Hot Tube Ignition

[Roger B]

Rather than Hijacking the Hardy and Padmore thread I will start a new one on hot tube ignition. To start with Graham's post:

Looking good 

I liked the hot tube trial    What is the smallest size tube you have used successfully?

Hi Roger.

Seasons greetings.

After years of making engines with hot tube ignition it seems that 3 mm internal diameter suits most IC engines of up to 50 cc  capacity.  Preferably made from 316 stainless Steel. The compression ratio also plays a major part too. Once above 4:1 you start getting pre ignition issues making them so advanced that they just won’t start and run properly. For larger capacity models an internal diameter of around 6 mm becomes the norm.

Heating is the main issue. They really need to be stinking hot for best results. This is why you’ll see many models running without the chimney cap because the flame becomes stifled at scale sizes.

Hot tube remains my favourite however, despite the many problems it can present to the modeller.

On an historical note most early gas engines were fairly low in the compression ratio area but as the knowledge and engineering advanced  it was soon discovered that  hot tube ignition was unsuitable without some form of mechanical means of ignition timing. Manufacturers started to favour electrical ignition systems in both low and high tension form as they gave an almost perfect control of the engines running parameters.


   Graham.


Addendum.

Just realised that I missed an important dimension ie. Hole depth.

We mainly used imperial measurements for our ignition tubes. 1/8”-2” deep or approximately 3-50 mm deep. If an engine was reluctant to start with the normal settings we would usually go up by 1/64” to cure the problem.

Another important point is that we’re also trying to make these engines run on a gas that was unknown to our forbears. A gas that isn’t very flexible in its combustion ratio of fuel and air.  😉

[Roger B]

Have you used hot tube ignition on a liquid fuelled engine, petrol/gasoline etc?

One of my next planned trials is to fit a hot tube to my 25cc horizontal four stroke. This is usually run on Alkylate (Colemans) fuel. The spark plug is fitted vertically on top of the cylinder head so is easy to replace with a hot tube. If I can get this to run I will then try using paraffin/kerosene with part of the inlet pipe being heated by the flame to produce, hopefully, sufficient vaporisation.

This will then be the proof of concept for my next build, the Saurer Doppel Phaeton engine, which uses hot tube ignition and paraffin injection with a heated inlet manifold

[Jasonb]

One Graham prepared earlier, I still have my set of castings under the bench. Running on paraffin with Hot tube.

<a href="https://www.youtube.com/watch?v=4MdSeVslvig" target="_blank">http://www.youtube.com/watch?v=4MdSeVslvig</a>

[Alyn Foundry]

Hi Roger.

The simple answer to your question is yes. The first attempt at using Paraffin/Kerosine ( on a model basis ) was done around 1985. I fitted a modified CO2 cylinder, those used for making fizzy drinks, to one of my Sphinx engines. It ran very well but showed the need of a governor to keep the engine running at a steady pace.

Moving on to the turn of this century I embarked upon the mammoth task of scaling a Hornsby Akroyd oil engine. This too proved successful but was dogged by very erratic running so the project was shelved. As Jason has shown our most recent model, a 1/3 rd scale Robinson patent oil engine model HA was built around a year ago.

For me personally the major drawback of using oil fuels is the smell, the exhaust seems to linger and stick to your clothes like glue.

I’m happy to share my experiences with making oil engines so please feel free to ask.

   Graham.
 

[tghs]

I came across this very early V twin,,(daimler) the interesting thing was for the marine version the tube heater burners were gimble mounted.. they did say that it only ran well in a small RPM range,, looks like a really long stroke..

[Roger B]

Thank you all 

Graham, what I am looking at is vaporising the paraffin externally like in a tractor running TVO and then igniting with a hot tube.

Is the Robinson injecting into the cylinder and using the hot cylinder for vaporising as in a hot bulb engine?

Yes, oil engines smell unless you can get really good vaporisation/atomisation of the fuel.

[Alyn Foundry]

Thank you all 

Graham, what I am looking at is vaporising the paraffin externally like in a tractor running TVO and then igniting with a hot tube.

Is the Robinson injecting into the cylinder and using the hot cylinder for vaporising as in a hot bulb engine?

Yes, oil engines smell unless you can get really good vaporisation/atomisation of the fuel.

Hi Roger.

The Robinson is very, very basic. The fuel is gravity fed and  metered by a needle valve above the atmospheric inlet. However Horace incorporated a rather clever double headed valve where the fuel would be atomised due to it rattling as the air was passing through to the cylinder. This valve was situated directly above where the permanent lamp was heating the heavy, wedge shaped cylinder head.  This enabled the atomised fuel to be vaporised before admission.

I have attached a couple of pictures of the patent and the cylinder heads. The engine had definitely worked hard for its living as there were two burned out cylinder heads found with its remains.

   Graham.