Re: How does a 'pocket torch' work?

Weena,

This was a fun question to find the answer to!  I discovered that there 
are several companies on the internet that sell these "pocket torches" or 
lighters.  Cigar emporiums seem to be particularly fond of them!  Also 
interesting is the fact that the price of this little item ranges from $10-
$70 depending on where you buy it, so make sure you do some comparison 
shopping!  Some suppliers (including www.hill.u-net.com and 
www.torchit.com ) were very willing to help me out with the science behind 
their products, and I have pieced together the following explanation.

You were right when you said that pocket torches run on butane, the same 
fuel found in an ordinary lighter.  You were also right when you said that 
the pocket torch produces a VERY hot flame.  In fact, the flame can reach 
temperatures of up to 1300 degrees Celsius.

The chemistry....Combustion (fire!) requires both fuel and oxygen (air).  
When butane gas burns completely, with sufficient oxygen, it burns with a 
blue flame at 1300 degrees Celsius.  With ordinary lighters the combustion 
of butane is incomplete, resulting in a yellow 'flame' due to the glowing 
particles of carbon oxidizing slowly to C02. 

The physics....The reason for the different combustion properties of 
pocket torches and ordinary lighters has to do with the 'head' (actually 
called a 'fire nozzle') that you described.  This nozzle is basically a 
metal plate containing very small holes.  Air is sucked in from another 
hole in the side of the nozzle and is then forced through the small nozzle 
holes.  The very small size of the holes causes a pressure build-up (and 
therefore very high gas flow velocity) which has two important effects. 
First of all, enough air (oxygen) is drawn in to completely combust the 
butane.  Secondly, the resulting flame shoots straight out and is "strong" 
enough to withstand windy conditions without blowing out.  A good analogy 
is the effect of putting your finger on the end of a water hose.  The 
smaller the opening, the greater the force of water exiting the hose.

Two other aspects of the pocket torch which you may find interesting are 
an internal catalyst coil and piezoelectric ignition.  Unfortunately I 
wasn't able to find out too much about the catalyst.  The piezoelectric 
ignition, standard to most lighters, involves a quartz crystal which, upon 
being hit sharply, produces a high voltage electric discharge (a spark) 
which ignites the butane/oxygen mixture.

Thanks for the great question!

Jessica