This is a small project of a bluetooth controled flamethrower made 3 years ago.
This is how it work:
Bluetooth phone -> HC05 bluetooth module -> Arduino -> transistor -> 5v relay -> 9v solenoid valve -> FLOUUUUUCHH

As you can see it's really basic;the solenoid valve is supplyed by a small 9v battery and there is a lot of "dead volume" between the output of the flamethrower and the valve. So a lot of amelioration can be done, but it's still fun :)
Oh, and there is a angle between the petrol reserve ( fire extinguisher ) and the output
to avoid damage. It's not on the 2&3th pictures.

See the flamethrower in action : https://youtu.be/Nu0JW-F5Rbs
The video are the firsts tests of the flamethrower, and as you can see the inflammable product used (oil+petrol+methylated spirit) was not good (too much petrol).