More Thoughts On CNG - PowerStrokeNation : Ford Powerstroke Diesel Forum
 
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post #1 of 8 (permalink) Old 02-13-2014, 05:12 PM Thread Starter
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More Thoughts On CNG

The price of diesel is in the $4/gal range and may stay there quite a while.

Around here, CNG sells for about $2/gal (gasoline equivalent) so it is worth a thought. The EPA is still making it difficult for one to do CNG conversions commercially, but that may change in the next year or so.

Diesel engines are naturals for natural gas because they have high compression ratios. Compression = efficiency.

Diesel conversions today are what anybody who has ever been in the oil patch calls "dual-fuel." The octane rating on natural gas is so high (~120 motor octane) that the stuff simply will not compression-ignite. It need something hot to make it burn. A "dual fuel" engine uses the diesel injector as a spark plug. Just a small squirt of diesel compression-ignites and blow-torches the natural gas into combustion.

Diesel CNG conversions use either a "fumigation" system that has a single point of natural gas injected into the intake manifold (technically an "air box") with what looks a lot like the throttle body injection used by older gasoline engines. The "electronic carburetor" if you will. The other alternative is the "port injection" option. Here, a port injection hole is drilled and tapped into the intake manifold and the injector is aimed at the intake valve. Just like with port injection gas engines.

In either case, the diesel injectors are reduced in output to a minimum volume squirt per combustion event and the engine output is controlled by varying natural gas flow. In either case, a throttle is not needed because the diesel "spark" is hot enough to fire the leanest or richest mixture of natural gas and air, so the engine always operates under an "excess air" situation.

In the short term, this is the conversion we will see if the EPA ever gets out of the way.

But for new engines, maybe you don't want to have the expense and complication of two fuel systems.

You could make a diesel into a very high compression spark-ignition engine by pulling out the diesel injection system and replacing it with a strong spark plug. But now you need to control air:fuel mixture to assure combustion unless you have a spark with the power of a lightning bolt. Most big diesel engine manufacturers have natural gas engines that are exactly that: Diesel engines with spark plugs.

The diesel racing community has some sharp cookies. I'd bet they could come up with a spark plug top replace injectors.




Another thing holding up CNG in diesel trucks is tankage. CNG tanks are necessarily pressure vessels. They are pretty much identical to SCUBA tanks. Heavy, bulky, and expensive.

I looked into CNG tanks for my truck. Because i drive so much I really need a minimum driving range of 500 miles. Using the "dead cat space" in my short bed, I could piece in the 24 gallons of tankage I needed but it rapidly got to be a $2,000 project. If CNG is gonna take off this has to be improved on.

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post #2 of 8 (permalink) Old 12-09-2014, 05:36 PM Thread Starter
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Re: More Thoughts On CNG

Update on fuel prices around here.
$3.57/gal for No. 2 diesel. about 80 cents more than regular gasoline.

Two CNG fuel stations have popped up. They sell CNG for $2.50/gge ($2.80/dge).

Suddenly home compressors are showing up on the market for less than the huge price they commanded a year ago. Figure 2.5 kwh to compress a gallon equivalent.

At Indiana prices thats $1.40/gge for Schedule 60 natural gas and 25 cents a gallon equivalent for electricity, adding up to$1.65/gge ($1.85/dge). Half price fuel has got to be interesting for the high mileage driver.

I'm looking for some of our PSN vendors to start offering CNG conversions.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
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post #3 of 8 (permalink) Old 01-28-2015, 07:17 PM Thread Starter
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Re: More Thoughts On CNG

Local CNG stations are not competitive.

CNG around here goes for $2.49 gge ($2.77 dge).

RUG is selling for around $2/gal and diesel for about $2.75/gal.

Who wants to pay for an expensive conversion AND pay more for fuel?

C'mon, guys.

Natural gas sells for about $4.75/decatherm ($0.59/gge or $0.66 gge) on the NYMEX. Add 25 cents per gallon equivalent and their total cost for it is less than a dollar. Even residential gas and residential electricity (for compression) would come in at about $1.60/gge.

At $2.49 I'd bet they aren't selling much.

There is an old Wall Street saying: Bulls make money, bears make money, and hogs get eaten. The CNG stations are being greedy and they might find themselves out of business.

2000 F-350 SC 4x2 6 speed
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Slammed 4"
Rugged Air Dam
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post #4 of 8 (permalink) Old 01-29-2015, 10:44 AM
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Re: More Thoughts On CNG

With low fuel costs I don't plan on a CNG dual fuel setup anytime soon. The payback due to the cost of equiptment takes a bit of time for an average commuter. There is also less btu in CNG than diesel.

97 250 7.3 Eaton VMP TVS, IDI performance T4 mount, S369SXE, my B code 350/200- my tunes- honey badger SR, Efuel, 5" SKY RSK TTB, BMW M3 seats, Toyo M/T
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post #5 of 8 (permalink) Old 01-29-2015, 02:20 PM Thread Starter
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Re: More Thoughts On CNG

Re: Post #4
"There is also less btu in CNG than diesel."

Per unit volume you are right, but only No. 6 residual oil has more BTU/unit volume than No. 2 middle distillate. CNG is sold in gge (gasoline gallon equivalents -125,000 BTU) or dge (140,000 BTU).

Yeah, compared to RUG or diesel No.2, CNG fuel tanks are bulkier and heavier. As always, there is no free lunch.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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post #6 of 8 (permalink) Old 01-30-2015, 08:02 AM
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Re: More Thoughts On CNG

Does seem to clean up the smoke quite a bit. That is another good reason to run CNG. If you dial the truck in correctly you can build good clean hp. If the price on diesel goes back up again I will consider building a basic CNG kit.

97 250 7.3 Eaton VMP TVS, IDI performance T4 mount, S369SXE, my B code 350/200- my tunes- honey badger SR, Efuel, 5" SKY RSK TTB, BMW M3 seats, Toyo M/T
54 GMC 453T
45 Chevy 451 diesel
51 Mack A51T
1916 Federal 1 1/2T
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post #7 of 8 (permalink) Old 08-28-2015, 01:16 AM
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Re: More Thoughts On CNG

Cng is going to be the way of the future in many states. You can get a complete conversion for a diesel of gas with tank for around $8000 in my area. The payback isn't very fast these days with unleaded at 1.94, diesel at 1.99 and cng at 1.69. I don't think these prices are here to stay.

Converting a diesel to cng/diesel is fairly cheap if you purchase a kit, ($400) and tank for ($1200) and install yourself it won't be EPA certified but I don't think that means a lot. Tanks in my area can be found between $500-$1200 for a used non expired tank. If you don't mind changing them often you can find tanks with a couple years left on them for next to nothing.

I have a 2002 7.3 I will convert within the next year hopefully.

(One seven eleven around here is sells there cng for .40 a gallon less than anyone in the state. The owner of the store owns the well or so the story goes.
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post #8 of 8 (permalink) Old 09-04-2015, 04:53 PM Thread Starter
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Re: More Thoughts On CNG

As of this morning natural gas is sold on the NYMEX for about $2.50/DTh. A natural gas station would buy their gas on the NYMEX. Figure a DTh is a million BTU so there are 7 diesel gallon equivalents in a decatherm. So the commodity cost is 36 cents per dge. Add maybe 4 cents per dge for pipeline transportation and 25 cents per dge for compression, the filling station has 65 cents per gallon cost basis. Allow 20 cents for operations and profit and CNG should sell for about 85 cents per dge or roughly about a third of what diesel costs.

CNG is currently not taxed like RUG or diesel but that will change. Government always wants a piece of the action.

If you have 240 single phase in your garage you can buy a "Phyll" for about six grand and run off you residential natural gas. My Rate 60 gas is about 50 cents per therm so allowing 25 cents for compression so that yield a buck per dge into my tank - about 40% of what diesel costs at the station.

There are currently two CNG stations within driving distance for me and they both sell CNG for about $2.50/gge (or about $2.85/dge).

The upfront costs are the killer. $8,000 per vehicle for conversion kits and $6,000 for a compressor setup means I'd have to drive at least double what I do now, and I drive a lot for a glorified commuter.

Also important is that gas control is still maturing. What i'd like to see is a refined version of the old 'dual-fuel" engine. The engine gets about 5% of its power from the "spark plug" injection of No. 2 and 95% from the CNG. GE and Caterpillar are doing this for LNG locomotive conversions. Fuel is about a third of their operating costs so this could be a huge opportunity for them.

2000 F-350 SC 4x2 6 speed
3.08 gears Gear Vendor Overdrive
Slammed 4"
Rugged Air Dam
315,000 miles
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