Electronic Fuel Meter

[potatoflinger]

I haven't been around on the forum much in the last few months, so please forgive me if this has already been mentioned on here. I did a few quick searches of the site and didn't find anything similar, so I figured I would go ahead and post.

I have started building a propane meter for a combustion cannon which is just a very small solenoid valve connected to a regulated propane source. I am using a microcontroller to precisely control how long the solenoid valve stays open, therefore regulating the amount of fuel.

I tested the system by opening the valve for set periods of time and measuring the volume of gas being released, and all of my results were very similar. I was then able to come up with a formula to give me the amount of time to keep the valve open in order to release a certain amount of propane.

My goal for this (at least for now) is to make a noise cannon, similar to a bird cannon. I am planning on using a microcontroller to control fueling, then ignition, and then a chamber fan to vent exhaust gasses, thus creating a fully autonomous noisemaker.

I am finished with the meter portion of the build, I just haven't done any work on the ignition system yet. Hopefully I will have a testable prototype by next weekend.

My questions are:

1: Has anyone else here on spudfiles tried using a meter like this before? I'm curious to see if it has been done before.

2: Would it be wise to put a check valve between the solenoid valve and the combustion chamber just as a safety precaution?

[Technician1002]

I remember one full auto.. Searched youtube and found it. Interesting, they meter by time, but with a spray can for a true full auto spray and pray.

[youtube][/youtube]

A check valve is a good idea both to protect the valve and to prevent combustion gas from entering the supply line causing variation in fuel delivery due to dilution of the next shot.

In the case of the video above, the issue was avoided by external injection.

[potatoflinger]

Just a quick update: I put together a quick prototype to test out this type of meter, and it worked the first time I am very happy with the result! I might upload a video a little bit later.

[Technician1002]

I have considered using an automobile fuel injector to build a gasoline powered combustion, but due to time and funds, this has not been started. Gasoline has a much narrower combustion range than propane so electronic timing and a pressure regulator will be required to have any reliability.

I have also considered using a fuel injector with propane to see if they will work dry for metering propane. If it does work, it may provide a nice source of 12 volt propane metering solenoids.

[mark.f]

Get out of my daydreams Tech.

[POLAND_SPUD]

Just a quick update: I put together a quick prototype to test out this type of meter, and it worked the first time Very Happy I am very happy with the result! I might upload a video a little bit later.

Do post a video... I think everyone was considering this method but I don't think I've ever seen any videos...

Here's some food for your thought
[youtube][/youtube]
Now that's fast isn't it?

[potatoflinger]

Okay, here is a short video of the prototype I came up with. If you listen closely you can hear the solenoid clicking as it opens and closes, then a few seconds later the ignition system kicks in.




I don't have much experience with combustion cannons, so what are your thoughts on the way that it burns? I feel like it would work pretty well if it had a barrel and a projectile or burst disk to seal off the chamber, but I'm not sure.

[POLAND_SPUD]

You can't really treat it as a real test when the chamber isn't sealed. Seal the chamber and repeat it

but kudos for actually posting it

[Technician1002]

The test is looking real good. The slow burn indicates a poor mix or running rich. See if you can get ignition with a shorter dwell time.

With a good mix and not too rich, it can get quite loud.

[potatoflinger]

The test is looking real good. The slow burn indicates a poor mix or running rich. See if you can get ignition with a shorter dwell time.

With a good mix and not too rich, it can get quite loud.

I'm thinking that part of the problem is that the propane is all just running to the bottom of my chamber, making it seem rich. If I seal off the chamber and add a fan to mix everything right before ignition, I'm wondering if it might work better.

Regardless, I have more work to do and not much time to work on it right now. It looks like this project might have to wait until next week.