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Model engine glow plug switch

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Corky

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Hi everyone,

I have a small engine which i am restoring, its from a model aeroplane i think, its a petrol compression engine( i know this sounds wierd but it definately is).

The problem im having isthe glowplug (needed to start theengine) is currently connected to a simple switch which is manually turned off when the engine gets going, is there a way i could get it to turn off after the engine has started? i cant think of a sensor that would do this.

Any ideas welcome even without the electronic idea to back it, im happy to research things myself but i dont know where to start
(glow plug is 1.5v, 3ohm) run from 6v battery pack(used for other electrics) dropped down by series resistors

Thanks Guys.
 
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What are you powering with the engine? If it is just for workbench display you could devise or buy some kind of a centrifugal switch but that seems overly complicated. If you're actually turning a propeller, you could put a vane in the airstream connected to a microswitch. Of course, you'll probably want to keep the manual switch in the circuit too, so you don't inadvertently leave the glow plug on after you're done demonstrating your engine and drain the battery (or worse, burn out the glow plug).

You might also want to put an LED or similar in a series-parallel arrangement with your dropping resistors so you can tell when the glow plug is getting current (not just when the power is on, because then you won't have any indication if the glow plug goes open).
 
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for now its just a working display piece, i dont mind it being complicated as im pretty new to electronics so i want to learn as much as possible about it

im thinking of running something from it in future but ot sure what, (ideas welcome) possible a new post in the furture though

thanks again
 
You might want to search for "on-board glow plug driver." One purpose for having an in-flight driver is to ensure smooth idle for long periods. There are various ways to control whether power is going to the glow plug. Many systems are simply based on the engine rpm or what is assumed to be rpm based on the throttle servo signal. Other glow-plug systems use simple timers. A more complex system will measure the glow plug or other temperature (e.g., CHT) and determine whether additional electrical heating is needed.

You describe your engine as a "petrol compression" engine. Most model aircraft engines run on methanol/nirtomethane or pure methanol. I would not call methanol petrol. There are also pure diesel model engines that don't have glow plugs and don't use petroleum fuel. It is also possible to have a petrol (gasoline) model engine that has a glow plug. And, I suspect somewhere there are true diesel model engine with glow plugs like modern full-size diesel engines. Which type of engine do you have?

Please give a little more information about what type of engine you have and which approach you want to take.

John
 
Hi Jpanhalt,

i have a petrol(Gasoline) with glow plug, at the moment im not sure of my approach but ill do a bit of research into your suggestions,

it doesnt HAVE to have anything at all just playing about with it trying some new things keeping me busy in my spare time

Regards
 
Gasoline/glow engines do run hotter than methanol/glow. Here's a commercial device that claims to be based on glow plug temperature: **broken link removed** With a pulsed glow-plug supply, you could monitor current and probably get the same result.

John
 
I havnt messed with model engines before, does the glow plug heat to initially start the engine or is it used throughout the running of the engine?

Regards
 
Generally, the glow plug is used only to get the engine started. Catalysis of the fuel with platinum in the plug and compression (like in a pure diesel) keep it hot thereafter. Added electrical energy is not needed at normal operating rpm's. However, under some conditions, e.g., slow rpm's and cold weather, additional heat may be needed for stable operation. That is one reason for an on-board supply. With your petrol engine, I suspect that the recommended fuel contains 10 to 20% methanol in the gasoline. That is to provide the catalytic heat. Gasoline itself, so far as I know, is not sufficient.

John
 
yer that was my way of thinking, ive worked alot with big deisel engines and a few small petrol and a couple of two strokes so my knowledge of a model petrol compression is adapted guesswork really,

i had the engine given to me broken and its almost ready to run, i thaught it was pure petrol but i may have to look into this now, it did come of a bit of a shock hearing it was like this,

ill have a look

cheers john
 
Is it 2-stroke or 4-stroke?

In the US, one popular adaption of simple, 2-stroke engines originally designed for methanol or gasoline is to what we call "gas-glow." Methanol fuel is $14/gal and up. Gasoline is now about $2.25/gal.

If the engine is a 2-stroke and originally designed for gasoline/oil and spark ignition, then add about 10 to 15% model airplane fuel, and it should at least start popping with a heated glow plug. You need to be sure the oil mix is no lower than when it ran on gasoline alone (usually 1:20 to 1:50). Most American gasoline now has 10% ethanol in it. What we call "marine" gasoline is ethanol free. I would use petrol without ethanol.

If the engine is 2-stroke and originally designed for methanol-based fuel, converting to gasoline is not a big deal, but you have to be mindful of the connecting rod bearings. Such model engines will almost always have just plain bearings and are designed to run with 10% (minimum) oil, so you must increase the oil to 10% or more when running with gasoline.

If it is a 4-stroke engine, the same considerations as to its original design (i.e., gas or methanol) must be taken into account. Plus, you need to consider plug cooling. Converting such engines to gas-glow is not done that often in the US. I suspect you may need a 4-stroke glow plug, which is designed to stay hot better, and you may need electrical heat at higher rpm's or even continuously to get a good running.

John
 
im not converting it john it was factory made that way as far as i know,

my presumption is gasoline=petrol, im in england where the petrol is roughly £4.80 a gallon

EDIT: sorry i missed your question, its 2 stroke
 
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How old is this engine? Many years ago model airplane engines actually used spark plugs, points and coils. Some of the plug holes were the same thread as modern glowplugs. Could you post a picture of you engine or the name of it? I never heard of a petrol compression engine and Googled it, seems like some auto makers are now toying with the idea.
 
Both RCUniverse and RCGroups have many threads discussing running engines with gasoline and glow plugs. Here is one thread from 2008 on the subject of using gasoline/glow fuel mixtures: https://www.rcuniverse.com/forum/engine-conversions-92/8009384-gas-glow-how.html RCUniverse, user= av8tor1977 has been particularly active in developing that fuel.

And here is a new announcement to an OS Engines glow-ignited gasoline engine: https://www.rcgroups.com/forums/showthread.php?t=2095471&highlight=gas glow

I think the TS established in post #5 that "petrol compression" was the equivalent of what we might call a gasoline engine running with glow-plug ignition.

John
 
Ok, I was going on your post #10 "If the engine is a 2-stroke and originally designed for gasoline/oil and spark ignition"
I used to have a couple of the smaller spark ignition gasoline engines from the 1930s. Didn't know they were doing this now.
 
I fly model airplanes with glow plug engines. Connect the 1.5 vdc battery to the glow plug after you have filled the tank and primed the engine. Choke the engine until it tried to fire then spin the prop quick it will start. Adjust needle for full throttle. Then remove battery clip form the glow plug. There is no switch or automatic off it is manual. You do not want to haul a battery in your airplane.
 
hello Gary, im not flying a plane mate just a static engine from an RC plane so weight isnt a problem,

cheers guys for this
 
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