Login    Register
User Information
We are a free and open
community, all are welcome.
Click here to Register
Who is online

In total there are 73 users online :: 5 registered, 0 hidden and 68 guests

Most users ever online was 155 on Mon Aug 15, 2016 1:40 am

Registered users: Bing [Bot], Exabot [Bot], Google [Bot], MSNbot Media, Yahoo [Bot] based on users active over the past 5 minutes

The Team
Global Moderators
global_moderators.png CS

What is this newbie doing wrong?

Post questions and info about combustion (flammable vapor) powered cannons here. This includes discussion about fuels, ratios, ignition systems, safety, and anything else relevant.
  • Author

What is this newbie doing wrong?

Unread postAuthor: Jim Beam » Thu Jul 22, 2010 8:13 pm

Hi all:

Sorry if this question has been posted before. I used the search function but didn't see what I needed.

I've been having great fun for the past year with my first spray-n-pray cannon, it's very easy to get the right fuel/air mix (16"L x 4" dia. combustion chamber, 44"L, 1.5" dia. barrel).

So, I thought it would be smart to build a pistol that could shoot all the leftovers from the big gun. It has a 2" dia. x 5"L chamber with a 22"L x 3/4"dia. barrel. I tried to scale it down from the big one.

But, it just won't fire! I have a nice ~1/16" spark between 2 screws, I'm injecting propane at 3% to 10 % (the explosive range), but nothing is happening.

Any suggestions?
  • 0

Jim Beam
Posts: 7
Joined: Wed Jul 21, 2010 7:15 pm
Reputation: 0

Unread postAuthor: Technician1002 » Thu Jul 22, 2010 8:18 pm

Your assumed fuel mix is most likely incorrect. After a fail to fire, unscrew the chamber and try to light the contents with a lighter. If you get a flame that burns for a sec, the mix was way too rich. The edge of the gas cloud burns and continues to burn as the flame mixes in air into the space containing the rich mix. This is most likely the problem.

If it is too lean, it won't do anything and just act like air to a lighter.

It is really easy to get way too much fuel in small chambers.
  • 0

User avatar
Chief of Staff
Chief of Staff
Posts: 5190
Joined: Sat Apr 04, 2009 11:10 am
Reputation: 14

Unread postAuthor: jackssmirkingrevenge » Fri Jul 23, 2010 1:04 am

Technician1002 wrote:It is really easy to get way too much fuel in small chambers.

Indeed, you should consider syringe metering:


Another thing, try widening the spark gap. 3/16 would work better in my experience.
  • 0

User avatar
Donating Member
Donating Member
Posts: 24225
Joined: Thu Mar 15, 2007 11:28 pm
Country: Holy See (Vatican City State) (va)
Reputation: 66

Unread postAuthor: jakethebeast » Fri Jul 23, 2010 3:20 am

i think you just but too much propane in there, try with little less :wink:
  • 0

User avatar
Brigadier General
Brigadier General
Posts: 934
Joined: Sat Jul 03, 2010 4:20 pm
Location: Jakes cave
Country: Finland (fi)
Reputation: 11

Return to Combustion Cannon Discussion

Who is online

Registered users: Bing [Bot], Exabot [Bot], Google [Bot], MSNbot Media, Yahoo [Bot]

Reputation System ©'