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Fuel injection question

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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Fuel injection question

Unread postAuthor: Walter103 » Sun Nov 17, 2013 5:33 pm

Hi!
I am building a fuel injection system for the gun I'm building. It employs a solenoid valve that will soon be controlled by an arduino board. I plan to solenoid valve to the chamber with barb fittings and tubing. Do you think I will have issues with hot gases entering/ blowing of the tube. Should I find some sort of one way valve? Thanks for any advice!!

Walter
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Re: Fuel injection question

Unread postAuthor: jackssmirkingrevenge » Mon Nov 18, 2013 6:30 am

I have done some experiments with arduino and solenoid valves, and even a direct acting valve has a relatively long response time, at least 10ms to open and 30ms to close. You will need a very fine nozzle for accurate metering. In this regard, a check valve is probably unnecessary.

I see a lot of trial and error in your future :) will you be introducing compressed air too?
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Re: Fuel injection question

Unread postAuthor: Walter103 » Mon Nov 18, 2013 12:48 pm

I have considered injecting compressed air aswell, but I am having trouble decideing between that and a simple chamber fan to suit my needs. And yes, lots of trial and error for me! I plan to use a gradulated cylinder and a bucket of water to dial in the amount of propane released.
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Re: Fuel injection question

Unread postAuthor: mark.f » Mon Nov 18, 2013 4:42 pm

jackssmirkingrevenge wrote:I have done some experiments with arduino and solenoid valves, and even a direct acting valve has a relatively long response time, at least 10ms to open and 30ms to close.


Have you tried a bona fide gasoline or diesel fuel injector? I keep saying I'm going to play around with it but I destroyed the injector I pulled from the junkyard trying to remove the jets... I was thinking of measuring the volume of gas for different time intervals and doing a regression for fueling my launcher...
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Re: Fuel injection question

Unread postAuthor: Walter103 » Mon Nov 18, 2013 5:52 pm

Do you think a 3/8 inch nozzle would be small enough?
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Re: Fuel injection question

Unread postAuthor: jackssmirkingrevenge » Wed Nov 20, 2013 6:28 am

Walter103 wrote:I plan to use a gradulated cylinder and a bucket of water to dial in the amount of propane released.


Good idea!

Solubility in water (1.013 bar and 20 °C (68 °F)) : 0.039 vol/vol


Negligible.

Have you tried a bona fide gasoline or diesel fuel injector?


Experiments were with compressed air for an auto, more news on that eventually.

Do you think a 3/8 inch nozzle would be small enough?


I was thinking of a 1/16 inch nozzle... what is your chamber size? If it's one litre, that's 42mL of propane to inject. That is not a whole lot of gas, and the explosive limits are pretty narrow so accuracy is paramount.
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Re: Fuel injection question

Unread postAuthor: Walter103 » Wed Nov 20, 2013 1:01 pm

I think what I may do in just cap a piece of vinyl tubing, drill different sized holes in it, and see what kind of precision I can get with the different diameter holes...

what is your chamber size?


I plan to use this system initially for a small gun to shoot .50 cal paintballs and other various projectiles. The chamber for that will be 2in x 3.5-4.5 in, so very small. I don't expect a whole lot of power out of that gun, but it should be fun regardless. I also may make this fueling/ ignition system interchangeable with my other larger gun.
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Re: Fuel injection question

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