Looking for Experiences / opinions on CNG Kits and/or Methods of Metering in CNG

deckerfl

Well-known member
Joined
Jan 29, 2011
Location
Falls Church, VA
TDI
2004 Passat Wagon TDI W/ Geared BSM, DUK 5Spd.
Hi Fellow TDI'ers,
I'm going to add CNG capability to my TDI, and was hoping to hear from others who have tried this on TDI's. Specifically, what Kit you used and your experiences with it, regarding installation, function and performance.
Most of the Kits I have seen are, as I understand it, mechanical in that a venturi is placed in the intake, before the turbo, and CNG is metered in based on the air flow going past the venturi (kind of like a carburetor). These kit, would likely be easier to install, and are cheaper, but there's probably no ability for finer control of CNG metering
The other method I've seen is an electronic ECU, which taps into Throttle and RPM signals for inputs and controls a stepper motor to control CNG metering into the intake (kind of like an open loop fuel injection). These seem to be a bit more expensive, but I imagine will allow finer control of CNG metering, if that is necessary.

I actually like the idea of the simpler mechanical system, but some situations worry me in that I'm not sure what the outcome would be. For example: say I'm on a highway, in gear at ~70mph, and I'm going downhill, I let off the throttle, so Throttle is 0%, but the downhill grade, is driving the engine, keeping the RPMs up, say at 2K RPM. Since the RPMs are up at 2K RPM, air is flowing into the engine at a higher ratethan Idle, would the venturi, be metering in CNG, thus fueling the engine, speeding up the car, and higher RPMs, leading to higher RPM's and more CNG, and so on leading to a runaway situation?
I guess I need to plug in my VCDS and log to Throttle, Airflow, and Diesel injected, (Maybe EGT too) to figure out the relationship between these paramaters under different engine loads and engine speeds.

Sorry for the long post, I'd appreciate and opinions and / or experiences.

BTW, the car is an '04 VW Passat TDI. These have the BHW engine, and an Auto transmission unfortunately, so i'll have to be careful with any increase in peak power output.

Thanks,
Dan
 

puntmeister

Veteran Member
Joined
Feb 3, 2013
Location
Arizona
TDI
2004 Jetta BEW
Where have you seen these kits? Very interesting conversion. I saw oodles of CNG converted diesel trucks (in Thailand), but never heard of a diesel car getting such a conversion.

I would love to hear any experiences.

I, too, would question how this would work out on a simple system which feeds into the intake, without accounting for all the other factors. I can't see such a system functioning smoothly without interfacing with the ECU. But I could be wrong...
 

puntmeister

Veteran Member
Joined
Feb 3, 2013
Location
Arizona
TDI
2004 Jetta BEW
I took a look at this idea - very interested - but found stations for CNG are few and far between, and the ones local to me sell CNG for about $2.50 gge. Not sure why the price is so high, given NG is dirt cheap right now. Maybe the localities have started to tax it?

Cheaper than diesel - but not by enough to make it worthwhile, at least for me. If the gge price were more like $1 to $1.50, then I'd take a harder look.

As for home fueling - the equipment cost is about $4,000....
 

deckerfl

Well-known member
Joined
Jan 29, 2011
Location
Falls Church, VA
TDI
2004 Passat Wagon TDI W/ Geared BSM, DUK 5Spd.

ducesrwld

Veteran Member
Joined
Jan 10, 2009
Location
WI
TDI
none
I looked into this stuff years ago but just got turned off on the large amount of space required to be able to have decent range without always refueling. if you have plenty of trunk space that you don't use go for it, I've invested in the biodiesel route has a lot better BTU output and can use the existing fueling system in the car.
 

darkscout

Grammar Scout
Joined
May 28, 2006
Location
Michigan
TDI
2003 Golf
The thing with the CNG is that you can run on it when you have it and swap back to full diesel no problem.
 

CNGVW

Vendor , w/Business number
Joined
Sep 15, 2009
Location
Bob Mann Auto, 111 High St, Pembroke MA 02359
TDI
Many TDI Jettas and a Beetle Race car run 2010 jetta tdi cup car build roadrace
Hello it comes down to price for CNG if you can buy or fill at home for $ 1.00 or under it is a win win. I do fill at home for about 60 cents. I run a 2002 A6 turbo,
2000 Nissan Xtara, 20004 VW V8 Torage , 1995 Eurovan Rialta all are Bi-Fuel CNG systems.
For the diesel market here in the USA it will take a long time for people to convert to CNG. It is the most eases and lowest cost of conversions to do.
Bob Mann
 

deckerfl

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Joined
Jan 29, 2011
Location
Falls Church, VA
TDI
2004 Passat Wagon TDI W/ Geared BSM, DUK 5Spd.
Thanks Bob, I looked at your youtube videos. You have quite alot of experience with conversions it seems.

@ducesrwld. I see your point. You lose cargo space to have any decent range on CNG. I don't want to lose any trunck space, personal preference, so I'm going to sacrafice range. I'm getting a 3.6gge tank. My Passat has 2 mufflers. With a turbo, EGR and (dpf? I think mine has one, not sure) in there, one muffler is really enough. So I removed the second muffler, without noticeably increasing the exhaust sound level. The Tank will go where the second muffler was.
I installed a used Natural Gas compressor at home. Marginal rates for Natural gas at home are ~$0.90 per therm(100kBTU)> but If I have problems with my compressor I can fill up at a station in the area for $2.10 per GGE. But I'm hoping to be able to fill up at home, so that my small 3.6GGE tank won't be too inconvenient requireing frequent stops at the CNG Station.
Dan
 

CNGVW

Vendor , w/Business number
Joined
Sep 15, 2009
Location
Bob Mann Auto, 111 High St, Pembroke MA 02359
TDI
Many TDI Jettas and a Beetle Race car run 2010 jetta tdi cup car build roadrace
There are rules on placement of tanks and lines as a Certified CNG Fuel System Inspector. The tank must not be below the frame rail or under body. If behind the axle it must be left to right placement and not behind the bump. And should have a cover. With a 3.6 GGE tank with a good CNG blend system you will double you miles per gallon on diesel at a 50% blend. I would place a 6.5 tank in the trunk up close to the back seat. That is were I place my tank installs.
Bob Mann
 

deckerfl

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Joined
Jan 29, 2011
Location
Falls Church, VA
TDI
2004 Passat Wagon TDI W/ Geared BSM, DUK 5Spd.
Thanks Bob,
I'll have to rethink the tank placement then.
Are you refer in to NFPA 52? It also calls for a gasket between the tank and the brackets. And the shield can't contact the tank.
If I comply with NFPA 52, I should be ok?
Thanks again Bob
 

CNGVW

Vendor , w/Business number
Joined
Sep 15, 2009
Location
Bob Mann Auto, 111 High St, Pembroke MA 02359
TDI
Many TDI Jettas and a Beetle Race car run 2010 jetta tdi cup car build roadrace
The NFPA 52 should be the bible for you to follow.
for the tank straps just use thin rubber or polymer strip.
And if the tank is in the trunk it needs to be bagged with a vent to the out side. I am updating my site www.DRVOLKS.com with my TDI fixes and my YouTube's clips I will add all my CNG stuff too soon.
I found my very first CNG install on a 1999 VW beetle 2L I videoed the whole thing just got to clean it up and load it to YouTube for those that may wish to learn the right way to do a CNG install.
Bob Mann
 

bjterry62

Member
Joined
Nov 11, 2011
Location
New England
TDI
Passat B5
Bob, I have an 05 Passat TDI and am thinking hard about adding CNG. Does the tank take up all of the trunk space or just the back area between the wheel wells? Tank diameter & length would tell me a lot. I also need some service work done and will be contacting you about that soon.

Thanks,

BT
 

CNGVW

Vendor , w/Business number
Joined
Sep 15, 2009
Location
Bob Mann Auto, 111 High St, Pembroke MA 02359
TDI
Many TDI Jettas and a Beetle Race car run 2010 jetta tdi cup car build roadrace
Hello A 6 GGE ( GAL ) tank will fit right up next to the back seat it has a 16 inch diameter an most will fit between the shock towers. Done right you can still get the spare tire out too. I did to a 2006 gas 2.5L I will have to find the PIC.
I am selling my 2002 Audi A6 turbo CNG Bi- Fuel. Just build a CNG Bi-Fuel 2004 VW Torage V8
for my wife. I have a 6 GGE in the back cargo space running the long way on the left side. ( the NFPA 52 says the tank if behind the axle should be placed left to right? But I am seeing new cargo CNG OEM vans with the tanks behind the rear axle placed front to back? )
I get about 100 miles to the tank of CNG.
Bob Mann
 
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AndyBees

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Joined
May 27, 2003
Location
Southeast Kentucky
TDI
Silver 2003 Jetta TDI, Silver 2000 Jetta TDI (sold), '84 Vanagon with '02 ALH engine
Since Compressed Natural Gas may be new to some, reading and following this Thread might be easier if the accronyms were explained..... such as, GGE (gasoline gallon equivalent).
 

deckerfl

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Joined
Jan 29, 2011
Location
Falls Church, VA
TDI
2004 Passat Wagon TDI W/ Geared BSM, DUK 5Spd.
I wanted to update my progress since I don’t see many TDI CNG (Compressed Natural Gas) installs. So here we go…
2004 Passat, w/ Geared BSM(Balance Shaft Module, BHW specific issue) and a Rocket Chip stage 2 Tune.
I bought a CNG kit from a company in Utah that also did installs but has since gone under. I had a turbo failure(un-related) which delayed my CNG kit install for a while until I got that squared away. I ended up installing the Type 1 tank inside, right behind the rear seats, just like Bob Mann had suggested. I should have chosen this place from the start.
Anyway, my next hurdle was that over time I had misplaced some of the fitting and had to do a fair amount of research on fittings to figure out what fitting I had and what I needed. This led me to Swagelok, where I found a lot of useful tips on stainless steel fittings and their installation. I ended up just replacing all the kit's fittings with Swagelok Stainless Steel (316) fittings that I know can handle the pressure. I then mounted all the other pieces in the kit, Regulator, to the right of the battery, Fill valve on the passenger’s side just inboard of the fog light. Then a Swagelok “T” that ties all the 6mm piping together, mounted between the Airbox and the Firewall for easy access.
I have ran most of the stainless steel 6mm piping that came with the kit, just have one more run to the Fill Valve. I thought I would need a pipe bender but none of the bends were tight enough to need it, I just bent it carefully by hand. The Rigid Tube cutter with a wheel for Stainless steel worked pretty well, but the wheel gets dull quickly requiring more prep work with a grinding stone.
Next step is I’ll pressure test the system with an air compressor and fix any leaks before going up to the system’s 3600psi nominal pressure. In hindsight, I should have demanded datasheets for the pieces in my kit, or at least more details on manufacturer and part numbers. The seller was hard to reach and vague on details. Anyway, I’ll post up if and when I get it running.
 
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deckerfl

Well-known member
Joined
Jan 29, 2011
Location
Falls Church, VA
TDI
2004 Passat Wagon TDI W/ Geared BSM, DUK 5Spd.
Short follow-up on my experience thus far; mounting the tank was the biggest challenge. After settling on the location directly behind the back seat, I pondered how to mount the tank and brackets. I pulled out the carpet, and pulled the plastic cover underneath, (both of which I cut to allow the aluminum plate mentioned lay directly on the steel floor) .
In this position the CNG Tank would sit right above the diesel fuel tank but I didn’t want to have to drop the fuel tank in order to mount the CNG tank and brackets. I got an Aluminum sheet, 0.25” thick, cut it to size and carefully installed 8 blind rivets into the steel floor, mostly where the steel looked re-enforced (Its pretty thin in some places) the and bolted the aluminum plate to the blind rivets. Then I made counter sunk holes in the bottom of the aluminum plate and flat-head bolts sticking up through it to mount the tank brackets to the aluminum plate.
I’m still a bit leery about how strong the blind rivets would be in a crash. I’ll probably add triangular supports from the wheel well to the aluminum plate to keep the aluminum plate down in the case, say of a horrific, spinning , upside-down, crash. In hind sight, ideally I would have dropped the fuel tank and have a plate above the fuel tank and below the steel floor that the tank brackets would bolt to.
All in all, my install is NFPA 52 compliant, except, I haven’t yet vented the interior piping to the outside, which I will do.
 

deckerfl

Well-known member
Joined
Jan 29, 2011
Location
Falls Church, VA
TDI
2004 Passat Wagon TDI W/ Geared BSM, DUK 5Spd.
Progress Update,
I’ve complete the fill valve install, pressured up the system via an air compressor to 100psi, and found some leaks, and tightened up fittings to fix them. Then I filled up at a CNG station, which was pretty cool, but I sprang a leak at the Tank valve, with the higher pressure. After cranking down on that, all the leaks were fixed an I activate the system. And It works!!
When steady state running on diesel, at 2K Rpm, and you turn on CNG, it pick up the RPM and more power comes on.
So, I am officially, Substituting Natural gas for diesel. The power comes on with a little delay as well, so after you add more throttle, there’s throttle lag, and the CNG starts fueling only when there’s more vacuum at the turbo inlet, so there’s a little of lag there too. Takes a little getting used to, but it’s much more lively now, and conversely, feels slower when I turn off the CNG.
I have the CNG at a low setting until I have a chance to log EGTs via VCDS.
 
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