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dieseltim 09-26-2012 03:18 PM

Diesel + lpg = big mpg
I have not found much about using LPG along with Diesel to boost MPG but after seeing it on a Chevy 6.5 a friend of mine has been running LPG on and reported 30% improvement in MPG, I decide to give it a try. I have an 06 Jetta TDI 1.9 PD that usually gets about 42-45 MPG hand calc. I added a LPG regulator and small 5 gal LPG tank, piped it into the intake just in front of the turbo inlet. My MFD claims that I have jumped from 48 to over 62 MPG. :thumbup:

I am testing a full tank of Diesel + full tank of LPG to see what the real numbers come out to be but it looks really good so far.

If any one else is interested in trying this it really is simple and not that expensive, maybe $200 if you have to buy everything.

The regulator that I am using came from Impco and is a mod. E. the rest is just hose and shutoff valve and a home made venturi, made from a 1/8 " brass "T", I installed in the inlet pipe to the turbo.


UFO 09-26-2012 03:38 PM

Ah, but the catch is you must calculate the cost and energy of the propane in your calculations too. With that taken into account I've not seen evidence that engine efficiency is actually improved.

Varn 09-26-2012 05:44 PM

We pay $1.85/gallon of propane. About twice that for diesel.
Just remember it didn't happen if you don't have pictures :)

Diesel_Dave 09-26-2012 09:33 PM

Yes, assuming your goal is economical, then you need to compare cost improvement (cents/mile). This will include the cost of diesel + the cost of the LPG. If you wish you could calculate an "equivalent fuel economy" on a cost basis like this:


M = miles travelled
Gd=gallons of diesel used
C= cost ratio of LPG to diesel, e.g. (price of LNG per gallon/price of diesel per gallon)
Gl=gallons of LNG used

That way if the cost per gal for LNG is half that of diesel it "counts" as half a gallon of diesel.

If you objective is technical equivalence, then you'll have to do something similar with energy content instead of price. If your objective is carbon dioxide related that you can weight it by the carbon content.

dieseltim 09-27-2012 12:29 PM

This am on the way to work.
Ok, well the forum will not let me post pic yet.

This am I got to work with the reading 66.4 MPG, and miles till empty 535, with 363.3 miles traveled on the MFD.

I realize that the MFD is not real accurate but I will be hand calc. the total diesel + the total LPG to see what the MPG verses dollar is.

If it comes out close to what it is looking like so far I will have about a 30% improvement in MPG over just D2 and only have used maybe 2 gal. of LPG per 14 gal of D2.

So, at $3.85 per gal D2, thats $54 dollars to fill up. That usually gets me real close to 550 miles to a tank. Yes it is a PD so it only holds 14.6 when dead empty, There is no way to purge the 06 Jettas.

So, if I use even 3 gal of LPG @ $1.99, that would be $5.97 per tank of diesel. Or, $59.97 per tank including the D2 + LPG.

So, now all I can do is drive and see how far I can go before I have to refill the D2, then refill the LPG and see how much I have used. :turtle:


metromizer 09-27-2012 02:56 PM

I read a very informative site where the blogger experimented with several improvised systems, one of which used a regulator scavenged from a small BBQ, and a small disposable Coleman camp bottle.

It looked like an interesting option for short term 'on demand boost', particularly for non-turbo'ed Diesels.

If it turns out you get lower combined fuel operating cost/mile, all the better!

Beau 09-27-2012 03:24 PM

I think it should be possible to use (re-purpose) a nitrous solenoid to introduce the LPG, similar to how nitrous is used, no? I believe they have jets of various sizes that can be used. Does that sound correct???

ecomodded 09-27-2012 07:10 PM

I think your right Beau, i found this wiki on Nitrous where it is mixed with Propane or CNG

It is possible to combine the use of nitrous with a gaseous fuel such as propane or compressed natural gas. This has the advantage of being a dry system and yet still maintaining proper air/fuel mixture. Such a system requires exact choice of jet sizes and gas pressure regulation to provide a consistent pressure to the jets. Other advantages include better air/fuel mixing and distribution and less risk of knocking due to the increased octane of propane and CNG.
Nitrous oxide engine - Wikipedia, the free encyclopedia

metromizer 09-27-2012 07:31 PM

Very interesting read for the Diesel propane injection DIY'er... discusses basis, different experiments, crude then more refined systems, safety, variable power level jets

sheepdog 44 09-27-2012 09:01 PM

So if piping LPG into your engine helps (whether for power or FE) what about piping pure oxygen? An ember in pure oxygen will burst into a fire, and gas would presumable burn cleaner. Say just double the atmospheric percentage of o2.

I've always wondered what would happen if you drove a car in the prehistoric dinosaur era when they say we had a much richer oxygen atmosphere.

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