# Spark Plug vs Glow Plug



## BronxFigs (Apr 21, 2013)

Can a four-stroke, single cylinder, or,V-Twin gas engine like e.g. the "NEMETT" and "HOGLETT", be converted to run on a glow plug?

I ask because there is a thread called "Vee Twin Selfcharger" posted today showing a V-twin glow plug engine that reminds me of the "Hoglett" functionally, excluding the outwards appearances.

I ask because I have the plans and drawings for the "HOWELL V-TWIN" and the "HOGLETT" and I'd like to know if both these engines can be made to run on glow-plugs?  I'd like to eliminate anything that's not really needed to get an engine to run, like: coils, points, wires, etc.  I hate extra work.

Just asking what the differences are between an engine designed to run on spark plug vs. glow plug?  Are cylinders, heads, con-rods, pistons different?  Fuel type, and delivery/metering must be different, I suppose?

Thanks,

Frank


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## wheeltapper (Apr 21, 2013)

Hi.
My Nemett Lynx runs on a glowplug quite happily.

[ame]http://www.youtube.com/watch?v=WYW1gqZjuV8[/ame]
It takes a bit of time to start as it was the first run and I had to get the settings right.( thats my excuse anyway

In the construction article the only difference between glow and spark was a sensor for the ignition timing for the spark.

Roy.


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## BronxFigs (Apr 21, 2013)

Roy,

Thanks for the quick answers.  Quite honestly, your answer was not what I expected.  I thought, after posting the questions that I would learn that major design differences would come into play.  I have watched your video of the Nemett "Lynx" many, many times, and did not realize that it ran on a glow plug.

Perhaps if I was more experienced, I would not have asked such obvious questions, and tipped my hand.  Thank you for the response.

Frank


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## Lawijt (Apr 21, 2013)

Compression & timing are very important. I have here a motor thats running very good with 2 stroke fuel & a sparkplug. But runs very bad with glowfuel with nitro & a glowplug.


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## chrsbrbnk (Apr 21, 2013)

there were a variety of hotbulb engines early  in the hit and miss era   pretty much a glow plug on steroids


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## BronxFigs (Apr 21, 2013)

So, can I assume that there are few major design differences for glow and spark engines, except fuel delivery and type, timing events, and compression ratio tweaking?  

Basically, would the construction be the same, but with some additional  modifications to run on either spark, or, glow plug?  Could the "Hoglett" be made to run on glow fuel and plugs?  Is there any advantage to running an engine as either a sparker, or, on a glow-plug?

Thanks for the additional information that was posted..  Interesting answers.


Frank


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## wheeltapper (Apr 21, 2013)

At the beginning of the construction aricle Nemett stated that the engine should be capable of running on glow or spark plug without modification.

Roy


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## 123RWO (Apr 21, 2013)

A glow ignition engine needs at least 8:1 compression ratio.   Many model engines designed for gas don't have this much compression as originally designed.  The ignition timing in a glow engine is controlled by compression ratio and any nitro in the fuel.  More nitro adds ignition advance.  A hotter glow plug will also increase ignition advance.  Racing engines use lots of nitro for the thermal boost as well as the increased ignition advance which is necessary for max power at high RPM.  It is possible to have too much of a good thing and the engine will go into detonation( some people call it pre-ignition) and can damage itself.  You can usually hear detonation as the sharp crackling sound over the basic exhaust note as full throttle is approached.

RWO


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## wheeltapper (Apr 21, 2013)

the lynx is 9 to 1.


Roy.


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## BronxFigs (Apr 22, 2013)

Very interesting information, especially about the engine's timing events with differing fuels, etc.

Frank


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## tornitore45 (Apr 25, 2013)

RWO said well.  The take away is that an engine that runs on glow plug can run on spark becasuse you can time the spark to happen at the same time (at least for a limited trottle range), on the other hand glow ingintion timing is controlled by many design, plug and fuel factors that need to be just right, most imortant the compression ratio.


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## mu38&Bg# (Apr 25, 2013)

Glow model airplane four stroke engine compression ratio has been all over the place, from 7:1 to 15:1. Most engines produced today are in the 8:1 range. Most engines run best with the OS "F" four stroke plug. Only one manufacturer makes four stroke plugs with different heat ranges. Most model four strokes have very poorly executed squish bands (unlike two stroke engines) due to massive squish clearance. It all comes together just fine. Most any production engine today will run on the same plug and 5-30% nitromethane fuel simply by tuning the needle valve to achieve proper running. Timing is controlled with air fuel ratio by the needle valve.

The only issue with glow and the typical rich running is rust in the crankcase. Wet sump engines should use an oil compatible with methanol, but that doesn't seem to be much of an issue.

Greg


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## Lawijt (Apr 25, 2013)

Here my Rogers engine with a glow plug & methanol with nitro & oil.
[ame]http://www.youtube.com/watch?v=jvbhCU3i7KQ&feature=share&list=UU1BXeMnWzIagQAC7fKYx0_g[/ame]

The same engine with a sparkplug , electronik ignition , 98 octane fuel & 2-stroke oil
[ame]http://www.youtube.com/watch?v=s5cP2TfKMjA&feature=share&list=UU1BXeMnWzIagQAC7fKYx0_g[/ame]

Best regards

Barry


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