DES 8/1 Propane Conversion project

[BruceM]

A propane carb seems more my speed, but it would be interesting to see what else is being done with propane fueled engines. 

[BruceM]

Here's my fugly jury rig for the spark system. The hall effect sensor is presently just taped to an aluminum plate mounted on the IP location.   The magnet self adheres to the IP cam follower/bolt head. I'll epoxy both magnet and sensor in place later.  An 8 pin 555 timer chip triggers from the low going hall sensor, turns on the coil through an N-channel MOSFET for 2.5 msecs, then shuts it off which makes a spark.  The solderless breadboard is being used until I'm sure I won't need more features such as retarded timing for starting.

The whole spark system will be in a shielded enclosure when I'm done.

[buickanddeere]

Gary, thanks, a CA110 carb would answer a lot of questions, that's very generous! I'm happy to share my work, and grateful for the support from you and the forum.  I'll email you.

Buick&Deere- thanks for the link. I think multi spark has it's place, for slow burning fuels.  The smart plug is a plasma torch and can even light off 50% water/alcohol; I doubted it just because it was new (for me) to this propane fueled application.  Since (single) spark has not changed the missing, I'm proceeding with the theory that I've got a carb/regulator/fuel mix issue. 

 For both the smartplug and the spark, I've had to eliminate advanced ignition timing due to very pronounced knock.  I read that propane is a fast flame front fuel; now I'm a believer.

 LP is going to knock with the diesel compression ratio as the octane is too low. Unless you restrict the air/fuel flow so the cylinder only fills to approx 2/3 to 3/4 of what it would with no throttle. This will bring the effective compression ratio down to approx 10ish, 11ish or 12ish   to 1 compression ratio.
  Just a wild estimate but ignition advance should be approx 12 to 18 degrees at 1800rpm. 
  The sites that cater to mini tractor pullers running modified 16HP Kohler 341 engine series. They are one stop shopping to add solid state ignitions to any single and twins.

[BruceM]

B&D-  Earlier in the thread compression and octane was covered- the Lister CS design is VERY easy to lower compression on, and I have . I'm not having pre-ignition problems at all after adjusting the spark timing by ear.  I'll be fine tuning the compression for maximum load later.

I installed the new two stage regulator Thob recommended, and had to cut it's spring to get the pressure down to 11 inches of water pressure. 

The engine starts missing  immediately at 11", won't start and run at all at 8", is happier at 15+ (off scale for my gauge).  While cranking, the pressure gauge shows swings down to 3.5" on each intake gulp. At speed it's a blur with movement, though not moving as much.   I'm going to  experiment a bit to see how much is regulator, 3/8 supply hose, etc., by moving the pressure gauge to just after the regulator instead of right at the carburetor inlet.   Perhaps a buffer tank before the carb is needed per 38ac's comment and/or a bigger diameter hose.

I'm looking forward to trying Gary's CA110, since IMPCO noted it as good for single cylinder gulpers, and there's the possibility that I've got a bum CA55 carb.   

I've got a vacuum gauge I'll rig up on the intake manifold, per Gary's good suggestion.

[dieselgman]

Regulator to carb hose size we use is 3/4" and although I have not done much about instrumenting, I think we are running very low pressures... certainly nothing near 11" to 15". If my memory serves, it is a lot closer to 5" (but I am likely confusing pounds psi with inches of water column). Of course much of this design is based on the Natural Gas equipment used for the Lister HRG twins and triples. The fuel flow in these is designed around high volumes and low pressures.

dieselgman

[38ac]

As to what Gary said about volume at low pressures this is the fuel set up on my Eclipse well engine. It is 4HP and in the same ballpark as to bore/stroke as the Lister. The fuel pipe going to the  demand regulator is 1/2" pipe. The feed pressure is about 16" it could be much lower if not for the same feed also going to the hot tube burner. The engine feed pressure is cut back considerably by the demand regulator. I cant say exactly how much because there is no place for a gauge. It has to be very low because the propane is fed through a ring of holes in the intake valve seat. I guess it isnt over  couple ounces or it would lift the atmospheric intake valve off it's  seat. This engine originally ran on well head gas but since the demand regulator is adjustable switching to propane was as easy as finding the correct pressure output from the regulator and changing the jet in the hot tube burner. Not sure what of this helps but it illustrates the need for the fuel pipes to have size when they are handling very low pressures.

[BruceM]

Thanks, Gary and Butch. I'm thinking of separating the two stage regulator, putting the small low side regulator right at the carb.
 

[BruceM]

I split the two stage regulator and put the low pressure half on the carb/pressure gauge inlet.  Much less pulsing, about -3.5 inches while cranking.  If I increase the pressure to 15 inches it will start and run continuously if adjusted full lean (edit), though missing significantly.  I wish I hadn't cut the spring on the regulator, as about 15" of water pressure is now the max I can get, and this carb seems to need more.

I think I have a carb problem at this point.  I'm hoping Gary's CA110 will be a game changer.

Bruce

[Tom]

From the looks of the neighborhood it's a good thing you're not trying wood gas. Try a shim under the spring for more pressure.

[BruceM]

Got some help later today and got in some long engine runs with the newly modified 2 stage regulator. Boosting the first stage regulator output to 15psi was helpful. After several runs and some fiddling, I've figured out that it starts well cold and runs well for a short while because it's TOO RICH.  I misread the carb adjustment indicator letters (oops, wrong glasses) and it's full lean that it likes.

Turning down the pressure to 6" helped a lot once it warmed up and started missing, but as it gets fully warmed up it still misses.  I tried pinching off the hose to the low pressure regulator, down to about 2-3" of water pressure at the carb.  That seemed slightly helpful but does not solve the problem.  It may be too low for the carb to regulate the fuel mixture properly.

I'm very frustrated with the CA55 carb- there is not enough range of adjustment of the fuel mixture.  The split two stage regulator was a big help, got it running well enough, long enough, to start figuring things out.  Thanks, 38AC for sharing your photo of your setup.  It got me thinking about two stage regulation and a regulator right at the carb, which really helped.

[dieselgman]

I think you are on the right track with leaning the mixture out, even though some of the symptoms appear logically the opposite. It will be interesting to see what the larger carburetors will do on this small engine. They have considerably larger diaphragms than the 55 and should be responsive with very low fuel pressures.

dieselgman

[BruceM]

I'm thinking about making more of an air bleed on the CA55 carb to lean the mixture.  There's a port that seems to be for priming that I can open, plus another screw that seems to be an air bleed as well.   I can't seem to reduce the fuel enough so perhaps more air will help. 

[buickanddeere]

15", not 15 psi I hope ?

[BruceM]

15 psi into a propane carb would certainly be interesting to watch, on someone else's engine and carb.   

[BruceM]

Still struggling with the lack of application data from IMPCO and their dealers.  One dealer thought my problem was not the CA55 but the regulator, and that I should be using an IMPCO model J regulator.  I found that the model J has -1.5" WC pressure output. Tonight I finally found a reference for the CA55-598-2 model on a retailer's web information. It seems the CA55 carburetor takes -1.5 " WC pressure.  A long way from the +3 to 15" I've been feeding it!  This would account for the rich fuel mixture.   I'm now in search of a low pressure regulator with -1.5" outlet, and 15 psi inlet. 

I got the CA110 and CA125 loaners from Gary a few days ago.  They are both single diaphram models that may handle one cylinder, slow engines better.  Thanks, Gary (dieselgman, DES), I'm very grateful for your generosity and support!