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Fuel Type?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
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Unread postAuthor: Technician1002 » Mon Oct 26, 2009 12:53 am

niglch wrote:Has anyone ever tried using methane (CH<sub>4</sub>)? I would venture to guess that it would be somewhat superior to propane due to chemical structure (all C-H bonds).


The heat content from combustion is about 1/2 that of Propane according to this table. Due to the low heat value, I believe the power would suck.

http://www.engineeringtoolbox.com/heating-values-fuel-gases-d_823.html
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Unread postAuthor: starman » Mon Oct 26, 2009 1:14 am

niglch wrote:Has anyone ever tried using methane (CH<sub>4</sub>)? I would venture to guess that it would be somewhat superior to propane due to chemical structure (all C-H bonds).


Any chemical bond "superiority", will be trumped big-time by dirt cheap, pre-packaged, pre-pressurized, ultra-available propane. You would be better off to just go to MAPP gas if you wanted a marginally more powerful and still safe improvement to propane.

What sources would you suggest one cheaply acquire methane?

This fueling discussion occasionally pops up and in my mind unnecessarily. Propane and MAPP are THE fuels of choice for combustion spudding. They are so easy to implement, I'm not sure why anyone bothers with aerosol sprays of any sort...with anything but the most basic demonstration combustion project.
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Unread postAuthor: SpudBlaster15 » Mon Oct 26, 2009 2:04 am

starman wrote:I'm not sure why anyone bothers with aerosol sprays of any sort...with anything but the most basic demonstration combustion project.


Nostalgia I suppose...

As far as Propane Vs Methane, they are very similar in terms of energy (heat) output per mole of reactants. Propane will give you slightly more performance, but I doubt anyone would be able to perceive the difference.

In terms of cost Vs ease of use Vs availability Vs performance, Propane is without a doubt the best spudgun fuel.
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Unread postAuthor: MrCrowley » Mon Oct 26, 2009 3:12 am

In terms of cost Vs ease of use Vs availability Vs performance, Propane is without a doubt the best spudgun fuel.

In NZ, MAPP and Propane are the same price and MAPP is just as easy to get as Propane, but I guess it's different in the States and Canada.
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Unread postAuthor: inonickname » Mon Oct 26, 2009 3:23 am

Technician; methane is used in many combustion light gas guns so I'd assume it is well superior.
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Unread postAuthor: jimmy101 » Mon Oct 26, 2009 1:22 pm

niglch wrote:Has anyone ever tried using methane (CH<sub>4</sub>)? I would venture to guess that it would be somewhat superior to propane due to chemical structure (all C-H bonds).

All saturated hydrocarbons are about the same in terms of their energy content in a spud gun.

Only acetylene and hydrogen have significantly more energy than the simple hydrocarbons and even then they are only ~10% more energetic.

Most alcohols have energies similar to the saturated hydrocarbons.

The only significant difference between all the various fuels is burn speed. Hydrogen and acetylene are not only slightly more powerful but they also burn 3 to 8 times faster.
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Unread postAuthor: niglch » Tue Oct 27, 2009 1:18 am

Technician1002 wrote:The heat content from combustion is about 1/2 that of Propane according to this table. Due to the low heat value, I believe the power would suck.
http://www.engineeringtoolbox.com/heating-values-fuel-gases-d_823.html


Yeah but you would be using an 11% methane/air mix for proper stoicheometry compared to 4% for propane. You need to account for the fact that you are burning over twice the amount of methane. Methane would indeed suck if you used a 4% mix. Anyway, I agree that the performance difference between propane and methane is probably small. Since we know propane tends to outperform butane, I thought the trend might continue for even smaller hydrocarbons.
methane > ethane > propane > butane

Of course propane's wide availability makes it the most viable of these.
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Unread postAuthor: SpudBlaster15 » Tue Oct 27, 2009 1:44 am

MrCrowley wrote:
In terms of cost Vs ease of use Vs availability Vs performance, Propane is without a doubt the best spudgun fuel.

In NZ, MAPP and Propane are the same price and MAPP is just as easy to get as Propane, but I guess it's different in the States and Canada.


Around here, Propane is $4/bottle, and MAPP is $11/bottle. I've used MAPP for most of my combustion applications since it does provide better performance, but it is far from the best value.

Yeah but you would be using an 11% methane/air mix for proper stoicheometry compared to 4% for propane. You need to account for the fact that you are burning over twice the amount of methane.


Yep, the best way to approach this is to calculate the heat output per mole of oxygen, since the quantity of oxygen in a sealed chamber is a fixed value. In that regard, Propane and Methane are almost identical.
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Unread postAuthor: Technician1002 » Tue Oct 27, 2009 3:38 am

SpudBlaster15 wrote:
MrCrowley wrote:
In terms of cost Vs ease of use Vs availability Vs performance, Propane is without a doubt the best spudgun fuel.

In NZ, MAPP and Propane are the same price and MAPP is just as easy to get as Propane, but I guess it's different in the States and Canada.


Around here, Propane is $4/bottle, and MAPP is $11/bottle. I've used MAPP for most of my combustion applications since it does provide better performance, but it is far from the best value.

Yeah but you would be using an 11% methane/air mix for proper stoicheometry compared to 4% for propane. You need to account for the fact that you are burning over twice the amount of methane.


Yep, the best way to approach this is to calculate the heat output per mole of oxygen, since the quantity of oxygen in a sealed chamber is a fixed value. In that regard, Propane and Methane are almost identical.


Here propane is about $2.50/gallon. :D I don't buy the little bottles anymore. Well unless I want to make another small cannon.
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Unread postAuthor: MrCrowley » Tue Oct 27, 2009 4:38 am

SpudBlaster15 wrote:
MrCrowley wrote:
In terms of cost Vs ease of use Vs availability Vs performance, Propane is without a doubt the best spudgun fuel.

In NZ, MAPP and Propane are the same price and MAPP is just as easy to get as Propane, but I guess it's different in the States and Canada.


Around here, Propane is $4/bottle, and MAPP is $11/bottle. I've used MAPP for most of my combustion applications since it does provide better performance, but it is far from the best value.

Wow, here it's $33NZD a bottle including the torch, so you still win. :P
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