DES 8/1 Propane Conversion project

[BruceM]

I'm going to attempt a propane conversion of a DES 8/1.  Using an Impco propane carburetor, lowered compression, spark in the injector hole.  I'm planning on about 750 rpm operation.  Application is AC power and compressed air for an off grid homestead in very rural 5600 ft elevation AZ.  ST-3 planned, 2200 watts continuous is sufficient.

Today I'm trying to find a 16-17" cast iron sheave for a B-belt in order to drive an LaPlant LP205 two stage compressor at about 800 rpm or a bit less.

Anybody know of a good source for large sheaves besides Grainger?  They have a browning but it's $200.

Has anyone tried driving a B Belt direct on the flywheel? I'm thinking there might be sufficient surface area to do that for a modest load.  I'm considering this for the ST-3 drive.  Lots more flexibility in sheave size.  A 10" sheave would match my desired 750 rpm.  A single B belt is more than adequate according to my belt chart.

[mike90045]

I would check the de-rate data for Propane and 5600 ft elev.   You may not make 2200watts at 750 rpm

[BruceM]

You may be right, Mike, it depends on how low I have to drop the compression.  One article I found suggests about 3.5% loss in power per point of compression. So if I have to lower to a compression ratio of 10 from 17, that would be a 24.5% power loss.  If a compression ratio of 12:1 is OK, then a 17.5% loss. The increase in rpm is good for about 15% increase.  So a net 2.5-10% loss over my 6/1 on diesel at the same elevation. I have plenty of headroom on my 6/1 so I think that will be OK. 

[Tom]

Up at that elevation you might be able to run 14:1 with no issues and preserve some of that precious HP.

[cujet]

Just out of curiosity, why not use the diesel injector set at the idle or pilot setting as the propane ignition? That way, you can retain good compression, but probably not full compression. Possibly 15 to 1 at your altitude. Your loads are modest, so you might be able to pull it off. Just thinking aloud here, but an intake restriction would help prevent propane detonation at higher compression ratio's.

[buickanddeere]

Just out of curiosity, why not use the diesel injector set at the idle or pilot setting as the propane ignition? That way, you can retain good compression, but probably not full compression. Possibly 15 to 1 at your altitude. Your loads are modest, so you might be able to pull it off. Just thinking aloud here, but an intake restriction would help prevent propane detonation at higher compression ratio's.

Best Idea here yet.

[BruceM]

Thanks for the good suggestion, cujet. That's a good way to get around the propane/diesel preignition issue. I might consider that for my own engine, but I'm going to try 100% propane on the DES 8/1.

Thanks for the higher compression suggestion, buickanddeere. 

[carlb23]

While I don't get to use my generator much since our power company doesn't have too many power outages, I setup my 6/1 with diesel pilot ignition and natural gas fumigation.  I run enough natural gas (set via a needle valve) to produce approximately 1800 watts with the rack in the mostly closed position, just enough diesel to keep the engine running.  My normal loads are 1800 to 1900.  If the load increases the amount of natural gas does not change the rack just opens to add some more diesel to make up the difference. 

this system is both simple and reliable.  I use an electronic gas valve (off an old gas furnace) that is powered by the generator so if the engine fails or a belt brakes or any other malfunction that would cause the generator to stop producing power it will automatically close the gas valve stopping the flow of natural gas. 

[BruceM]

I think your setup is sweet, Carl.  Natural gas and diesel are a sweet mix, up to 85% NG is possible as I recall. 

Both my future neighbor, and I have severe MCS, thus we're living in the sticks surrounded by high desert grazing land.  Handling diesel fuel is still hard for me as well, I miss the biodiesel I ran the first few years on my Listeroid.  No sources for that now within 100 miles.  Propane is an ideal fuel for our situation; it burns clean, no fuel handling/transport issues.

Cujet's idea is intriguing, I wonder what the max propane level would be to still allow enough compression for the diesel fuel to ignite.

I'm going to try a cheap ($50) made in China, shielded CDI spark ignition system (designed for RC airplanes) and see if I can get along with it. It doesn't take much time near a typical ignition system to set off my epilepsy.  Plan B is a homemade version of Mark Cherry's smartplugs (smartplugs.com).  It's sort of a modern, compact, platinum catalytic version of hot tube ignition.  I used a copy of Mark's basic patent method successfully on a small Honda outboard conversion about 10 years ago.

Best Wishes,
Bruce

[Tom]

Another possible ignition would be a CDI from a pit bike engine. Every thing needed could be had for < $30.

[dieselgman]

Just for another variation in thinking... The HR gas engines drop the compression ratios with a dramatically concave piston crown. I would bet that this piston mod could quite easily be done with a CS diesel piston. Direct injection head design is also a preferable configuration for running spark ignition gas fuels.

Ignition timing becomes critical, and combustion stresses greatly increased in a gas fueled setup. We use special nodular iron rings, hardened valve seats, and specially hardened valves in our natural gas engines to give them a reasonable life expectancy. Timing has to be adjusted for propane vs natural gas, they have pre-ignition issues otherwise. We also use inlet air restrictors to help control that destructive pre-ignition (detonation) tendency.

Dieselgman

[BruceM]

Thanks for the ideas, guys.
I've read about intake air restrictions being used in propane conversions on the IMPCO website-  could someone please explain why that is used?
Is this because ignition timing needs to be changed with throttle position but can't be in a typical retrofit?  I can manage that electronically if I must.

[veggie]

Has anyone tried driving a B Belt direct on the flywheel? I'm thinking there might be sufficient surface area to do that for a modest load.  I'm considering this for the ST-3 drive.  Lots more flexibility in sheave size.  A 10" sheave would match my desired 750 rpm.  A single B belt is more than adequate according to my belt chart.

BruceM

I have done this on many of my systems.
Here is a unit I built for sale 2 years ago. It uses two "B" series belts to drive a 4kw generator.
The belts did not flop on their sides due to belt tension, however I would recommend using a "banded" belt where the
common backing keeps the belts from rolling.
https://www.youtube.com/watch?v=IbpiYeCJbNs

As you know V-belts are designed to carry load on the sides of the belt and not the inner surface. I counter this by over-sizing the belt drive by a factor of 2.
So, if 1 belt can normally carry the HP, I use 2 belts.
The surface area of the flywheel is so great that no slippage occurs.


My suggestion is to use a multi-ribbed "3V" series belt and a "3V" pulley on the ST-3 head. The 3V series belts have a much higher HP capacity than the "B" series. They also conform to smaller diameter pulley's (sheaves) better than a "B" series belt.

On my current listeroid I run a 2 groove (3V section) pulley on the generator and routinely pull 2.5 kw with no slippage (2.5 kw gen head).
When running the 4kw gen head on this engine I used a 3 banded "3V" belt and a 3 groove pulley.
If you want to over-engineer a bit, use a 3 groove pulley and a 3 banded 3V belt. Get the banded ones and not 3 individual belts.
the banded version is necessary to stop the belts from wandering and flopping over on their sides.

Here is another example of a unit I built using a 2 banded 3V belt.
The head has a 3 groove pulley but I only used 2 of them.
This generator can pull 3kw.
https://www.youtube.com/watch?v=f-hl2yfODME

cheers,
Veggie

[BruceM]

Thanks for sharing your experience with driving V-belts on the flat flywheel, Veggie!  Good to know it's been done successfully.  Since I'm driving a 10" pulley and only 2200 watts load for this setup, I may try a single B.

For a 17" single B pulley for the compressor drive,  jdv-belts.com  seems to be the best deal I can find.  I'll be using a LaPlante 2 stage compressor this time, as Eaton doesn't carry the nominal 5HP model I used on my system anymore.  Their current 5HP 2 stage unit is only rated 800-1000 rpm, a pretty narrow band and a bit too much power required.  HP ratings are for electric, and for gas, about double that is recommended. The LaPlante two stage LP205 is a good match for this setup, as rpm can be widely varied to match the engine, plus they have engineering data for power and air at all rpms.  see LPcompressor.com/pumps 

[veggie]

Nice units.
Will you be getting the "head Unloaders" which unload the compressor when the receiver tank is at full pressure ?

Veggie