Chainsaws have more compression and this changes the timming and tuning of the engine.

Perhaps you could lower the compression by adjusting the glow adapters depth into the cylinder.

I talked to the 'car racing guy' and what he said, the Nitro will not cause preignition. The same with methanol.
I remember, when I was using 50-50 mixture, I used 91oct gasoline, but for nitro test I used 87. So you might be right that the pinging is caused by using a gasoline with not enough octan grade. I think this will call for my next test: mixing 91 oct gas with methanol and glow fuel. I have some premix 91oct gasoline with Motul oil 1:33. I will need then less oil from the glow fuel, so I will need to use higher nitro content. I have some Norvel fuel (35% nitro) so I will mix:

0.5 oz of Norvel fuel (35% nitro)
3 oz of my 91oct gas/oil mix (1:33)
2.5 oz of pure methanol.

This will give:
45.6% Methanol
48.5% Gasoline
3% Oil
2.9% Nitro

Let's see if I still hear pinging.

RysiuM

Hi,

I have to disagree with the car racing guy. All the model airplane glow engines need lower compression to use more nitro. Often times when you use more nitro than the engine was designed for, you have to add head shims to lower the compression. Nitro itself burns slowly, but it raises the heat of combustion, and therefore requires less compression to avoid detonation or preignition.

AV8TOR

Hmm.. it makes sense too. Higher engine temperature, so less compresson require to ignite the thing.

I feel so ignorant (I guess like many of us ) as what we are doing here is absolutely unique. Racing car guys use methanol, gas and nitro, buy they don't deal with the glow plug - they use spark ignition. RC guys deal with methanol and nitro on glow, but nobody is adding a gasoline to that thing. And RC engines area a little different talking about compression. On the top of that every weed whacker/blower/chainsaw motor is different and never intended to run on glow fuel.

So I guess my only option is to ask questions, share with results, and experiment till the head blows off

RysiuM

RysiuM ,,,,,,,,, Great testing, keep up with the experiments, many of us are following your progress. Thanks for sharing your results.

Just as an aside - back in the '40's when we were first learning how to run Glo plugs, Ardens & Champions, a lot of experimenting was done using white gas, sae 70 oil and Nitro-Propane. Yes the old Forster 29's ran well on it, but of course, control line had no use for idle. Has nitro-propane been banned by EPA ? Might be an interesting experiment.

Phil Heller

This is non sceintefic, but I noticed adding nitro to the mix inceases the temp of the motor too much. I ran some gas/methanol/nitro/castor mix and while the bench run it seemed to run fine. When in flight it seems the motor got WAY to hot. It got hot enough to melt the solder joint off the glow plug.

I can confirm that too. Motor is not only pinging but gets very hot including the shaft. I'm afraid loctite on the prop adapter might give up. Anyway I don't use nitro any more. Now as I have 6 ounces of absolutely useless gas-glow nitro fuel I wonder if it can be used on regular small RC engines


RysiuM

"Now as I have 6 ounces of absolutely useless gas-glow nitro fuel "

pour it on a fire-ant hill or into a full tank in the car...

[:-]

Looks like to me....the price of gas will be higher than alky fuel per gallon. Could this mean just forget about spark and gasoline for a fuel? Regards Capt,n

This may be dummy question: Can the glow fuel be ignited by spark plug?

RysiuM

"Can the glow fuel be ignited by spark plug? " yes

Glow fuel with spark ignition give a very low idle speed also. The glow mixture also helps to cool the engine too!!! Capt,n

Cool. However I found that my Poulan doesn't like to have magneto closer to the flywheel than 0.5mm The magneto support flexes and with the flywheel closer than 0.5mm the magntic force is so strong, that flywheel touches the magneto core. With 0.5mm gap I can't crank the engine by hand fast enough to get a spark. So for me the best option is electronic ignition or glow plug (I hate starters). Because glow plug works great I will play with that for now.

I read in the other thread guy did the whole bunch of calculation for Poulan 25cc. The first thing was increasing compression to 10:1. This was done by shaving 0.5mm from the bottom of the cylinder. I did that and I can fill the compression is stronger.

Then I run the comparision test: before and after increasing compressiion. Motor gaind 140 rpm (APC 17x6). Quite qool. I used the mixture of 40 cc gasoline with Motul (1:33) + 40 cc Methanol + 2cc Castrol oil. This result the fuel: 47.6% Methanol, 46.2% 91 oct gasoline, 6.2% oil (Motul/Castrol mix). It is like 1:16 oil. I wanted it very wet as I don't know how the motor would react to higher compression.

So here is the test: 7160 rpm (7020 witl oryginal compression), easy to start by flipping the prop a few times (this time starts like normal gasoline engine with electronic ignition), 1700-2000 idle. After running idle for about a minute I opened the throttle WOT and engine jumped to high rpm without hesitation.

As a note, I didn't hear any pinging (no nitro used).

After the run I examined internal parts of the engine. I found a lot of oil everywhere. It looks like 1:16 is a little to much. Next time I will try something like 1:25.

Now before I start to modify it more (cut ports) I need to test bigger carburetor. Any suggestions for Walbro 11mm venturi (my Zama C1U is only 8mm venturi) that will be compatibile (mounting holes ) with ZAMA C1U?

BTW I tested also another prop: APC 17x4 - I got 7550 rpm.


RysiuM

fishmasterdan -
If your engine got that hot you probably were way too lean!

Phil

On the side note I just saw $2.77 for 87oct in my cheap ARCO. Comparing it to methanol $2.99 (per gallon) or below 2 dollars (in drums) soon it wouldn't make sense to run RC on gas. We will be converting all 'brand name gassers' to glow fuel soon .

I just wonder if I could run Poulan 25 on methanol/oil (no gas) will I get power of OS 160 ?

RysiuM

Funny, that actually increasing compression on Poulan 25 (weede) improved things on glow plug. Calculated (not measured) compression of my engine is about 10:1 (after mod) and the engine runs better than before. Also starts easier by hand.

RysiuM

Hi,
if you raised compression by simply shaving the bottom of the cylinder or a thinner gasket, the port timing would be slightly retarded. This could possabily provide easier starting. It would also cause the intake to open earlier.

Dave

Dave, Yes, I did.

RysiuM

Is your 25 weede a chainsaw or a string trimmer

Weede = weed whacker = string trimmer . I believe it is Featherlite type.

RysiuM

Just as I thought.

A string trimmer would gain from added compression.

Because the chain saw comes in a higher state of tune, more compression, larger ports and more agressive timing
you are actually detuning it, lowering the compression, to deal with preignition.

You should also be able to adjust the timing, change grades of fuel or lessen the load to deal with preignition.

That's what I did. From calculated 8:1 I got 10:1

Taking out the Nitro from the fuel mix solved the problem. Metanol-Gasoline-Oil mix is not pinging. Increased compression (without changing anything) rised the top rpm from 7020 to 7160 (APC 17x6). Original ZAMA carb (about 8mm venturi) and gutted mustock muffler.

RysiuM

Nitro is an oxidizer, when it burns it creates it's own oxygen.

There by artificially raising the compression.

Higher grades of gas take more energy before they start to burn.

"Perhaps" if you ran a true racing fuel, 101 plus octane, in your mix, you "may" of been able to utilize the Nitro and squeeze out a

few more rpm. I know it made all the difference in my modified 121cc chainsaw.

Seems like I mentioned something like this a while back....

AV8TOR