DES 8/1 Propane Conversion project

[mike90045]

You may have sized your carb for a  4 cyl 1600CC, 4000rpm engine, but will it work properly for the long delay between intake "gulps" on a 700 rpm?   It's bleeding propane into the manifold while nothing is happening, then a big intake pulse comes along, can it support a quick huge draw of mixture then cease while waiting for the next?

[BruceM]

Good points, Mike.

Since the size range is so large, and the gas metering is by diaphram/ intake vacuum, I think the IMPCO CA55 should work OK at my 786 rpm.  It does not release gas when there is no intake vacuum.  It also handles large engines at idle, so I there is a match there, sorta.  It starts  immediately and sounds fine until it starts missing, so hopefully it's something simple.

[Tom]

Bruce, some where back in time we discussed using a regular spark plug in the injector hole. It looks like a piece of cake to make that conversion and just use a regular plain old boring automotive coil with a set of points triggering off the IP cam follower. Kohler or Wisconsin parts would work just fine and be easily replaceable with off the shelf parts.

[Thob]

Raining now but I was able to open up the BBQ LP regulator and can now adjust it.  Thob's simple water bucket calibration method I can do while waiting for the pressure gauge to come on Monday. (Thanks, Thob.) I will place the pressure gauge right at the carburetor so there will no more mystery on that issue.

You're welcome.  But I have to give credit for that idea to ReedEngine over on the oilfield engine forum on smokstak for that idea.

After you've got a good ignition system working, if you're still having problems you may want to look at a different Impco carb.  From the catalog:

"The Model 110 carburetor/mixer is designed primarily for one and two cylinder engines where severe intake
manifold pressure pulsations are present."

I suspect that fixing the ignition will get it running quite well, but wanted to mention this just in case.

[BruceM]

Hi Tom,
You remembered correctly. Earlier in the thread you'll see my picture of the spark plug replacement for the diesel fuel injector.  Points certainly could be used but I'm using a hall effect sensor with a tiny magnet on top of the IP cam follower. It is simpler mechanically, since coil dwell does not have to be incorporated into the cam.  A simple 555 circuit triggered by the hall effect sensor turns on the coil for an adjustable dwell of about 4 msecs.  That charges the conventional 12v ignition coil and it sparks when the current is stopped and the magnetic field collapses.

At the target 786 rpm, it's 76.3 ms per revolution.  To allow a 4 msec dwell,  the spark trigger must occur at 19 degrees advanced, plus whatever advance is desired.  Propane has a fast flame front, so I'll start at 19(dwell) +10 degrees= 29 degrees BTDC.

The smart plug required a minimal chamber beyond the glow plug (least possible advance).  I'll learn from that lesson.

Thanks for the carb tip, Thob.  I'll take a look at the model 110.

  



 

[dieselgman]

We use the Impco 110 model in updraft configuration for our HR engines in 2 and 3 cylinder versions. Parts are readily available and they adjust and run without much fuss IF the electrical side of the equation is in very good order. One backfire is all it takes to blow out the diaphragm though, and that can get to be an expensive pain in the neck while tuning - on occasion.

dieselgman

[BruceM]

Checked the propane BBQ regular in a 5 gallon bucket- huge flow at 13" deep.  Adjusted for minimum pressure (screw all the way in), still more than 13".  So for starters, the regulator must be replaced.

[Thob]

I thought that running the screw out would be lower pressure???  Did you try the other way?

[BruceM]

Thob, yes, it bellows out gas with the screw out, all the way in it's a smaller stream in the bucket.  I've ordered the adjustable 2 stage regulator you recommended.  

Got the spark timing working on the engine.  

I reduced the 555 produced dwell time to 2.5 msecs.  I can't see any difference in the spark quality there, much shorter and the spark gets weak.

I'm going to make a temporary mount for the coil now so I can give sparks a try.

I forgot to mention that yes, 38 coupe,  I'm very familiar with RC glow plugs and am using a hot plug. I was also once an RC airplane fan.   Propane just doesn't seem to react with the platinum much. Mark Cherry ( smartplugs.com ) solved this by increasing the platinum area and forcing fuel mix over the platinum surface.  I know in some fuel applications (maybe propane?) he had to provide constant current to the smartplugs for running, and changed that current to affect timing.   I don't have the time or budget for re-doing his development work, and he's to busy to return my call.  I tried varying the glow plug current in my DIY smartplug , and it made no difference in the missing problem, which I think now is just a bad propane regulator.

I haven't forgotten 38AC's comment about providing a low pressure reservoir for the intake fuel, either.  Regulators may have trouble with a pulsing input and smoothing out that demand might be helpful.  









 

[BruceM]

I noticed a timing problem on the IP cam follower when I was timing my magnet/hall effect spark setup.  I just checked it carefully again; my IP cam is centered on 17 degrees ATDC.   That's not a typo, the cam high spot is 17 degrees after top dead center.  My question is: will this prevent diesel operation with the IP?

[BruceM]

Ran it on the breadboard spark circuitry today.  No change from my DIY smart plug, runs nice, then starts missing after a minute or two, then almost stops.  I found I can bring it back to life by nearly closing the carb.   New regulator and fuel pressure gauge next, early this week.

I had to retard the spark timing via the IP cam follower bolt to near 0 BTDC to avoid knocking.  Propane doesn't need much advance!   

[buickanddeere]

 A MSD multiple spark box maybe a consideration ? http://www.msdignition.com/Products/Ignitions/Daily_Driver/5520_-_Street_Fire_Ignition.aspx

[dieselgman]

If choking or closing the carb "brings it back to life", it sounds a little like the carb dashpot is not properly responding to your normal engine vacuum - at least not until the vacuum spikes. A cracked or deformed diaphragm might produce this kind of symptom. For interest in what the cause and effect of the situation is, it might be valuable to also have a vacuum gauge on your inlet manifold during testing and adjustments.

At any rate, I would not rule out a defective or malfunctioning carburetor from what I have read of your situation. Impco makes an excellent device, but it has its inherent weaknesses and can be very finicky when something is just a little off spec.
If you wanted to do some trials or experiments with 110s, I would be willing to supply them for you gratis. Just document and share your results here.

dieselgman

[BruceM]

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.

[32 coupe]

Just thinking out loud.....
Has this been done before ? Will this type engine work with this type catb ?



I was thinking about a newer type electronic injector and one of Bruces homebrew
timer to set the ignition timing as well as a open/close timer for injector.
 
Is this sort of thinking even plausible or is my thinking just plain crazy ?

Gary