Combustion – Process of combustion or burner operation – Heating feed
Patent
1980-02-02
1982-12-21
Favors, Edward G.
Combustion
Process of combustion or burner operation
Heating feed
236 15BD, 431 12, 431 75, 431 90, 431242, 431247, F23D 1144
Patent
active
043647243
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a method and an apparatus for dosing the air-fuel mixture in burners of the type which is formed with an evaporating tube, through which the fuel and some amount of combustion air is introduced in a burner chamber and is mixed with further combustion air and is inflamed.
Burners of this type are intended to be used in case a high efficiency is wanted like in burners for all kinds of heating purposes as villa burners, gas turbines, steam turbines etc. A special field of use is burners in such types of engines in which a working fluid in a closed fluid system is subjected to heating and cooling respectively and in which the said temperature differences are utilized for driving the active parts of the engine like for instance pistons. A such type of motor is the so called Stirling motor. For the sake of simplicity the invention will mainly be described in connection to such Stirling motor, but it is to be understood that the invention is not restricted to the said field of use and that the invention can be used for many other purposes.
In all combustion where it is tried to get a high efficiency and low emissions of harmful products the fuel and the air must be dosed to a particular relationship. In order to get a good combustion the reaction ought to follow by excess of air. The theoretical amount of air which is needed for combustion of a special amount of fuel is named .lambda. (lambda), and excess of air consequently means that .lambda. is higher than 1. The optimum .lambda.-value varies depending on the design of the burner, the type of fuel, the load of the burner etc. Emperically the optimum .lambda.-value can be determined, and the said value may simplified often be represented as a straight line. In a special burner the optimum .lambda.-curve shown in FIG. 3 has been obtained.
In FIG. 3 the amount of fuel is given in grams per second, and along the horizontal axis the excess of air .lambda. is stated. It is evident that the .lambda.-value varies depending on the amount of fuel and that the .lambda.-value is reversed proportional to the amount of fuel, i.e. that a high amount of fuel claims a relatively low .lambda.-value, whereas a little amount of fuel claims a relatively high .lambda.-value. In varying the load of the burner a varying amount of fuel has to be injected, and thereby also the .lambda.-value must be controlled.
In a previously known apparatus the control of the .lambda.-value is made in that the fuel pump and the fan for the combustion air are connected to the same shaft but with a predetermined gear change, so that the amounts of fuel and combustion air theoretically follow a calculated or empirically stated curve for the optimum .lambda.-value. Such apparatus may during some condutions give a satisfactory result, but after some time of combustion large differences from the optimum relationship may appear depending on leakage both in the fuel system and the air system, that the temperatures of the injected fuel and air vary etc.
In another previously known control apparatus for dosing the air-fuel mixture a chemical sensor or probe of special type is applied inside the burner or in the flue- gas channels for sensing the chemical composition of the flue gases. Such proves, however, are exposed to very strong thermical action, to risks of being oxidized or being sooted etc., and therefore the chemical probes have a restricted lifetime and give an unsafe result. No .lambda.-probes of the said type appearing on the market today are capable, for different reasons, to measure or control .lambda.-values which are higher or lower than 1,0, and the said probes therefore can not be used in the burner systems intended with the present invention in which the optimum .lambda.-value is substantially higher than 1,0.
At present the .lambda.-value in combustion is controlled in that the amount of air pumped into the burner chamber through an air channel is measured, and the said amount of air is allowed to define the flow of fluid according to a predetermined .lambda.
REFERENCES:
patent: 3072468 (1963-01-01), Stitzer
patent: 3299841 (1967-01-01), Hemker et al.
patent: 3768955 (1973-10-01), McLaughlin
patent: 4043742 (1977-08-01), Egan et al.
patent: 4063870 (1977-12-01), Deruelle
patent: 4118172 (1978-10-01), Noir et al.
patent: 4255116 (1981-03-01), Zwick
patent: 4255122 (1981-03-01), Alpkvist et al.
Favors Edward G.
Forenade Farbiksverken
Wray James C.
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