Test, glo plug versus spark ignition

[cfellows]

So this is one of the more exciting things I've discovered. I made an adapter for my Plumbing Parts engine, my test bed for new ideas and such, for a glo-plug. I'm really excited about how well it works.

[ame]http://www.youtube.com/watch?v=AXydzBWrHEY[/ame]

The secret to getting a glo plug to work properly is the timing, which is achieved by the distance the fuel mixture has to travel on the compression stroke to reach the glo plug. My initial length was too long, so I put the adapter in the lathe and shortened it by turning off 1/16" from the end. Put it back in the engine, installed the glo plug and surprise, surprise, it took right off. The good news, I got rid of the troublesome misfire I was having with the spark ignition.

Now a glo plug and a large battery set me back less than $10, compared to almost $100 for the CDI ignition module, the spark plug, batteries and case. The other nice thing, is, this pretty much demonstrates that the engine would operate equally as well with a hot tube set up, which would be more "period correct" for antique model IC engines. The glo plug (and I assume hot tube) seems to be less sensitive to fuel mixture as well.

One additional note, in this video, I have the air bleed completely off. I actually put a piece of tape over the air bleed hole and readjusted the main mixture for it to run right. Not sure at this point that air bleed adds any value to the carburetor. I was able to get the engine to idle quite comfortably at around 200 RPM with the glo plug and my new carburetor design.

Chuck

 

[barnesrickw]

How can you tell if too long or short is the problem? And would this work as a compression ignition?

 

[Goldflash]

What fuel were you using with the Glow Plug. IE Was it Methanol

 

[bmac2]

Very smooth "running like a Swiss watch"
I’m leaning toward an IC engine for my next build. Just don’t know what or when.
I don’t know what voltage you have going through the ignition contacts but I have to wonder if a simple debounce circuit could be used.

 

[cfellows]

How can you tell if too long or short is the problem? And would this work as a compression ignition?

If too short, the engine will fire too far before TDC and kick back. If too long, the engine won't run. My plan was, start with something I think is too long, then keep shortening it by a little until it runs.

What fuel were you using with the Glow Plug. IE Was it Methanol

The same fuel as before, Coleman Fuel.

Very smooth "running like a Swiss watch"
I’m leaning toward an IC engine for my next build. Just don’t know what or when.
I don’t know what voltage you have going through the ignition contacts but I have to wonder if a simple debounce circuit could be used.

Debounce circuitry would be pretty tough. The best solution is to use a hall effect circuit, but I've not had good luck with those, personally.

At this point I'm leaning toward a hot tube. You just make it pretty long, then time it by how far up or down the tube your heat it.

Chuck

 

[barnesrickw]

So you could you get a close start on length by trying for % stroke volume at a few degrees BTDC. Sorry for using you as Googke, but since I'm here?

 

[DICKEYBIRD]

Wow, that's fantastic Chuck!

I've been running glow engines for over 50 yrs but never would've thought to try straight petroleum based fuel. We used to cheat and add 10% gasoline to Cox 1/2A fuel (methanol/nitromethane/castor oil) to coax a few more laps out of our controline mouse racers but only in cold weather as they run hotter with the gas....not good for the finicky little Cox beasties.

I guess you have to leave the battery hooked up all the time it's running? I think there wouldn't be any catalytic reaction between the platinum in the glow plug & the Coleman fuel as there would be with methanol to "keep the fire burning."

Kudos!

 

[kadora]

Coleman fuel ignited by glow plug ???
It is very very interesting.
Chuck what kind of glow plug do you use.
As Kudos wrote there is not catalytic reaction with petroleum based coleman fuel and hot platinum glow wire so what ignites fuel.
In your engine fuel ignition must be perfect because engine has excellent idling.
Thank you

 

[barnesrickw]

I know platinum glow plugs require methanol for the catalytic reaction mostly to keep the plug hot and glowing. Other fuels could work if the battery were to remain connected. The only other thing I can think of would be compression ignition.

 

[kadora]

Chuck you wrote :
The secret to getting a glo plug to work properly is the timing, which is achieved by the distance the fuel mixture has to travel on the compression stroke to reach the glo plug. My initial length was too long.

I am not sure if i understand properly.
Did you rise compression ratio ?

Thank you

 

[Goldflash]

If my memory serves me right most model aircraft engines running on glow plugs using Methanol fuel need about 8-1 compression ratio.

 

[Lawijt]

But there are 2 types off glow plugs. For 2-stroke engines & for 4-stroke engines.
You need one for a 4-stroke engine.

I try the same with my little wonder engine. With Methanol fuell it runs & I can take the battery off. I try gasoline with 2-stroke oil & the engine runs also , but I have too keep the battery connected than.

 

[mu38&Bg#]

In the RC world we have glow plug engines burning gasoline. Enya 180X-GS and Norvel GX-40. For years it was my intention to try gas with plugs as I know the platinum is active with virtually all hydrocarbons ( platinum is after all the used in the catalytic converter in your car). The Enya hasn't been popular due to cost, but the Norvel has seen reasonable sales and it works.

 

[barnesrickw]

I found a chemistry experiment for students explaining the reaction between methanol and platinum if anyone is interested. http://chemistry.slss.ie/resources/downloads/ch_pr_oxidnofmethanol.pdf

 

[petertha]

In the RC world we have glow plug engines burning gasoline. Enya 180X-GS and Norvel GX-40.

Had not heard about the Norvel before, interesting. I forgot about the 180X. One of the local modellers was considering it, but got cold feet in the end. I heard it required its own special mystery oil which was hard to source & the special plugs were like 25$ a pop. But maybe that was a local supplier issue.

http://www.modelairplanenews.com/blog/2011/10/12/enyas-180x-gs-gasglow-engine-a-closer-look/

Not that it really matters in Chuck's case one way or the other, but I'd be interested to see if it ran with power wire removed.

 

[mu38&Bg#]

Enya shot themselves in the foot by not looking for other compatible oils on the market. The oil they suggest is an ester type. Why they wouldn't find other labels which were acceptable I don't know. I think the plug is a regular plug. The Norvel uses a standard turbo plug. 30cc engine it makes no sense to save a few ounces of ignition weight for the sake of gasoline fuel. The Norvel is a practical way to run gas in small airplanes. I've flown spark ignition in .40 size models.

Enya also used a nichrome wire in the early days of glow. It ran on heat from combustion alone, no reaction.

Chucks engine might run without plug current, but the plug will probably have to be in the combustion chamber.

 

[cfellows]

So you could you get a close start on length by trying for % stroke volume at a few degrees BTDC. Sorry for using you as Googke, but since I'm here?

Sorry, I don't really know the mathematics of it. I assume it would be a function of the cylinder swept volume, the head space, and the diameter and length of the glow plug adapter. I just picked an arbitrary length that looked about right and, as it turns out, I got lucky. Only had to remove 1/16" for it to run. Could be I might be able to remove some more, but have no way of knowing how much.

I have to confess I'm pretty ignorant about glow plugs. I just bought a cheap one at the local hobby shop. Have no idea if it's for 4-stroke or 2-stroke. I'm guessing it's just the heat of the glow plug that causes the engine to fire. It won't run without the batter connected, no matter how fast the engine is running.

To answer Kadora's question, I made a stand off adapter, a hollow tube about an inch long that screwed into the spark plug hole and the glow plug screwed into the outer end. This basically placed the glow plug tip about an inch away from the combustion chamger. Then I tried starting it, and when it didn't start, I removed the tube, chucked it in the lathe and shortened it by 1/16" and tried again. I was prepared to repeat this process as many times as necessary, but as luck had I, I only had to shorten it once.

Chuck

 

[kadora]

thank you Chuck now i understand.

 

[barnesrickw]

I'm going to talk to my chem-eng friend about the glow plug on methanol compared to gas. I'm curious now.

 

[barnesrickw]

According to my chemical engineer friend that it is the reaction between Hydrogen and the Platinum wire that keeps it glowing. The surface area and density of the wire is matched to the vapor pressure of the fuel. Methanol having a lower vapor pressure than gasoline means it requires a less dense platinum wire. Gasoline should use platinum that can retain more residual combustion heat. Also, if the vapor pressure of methanol was not low, and there was no evaporative heat loss, the combustion heat would be a bit much for aluminum pistons that some engines use.