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What gas for a Centaur?

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AJW12/03/2019 22:53:39
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Been running my new Centaur engine on petrol but now wish to try it on gas.

I am making a gas control valve at the moment but would like advice on what type of gas it might like? I have a couple of cannisters containing a butane/propane mix and without guidance was going to try that.

Alan

not done it yet13/03/2019 11:33:51
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I doubt it makes a lot of difference.

Hydrogen, methane, propane or butane are the common gaseous fuels (ethane could be included, but doesn't get used as a fuel so often) and all are either gases or vapours at the temperature you are likely to be running your engine at.

I expect, if you intend the item to be mobile, propane or butane are the most obvious choices. More energy density with butane, but I suspect the vast majority would be using propane. The differences are the pressure regulators, mainly (I suspect).

JasonB13/03/2019 11:40:39
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Typical blowlamp or camping canister gas mixes will be fine and are the most practical, I have also run off my large propane bottle which is OK at home but a lump to lug around if showing.

I just got some castings that include a nice vapour carb so will be making that, I have lashed them up in the past when testing engines that had a tendency to flood but this one looks nice and I have bought the Ball "Mason" jar already

Edited By JasonB on 13/03/2019 11:42:21

AJW13/03/2019 13:21:26
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Thanks for your comments, I just had a look at the gas bottle I was proposing to use. They are sold for use with a weed blowlamp and contain 70% Butane and 30% Propane and I was hoping to incorporate it in in the engine base.

Alan

John Rudd13/03/2019 14:04:23
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You could make a smaller volume gas tank to fit in the base, just decant from your blowlamp canister to fill it...

duncan webster13/03/2019 14:22:51
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There was an article in ME about running engines on gas not that long ago. I seem to remember that it's not as easy to get the mixture right as using petrol or coal gas. No doubt someone will come up with issue number

AJW13/03/2019 16:12:26
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Thanks, I have the gas valve in position ready to administer the gas but I'm thinking that it should be linked to the throttle? so as the throttle is opened the gas valve also opens to supply more gas and retain the correct ratio.

Or am I thinking too deep! and just leave the throttle open and control the engine from the gas supply.

I'm quite sure all will become clear once (if!) I get it running.

Alan

JasonB13/03/2019 16:22:59
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It's usual to have a demand regulator as well as a means to control the gas amount which will allow gas to flow when there is a vacuum in the carb much like fuel will only be sucked into the venturi on the intake else you get flooding or in this case too big a percentage of gas

AJW13/03/2019 17:40:06
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Just checked the cannister and it's pressurised to about 50psi.

My carburettor has a disc valve which is held shut under spring pressure in theory cutting off gas and petrol supply so I think if I establish the pressure that can be 'held back' by this, a gas can regulator could be set to just under that?

Alan

JasonB13/03/2019 18:23:20
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That will be fine, my Robinson has a similar valve. ideally you want a valve as close to the engine as possible as if using one on the bottle with a long length of hose the pressure can rise in the hose while the carb valve is closed, but try it with what you have first of all.

Graham Corey (Alyn Foundry) suggested to me a good way to check your mixture is right. If you remove the silencer and hold a flame just beyond the open exhaust pipe and turn the engine over by hand with the ignition off then the type of flame produced will indicate the mixture. If it is a soft orange flame then you are too rich if a smaller blue flame you are in the right area, just watch your eyebrows. Also works for petrol engines.

AJW13/03/2019 18:38:29
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Thanks Jason, lots of useful information there, I will be having a play shortly! (after I locate a regulator)

Alan

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