Rockerblock I.C.--Something a little different-

[Roger B]

I'm still following along with interest  Good luck   

[Brian Rupnow]

I thought about this today while I was across town doing some "real" work, and I may have been smoking rope when I posted that propane carburetor drawing. I have to think on this a bit more, and I will post a different idea that is coming together in my head, after it has cooked for a while.---Brian

[Brian Rupnow]

After watching a YouTube video on converting a larger two cylinder engine  to run on Propane, I have decided to try this "conversion" instead of an entire new carburetor. This would be very simple to make and add to my existing Traxxas carburetor. There is only an hours work in this, and if it works as well as the engine in the video I would be very pleased.---Brian

[MJM460]

Hi Brian,

Thanks for the model in your post #254 showing the throttle plate.  With the air flow direction shown, the propane inlet is in the low pressure area after the throttle plate, and this low pressure is seen by your demand valve on the under side of the diaphragm.  As you mentioned earlier, this pressure is lowest with the throttle in the idle position, highest vacuum when you need the least fuel.

Your demand valve is a differential pressure controller, it responds to the difference between the pressure above and below the diaphragm.  The lower the pressure on the needle valve side compared with the top side, the more it opens its needle valve against the spring, to admit more fuel.  If you put the very low pressure (high vacuum) on the engine side of the throttle to the underside of the diaphragm, the demand valve with atmospheric pressure (no vacuum) on top, it will open full and give maximum fuel.

You have to separate the throttle valve effect (lowest pressure at idle) from the carburettor Venturi effect which gives lowest pressure at max engine speed to give more fuel.

If you run a tube from the top of the demand valve diaphragm to a tapping on the manifold which is also on the engine side of the throttle, the demand valve diaphragm will see the difference due to velocity (which increases with engine speed) which is what you need to drive fuel flow.

There is another factor that I am not sure how it will pan out, due to the close proximity of the parts.  Immediately downstream of the throttle, you will see the lowest pressure.  Then shortly after that, there will be a little pressure recovery to the point where the actual permanent pressure loss due to the throttle is seen.  So a little hard to predict just where to put the sensing point for your tube from the top (labelled atmospheric) side of the demand valve diaphragm.  It may be simpler to put the throttle on the engine side, as the turbulence around the throttle will ensure the air and propane are well mixed.  Probably not the preferred side with liquid fuel, where you would get a wet throttle plate and poor mixing.

Possibly need a little experimenting with a sensitive differential pressure meter (aka plastic tube held in a U tube shape, filled with some water).  You can then measure the differential pressure in mm or inches of water with your steel rule, and see how it varies with tapping location and engine speed (via the variable speed drill at the moment).

Sorry it's taking me so many words to paint the picture, would a sketch be more useful?

MJM460

[Ye-Ole Steam Dude]

Hi Brian,

Stand by generators like Generac (by brand) convert their gas engines to run on propane. They offer conversion kits on the internet. These might be too large for your engine but you might be able to get a parts list to learn what is required. Hope this will help and looking forward to see your engine running.

[Brian Rupnow]

So here we are, ready for round two of the propane game.  This set up is as per the video I watched, with a separate venturi tube extending out in front of the carburetor  air intake. The small metal pipe which the clear flexible tube is attached to, protrudes approximately half way into the "venturi tube. This will create a restriction in the inrushing air so it will create a low pressure area where the end of the tube is. The carburetor has not been changed in any way. The liquid fuel line which runs up to the bottom of the carburetor has been plugged with a piece of 1/8" steel dowel inserted into the original fuel feed line. The new brass "venturi tube" is a very light press fit over the carburetor air horn with a bit of green Loctite to help it stay in place. The original carburetor throttle should work to control engine speed, same as it always did. I will give the Loctite a few hours to set up, then try the engine again to see what happens.

[Ken K]

 Don't know if this will help, but some pictures of the system used on the Marion engine. The Marion was a big engine, over 100 pounds, so the model demand valve, would not run it.
 The demand valve is, per paper work, able to run up to 18 HP, on natural gas. Natural gas must have low pressure, as if I put, the Colman reg., any where, but on low, it was to high, and demand valve  leak gas.   
Ken K

[MJM460]

Looking good, Brian.  Keeping my fingers crossed for some encouraging sounds when the loctite cures.

MJM460

[Brian Rupnow]

Sadly, I must report that I had no luck at all with Propane. I have tried all of my bag of tricks, and the engine simply won't fire and run on Propane. This is not a really big deal, and like many other things, you don't know until you have tried. I do have a spare gas tank setting around, and by making a simple bracket I can add it to the existing Rockerblock assembly. With the coming of summer, I don't want to spend a lot of time in my machine shop, so I will end this thread now and say a big Thank You to all the people who have followed my build.---Brian

[Ye-Ole Steam Dude]

Brian thanks for sharing this build with us.

[bruedney]

Just a thought - When I owned an LPG powered 6 cyclinder car, the ignition timing was completely different for LPG than petrol. I can't remember if it was more advanced or retarded but this may be the reason you can't get this running.

I also can't remember if the LPG inlet was pre or post carb but I think I have seen both and either would also have an air cleaner which would create more vacuum.

Cheers

Bruce

[MJM460]

Unfortunate that you still do not have it running on propane, but it did run on liquid, definitely a runner.  And beautiful at that.  I have really admired your design process, and the efficient way you machine the parts.  I don't know if it is a beginners project, but I would like to build one one day.   Perhaps a few more steam engines first.

But I am with you on getting out enjoying the summer after the long winter.  Though I did enjoy the Pinery provincial park both summer and winter.  I hope then the gas regulators can come out again with success.

Thanks for a wonderful design and build.

MJM460

[Brian Rupnow]

After my failed attempt to even have the engine fire on Propane fuel, I was beginning to wonder if perhaps the ignition timing or valve timing had "slipped" from the original settings where it ran so well on naptha gas. I had a spare gas tank setting around, so I installed it on the engine, and without readjusting anything the engine fired right up and ran well. I decided to have a 40 minute "endurance run", and about half way thru the run I picked up my camera and shot a short video. That explains the nasty oil on everything.---I had given all of the bearing surfaces a good squirt of lubricating oil and filled the water reservoir before starting the run. The water stays in the reservoir with no problem, but the oil quickly turns black and splashes all over the place.---Brian
<a href="https://www.youtube.com/watch?v=dp0CgAwvBss" target="_blank">http://www.youtube.com/watch?v=dp0CgAwvBss</a>

[MJM460]

Clearly a runner, Brian.  Lovely to see it run again, a great little engine.

Got to be something simple with the propane, like getting the right mixture, it will come to you eventually, but in the mean time let your mind work on it while you enjoy the summer.

MJM460

[Brian Rupnow]

I have a few people around the world building this engine now, and I am being asked about setting the valve timing. The set screws in the cams are difficult to access. I covered how I did this back on post #195, but here is a repeat of the way I did it. I was very lucky and the very first setting I used seems to work fine.
--There is a bit of trickery involved in setting the valve timing. You must have the cylinder head and lifters and rockers all in place, and have the valve lash set at about 0.010" when the lifters are not "up" on the cams. I sawcut a 0.030" slot in the end of the camshaft that is on the same side as the cam gear, so that I could turn the camshaft with a screwdriver. I removed the flywheel on the side where the timing gears are and turned the other flywheel in the direction I intended the engine to run (clockwise when viewed from the side with the gears on.) The set screws in the exhaust cam were tightened at any random spot by reaching up through the bottom of the engine. The intake cam was left loose on the shaft. The setscrews in the cam gear were left loose. The crankshaft gear was tightened on the crankshaft at any random position. I turned the flywheel until the piston was about 40 degrees or so before bottom dead center, then used a screwdriver to turn the camshaft in the opposite direction to the crankshaft until the cam lobe was just beginning to influence the exhaust valve. At that point, I tightened the camshaft gear setscrews. That "locked in" the exhaust valve timing. I then kept turning the flywheel until the piston was about 30 degrees before top dead center. At that point I reached up through the bottom of the engine (with great difficulty) and rotated the intake cam until it was just beginning to influence the intake valve, then I locked it in place. The cam set screws are "accessible" either through the underside of the engine or through the vertical slots in the "bolster" which stiffens the cylinder head plate. If you simply can not get at the screws for the intake side cam, you can remove the other flywheel, the ignition cam, and the entire sideplate to get to the intake cam set-screws to tighten them. ---Brian