I dont think the compression has to be different than propane, but is different/higher than gasoline) however the tanks to my knowledge are different/cant just run CNG in a propane tank or anything and I think a fair bit more expensive, I think they have to be stronger due to high pressures. (and propane everything is already seeming too expensive vs gasoline due to demand right now) If I remember right refueling CNG tanks is more of a pain in the a** than propane, which is why we dont use it on our grills and stuff already. The high pressure tanks would cost way more and be more of a hazard if punctured.
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Old 05-18-2009, 09:38 PM   #4
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Join Date: Jan 2008
Location: Adirondack Mountains NY
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Re: What do you know about CNG

IIRC the new york state highway department had succesfully made the change with all of their trucks
I haven't seen any CNG trucks, but many of the engineers' and inspectors' cars run on it. They have card-operated fuel points outside the perimeter fence at the larger garages. Employees who live too far from the fuel points get waivers to use liquid dinosaur fuel cars. There is also an H2 fuel point in Albany for a test Honda or two.
Someone said "Making good decisions comes from experience, experience comes from bad decisions." I say there are three kinds of people: those who learn from their mistakes, those who learn from the mistakes of others, and those who never learn.
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Old 03-01-2010, 05:30 AM   #5
Join Date: Jan 2010
Location: Bay Area
Posts: 41
Year: 2001
Coachwork: AmTran
Chassis: International 3800
Engine: DT466E
Re: What do you know about CNG

I just bought a CNG-powered bus and did a lot of research so I can probably add a bit here-

For the most part, all buses I saw were purchased as-new with CNG and all were engineered systems.
(meaning the engine manufacturer sold the system, versus someone else doing a conversion)
It appears to be very easy to convert a gas motor to run on it.

My own is an 8.1L made by John Deere which normally is a diesel used in tractors etc.
I believe all JD did was replace the glow plugs with spark plugs, and maybe alter the pistons, and of course change up the software.
I'm sure it *could* be converted back- but why bother? It's a unique system that has both its benefits and drawbacks.

Advice: CNG is relatively new even for established engine makers but there are many systems in use today, so if you see a bus that runs on it chances are there's some sort of history around about how well the setup works.

Clean burning and thus very easy on engines and oil
(mine has 460,000 miles, doesn't puff any smoke at all, and it feels like all 250hp is still there)
Ultra cheap fuel: (at 1/3 the price of diesel, it's like I get 27mpg!)

Fuel is either plentiful or non-existant depending on where you live:
The tanks take up a lot of room- my bus has no underbody storage because of all the tanks and holds only 50GGEs (like 50 liquid gallons of gas)

The tanks themselves must be inspected every 3 years and have an expiration date of 15 years after they were built.
(my understanding is that there's no actual reason that the tanks have to be destroyed after 15 years, but if you are going to use the vehicle commercially you probably will get in trouble for having expired tanks- and replacement tanks are $$$$)
If you want to spend some money, you can get a compressor for your home that will fill the bus up overnight.

Driving around in a 3600psi bomb waiting to go off? No thanks!
The tanks are over-engineered beyond belief and CNG appears to be about as safe as diesel, and *far* safer than gasoline:
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