More free plans: 40 pound Chinese

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Redstone
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Re: More free plans: 40 pound Chinese

Post by Redstone » Sun Feb 02, 2025 7:09 am

Surely this is enough air and fuel? The sparklers burn out very quickly because the flame in the combustion chamber ignites the whole thing at once.
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Re: More free plans: 40 pound Chinese

Post by Redstone » Mon Feb 03, 2025 7:49 am

My propane tank is starting to run a bit low, and I've seen several people mention that for engines of this size you absolutely need a full propane tank. From my understanding the vapour pressure should remain the same no matter how much liquid propane is in the tank, so is the issue that when the tank is low there isn't enough liquid to boil off fast enough to keep the tank at a suitable pressure, or does the liquid cool down too fast when there's less of it?

metiz
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Re: More free plans: 40 pound Chinese

Post by metiz » Tue Feb 04, 2025 11:04 pm

Well you're definitely getting enough air now. The propane tank does need to be fairly full, 40+%. Try heating up your tank to get a bit more pressure, like putting it in front of a radiator or submerging it in hot water. (I've heated up tanks with the open flame of another propane tank, although that isn't....really advisable.) If the tank is still fairly full/ hot, try fiddling with the injector depth. Also don't be afraid to give it FULL gas when trying to start by quickly flicking your wrist.

I'm not sure, but I think the larger area of the empty propane tank will cause it to cool off more quickly, decreasing pressure.

*edit* google replies with this (AI generated I think, but sounds plausible) "As you get low, there is less mass containing heat, so the evaporation of the propane causes the liquid propane to cool down faster. This lowers the vapor pressure of the propane and therefore the rate at which it can boil off and be used as gas"
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Redstone
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Re: More free plans: 40 pound Chinese

Post by Redstone » Sun Feb 09, 2025 9:17 am

I've replaced my 3mm internal fuel line with an 8mm ID one. Is it necessary to crimp the end of the fuel lines to increase the gas velocity for better mixing, or is that only important for liquid atomisation if I were trying to draw liquid from the tank and not necessary for gas if I get the right injector position (e.g. moving it back to allow for more mixing time)? I've moved the injector around a bit from 80mm to 100mm in. Best I could get was the occasional buzz that may have been the engine running for a hundred milliseconds or so. The LPG tank is at less than 10%, so I think I'll get it swapped now.
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Re: More free plans: 40 pound Chinese

Post by metiz » Sun Feb 09, 2025 4:36 pm

You were running 3mm id fuel lines? That could be your problem: Too much restriction and/ or speed. I recommend a 4mm id fuel line, I don't think the 8 is going to work. You should snip the end of the fuel lines off and then slightly open the resulting slit to get a Rosscojector. A straight pipe is not going to work, definitely not with 8mm id
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Re: More free plans: 40 pound Chinese

Post by Redstone » Sun Feb 09, 2025 11:07 pm

I've pinched the ends of the injectors to make Rosscojectors, will give it a test later today. Because I only have access to 60:40 propane:butane, I think I will benefit from the larger 8mm fuel line to avoid any unnecessary pressure drops. By pinching the end, I should be building up the static pressure inside of the fuel line and creating a larger pressure drop right at the exit to increase the gas velocity, and having a larger fuel line ID shouldn't work against me so long as I've pinched the end enough to get the gas velocity high enough.
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Re: More free plans: 40 pound Chinese

Post by Redstone » Tue Feb 11, 2025 6:56 am

Pops and bangs louder than I've ever heard before, but still no dice. My neighbours probably want to crucify me. Gotta return the leafblower now.
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Re: More free plans: 40 pound Chinese

Post by metiz » Tue Feb 11, 2025 6:30 pm

You're really close now
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