 |
|
|||||||||||||||||
Portable stove
There are several main types based on the type of fuel used:
Simple single-burner designs
The two most popular of these are the solid fuel stove, using Hexamine tablets, and the liquid fueled stove using methylated spirits. Both types are available commercially. There are also many designs published for similar home-built stoves, like the Pepsi can stove. While solid-fueled stoves may be refueled while burning with care, with a liquid-fueled stove it would be reckless to attempt this. Both solid alcohol fuel and stoves for using it are produced by Esbit, and fuel is produced by several other makers. While most brands of firelighters can be used in such stoves, some types will produce a troublesome residue that may be impossible to remove from cookware, and will taint any food exposed to the flame or fumes. One popular make of simple liquid-fueled stove is the Trangia , available in many different models from a single bare burner to an integrated expedition cooking system. Some of these come with a sealing cover, allowing the burner to be packed while containing fuel. Pressurised burner stovesHistoryThere is some controversy over the invention of the pressurised burner. Most have given the credit to F.W. Linqvist , who was granted a patent for a kerosene-fueled burner in the late 1880s and went on to develop the Primus brand name of stove into a market leader. Some have however suggested that he in fact bought the design. The Primus stoves and their imitators were a significant advance over previous designs that had used a wick to supply liquid fuel to the burner by capillary action. Instead the Primus burner vaporised the fuel in a loop of pipe, and used this to both supply the fuel to the burner as a gas and to maintain pressure in the fuel tank. Initial pressure was provided by a small hand-operated pump. It was also necessary to pre-heat the burner with methylated spirits. This burner design was also successfully adapted to portable lamps, lighthouse lamps and blowtorches. Current modelsPressurised burner stoves are now available to burn almost any volatile, inflammable liquid, including alcohol, diesel or other motor fuels, kerosene, jet propellant, and many others. Work is proceeding on vegetable-oil burners. Some can burn multiple fuels or even mixtures. Some require special low-residue stove fuel, others are either designed to resist clogging or to be easily and regularly cleaned of the residue. Most provide some control over the amount of heat produced. Some fuels permit preheating (or priming) with the fuel, others require use of a more volatile fuel, such as methylated spirit or alcohol priming paste, for preheating the burner. Most provide an integrated pump for initial pressurisation, others require the use of a separate pump, while a few need no pump but pressurise themselves when the burner is preheated. Although heavier than the simpler designs and more complex to maintain and operate, these stoves can heat food more quickly, and as standard issue to many units in the second world war they enjoyed a large base of competent users in the years immediately following. Another advantage is that hydrocarbon fuels have a higher heat content weight for weight than alcohol fuels, so for extended expeditions the weight advantage of alcohol-fueled stoves is reduced or even reversed. Gas stovesThe greatest variety in designs is in this category. They include gas-cartridge stoves and refillable gas-bottle stoves. In most of these the gas is stored as a liquid under pressure, but vaporises immediately it leaves the storage bottle and so arrives at the burner as a gas. Smaller, lighter designs tend to use non-refillable gas cartridges containing butane, propane or a mixture of hydrocarbons. There is little compatibility between different makers and systems, and cartridges for older stoves are often unobtainable. In addition, the single-use cartridges are considered objectionable by some on environmental grounds. Refillable gas bottles are heavier and tend to be used on larger stoves intended for car-camping or expedition base camps. However a great variety of gas-fired stoves is available, some integrating the gas cylinder, some connecting it by a hose. Gravity-fed spirit stoves The traditional "spirit stove" still found in many pleasure boats is a unique design, largely replaced by gas stoves but still with a following. It consists of a tank that supplies methylated spirit under gravity to the burner or burners, where it is vaporised and burned.  Around each burner is a priming pan used to preheat the burner. To light the stove, the burner is first turned on to allow a small amount of fuel to pass through the burner and collect as a liquid in the priming pan. The burner is then turned off, and the fuel ignited to preheat the burner. When the fuel in the pan is almost all gone, the burner is turned on again, and fuel passes into the burner where it is vaporised and passes through the jets. These stoves look and even sound a bit like pressurised-burner stoves, but the fuel tank is under no pressure. They remain popular for small boats owing to the minimal fire risk they pose in a confined space. General considerationsThe difference between backpacking and camping stovesStoves differ widely in their size and portability. The smallest models are generally termed backpacking stoves. They are designed for use in backpacking and long-distance cycling, where light weight and small size are paramount considerations. Backpacking stoves consist only of the burner and any related systems, and some (usually crude) devices to support the stove and cooking vessel. The legs are collapsible to minimize the space required. The weight may range from 300 grams to nearly one kilogram. Camping stoves are designed for use by people travelling by car, boat, canoe, or on horseback. They are similar in function and ease of use to kitchen stovetops, usually with two burners set into a table-like surface, and often with a folding lid for stowage and wind protection. This increases the weight to at least one kilogram, and sometimes as much as eight kilograms. Wind protectionA common problem in the use of stoves outdoors is the wind, which often tends to extinguish the flame. Even if it does not do so completely, it may extinguish it on the upwind side, reducing the stove's effectiveness, and cause the hot gas to flow away from the vessel being heated. In camping stoves, the fold-out lid makes an effective wind shield, and some stoves also have protection on the sides. Backpacking stoves do not include such features. They would interfere with the stove's collapsibility, and many backpackers erect makeshift shields out of materials on hand. However, there are specially designed cylindrical shields that are placed around the burner. In addition to keeping out the wind, they also trap heat that might otherwise escape. Self-lighting mechanismsMany camping and backpacking stoves have self-ignition mechanisms so that they can be lit without a match. They use the mechanical work done by the operator in depressing a button to create an electric spark. These devices provide an advantage in windy conditions, because matches blow out easily. Matches are also less convenient to use, and pose a fire hazard if used improperly. Fuel specificsGas fuel is sold in canisters, typically under sufficient pressure that most of it is actually in liquid form. For backpacking stoves butane or a mixture of propane and isobutane are used. Camping stoves use either these or pure propane, which requires a particularly heavy-walled container. A variety of liquid fuels are used as well. While gaseous fuels have relatively simple chemical names that transcend language barriers, any discussion of liquid fuels is complicated by regional differences in terminology. (See the External Links for more information about alternative nomenclature.) Broadly, four types of liquid fuel are used:
Differences between liquid-fuel and gas-fuel stovesDesignMost stoves can use either liquid or gas fuel, but not both (One exception is Primus Omni/Multi-Fuel). Gas-fuel stoves are notably simpler, because the fuel is easier to work with. The gas, being already pressurized, flows from the fuel canister into the burner, where it ignites, in the same manner as a domestic kitchen stove. Liquid-fuel stoves are more complex. Though the fuel is a liquid at room temperature, it burns better as a vapor. Thus, the stove is designed to bring it into contact with a hot piece of metal before it reaches the burner, so that it can boil there. This device must be heated before the stove is turned on. Many stoves require the operator to open the fuel valve briefly without igniting the fuel, so that it flows into a small pan. This small quantity of fuel is then lit and allowed to burn down. When the fuel valve is opened again, the fuel vaporizes from the heat of the pan. Some stoves do not have this apparatus, and must be preheated by the application of an external heat source such as a solid fuel block. Priming a stove in using either of these methods can be dangerous particularly in a tent on a windy night. In many stoves, the priming pressure is generated by a small hand pump that forces air into the bottle. As the fuel is consumed, the pressure decreases according to Boyle's Law, so the pump must be operated frequently to maintain steady stove operation. Advantages and disadvantagesThe preheating mechanism makes liquid-fuel stoves larger and heavier than gas-fuel stoves. In addition, many liquid fuels do not burn cleanly. While they leaves less residue than solid fuel, they do produce an oily black film that eventually coats both stove and cooking vessels. When liquid fuel leaks, it soils equipment, making it a fire hazard. The odor of fuel may also attract dangerous wild animals. The principle advantage of liquid fuels is their ubiquitous availability around the world. Gaseous fuels have many advantages; they are clean and relatively simple to use. Because there is no priming they are generally safer (although undetected leaks in larger gas bottles can cause explosions). Gas fuel bottles of a particular make may be widely available in some countries but not in others, so international travellers have to be particularly careful. Some disadvantages of gas fuel are the impossibility of transferring fuel from one container to another and the difficulty of accurately gauging how much fuel remains in a container. Gas fuel is also far less efficient at higher altitudes and low temperatures. Gas fuel canisters are heavier than liquid-fuel bottles, because it must be stored under greater pressure. When a canister runs out, it may have to be treated as hazardous waste. Canisters tend to deteriorate and leak if stored for several years. Solid-fuel stovesA quantity of liquid fuel sufficient to cook a meal, if simply placed in a container and ignited, would burn violently and consume itself in a matter of seconds, and a similar quantity of gas fuel would simply explode. The primary design principle of stoves that use these fuels is to provide a steady flame and prevent the fuel's escape. Solid fuel, however, is more manageable. A solid-fuel stove may consist of no more than a metal plate to hold the fuel, a set of legs to keep it out of contact with the ground, and some supports for the cooking vessel. This design is highly scalable, and may be used for anything from tiny backpacking stoves to large portable woodstoves. While admirably simple, solid fuel has many disadvantages. First of all, its burn rate may be controlled only by varying the amount of fuel placed on the fire, while fluid fuels may be controlled precisely with valves. Second, no solid fuel burns completely. It produces considerable amounts of ash and soot, which soil both the stove and the cooking vessels. Some of the chemical energy of the fuel remains locked up in the ash and soot, so solid fuel releases less heat, gram for gram. Firewood may often be used in solid-fuel stoves, but manufactured fuels are also available. One type is sold in the form of small blocks, on the order of a centimeter in size. Sterno™ is a viscous fluid that is also used in solid-fuel stoves. Simple stoves are sometimes used in ice houses and large tents, both to provide warmth and for cooking. They burn wood, and have a small flue used to exhaust the smoke. When used in tents, they are used in a larger tent made of fabric that does not burn readily, and are most often used in base camps that move infrequently. HistoryThe widespread use of backpacking stoves began with increased awareness of the environmental impact that backpackers had on the areas where they travelled, beginning in the 1950s in parts of Europe and the 1960s in the United States. Prior to their use, the usual practice when backpacking was to build an open fire for cooking from available materials such as fallen branches. The fire scar left on the ground would remain for two or three years before the vegetation recovered. The accumulation of fire scars in heavily travelled areas detracted from the pristine appearance that backpackers expected, leading to more widespread use of stoves. Related topicsExternal links
These websites list the names and availability of different liquid fuels in different countries: Suppliers' sites with information on portable stoves:
The contents of this article are licensed from Wikipedia.org under the GNU Free Documentation License.
How to see transparent copy 01-04-2007 01:21:04 |
|
