what keeps the glow plug hot?

[kbeckwith17]

Can you guys settle an argument for me? There is a friend of mine who believes the glow plug stays hot primarily from compression and I believe it stays hot primarily from the fire in the engine. This friend of mine is pretty well known on this site and I don't want to call him out.....

Kevin

 

[Lessen]

well, I'm no engineer but I would think it would be the fire that lights up the plug, it stay hot for an instant while the piston goes through the cycle then the piston compresses the fuel and air and then the plug ignites the mixture. The way I think about it, the plug is already hot and glowing when compression starts. It seems to me that it's the combination of compression and the glow plug that creates the combustion thus keeping the plug hot. So I'm guessing it's primarily the engines firing that keeps the plug hot. But let's see what the techies have to say....

 

[Revo Rancher]

Lessen, I think you talked yourself into a corner there. :jk:


The engines work off a principle similar to diesel engines. The glow plug gets the cylinder environment hot enough to fire off. Once going, the engine develops enough heat through compression to fire the fuel charge. The glow plug may still be warm and contributes to the effect, but it is the compression (read; friction of compressed molecules) that provides the necessary heat to fire the fuel mixture.

 

[Lessen]

like I said, I'm not an engineer. I'm here to learn just like him.

I was just guessing.

So since compression provides the heat necessary for combustion, is the glowing of the plug actually necessary after the initial start of the engine?

 

[4u2nv]

burning fuel..the fuel keeps being pushed into the cylinder and the fuel keeps burning. When shut off, there is no more fuel being pushed into the cylinder and it goes out. Basically what rancher said, just in dummy terms..lol

 

[Lessen]

burning fuel..the fuel keeps being pushed into the cylinder and the fuel keeps burning. When shut off, there is no more fuel being pushed into the cylinder and it goes out. Basically what rancher said, just in dummy terms..lol

ok. Believe me guys, I'm not trying to start an argument here but that's not what Rancher said. Rancher said that it is mostly the compression that initiates the combustion of air and fuel. your saying that it is the "burning fuel" (I understand that as being the same as combustion) that keeps the plug hot. I think we may be splitting this up a tad. what keeps the plug hot vs. what causes combustion. I just think combustion keeps the plug hot and compression + the plug create combustion. But I'm probably just plain wrong and I'm sure somebody will be more than willing to point it out. hehe.

 

[Tucker]

I think you're all wrong.

The glowplug glows because of the reaction between the platinum element and the methanol, this reaction is only possible at certain temperatures and pressures.

Nitro engines do not work on the same principle as a diesel engine.

 

[Lessen]

IThe glowplug glows because of the reaction between the platinum element and the methanol, this reaction is only possible at certain temperatures and pressures.

this reaction wouldn't happen to be called combustion would it? LOL just playin around dude..

Doesn't the glow plug get hot because it's smack dab in the middle of a hot enviroment? Or because you can hook it up to an electrical source... that creates heat?

damn, I gotta go to work.. This should be an informative thread by the time I get home.

 

[kbeckwith17]

I'm firmly in the camp that says the fire keeps it hot. The reason I don't buy into the compression theory is because if my engine doesn't start, it doesn't get hot. These things are turning ridiculous RPM's and it doesn't get a chance to cool off. Just my two cents. C'mon guys, give us your opinions! (Or facts if you know for sure)

Kevin :boxing:

 

[cobra198]

This is a good question! I have always wondered about it also. I thought it was weird that no wire needs to be connected to the glow plug (like in a gas engine) to creat a spark or heat every time the engine cycles. I'm pretty into go peds also and i know that when you disconnect the wire from the plug, the engine no longer runs. I was wondering why it isnt the same for nitro engines. To my understanding, it is also because of the compression inside. I could be wrong though. Good question!

 

[Slip]

Two-stroke engines are technically compression ignition engines. As you compress the air-fuel mixture, heat is generated which ignites the mixture. Our model engines rely on the "glow plug" as well as compression temperature for ignition and as a result can run at much lower compression ratios, generally in the range of 7 or 8 to 1 (diesels run 22-1). If you direct a flow of methyl alcohol vapour over a fine strand of platinum wire it will cause the wire to get hot and even glow due to catalytic reaction. This is the principle of the glow plug first put to use by Ray Arden back in the late 1940's.

The original plugs used plain platinum wire, but over the years other alloying elements were added which improved the performance and element life, namely Iridium, Tungsten, or Rhodium. The wire used, diameter of the wire, the number of turns in the coil, the size of the cavity, the shape of the combustion chamber, and the amount of nitro in the fuel all play a part in the heat range and performance of the plug.

I hope This sheds a little light on the subject and I guess Your all right to a degree

 

[Rolex]

Slip and Tucker are correct. The glo-plug is heated initially, just like a lightbulb filament. Once the engine is running, the combustion maintains a certain heat range, but it's a catalytic action between the fuel and the platinum or other metal in the coil that keeps it hot. Diesel engines have very high compression which creates enough heat to keep them firing.

 

[Tarant]

This website has a good explination
Here

 

[Lessen]

very interesting.. I had no idea there was any other kind of "reactions" aside from the actual combustion. good job tucker! great explanation Slip!

 

[Revo Rancher]

Two-stroke engines are technically compression ignition engines. As you compress the air-fuel mixture, heat is generated which ignites the mixture. Our model engines rely on the "glow plug" as well as compression temperature for ignition and as a result can run at much lower compression ratios, generally in the range of 7 or 8 to 1 (diesels run 22-1).

This is exactly what I was trying to say.

I used to drive semis while in college. We had some real old yard tractors made back in the 50's. These were powered by a 2-stroke diesel engine, and they worked off the glow plug nitro concept exactly the way. They had lower compression than 4-stroke diesel engines because of the style of compression. Thay also used a blend of diesel that had alcohol in it. Same concept as our R/C nitro cars.

The way their energy was produced was this:

Engine heated initially by glow plug. Compression combined with fuel mixture and heat from start up charge from glow plug got engine going. Due to the mass of metal that needed to be fully warmed up these suckers would smoke something awful for 30 minutes or more. Once at ideal operating temp, full power, smooth idle, and lessened amounts of smoke would be found. (sound familiar?) Continued operation had a cycle that has fuel mixture introduced to the cylinder, compression of the mixture causing it to heat and reach high enough of a temp for firing, firing, and finally caloric heat as a consequence of the cycle. Therefore, the glow plug was kep hot by the COMBUSTION of the engine, which first required COMPRESSION to heat it further (remember, we need a core operating temp, as per the glow plug ingniter) and then due to combustion, HEAT would be produced, keeping enough heat energy available for the next cycle. The little amount of ethanol in the fuel was mainly to LOWER the combustion temp range, making it easier for the compressed charge to combust without detonation. The one detail I do not know is if they used a platinum material in the plug to help the diesel ignition, which the comment above that the need for platinum is to aid in combustion is correct as that is part of the theory perfected by the inventor of the nitro engine.

 

[david93073]

For some reason this is a very popular misbelief about glow engines being diesels. :shrug: I thought the website Tarant provided would put this to rest?
Heres a pic of 3 RC airplane engines(Irvine .40's) notice the two on the outside have glowplugs and the middle engine dosnt,(it is a diesel) but instead has a thumb screw to adjust compression. Also runs on a different fuel than glow engines. RCuniverse and forums dedicated to diesel RC engines and conversions(Davis Diesels, AJ industries)
Just ponder this scenerio, You start up your glow engine using the glow ignitor. You let the engine warm up and as soon as you pull the ignitor off the glow plug the engine dies. You think to your self it was running fine yesterday. You try agian and this time you blip the throttle to clean it out, but it still dies as soon as you pull the glow ignitor off.
Finally you install a new glow plug and the engine stays running without the ignitor and all is well. Why did it stay running?

 

[Tarant]

I am just a student in high school (16)so if I am wrong dont get mad.
isnt it like a lightbulb.
Cause in a LB the tungsten piece the filiment would glow when electricity runs through it but since a light bulb is not air tight oxygen enters the LB and causes corrosion so after time the LB will not glow cause its filiment is to corroded. So in a glow plug the platnium filiment will glow but after so long it is just to corroded to work.correct or way off

 

[Revo Rancher]

Sooooo, why does my diesel motorhome and the 2 STROKE diesel yard dogs run AFTER the glow plug cycle is OFF?!?!? The two stroke diesel trucks only use about 12:1 compression!!!! In the case of my diesel MH it is because sufficient heat builds up partly due to the glow plug and partly due to the compression ratio, but in the 2 stroke, extremely high compression has nothing to do with it. For 4 stroke diesels you may be right, but for two stroke, you are dead wrong.

 

[SkyMaxx]

Are we talking about RC engines or 1:1 diesel engines? Just curious, because often things that look similar can be totally different animals. One two stroke technology can easily be engineered to run completely differently from another two stroke technology.

From a purely physical standpoint....

- The compression stroke generates heat.
- The catalytic reaction between the methanol in the fuel vapor and the alloy used in the wire filament of the glo-plug also produces heat.
- The introduction of electicity into the glo plug also heats the filament in the glo plug.
- Last but not least, the combustion cycle that occurs within the engine produces heat.

Which of the four keeps the filament hot once you remove the glo ignitor/heater/driver (or whatever you want to call the electrical input)? Obviously not the electrical one. So, that leaves three to choose from.

How about this for some food for thought...all three contribute to keeping it hot. Why does a new one solve the problem that an old or damaged plug produces? How about by having more alloy remaining to produce a catalytic reaction with.

Aside from the chest poking that seems to be going on here, how about we try and find the correct answer without calling each other out.

BTW the link Tarant provides covers the answer fairly succinctly. Give it a read.