'12 now on CNG

[Roostre]

Just thought I would document my little experiment here. After doing tons of research and mulling it over for literally years, I decided to take the plunge on my 2012 with 7500 miles on it. Please feel free to criticize, question, or just poke fun.

Doing this safely is my highest priority. I have 2 close relatives that are certified installers. It has been good to be able to ask them questions whenever needed. One of them has converted and maintains a small fleet of diesel Sprinter vans. These have racked up well over a million miles on the CNG.

The regulator I am using is a combination unit that is actually used for naturally aspirated gasoline car conversions and will support up to a 5. 0L gas motor. It drops the pressure from 3600psi down to less than 2 psi to feed the low pressure hose. The plumbing under the hood consists of 2 tee'd in 5/16" coolant lines off of the heater hoses and 1 teed in line just before the turbo. The coolant lines keep the regulator at a constant temperature to prevent a 'freeze up'. (As gases expand and drop pressure they cool rapidly)

For this initial testing I only bought one CNG tank, which I found locally on Craigslist for $250. It is about 6 GGE (Gas Gallon Equivalent) , which means it will hold about the same number of BTU's CNG as 6 gallons of gasoline. I plan to add another tank the same size to the left front corner of my bed. They don't take up too much space here, and I want to be able to put a toolbox ever the top of it all down the road.
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My average miles per week is about 300. With 12 GGE worth of tanks I would only need to refill once a week.

I put my fill valve on the drivers side, so it would be easy to remember - all fuels go in the drivers side! :-laf
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The wiring is pretty simple. I have a switch on the dash that powers the system up. It is wired to a Normally Open Hobbs switch that I have set at about 1. 5 psi. From the Hobbs the power runs to a built in solenoid on top of the regulator. The switch is grounded under the dash and the solenoid is grounded to the bed. I am considering adding an oil pressure switch in the series for additional safety.

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(I had not hooked up the solenoid wires when I took this photo- you can see the two prongs - one is ground and one is 12V. Simple. )

I did a few test runs last night with the help of my lovely and talented better half. It only cost me a trip to Texas Road house to have her take notes as I made adjustments incrementally and then tested it. We did these runs on a fairly flat section of highway and tried to maintain 65 MPH at all times for the test.

Initially there was not much of a difference, but as we increased the output of the system things got better and better!! I tried to get some photos of the dash at 65 MPH, but my phone camera just couldn't hack it. So here is a shot just after we got off the highway and hit a nice smooth stretch of side road:
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Cruising on the flat at 65 the instant readout was pegged over 30. My goal is to hit a 50/50 ratio of diesel and CNG. My truck normally runs between 16-19 MPG on these flat stretches, so the instant gauge won't quite help me get there. I will need to do a few fills and compare quantities used (hand calculated) to get a better handle on my mix.

We drove about 100 miles and I only reset the lie-ometer at the beginning. It was a pretty cool feeling driving a CC dually down the highway and getting 25-30 MPG! Around town the CNG can really be felt when it kicks in right after you take off from a light.

Also, I should add that I am running a Smarty on SW#0 to minimize any risk of over-fueling. Power delivery feels a little better than stock and much smoother.

 

[HBarlow]

What's the reason for the system?

 

[NIsaacs]

It will be interesting to see what you hand calculate and don't forget to add the gas usage I would guess the lie-o-meter will lie even more with the help of the CNG.



Nick

 

[Roostre]

What's the reason for the system?

25% overall fuel savings
less demand for foreign oil
cleaner burning~ longer oil change intervals
more power/torque
fun experiment
fewer Regens on dpf if equipped

 

[RustyJC]

25% overall fuel savings

Doubtful. X horsepower requires Y BTU, regardless of whether the BTU comes from the diesel fuel or natural gas. The total BTU will be roughly the same - there's no free lunch here (and yes, our company builds dual-fuel engines, so I know the dyno BSFC results).



Rusty

 

[HBarlow]

I see Rusty has already expressed a professional engineer's opinion. That's what I thought I had read. CNG has a cost per unit plus installation costs that have to be calculated into your comparison.

I not an engineer but believe I've read CNG doesn't produce as much power per relative quantity as diesel fuel.

Sounds like pie in the sky dreaming to me.

 

[rscurtis]

IMO, Rostre is using CNG in a very practical fashion, as an added source of (cheap) fuel using the diesel process as an ignition source. There is no usage variance in BTU's, but there is the price variance with CNG being so cheap in the present market. It also eliminates the need for a spark ignition system and the range anxiety normally associated with alternative fuels. With the computing power available today, it could be used as an admixture in a seamless fashion, with the engine reverting to pure diesel operation when the CNG is exhausted.



It makes a lot more sense than RAM's $10,000 CNG option with its limited range and 8 gallon (IIRC) gasoline tank.

IMO, this is the way to make it practical as an OTR truck fuel.

 

[Roostre]

Doubtful. X horsepower requires Y BTU, regardless of whether the BTU comes from the diesel fuel or natural gas. The total BTU will be roughly the same - there's no free lunch here (and yes, our company builds dual-fuel engines, so I know the dyno BSFC results).

Rusty

Yes- but if I can replace $4. 00 BTU's with $1. 49 BTUs there is my overall savings.

 

[RustyJC]

You might then have a 25% cost saving, but that's entirely different from a 25% fuel saving as you claimed.

Rusty

 

[Roostre]

Just did a little road trip up north to do the annual egg hunt. While there I topped off the CNG and the diesel... drove with A/C on most of the way and speeds between 65 and 80, averaging around 72 or so.



Covered 94. 3 miles. One pass over that was 5969 feet. Home elevation is 4315 feet.



Refilled both tanks:

CNG

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Diesel:

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CNG used: 2. 107 GGE

Diesel used: 3. 950

Total : 6. 057



This shows that I am adding CNG at about 26-27% overall. ( I would like to up this to 50%)



94. 3 miles / 6. 057 total gallons= 15. 56 MPG which is in line with what this truck would normally get and what RustyJC has said.



As for dollars:

$14. 61 on diesel

$3. 15 on CNG - Would have been $3. 69 x 2. 1= $7. 75 in diesel.



Savings= $4. 60 or about $0. 05 per mile.



Now if this holds true at 50% CNG to Diesel I should save $0. 09 - $0. 10 per mile. My system has cost me about $700 to install - tank and all.



Complete payback is about 7000 miles and 4 months away if I did the math rightish.

 

[Roostre]

I see Rusty has already expressed a professional engineer's opinion. That's what I thought I had read. CNG has a cost per unit plus installation costs that have to be calculated into your comparison.

Hopefully the above helps. I know it is just a snapshot, but its a start.

I not an engineer but believe I've read CNG doesn't produce as much power per relative quantity as diesel fuel.

True. But the CNG does have a positive effect on the motors power output. Great article here explains it all very well: http://www.rasoenterprises.com/index.php/alternative-fuels/diesel/38-general/85-dual-fuel

Sounds like pie in the sky dreaming to me.

False... so far it looks to be working just the way it should. Only further testing and time will tell.

 

[Roostre]

You might then have a 25% cost saving, but that's entirely different from a 25% fuel saving as you claimed.

Rusty

Good catch. I really meant fuel cost savings. Really. Honest.

 

[jgillott]

Back in the mid-late '90's, there were a number of guys, including several here locally, that were playing with propane injection on the old 12 and early 24-valves. This doesn't appear to be much different in concept. I'm sure that there are some threads back from the early days of TDR that discussed it.

 

[jgillott]

If anyone is interested, here is an easy to read chart that compares properties of common and alternative fuels.

http://www.afdc.energy.gov/fuels/fuel_comparison_chart.pdf

 

[Roostre]

If anyone is interested, here is an easy to read chart that compares properties of common and alternative fuels.

http://www.afdc.energy.gov/fuels/fuel_comparison_chart.pdf

Nice chart! Thanks.

 

[NIsaacs]

Yes- but if I can replace $4. 00 BTU's with $1. 49 BTUs there is my overall savings.

Is that $1. 49 including road tax or how does that work?



Nick

 

[moparguy]

Corey, First of all congratulations on the project. Over the years I've mentioned that in my past corporate life I was for a time, the lead for cng in our company. Installed a fast fill public station in my town along with several slow fills at customers locations. I drove a cng dual fuel vehicle as did several of my techs. We also did installations and conversions.

One thing I learned is, yes you can reduce miles per gallon fuel cost by a substantial amount, but there are other more subtle benefits, if you do oil analysis you can extend oil changes to almost unbelievable intervals. If you can source and install a home slow fill unit it's so nice to not deal with public stations, you get home in the evening, spend 5 sec hooking up, unhook next morning and have full tanks. I'd go for many weeks not having to deal with service stations. Of course (with diesel) you still have to buy diesel occasionally, but cutting those purchases by half will be great.

One last closing observation from the 90s, supporters of cng were always happy with their conversions, nay sayers never were. CNG does have the occasional inconvenience, it takes a bit of effort, but I found if a potential conversion customer was open minded, willing to listen and learn, they could be happy conversion customers.

Good luck and keep us posted.
RR

 

[Roostre]

Is that $1. 49 including road tax or how does that work?

Nick

Yes, road taxes are included in the $1. 49. The gas company does use residential fees to subsidize their infrastructure expansion and maintain the pumps. I don't necessarily agree with that, but I will take advantage of it.

 

[Roostre]

Corey, First of all congratulations on the project. Over the years I've mentioned that in my past corporate life I was for a time, the lead for cng in our company. Installed a fast fill public station in my town along with several slow fills at customers locations. I drove a cng dual fuel vehicle as did several of my techs. We also did installations and conversions.

One thing I learned is, yes you can reduce miles per gallon fuel cost by a substantial amount, but there are other more subtle benefits, if you do oil analysis you can extend oil changes to almost unbelievable intervals. If you can source and install a home slow fill unit it's so nice to not deal with public stations, you get home in the evening, spend 5 sec hooking up, unhook next morning and have full tanks. I'd go for many weeks not having to deal with service stations. Of course (with diesel) you still have to buy diesel occasionally, but cutting those purchases by half will be great.

One last closing observation from the 90s, supporters of cng were always happy with their conversions, nay sayers never were. CNG does have the occasional inconvenience, it takes a bit of effort, but I found if a potential conversion customer was open minded, willing to listen and learn, they could be happy conversion customers.

Good luck and keep us posted.
RR

Thank you! Our company has been converting over for about a year now. It is like you say- those that see the benefits love the trucks, those that just see it as an inconvenience hate them.

 

[EMAC2]

Very interesting information! Thanks for sharing this.