Listeroid Propane Conversion

[BruceM]

We've decided to stick with a Listeroid for my new neighbors off grid generator/air compressor...copy of my setup except if I can do it, he'd like to use propane.
I found a propane carb and a cdi igntion, will try the injector hole method.

Dieselgman has a few 8/1's left and I think that might be a good match as with the loss of power from reduced compression and propane, I suspect 650 rpm will no longer be adequate.

Anyone able to make a good guess as to a target operating rpm for 6-6.6 hp on propane?  (I've got to order a genset pulley.)

Most small engines run about 9.5:1 compression so I assume that's about it for propane.  Could anyone guess what shim thickness under the cylinder would that be?

[billswan]

Bruce
Google the octane rating of propane. I believe it is high like 110. You will be able to run much higher than 9.5 to 1.
Like 12 to 1 plus or minus........................ more power............................... 

Billswan

[LowGear]

How about the hybrid method that Carl uses?

Casey

[Tom Reed]

I've heard that as much as 14:1 CR can be used with propane. This will get a lot more power out of the engine. Since you're looking at a 8/1 just run that sucker at 850 rpm and call it good. It might only take a .050 steel shim cylinder base gasket to get it where it needs to be.

[mike90045]

What about keeping it diesel and fumigating with propane ?

[BruceM]

Fumigation with propane is not as appealing as with natural gas since you can only run about 25% propane before pre-ignition trouble, so too much bio/diesel handling for too little benefit.  STILL no biodiesel sources in the White Mountains of AZ. Grrr.  I loved running on biodiesel while I could get it from a friend in Prescott.

14:1 would be great, Tom, not much power loss.  Your 0.050 shim seems a good place to start. 

[TimSR2]

At 14/1 cr you better think to retard the timing under heavy load or you will be into  the destructive testing mode. Also will be very hard to start without retarding the initial spark timing to near TDC.

I'd be comfortable with 12.0  to 1, 25 degrees total, 10 initial, so long as your load is kept reasonable. You will need an advance mechanism of some sort.

Old school truck engine conversions with fogger systems and distributor ignitions (pre OBD) never exceeded 10 to one comp  in severe service at 25 degrees total.  I run 9.7 to 1 in an 83 chevy 350.  Motorhome,   8500 lbs and 4.10 gears (severe service) Cylinder compression is 195 per hole. Any more than 25 degrees total advance,  she melts the spark plugs.  YMMV.

[BruceM]

Thanks, Tim. We won't be pushing the load.  I'll look into dynamic timing adjustment, based on throttle position, plus starting retard. 

If anyone knows of an electronic ignition system with dynamic timing please let me know.

[Tom Reed]

Since the application is fixed RPM, as long as it can be safely started and not get into detonation a fixed advance should work. If you want to get fancy just put 2 triggers in the system with a switch for advance and retard for starting. With the big flywheels I wonder how bad a kick back could be.

On the other hand advancing the spark while under no load may provide some economy. IIRC this is going to be a battery charger so it's going to spend a lot of time at full load.

[BruceM]

Thanks Tom.
I guess I could start simple (semi-fixed timing) and see how it goes.

As a generator it will mostly run at about 2000 watts, for a 1/2hp submersible pump and 1/2 hp washing machine.  Battery charging is only 1500 watts peak, only to 80% and lasts about 1.5 hrs, very rarely done.  I coddle my cheap, wet marine battery string, keep it charged every day, and get 4 years out of a set of ten. 

[buickanddeere]

   It's not just the mechanical compression/expansion ratio. It's about the combustion chamber pressure and air/fuel temperature as the piston approaches TDC during compression. Cam timing and rpm has as much to do with combustion chamber pressure/temperature as compression/expansion ratio.
    max power would be reduced but efficiency increased if the diesel ratio was kept but the combustion chamber only partly filled even at wide open throttle due to later intake opening  and later intake closing.