Date: Mon, 23 Aug 2010 03:13:56 -0400
Reply-To: frankgrun@AOL.COM
Sender: Vanagon Mailing List <vanagon@gerry.vanagon.com>
From: Frank Grunthaner <frankgrun@AOL.COM>
Subject: Re: Propane power...anyone know about that?
In-Reply-To: <BAY152-ds18E0CBE489F133AF59559DA0820@phx.gbl>
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Thought I would add a few comments to Dennis' take on the propane carburation. While it is true that liter by liter (or more precisely, molecule by molecule) the LPG mixture has less energy than gasoline, the pragmatically observed difference is about 10% less distance on average per liter of LPG. The molecular energetics corrected for density are closer to 30% and the difference is often attributed to more efficient fuel mixing as well as more efficient combustion.
The majority of dual fuel vehicles (discounting forklifts and the like) are older carburated vehicles running low compression smog motors. The effective octane rating of LPG is around 104 and the 1.8L to 2.0L I4 VW engines are ideally suited for dual fuel conversion. The burn profile of LPG in the combustion chamber is quite different from gasoline and to properly run a dual fuel vehicle, the ignition timing should be set from 12 to 15 degrees advanced (relative to gasoline) up to about 4,000 rpm. Five years ago and earlier, an electronic ignition modifier was available from DualCurve (now MSD) that electronically generated an advanced timing curve using the gasoline timing signal as an input. This synthesized ignition profile generated a propane specific timing curve from idle to 6,000 rpm when triggered on for propane (read LPG) operation. These units are now obsolete, but I know of a reliable source, should anyone need the information.
To convert to dual fuel, one needs a LPG tank, a LPG and a gasoline lock-out solenoid, a converter (to convert LPG liquid to gas and regulate the LPG fuel pressure), a mixer (to add the LPG vapor to the inlet airstream) and the appropriate plumbing to bring it all together. The mixer is mounted after the air flow or air mass sensor and before the throttle in a simple installation. A multipole switch is flipped to select LPG or gasoline operation. In the gasoline mode, the the LPG source feeding the converter is valved off. In the gasoline mode, the fuel injectors are switched off and a solenoid shuts off gasoline to the injection manifold. In simplistic conversions, the gasoline is switched off and the injectors are permitted to continue firing. Without liquid flowing in the injectors, the solenoids can overheat leading to injector damage. The same ignition is used for LPG or gasoline operation, but it must be in top condition as the LPG does require a higher ignition potential. In LPG operation, the engine output is still controlled by the throttle. Propane systems respond very well to a turbocharged configuration - difficult to force into detonation.
The primary components are available, periodically, used from Craigslist and eBay for $200 to $400. Should you decide to take such a project on, you should at least have your installation and configuration checked by a certified LPG inspector.
Dual fuel operation has two main practical drawbacks: 1).Cost and placement of LPG tanks with adequate volume to achieve the necessary range (room for perhaps 3 tanks under the floor and between frame rails) and 2).The paucity of LPG fuel stations. There are also several positive points including cost, cleanliness and efficiency as discussed by Dennis. Note that LPG has all the advantages and characteristics of gaseous fuels. I need not point out that LPG refueling stations outnumber hydrogen fuel stations by 4 or 5 orders of magnitude on the North American continent!
For what the comments are worth,
Frank Grunthaner
-----Original Message-----
From: Dennis Haynes <d23haynes57@HOTMAIL.COM>
To: vanagon@GERRY.VANAGON.COM
Sent: Sun, Aug 22, 2010 9:07 pm
Subject: Re: Propane power...anyone know about that?
Propane is significantly cheaper than gasoline partly due the road use and
other taxes not being applied. When I get propane for my motor home while
traveling I am usually required to sign an "affidavit" that the propane is
not being used as a motor fuel.
Propane has significantly less energy per gallon than gasoline, you will
need more of it.
On the plus side it is cleaner, naturally higher octane and metering systems
are simple and often bolt on. I have dealt with propane engines on forklifts
and small street sweepers and natural gas for larger generator engines.
Natural gas for a vehicle has the disadvantage that it has to be compressed
or liquefied to provide any reasonable range. LPG is normally distributes as
a liquid.
Dennis
-----Original Message-----
From: Vanagon Mailing List [mailto:vanagon@gerry.vanagon.com] On Behalf Of
Don Hanson
Sent: Tuesday, August 17, 2010 10:08 PM
To: vanagon@GERRY.VANAGON.COM
Subject: Propane power...anyone know about that?
Just curious. Today I saw propane for $2.11 per gallon just off the
freeway (I-84 in north central Oregon) whereas gasoline is now about $3.10.
I borrowed a pickup that was a propane conversion once and drove it from
Jackson Hole, Wyoming to Salt Lake and back...seemed to work pretty
well..this was years ago. Is anyone still doing that, converting gas motors
and driving on propane? Vanagons ever do that? Anyone have any discussion
about that possibility for a Vanagon? It's probably cleaner and it doesn't
come from import or get drilled out of our oceans, leaving a big mess..Just
curious..
Don Hanson
