In reply to PeterM:
A slightly bodged description, there are several factors that are important (i've missed a few) - apologies:
- If you invert they cylinder you'll be drawing off liquid; liquid is more dense than gas so contains more fuel per unit of volume. The burner (hole size, flame spreader etc) is optimised for a small range of flow rates.
The valve controls the volume passing through it in a given time so you get more gas going through the burner which causes flaring and flame lift off which are a bad thing (if the stove doesn't blow out you'll get a huge fireball). You need to redesign the valve to allow tighter flow control.
- Liquids don't burn generally so you need to vaporise them. If you blow liquid through the burner you get a jet of liquid out which then vaporises and burns this moves the 'flame front' up a long way probably to beyond the base of your pan. So you need to pre-vaporise the fuel by heating it before it reaches the nozzle. This is normally done with a heater coil in the flame area (you can just see it if you look closely at the Jetboil helios photo above).
To give you an idea of how much difference putting liquid 'v' gas up a burner makes:
In 1999 I was involved in a little engineering project to build a gas powered beacon as part of the millenium beacon chain across the UK. Our beacon was powered by a domestic propane cylinder which had been inverted to draw off liquid (we'd intended to use a comercial dip-tube cylinder but ordered the wrong adaptor). This beacon burnt through 47kg of propane in not much over half an hour. This burner was designed deliberately without a pre-heater coil to give a taller flame; we ran it on gas once as a test and it produced a soft flame about 3ft, high we ran it on liquid and it produced a 20-25ft high flame. The jet of liquid in the middle of the flame was still visible at over 8ft above the burner!