Natural Gas or Propane Dual-Fuel w/Diesel?

radmatty

New member
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Feb 4, 2018
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Chicago. IL
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2005 Passat
Anybody on the board had any experience with compressed natural gas or propane as a supplemental fuel for performance enhancement or as a dual-fuel scenario?

I saw a couple of YouTube videos created by people seeking to sell equipment to make it possible. They made it look like it was pretty easy to inject a metered stream of natural gas just upstream from the turbo and be running as much as 75% CNG. The benefits seem to be pretty substantial. A cleaner more complete burn of the diesel fuel, increased performance and the ability to use a less costly fuel, in the case of CNG. Of course, carrying any amount of CNG is a pain in the neck due to the high cost of the equipment and the bulky nature of the storage tanks.

Nevertheless, the idea appeals to me. And since I'm contemplating a TDI swap into my Toyota pickup I would have the room and a convenient location to keep a tank or tanks for CNG. With 19 gallons of diesel onboard and 12 gallons equivalent of CNG my truck would have roughly an 1100 mile range.
 
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turbobrick240

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Nov 18, 2014
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maine
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Running on 75% CNG or LPG would give significantly less performance than straight diesel. Unfortunately, both gasses have pretty poor combustion characteristics for compression ignition engines designed to run on diesel fuel.
 

TDIMeister

Phd of TDIClub Enthusiast, Moderator at Large
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Negative on running that high %age CNG/LPG, especially with the rudimentary controls to use it in a car and have it properly interact with the existing Diesel fuel injection system and ECU. 10-20% max as a performance enhancer, and I'm sure Bob Mann (CNGVW) will wax poetic about it so I need not say more about it here.

True dual-fuel (gas + pilot Diesel ignition) setups are far more complex and are seen more for truck and stationary engines, but even then are going more towards to mono-fuel natural gas / propane with spark ignition because recent advances have closed the torque and efficiency gaps but at far lower costs and much easier emission control.
 

CNGVW

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Thank for the kind words TDI Master
Let's see one of my ALH street setup with a computer control system did for added HP and Torque red is with CNG first time on the dyno

This on the Ford truck 70% CNG 30% on one test
the cost of CNG at the time was $1.00 a GAL below is a3 pulls with 2 CNG/D one for max power and one forever day driving


I do not do any more system cost of CNG is too high got a bunch of systems and support stuff I will sell off
Negative on running that high %age CNG/LPG, especially with the rudimentary controls to use it in a car and have it properly interact with the existing Diesel fuel injection system and ECU. 10-20% max as a performance enhancer, and I'm sure Bob Mann (CNGVW) will wax poetic about it so I need not say more about it here.
True dual-fuel (gas + pilot Diesel ignition) setups are far more complex and are seen more for truck and stationary engines, but even then are going more towards to mono-fuel natural gas / propane with spark ignition because recent advances have closed the torque and efficiency gaps but at far lower costs and much easier emission control.
 
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wrenchtech

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Joined
Feb 1, 2018
Location
Lake Geneva, Wisconsin USA
TDI
2005 Golf TDI
I was seeing stuff on youtube that made it seem like a thing to look into. It looks like a number of individuals have tried to create businesses selling CNG dual fuel systems, but they seem not to last very long.

Glad to get the straight dope here on TDIclub.

So if anything, CNG or propane are best used as a performance enhancer at low concentration (10 -20%). Any benefits of one of those fuels, one over the other?
 

TDIMeister

Phd of TDIClub Enthusiast, Moderator at Large
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Canada
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Propane stores as a liquid, so it has a much higher BTU per volume stored - a tank that fits in the spare tire hole holds more propane than a CNG tank that sits between the rear shock towers.

OTOH, CNG has a higher octane rating and autoignition temperature, making it more resistant to knocking and preignition when fumigating it into the intake of an engine and compressing it 19.5:1.
 

NewTdi

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NorCal
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Bob Mann, do you have a kit that you are selling for the CNG?
I believe I came across one of your YouTube videos which caught my attention.
 

deckerfl

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Jan 29, 2011
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Falls Church, VA
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2004 Passat Wagon TDI W/ Geared BSM, DUK 5Spd.
I have a CNG setup in my Passat TDI (BHW engine) I run about 35% CNG, (my MPG readout shows ~65 MPG vs 40MPG on diesel alone) There is more power but I haven't really tuned it yet for the CNG, so I think overfuelling is limiting my power. Propane is denser, for sure but more expensive. Natural gas at home for me is around $1.00 for 1 GDE, gallon diesel equivalent. but that's ignoring the compressor I have to compress it and repairing that and keeping it running is a whole other expense / time consumer. In fact, in my mind it's the lack of quality home CNG compressors that prevent CNG from being more widely used. I'd do a search and see the cost of CNG at a local CNG pump nearby, and the price of Propane. that maybe the deciding factor.
 

Pat Dolan

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Propane stores as a liquid, so it has a much higher BTU per volume stored - a tank that fits in the spare tire hole holds more propane than a CNG tank that sits between the rear shock towers.

OTOH, CNG has a higher octane rating and autoignition temperature, making it more resistant to knocking and preignition when fumigating it into the intake of an engine and compressing it 19.5:1.
With ignition temperatures under 600C I would think in a highly boosted and loaded diesel detonation would become a limit, not so?

I have recently seen some interesting technology for handling liquid hydrogen as a motor fuel, but wonder about once more detonation of an aspirated charge and of course hydrogen embrittlement of steels in liner and rings. Could fix the liner issue with Reynolds 390 or similar aluminum/silicon alloy cylinders but not so sure about rings. May be possible to simply inject Hydrogen from one side and diesel on the other side of chamber to act as pilot charge to control ignition.

Any thoughts?
 

Lightflyer1

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Banned subject.

 

[486]

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MN
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02 golf ALH
There is a section of “alternative fuel corridor” from the MS-LA state line out to around El Paso, TX IIRC and I’m sure there are many more areas around the country offering this option. My father worked in Brazil for many years and he told me that most of the more sparsely populated areas were running some form of compressed gas. Said that they could easily hot tap the pipelines and set up impromptu stations for everyone.
I’ll be digging a little more into this concept to see if it would be a viable and cost effective option for myself.
sadly you end up putting more energy into compression than the fuel's got in it when working at the higher pressure levels
you could probably do a very limited range homebrew sorta deal with a 100lb propane tank filled to 300 psi or so using a refrigeration compressor fed from your 1/2psi home natural gas hookup, but for most... well, the juice ain't worth the squeeze
if everything's ticking along just fine before you show up then is it really necessary to point such things out?
 

Lightflyer1

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Talk to the moderators, they are the ones who banned the subjects and whomever posts are the ones violating the ban. There is a reason they banned this stuff.
 

[486]

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had a 100lber that the valve was leaking on, dumped out what liquid I could into a different tank, but there's always the residual vapor pressure
anyways, figured I'd get some use outta it so I plumbed up a needle valve to meter it into the hose I use for installing starting fluid into the intake from the driver's seat

I couldn't really tell much difference going down the road with the valve open or closed, and the exhaust that normally gets into the cabin sorta smelled like unburnt propane.
I guess I wasn't putting in enough for it to reach the lower flammable limit and it was just too lean to be ignited by the diesel flame?
Kinda confusing because I thought the whole point of it was you put in a very small amount nowhere near stoich so that it doesn't ignite just from the compression alone.

When I was running along WOT, it did smoke black a little more with the propane running, so it was certainly doing something in that case. Just kinda confused by the lack of it doing much of anything at low load cruise.
 

TDIMeister

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If you were smoking before adding propane, adding it will not magically make it go away because you're shifting the trapped stoichiometry even richer by not one but two mechanisms - chemically adding fuel without more air and volumetrically displacing said air with fuel.

All previous talk about propane being a combustion "catalyst" is totally and utterly BS. A "catalyst" by definition does not itself get consumed. Now, you might want to get smart and argue that the smell of unburned propane is evidence of this, but that is circular thinking.

Dual-fuel engine OEMs (e.g. Cummins-Westport) learned long ago that premixing the gaseous fuel causes HC emissions to skyrocket. Part of the reason does have to do with the lower flammability limit, but the LFL is not constant. The reported values in the literature, usually in vol% in air, are tabulated from experiments done on what's called a constant-volume bomb ignited from a spark in the center) and only assume a certain initial pressure, temperature, no other species present and lack of charge motion and turbulence - usually ambient, quiescent, stoichiometric, pure and thoroughly premixed conditions. Changing any of those parameters will affect the LFL.

Perhaps a more important cause of high unburned HCs aside from stoichiometry and LFL is the presence of fuel species in crevice volumes (e.g. above the top piston ring) and in dead volumes adjacent to relatively cold walls, like in the squish region. The squish zone is also called the "quench" zone for this exact reason - because the flame gets quenched from the cold walls.
 
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miningman

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Sep 3, 2007
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alberta
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Burning 100% raw propane in a gasoline motor used to be very effective and economic. Dont see it much these days and it isnt very relevant to diesel combustion either.
 

[486]

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If you were smoking before adding propane, adding it will not magically make it go away because you're shifting the trapped stoichiometry even richer by not one but two mechanisms - chemically adding fuel without more air and volumetrically displacing said air with fuel.
well yeah, that's why I said it, means it's obviously burning in there, the strange bit to me was it not burning at low load
was sorta halfway wondering if they maybe ran an impco style mixer and regulator on the diesel pilot ignition motors, just to keep it at a flammable mixture, but that'd just be a runaway... Neat bit of info that they also ran into the HC emissions going way up, must be why you see cummins c-series motors with a throttle plate and spark plugs.
 
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