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| Gunner |
 Posted: 07/16/2008 8:45 AM Post subject: |
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Staff Sergeant
Joined: 21 Oct 2007
Posts: 107
165.81 Spud Bux
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OK...what is the volume ratio because I have LP gas, can I use 0.96:0.04?
(Edit: No problems anymore  ) |
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| LCTChamp |
| Posted: 10/19/2008 17:22 PM Post subject: |
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Sergeant Major
Joined: 21 Aug 2008
Posts: 188
118.03 Spud Bux
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| i understand the how much propane to put in its the air thats confusing me. For a 2x mix you would just add 14.7psi of air? |
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| LikimysCrotchus5 |
| Posted: 10/19/2008 17:58 PM Post subject: |
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Brigadier General
Joined: 04 Sep 2007
Posts: 1113
2657.59 Spud Bux
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| Yes but you would also add twice as much propane so that your mixture is combustible. |
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| fogus |
| Posted: 11/11/2008 17:18 PM Post subject: |
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Private First Class
Joined: 22 Oct 2008
Posts: 33
118.82 Spud Bux
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OK, I believe I have a recipe for filling a hybrid combustion tank in my head.
It is:
1. Decide on what --X (compression ratio) you want to end up with.
2. Assuming your chamber is filled with 14.7PSIa of air:
3. Raise the pressure of the chamber to 14.7 + 0.62 = 15.32 PSIa using propane. (I will consider this a nominal 1X mix).
This will read 0.62 PSI on a gauge.
4. Continue to raise the pressure of the chamber using propane, until it reaches 15.32 + 0.62*(X) PSIa, where X is the compression ratio you are using.
This will read 0.62*(X+1) PSI on your gauge.
5. Using air now, raise the pressure to 15.32 + 0.62(X) + (14.7-0.62)*(X) = 15.32 + (X)*(14.7) PSIa. This will read 0.62*(X+1) + (14.7-0.62)*(X)
= 0.62 + 14.7(X) PSI on your gauge.
Did I screw up anywhere? |
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| POLAND_SPUD |
| Posted: 11/11/2008 18:04 PM Post subject: |
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Lieutenant General
Joined: 13 Oct 2007
Posts: 4387
11901.36 Spud Bux
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uhmmm yes you did....
1x mix is a 'proper' mix of air and propane at atmospheric pressure
2x mix is a mix of air&propane at 2atm and so on |
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| fogus |
| Posted: 11/11/2008 18:38 PM Post subject: |
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Private First Class
Joined: 22 Oct 2008
Posts: 33
118.82 Spud Bux
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| POLAND_SPUD wrote: | uhmmm yes you did....
1x mix is a 'proper' mix of air and propane at atmospheric pressure
2x mix is a mix of air&propane at 2atm and so on |
Yes, that's why I called it a nominal 1X mix. It is 0.62 PSI above a true 1X mix, but it makes it easier to do the calculations. A my starting nominal 1X actually about a 1.042X mix. |
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| FishBoy |
| Posted: 12/08/2008 15:26 PM Post subject: |
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Colonel
Joined: 27 May 2008
Posts: 584
710.06 Spud Bux
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| For manometric metering, how accurately should the chamber volume be measured? (I am planning to fill it with water and then pour the water into graduated cylinders) |
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| Ragnarok |
| Posted: 12/08/2008 15:44 PM Post subject: |
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Lord of Karma
Joined: 19 Dec 2006
Posts: 5158
16113.53 Spud Bux
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| FishBoy wrote: | | For manometric metering, how accurately should the chamber volume be measured? |
Your error can be as large as all the oceans in the world, and it still wouldn't matter.
You don't need to know any chamber volume for a manometric meter. You could take one off a cannon of one size, then bolt it to one of any other size, and you wouldn't need to adjust a single thing. |
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| FishBoy |
| Posted: 12/08/2008 15:58 PM Post subject: |
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Colonel
Joined: 27 May 2008
Posts: 584
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| I understand that, I just had a brain lapse/poor wording combo. Anyway, for the mix calculations, how accurately does the chamber volume need to be measured? |
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| Larda |
| Posted: 12/09/2008 0:22 AM Post subject: |
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Donating Member
Joined: 18 Jul 2007
Posts: 108
274.88 Spud Bux
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FishBoy:
You can use the same numbers for any chamber size. |
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| trigun |
| Posted: 02/10/2009 16:27 PM Post subject: |
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Master Sergeant
Joined: 26 Jan 2009
Posts: 165
62.90 Spud Bux
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| I built my hybrid i cant get it to fire. My gap is .01 of an inch. I know as a fact it is firing due to small circuit gap installed by the firing switch. Idea from one of PCguys guns. My chamber is 61.023 cubic inches. Meter is 5.858 cubic inches. I am using manometric metering for air and filling it to 3 bar for a 4x mix. Does that sound correct. Also with 26.494 psi in the meter. |
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| starman |
| Posted: 02/10/2009 17:22 PM Post subject: |
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Big Daddio
Joined: 11 Dec 2007
Posts: 3076
7546.07 Spud Bux
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I'm guessing your total mix is rich.
I did a quick calc on it and it's tad rich but I think in the ball park. Are you injecting your fuel first in a freshened atmosheric pressure chamber? That's going to add about 2.5 psi to your chamber. After that, you'll need to run the total pressure with air up to about 46.6 - 47 psi. This is all assuming you're still getting a good spark...the gap sounds plenty small.
If still no success, step back a bit and try a much smaller mix, 2x or even smaller. Ignition troubles won't show up as much then. Your chamber is smallish but not out of the typical hybrid realm. However, small chambers require more precise fueling.
Edit: OH.. did you burp your meter well first...meaning, it's originally full of air. Loading it with fuel mixes the fuel and 1 atm of air making for a lean overall shot. After the meter shot, 1 atm of a fuel air mix is left behind.
Burping means just filling and shooting the meter several times to where the gas left behind in the meter is all fuel and no, or very little air.
Edit 2: And another...since your meter is a fairly low pressure model, you may need to compensate for the fact that the chamber pressure rise to 2.5 psi will also be the final resting pressure in the meter, therefore not allowing all of the fuel to release from the meter. However, since your fuel load looks a tad rich you may have already compensated for that. Just something to check. |
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| trigun |
| Posted: 02/10/2009 17:57 PM Post subject: |
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Master Sergeant
Joined: 26 Jan 2009
Posts: 165
62.90 Spud Bux
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Thanks starman i actually found out i made a very critical error in my fuel meter volume. I was off by about a 3 cubic inches which adds up really fast ! thanks for the suggestions i did burp by meter actually.
Your peanut apprentice, trigun |
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| ramses |
| Posted: 03/03/2009 16:13 PM Post subject: |
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Major General
Joined: 29 May 2008
Posts: 1519
3981.54 Spud Bux
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noob question, but would this be acceptable for manometric metering. Apparently it is "accurate to 1.0 psi." it reads to .1psi, so it is probably more precise than that.
I am hoping that the seller knows about the difference between accuracy and precision, so that once I know by experimentation how much it is off, I can adjust accordingly. As a bonus, it has a built in regulator. |
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| fogus |
| Posted: 03/03/2009 16:48 PM Post subject: |
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Private First Class
Joined: 22 Oct 2008
Posts: 33
118.82 Spud Bux
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It almost seems like a mistake. He might have meant to say, "precise to within 0.1 psi".
I'd ask. |
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