My second post. Be gentle. I’ve been reading about how the vapouriser works in an X246. if I’ve understood properly, the paraffin is sprayed under pressure through the needle hole at the top of the column and into the dome at the top. Assuming the lamp is at temperature already, the spray “boils” due to the heat in the dome. Then it mixes with the intake air and falls down into the mantle where it combusts. The combustion makes light but also heats the tube where the paraffin is rising to help continue the vaporization. Two questions then 1. Is it the dome or the tube where the mantle is that actually needs to be hot? If it’s the dome then: 2. Why design the lamp so the meths preheater is as far from the dome as it is? Obviously heat rises and it’s convenient for the user, but why not engineer a solution where the heat was more directly applied, resulting in less meths use and faster startup times? One more question - what is the mantle made from that allows it to incandesce but also cope with the direct flame of the meth? I should say, not trying reinvent the wheel here, more to understand the history / engineering choices. cheers!
The clue is in the name. Paraffin is vapourised (i.e. transformed into a gas) in the vapouriser (tube). The top of the vapouriser is immediately below the invert of the air tubes and the stream of vapour rushing past them draws in air. The vapour and air swirl round in what Tilley refer to as the mixing tube (even though it's dome shaped) before exiting through the holes at the bottom of the burner. See here for the mantle Gas mantle - Wikipedia and here Carl Auer von Welsbach - Wikipedia for the man who invented it.
1) the vaporiser with dome has to be hot to evaporate the fuel. But the mantle needs the heat of the flames. 2) the point where you start vaporising should not be at the top. It will take time for the process to get all the liquid into gas. Then there is also the space needed to fill a cup or mount a heater clip and the mantle needs some space too.
Thanks Henry, this makes a lot of sense. I know they aren’t quite the same but there’s definitely some cross over in principles here with a carburettor in terms of atomising fuel and generating the right fuel/air mix.
Primarily, all naturally aspirated fuel-air burners use the same basics as the Bunsen burner with the Bernoulli's principle being in action. For Tilley-styled lamps, the liquid fuel(kerosene/paraffin) does not start to vaporize in the top dome. It is only maintained in vapour form for mixing with air over there. Conversion of the liquid fuel into its gaseous state is done at the vaporizer and jet. Carburretors do have similar workings in terms of fuel-air mixing but operate at a lower temperature and do not require deliberate vaporization of the fuel before it is mixed with air. However in general, pressurized liquid-fueled lanterns do not follow the same workings as modern fuel injection systems for engines and some industrial burners where mechanical atomization of the liquid fuel is essential. The atomization is done with pressure being applied on the fuel and then forced through a series of special nozzles so that the discharge droplets appear like a vapour. A separate air injection is often necessary to complement the mixing. This is unlike the pressure lamp's working principle where the fuel is heated so that it attains a temperature above which it becomes gaseous at atmospheric pressure. The jet or gas tip in pressure lamps are totally different in design from atomizing nozzles. The fuel (without preheating) discharge at the outlet is a straight liquid stream, not a vapour. The fuel must be preheated to above its vaporizing temperature before anything works. Therefore, once it is discharged through the jet or gas tip, the preheated fuel completely assumes its gaseous form because of the sudden reduction of the pressure surrounding it (atmospheric / outside the vaporizer). Just like what you'd see in the regular propane or lpg stove. This gaseous fuel would be directed into the mixing chamber. The velocity of the vaporized fuel is pretty high. It will induce a pressure reduction of the surrounding medium along its flow path. As it flows past the air inlet ports, the surrounding air is drawn in together into the mixing chamber. Once inside, the fuel-air flow turns into a somewhat swirling or twirling motion so that mixing could be effected before being distributed over the burner's outlet ports. Mixing chambers are usually located at the top where the heat is sufficient to maintain the temperature of the fuel so that it does not recondense into liquid.
