An alcohol fuel such as ethyl alcohol, a benzine fuel of the petroleum benzine type or a liquid gas fuel such as butane gas or propane gas is generally used as the fuel of a cigarette lighter, fire-lighting device, torch, lamp or other such burner.
The performance, ease of use, and structural design of such burners differs depending on the kind of fuel used, and each has its own characteristics. In the case of a liquid gas fuel, for instance, the gas pressure is high in the use temperature range of the burner and the vessel storing the fuel has to have a pressure-resistant structure. Moreover, the flame length changes with variation in the gas pressure and since it is a characteristic of the gas pressure to vary logarithmically and greatly with temperature, large change in flame length with temperature becomes a particular problem. In order to reduce this flame-length variation, the fuel supply mechanism of the burner requires a special design countermeasure for effecting temperature compensation, which complicates the structure and is disadvantageous from the aspect of cost.
In contrast, since a liquid fuel such as an alcohol fuel is a liquid at ordinary temperatures and is also relatively low in vapor pressure, it does not require a pressure-resistant vessel in the fuel storage section and, as such, simplifies the structure of the burner and is advantageous from the aspect of cost. Further, in the liquid fuel burner, the means used to supply the liquid fuel from the fuel storage section to the flame-producing section is generally a wick that utilizes the surface tension of the liquid fuel to draw it up through continuous fine holes or fine voids among bundled fibers by capillarity and burns it at the tip portion thereof.
Specifically, the wick used for drawing up the fuel is a string-like one obtained by twisting fibers, one obtained by bundling fibers, one using both of these with the glass fibers enclosed in cotton yarn and the result interwoven with fine metal wires to prevent disintegration, or the like, whose the lower end portion functions to draw up fuel to be burned at the upper end tip portion.
However, the burner using such a wick has problems in that the liquid fuel leaks through the wick owing to the difference between the internal pressure of the fuel tank retaining the liquid fuel and the external pressure and that a phenomenon of drawing in external air arises.
Specifically, after draw-up and combustion of the alcohol or other liquid fuel by the wick has been initiated by lighting (igniting) the liquid fuel at the wick, liquid fuel is consumed at the flame-producing section at the tip of the wick and liquid fuel for maintaining the combustion is drawn up from the fuel tank and supplied to the flame-producing section. The flame length varies until an equilibrium is reached between the amount of liquid fuel consumed at the flame-producing section and the amount of fuel drawn up from the tank and supplied to the flame-producing section.
When the burner is a fire-lighting device such as a cigarette lighter, the flame is preferably stabilized at the set flame length as quickly as possible after ignition. For this, the draw-up section of the wick should preferably have the maximum possible liquid fuel draw-up capacity, while attention must also be given to preventing occurrence of a pressure differential between the fuel tank and the external air to ensure that the outflow of the liquid fuel from the fuel tank does not produce a reduced pressure state that hinders draw-up through the draw-up section of the wick.
On the other hand, as regards the opposite case of a high pressure arising in the fuel tank, attention must be given to ensuring that liquid fuel stored in the fuel tank does not leak to the exterior through fuel passages formed by the wick, particularly to ensure that liquid fuel leakage does not occur in a pocketable fire-lighting device or the like.
Thus, when a difference arises between the internal pressure of the fuel tank and the external pressure owing to the aforesaid depletion of fuel with use or to a change in the surrounding temperature or the ambient pressure, the liquid fuel burner is liable to become inconvenient to use, i.e., to experience leakage of liquid fuel through the wick when the internal pressure of the fuel tank becomes high and to experience lighting (ignition) failure when the fuel tank internal pressure becomes so low as to allow external air to be sucked in through the wick.
Moreover, suppression of evaporative dispersion of liquid fuel from the wick of a burner using one of the aforesaid wicks is important for increasing service life (number of uses), while it is also preferable to make the overall configuration compact.
Vaporization from the wick is prevented by covering the wick portion alone or the whole upper surface portion including the wick with a cap to seal the wick and suppress vaporization during non-use periods. Completely reliable sealing is, however, hard to achieve. This is particularly true when covering is effected by causing the cap to swing along an upward arc, because the need to provide the seal portion in conformity with the locus of rotation results in increased spacing between the wick and other components such as the igniter, making it difficult to secure sealing property and compact configuration.
Particularly when a striker wheel is used for the igniter, separation between the wick and the striker wheel degrades igniting performance and lowers the reliability of the product.
In view of these circumstances, the invention is directed to providing a liquid fuel burner enabling rapid elimination of pressure difference between the interior and exterior of the fuel tank.