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Old Aug 11, 2008, 03:23 PM
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Benefits with a Spark Ignition on a Glow engine.

Hi every one. I'm a silence watcher of the forum for some time now, but after search and read many, many post I can't really understand the whole benefit of using a spark ignition on a glow engine. It looks very interesting

Can any one explain some things?

Thanks in advance.

1) Can any glow engine use a spark ignition?

-I think any glow engine can use a spark ignition, but I read that small engines (below 120) receive no benefit because the components of the ignition are too heavy. Did I understand right?

2) Does a glow engine running with a spark ignition spend better the fuel?

-As I read the spark ignition systems make the engine able to use every fuel put into the engine, not like glow plugs that make the engine unable to burn all the fuel and many of it goes out of the engine by the exhaust. Did I understand right?


3) Is a glow engine with spark ignition easier to tune than normal glow plugs engines?


All the information you can provide about this will be welcome.

Thanks.
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Old Aug 11, 2008, 07:05 PM
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1. Yes. In reality the weight penalty allows ignition systems to be used on models of about .40 size at the smallest. There are a few systems that could be used on .20 size models.

2. The carb can be tuned leaner and still run well. This is because the glow plug and fuel mixture interaction is eliminated. Ignition occurs when spark occurs so timing is set by the ignition and not by glow plug, air-fuel mixture, and compressions ratio. I believe that many glow engines are set up such that they must be run relatively rich.

3. Yes. High end is non-critical and low end is easy. The low end can be extremely rich and it will still fire and run. In general mixture is non critical.

Greg
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Old Aug 12, 2008, 03:46 AM
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Thanks "gkamysz".

More things.

4) Will the ignition give more torque and more rpm?

5) What the right mixture 18% oil - 5% nitro... 20% oil - 10% nitro? Or simple can I change the mixture for each diferent kind of flight?

Thanks again.
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Old Aug 12, 2008, 07:31 AM
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Ignition does not have a significant impact on the power output. It might if the engine was not optimized with glow.

You can run the same oil ratio as recommended in the engine manual. I was running only 5% castor oil and balance methanol in my Enya 46-4C. Peter Chinn's old four stroke book suggests that many four stroke engines could be run on much less oil than manufacturer recommended at the time. The engine was doing fine, but only had about a liter of 5% oil fuel through it when I broke the airplane. It's waiting for repairs.

I'm going to convert an OS FS-52 to ignition and increase the compression ratio to 13.5:1 to see how this influences power.

Greg
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Old Aug 12, 2008, 07:55 AM
Zor
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Kikerumbo
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Quote:
Originally Posted by Kikerumbo
Thanks "gkamysz".

More things.

4) Will the ignition give more torque and more rpm?

More torque and more rpm is power.
More power comes from the average pressure in the firing chamber. That is obtained by the optimum fuel / air ratio.
A fixed amont of mixture comes in every IC (internal combustion) cycle depending on the carburetor opening.
On a rich mixture less air (oxygen content) is available to burn the fuel (less pressure) .
On a lean mixture less fuel is available to burn (less pressure).
The max power is obtained at the optimum fuel / air ratio.

5) What the right mixture 18% oil - 5% nitro... 20% oil - 10% nitro? Or simple can I change the mixture for each diferent kind of flight?
Do not confuse oil mixture and nitro content mixture.
Oil does not basically produce power. It lubricates the metal parts. More oil % means a little less burning content. High oil % in model engine is required by the nature of the metals used and the high rpm involved and the absence of a lubrication system.
The nitro % is to add some available oxygen to burn the fuel and thus produce a little bit more power in a given size engine. The added power is not "out of this world". The added nitro also makes the fuel / air ratio less critical for ignition and as a result the engine is less crtical on so called "tuning the engine" with the needles.
Thanks again.
Hoping this helps to answer you questions.

Zor
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