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Old 05-13-2009, 06:27 AM   #1
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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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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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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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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
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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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Old 07-09-2020, 08:42 PM   #6
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Finding this thread some 10 years later - just checking for an update - is it easier to find CNG fueling spots for cross-country trips now, as compared to 2009 or 2010?

Thanks for any information you can provide - I'm looking to buy a bus, and CNG is appealing to me.
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Old 07-09-2020, 09:30 PM   #7
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Here's a map of CNG stations:

I don'k know tank size or range of the vehicle, but some places you won't go, like Glacier National Park. I'd be more worried about the regulatory aspect. The tank, and I assume the piping, are certified and inspected items. I would also think getting insurance might be even more of an issue.

Most people here avoid the electronic and particulate control systems of
modern diesels. But if you wanted to go green I'd think a 35 foot or under modern diesel bus with a 6 speed automatic might be the way to go.

I was working on a small ferry boat in shipyard. The top-ends were done on a pair of Cat 3508's. Two guys from the local Cat place replaced the heads, hauling them in and out of the boat, and up and down the dock. When they were done a guy in clean bright white coveralls comes down with a couple of cans of Cat white spray paint and a laptop. He touches up all the wrench marks on the engines then plugs in his laptop and starts an engine. He then does an electronic injector adjustment by laptop. Now, can anyone guess who makes the most money?
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Old 07-10-2020, 09:32 AM   #8
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I had a CNG powered Crown Vic at work. It had a very short range, poor get up and go and was easy to over heat if it was pushed hard. It was disposed of with less than 25,000 miles on it. YMMD
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Old 07-10-2020, 05:09 PM   #9
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Here in Australia, CNG cars and light trucks are common. A few are dual-fuel, starting on gasoline and switching to CNG, but that isn't optimal. The dedicated CNG vehicles run much higher compression to take advantage of CNG's higher octane rating, and are great. I had a Ford Falcon (Australia-only full size wagon, RWD with a 4.0 straight six) that was a dandy, and had a 600+ mile highway range on twin tanks that worked out to about 38 gallons of gasoline. Bone stock from the Ford dealer. I sold it a few years before the tanks expired, which IIRC was 20, with a recertification required at 10.

CNG is plentiful here, probably 80% of gas stations in Western Australia have at least one pump for it. Its a little cheaper than gasoline, but you use about 15% more of it, because the fuel holds that much fewer btu of energy compared to gasoline, so its kind of a wash on cost. The motors seem to last forever, though, getting bad fuel is almost an impossibility, and the oil and spark plugs stay super clean for a very long time.

CNG diesels are rare. The motors are significantly different, with lower compression and spark plugs. They seem to be essentially Otto-cycle (gasoline) conversions of a Compression engine (Diesel) block and heads, but I don't know exactly how they work. They haven't caught on because nothing packs as much energy per tanked pound than diesel fuel, so CNG trucks lave limited range and need enormous fuel tanks. Since everything here is so far apart, and "road train" trucks here already have enormous fuel capacity, (200-400 gallons of diesel,) CNG just doesn't make as much sense as it might for a transit bus in a polluted city.

If you're thinking about buying a CNG bus and converting it back to diesel, forget about it. The motors, control electronics and fuel systems have nothing in common, and the expense would overwhelm any savings in a lower bus purchase price or down the road. The CNG buses I've seen just don't have the range to do anything but white-knuckle it between the few and far between refueling spots in North America over the road. Adding range is prohibitively expensive, and eats up nearly all the available space under and/or above the coach. This isn't going to change. It will be far easier and cheaper to buy and store diesel fuel or gasoline on board for the foreseeable future.
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Old 09-11-2020, 01:47 PM   #10
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Who does the vehicle "service" on these buses? I wouldn't imagine it is easy to find a garage that you could take it to. We have a CNG opportunity but the drawbacks of living on the road seem too high.
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Old 09-17-2020, 02:54 PM   #11
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I personally would not mess with a specialized CNG vehicle. Ive bought fancy specialized items before and run into hassles trying to use them. Iím trying to get by with standard equipment now.
I had a propane powered shuttle bus at one time originally from the SanDiego airport. I gave away the engine and used the bus for storage . A guy was glad to pull the engine and take it. I later gave away the bus chassis and a guy was glad to take it because it was aluminum.
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Old 09-17-2020, 03:00 PM   #12
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Costs less, but makes less power, so you have to use more. No real savings in the end. CNG is not as available as gasoline or diesel.
More beneficial for fleets as they buy the gas in much larger volumes than an individual would.
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Old 09-21-2020, 05:43 PM   #13
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Only worth it if you live in or near a city and don't travel much.

A CNG vehicle is not worth converting back to gasoline or diesel, because with OBDII engine management, EVERYTHING is different.

Ironically, it is easier (and slightly dangerous) to set up a poor man's propane system via intake vacuum port on an existing gas engine so you can run both easily. It must be done VERY CAREFULLY, though, and I wouldn't do that on a diesel.
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