the present invention relates to a portable cooking stove . by portable we mean that the stove can easily be carried by one person . the portable cooking stove of the present invention comprises a base . by base , we mean a solid face . the lower section of the stove extends from the base to form , during use , a combustion chamber . accordingly , during use fuel is supported on top of the base . the base protects the ground from being damaged or contaminated by the burning fuel , and protects the fuel from any water in or on the ground . optionally , the base may be perforated , wherein the perforated regions of the base are raised so as to not contact the ground . preferably the base is blank , i . e . is not perforated . the base allows for the cooking stove to be placed on multiple surfaces or even to operate while suspended above the ground . the portable cooking stove of the present invention additionally comprises a lower section and an upper section . the upper section extends from the lower section , which itself extends from the base . the upper section and / or the lower section is tapered or the upper section is stepped out from the lower section , so that the upper section defines a larger cross sectional area than the lower section . the larger cross sectional area means that it is possible , during use , to support a cooking vessel in the upper section , which does not extend into the lower section , thereby leaving the lower section free to act as a combustion chamber . it is preferable that the upper section can form an intimate fit with a cooking vessel , while the lower section is shaped to block entry into the lower section of the cooking vessel . this can be done by providing an indentation in the lower section , or can simply be a result of the lower section having a smaller cross sectional area than the upper section . by defining a separate lower section and upper section , it is intended that the stove is visibly divided into two parts , through the shape of the construction material . therefore , where the upper section and the lower section are both tapered , they are not tapered to the same degree , or a step is additionally provided between the upper and lower section to make it clear where the lower section ends and the upper section begins . the whole stove is preferably made from a single sheet of material . in other words , the portable cooking stove of the present invention is integral . by this we mean that it is one piece . the base , lower and upper sections are joined together and are not detachable . the lower section of the stove extends from the base . it may extend from the base at 90 °, or may be tapered . where the lower section is tapered , it is generally outwardly tapered at an angle of 90 ° to 120 °. whether the lower section is tapered or not , the upper section may also be tapered . if the upper section is tapered , it is generally tapered to a small degree , such as 90 ° to 100 °. the tapering is outwards . tapering of the lower section or the upper section , or differential tapering between the upper and the lower section allows the upper section to define a larger cross sectional area that the lower section . by a larger cross sectional area , we mean that at least a portion of the upper section defines a bigger area , or in other words , has a bigger footprint , than at least a portion of the lower section , preferably the whole of the upper section defines a larger cross sectional area than the whole of the lower section . the cross section is to be taken horizontally , i . e . substantially parallel with the base . a further possibility for achieving a larger cross sectional area for the upper section , is that the upper section is stepped out from the lower section . in this case , an indentation can be provided in the upper most part of the lower section which is adjacent to the upper section . usually the stove of the present invention is around 8 to 20 cm high , and usually 10 to 15 cm high . the lower section is typically comprises less than half the height of the stove , and is usually around 20 to 50 % of the height of the stove . the stove is typically 5 to 15 cm wide , usually 10 to 15 cm wide , at it &# 39 ; s widest point . these preferred sizes are intended to ensure that the stove fits well with a range of military cups , which typically are designed to hold 500 ml or 1 us pint of water . the lower section , and the base , have a smaller cross sectional area than the upper section . typically , the surface area of the base is about two thirds of the area of the largest cross sectional area of the upper section . the purpose of the upper section defining a larger cross sectional area than the lower section , is that the upper section is able to support a cooking vessel , which can sit in the upper section without extending into the lower section . in this way , during use , the lower section of the stove forms a combustion chamber . the upper section can be shaped to form an intimate fit with a specific cooking vessel . the stove of the present invention is preferably suitable for use with a kidney shaped military style cooking vessel , often referred to as a “ cup ”. accordingly , in a preferred embodiment , the upper section of the stove is substantially kidney shaped , and preferably the lower section is also substantially kidney shaped . by kidney shaped we mean having a shape similar to a human kidney , or a kidney bean . this a roughly oval shape , but with one convex side and one concave side . in a preferred embodiment , the lower section tapers outwardly from the base , and the upper section tapers outwardly from the lower section with a smaller taper angle than the lower section , or the upper section is not tapered . preferably the upper section is not tapered , so have walls that are substantially parallel . by intimate fit , we mean that when the cooking vessel is inserted into the cooking stove the size and shape of the cooking vessel is similar to the stove so that the outer perimeter of the cooking vessel is very close to or touches the inner perimeter of the cooking stove , around the majority of the perimeter . forming an intimate fit means that there are not large gaps between the cooking vessel and the stove , from which exhaust gases can freely leave the stove . instead , exhaust gases primarily leave the stove through the exhaust ports . in this way , a restriction of airflow through the stove is effectively implemented by the exhaust ports . this restriction of airflow is not provided for by existing stoves . the combustion chamber must have the ability to draw air in from the surroundings . in the present cooking stove air is allowed to enter the combustion chamber through the one or more air inlet ports . accordingly , the lower section has one or more air inlet ports . the air inlet ports must generally be arranged so that , in the cooking configuration , they allow air to enter the combustion chamber level with , or below , the burning fuel . it is preferred that there is a single inlet port . in a preferred embodiment , the single air inlet port is approximately triangular , as shown in fig6 and 8 . the inlet port is preferably positioned in the lower third of the lower section , with the longest side of the port horizontal to the base . the upper section has one or more exhaust parts . in use , an intimate fit with a cooking vessel can prevent exhaust gasses and heated air from exiting the stove , except for through exhaust ports . by exhaust port , we mean one or more holes cut into the upper section of the cooking stove to allow exhaust gasses and heated air to leave the stove . it is preferred that there are multiple exhaust ports , preferably 4 to 8 exhaust ports . in a preferred embodiment , as shown in the figures , there are 6 exhaust ports . the exhaust ports are preferably rectangular slits from empirical data generated by the inventor , it has been determined that it is important that the ratio of air allowed into the stove , to the freedom for exhaust gases to leave the stove , be tightly controlled . in a preferred embodiment of the present invention , the ratio of surface area of the exhaust port or ports to the air inlet port or ports is in the range 0 . 8 : 1 to 2 : 1 , preferably wherein the range is 1 : 1 to 1 . 5 : 1 . this is found to be the optimal ratio for good performance of the stove . when the ratio drops to below about 0 . 8 , too much exhaust gas can accumulate in the combustion chamber resulting in the preclusion of sufficient oxygen entry into the stove . this results in two undesirable consequences , the generation of white smoke from unburnt volatiles , followed by the inability to sustain fuel burn , leading to eventual extinguishing of the flame . above a ratio of around 2 , the exhaust gases exit too freely resulting in excess flame leaving the exhaust ports . this wastes heat energy , as well as allows for visible luminous flames to be seen at some distance . this could potentially endanger a soldier in a combat situation . the total surface area of the inlet ports is typically in the range 2 , 000 to 2 , 250 mm 2 the total area of the exhaust ports is typically in the range 1 , 600 to 4 , 000 mm 2 . in the preferred embodiment of the present invention , an additional slot ( by this we mean additional to the exhaust ports ) is cut into the upper section of the stove . the purpose of this additional slot is to accommodate the handle of a cooking vessel . some cooking vessels , such as military cups have a protruding handle that would hinder or prevent insertion into the cooking stove . a slot can be cut into the cooking stove so that when the cooking vessel is inserted with the handle aligned with the slot , a neat fit occurs . typically , an intimate fit would be maintained in the region around the handle without any opportunity for exhaust gases to escape the stove . an important feature of the portable cooking stove of the present invention , is that at least one side of the cooking stove is free from both air inlet ports and exhaust ports . by “ one side ” we mean that if a cross section is drawn vertically through the stove ( i . e . perpendicular to the base ) to divide it roughly in half , there is always one 180 ° angle through which the lower and upper sections of the stove can be viewed without seeing any inlet or outlet ports . if the stove was roughly a cube shape , this would mean that at least one face was free of inlet and outlet ports , preferably three faces would be free of inlet and outlet ports . where the stove is roughly kidney shaped , it is usual to have the inlet and outlet ports on the concave surface of the stove , rather than on the convex surface of the stove . the portable cooking stove of the present invention can be made from any suitable material . it is usually made from metal , preferably wherein the metal is selected from the group consisting of aluminium , titanium , nickel , copper , or an alloy which is mild steel , stainless steel or brass . according to a second aspect , the present invention relates to a kit comprising the portable cooking stove of the first aspect of the invention , and one or more solid fuel blocks . an advantage of the present invention is that any fuel can be used in the stove . this includes pre - packaged solid fuel blocks , liquid fuel burner , for example a trangia spirit burner or a gas burner . it is also possible to simply use wood or other combustible materials that are readily available in the environment . however , in a preferred embodiment , the present invention makes use of solid fuel blocks . the solid fuel block preferably comprises hexamine , trioxane , or solidified methyl decanoate . preferably the solid fuel block comprises solidified methyl decanoate . the present invention also relates to a kit comprising the portable cooking stove of the first aspect of the invention , and a cooking vessel capable of forming an intimate fit with the upper section of the cooking stove . the cooking vessel can be a saucepan or a round or oval cup but is preferably a kidney shaped military cup , such as the current uk or us standard issue military cups . the uk military cup is shown in fig8 . according to a third aspect , the present invention relates to a method of heating a portable cooking vessel using the cooking stove of the first aspect of the invention , wherein the portable cooking vessel is in intimate contact with the upper section of the cooking stove , a fuel block is inserted into the lower section of the cooking stove , and the fuel block is set alight and allowed to burn . fig6 to 8 show a stove ( 13 ) according to a preferred embodiment of the present invention . fig6 shows the back of the stove with base ( 14 ), lower section ( 15 ), and upper section ( 16 ). the lower section includes one air inlet port ( 17 ). the upper section shows six exhaust ports ( 18 ). fig7 shows that one complete side , in this case , the convex front of the stove is free from inlet or exhaust ports . fig8 shows the stove containing a cooking vessel which is a 500 ml uk military cup ( 19 ). the cup has handles ( 20 ). the stove has a corresponding slot cut in the upper section ( 21 ) to accommodate the handle of the cup . the lower section ( 15 ) of the stove ( 13 ) is tapered outwardly . the upper section ( 16 ) is not substantially tapered and has approximately parallel walls . the upper section is stepped out from the lower section by providing an indentation in the lower section ( 22 ). the stove is made from stainless steel . the following examples provide details of the performance of a specific embodiment of the present invention , a stove designed to fit a uk military cup , and compares the performance of this embodiment against prior art stoves . the stove of the present invention used in the examples is that shown in fig6 , 7 and 8 as described above . this is named the edb stove . wind : is given in metres per second ( and miles per hour ) and was measured using a testo - 410 - 1 handheld anemometer . air press : refers to air pressure , and is given in kpa . it was measured using a wall mounted digital barometer — fischer scientific . dew pt . refers to dew point , and is given in degc . it was determined on - line using acuweather . com ; for the location of the experiment , moncarapacho , pt . rh : refers to relative humidity , and is given in %. it was measured using picolog combination digital humidity probe / ambient temp . amb t : refers to ambient temperature , and is given in degc . it was measured using picolog combination digital humidity probe / ambient temp . comparison of the current us stove using 1 and 2 zip fuel blocks ( fig9 ) with the inventive stove using 1 and 2 zip fuel blocks ( fig1 ) fig9 uses current standard issue us military cup and stove , as shown in fig3 to 5 . using , as fuel 1 × zip 26 gm block , the results are as follows : using as fuel 2 × zip 26 gm block , the results are as follows : fig1 uses the inventive edb stove with a uk military cup , as shown in fig8 . using as fuel 1 × zip 26 gm block , the results are as follows . and using as fuel 2 × zip 26 gm block , the results are as follows . a comparison of fig9 and 10 demonstrates that the edb stove according to the invention performs significantly better in terms of time taken to boil , and total burn time , than the current us military stove , irrespective of whether one or two zip fuel blocks are used . comparison of the current us stove using 1 and 2 hexamine fuel blocks ( fig1 ) with the inventive stove using 1 and 2 hexamine fuel blocks ( fig1 ) fig1 uses current standard issue us military cup and stove , as shown in fig3 to 5 . using , as fuel 1 × hexamine 26 gm block . the results are as follows . using as fuel 2 × hexamine 26 gm block , the results are as follows : fig1 uses the inventive edb stove with a uk military cup , as shown in fig8 . using as fuel 1 × hexamine 26 gm block , the results are as follows : using as fuel 2 × hexamine 26 gm block , the results are as follows . a comparison of fig1 and 12 demonstrates that the edb stove according to the invention performs significantly better in terms of time taken to boil , and total burn time , than the current us military stove , irrespective of whether one or two hexamine fuel blocks are used . comparison of the current uk military stove ( fig1 ) with the edb inventive stove ( fig1 ) using a 1 zip fuel block , with and without a simulated wind fig1 shows the uk military stove , as shown in fig1 , with a single zip fuel block as fuel . with no wind , the results are as follows : with a 2 . 24 ms − 1 ( 5 mph ) wind , the results are as follows : fig1 shows the edb stove , as shown in fig6 - 8 , with a single zip fuel block as fuel . with no wind , the results are as follows : with a 2 . 24 ms − 1 ( 5 mph ) wind , the results are as follows : a comparison of fig1 and 14 demonstrates that the edb stove according to the invention performs significantly better in terms of time taken to boil , and total burn time , than the current uk military stove , particularly in the presence of wind , where the uk stove performs very badly , without ever reaching boiling . comparison of the current uk military stove ( fig1 ) with the edb inventive stove ( fig1 ) using a 2 zip fuel blocks , with and without a simulated wind fig1 shows the uk military stove , as shown in fig1 , with two zip fuel blocks as fuel . with no wind , the results are as follows : with a 2 . 24 ms − 1 ( 5 mph ) wind , the results are as follows : fig1 shows the edb stove , as shown in fig6 - 8 , with two zip fuel blocks as fuel . with no wind , the results are as follows : with a 2 . 24 ms − 1 ( 5 mph ) wind , the results are as follows : a comparison of fig1 and 16 demonstrates that the edb stove according to the invention performs significantly better in terms of time taken to boil , and total burn time , than the current uk military stove , particularly in the present of wind , where the uk stove performs very badly , without ever reaching boiling .
this invention relates to cooking stoves and in particular , to lightweight , efficient and portable outdoor cooking stoves . the cooking stoves are primarily for military use , for example by the dismounted infantry soldier , but are also suitable for other outdoor leisure pursuits such as backpacking , hiking and boating . the cooking stoves are designed to make efficient use of pre - packaged fuel blocks , to withstand cold temperatures and high winds , to protect combustible surroundings and to mask flames from an enemy .