Combustion – Process of combustion or burner operation – Controlling or proportioning feed
Reexamination Certificate
2002-09-13
2004-06-22
Yeung, James C. (Department: 3749)
Combustion
Process of combustion or burner operation
Controlling or proportioning feed
C431S076000, C431S089000, C431S354000, C126S0390BA, C126S01900R
Reexamination Certificate
active
06752621
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention is directed to a method for setting the performance of a gas-operated cooking device as well as to a cooking device that uses the method.
Problems can occur in the operation of a gas-operated cooking device, particularly in mobile employment or given an operating in a gas network, wherein the gas quality changes. On one hand, a different gas quality, particularly a change in the type of gas employed, will lead to a change in the air ratio of a combustion gas/air mixture supplied to a gas burner arranged in the cooking device. The ratio of air quantity to combustion gas quantity referred to the stoichiometry of the combustion gas and a change in the ratio of air quantity to combustion gas quantity causes a deviation in the combustion from a desired ideal value for a hygienic, complete combustion, so that increased emissions of pollutants can occur during the combustion. Both increased emissions of pollutants as well as increasing stresses on the component parts will occur from incorrect settings of air quantity and/or combustion gas quantity. On the other hand, a deviation from the ideal air ratio leads to a modified calorific output or heating capacity of the gas burner, which, given a continuous operation of the gas burner during a cooking process, leads to modifications of the cooking time and, thus, to a deterioration of the quality of the cooked product that is being prepared. A modulating operation of the gas burner, in fact, makes it possible to slightly reduce the influence of variable environmental conditions, which, in addition to gas quality, also includes changes in air or gas pressures and contamination of the cooking device, on the quality of the cooked product without, however, being able to completely eliminate this problem. Given cooking devices known from the prior art, a manual intervention is necessary for actuating components of the gas feed and of the air feed in order to adapt the cooking device for the variable environmental boundary conditions, which are usually not to be implemented technically correct by an untrained user.
Additional various methods for optimizing the combustion of a gas burner in and of itself are known from the prior art. German Patent Document DE 196 39 487 A1 discloses a method and an apparatus for optimizing the operation of a gas burner. Even without utilization of an oxygen sensor in the flue gas exhaust, the air-gas mixture for a gas burner is thereby optimized given employment of combustion gasses with different Wobbe indices in that the gas burner is first supplied with an air-gas mixture with a gas excess, and this is ignited. Subsequently, the air part in the air-gas mixture is increased until the flame lifts off from the gas burner, which is detected via a flame sensor. The air-gas ratio is then modified to decrease the air excess in order to set an optimum combustion. A disadvantage of this method, however, is that the gas consumption is elevated during the setting procedure when the air-gas ratio is set proceeding therefrom that the gas part is reduced proceeding from a high initial value given a constant air feed, which will lead to an increase in the operating costs and deflagration can occur given the ignition of the rich gas to air mixture, which reduces operational safety.
Additional methods or devices are known from the prior art that enable the determination of the Wobbe index and/or of the calorific value of a combustion gas supplied to a gas burner in order to set the air ratio needed for a hygienic combustion with the data acquired therefrom.
German Patent Document DE 41 18 781 A1 discloses a method and apparatus for a combustion-free determination of the Wobbe index and/or of the calorific value of a gas. For determining the Wobbe index, the volume stream of a flowing gas is measured and further characteristic properties, such as pressure drop, density, viscosity or the like are measured or kept constant. With the assistance of approximation functions, the Wobbe index of the combustion gas is subsequently identified from the measured volume stream and, thus, mass stream and at least one further characteristic. It is also proposed that the identified Wobbe index be used in order to set the quantity of the heat supplied to a gas burner by varying the pressure and, thus, the volume stream of the delivered gas or by varying the mixing ratio of the two gas grades. A disadvantage of this method, however, is that it requires an additional measuring instrument, which increases the structural outlay of the gas burner mechanism, the manufacturing costs of the device and also has an increases susceptibility to malfunction.
German Patent Document DE 198 24 523 A1, which discloses a regulating method for gas burners, and German Patent Document DE 39 37 290 A1, which discloses a method and a device for producing a fuel/combustion mixture to be supplied for combustion, disclose that an ionization electrode is arranged in the flame region of the gas burner with the result that an electrical conductivity is measured in this region and the stoichiometry of the supplied fuel can be determined therefrom. The calorific value can then be derived from the identified stoichiometry. A disadvantage of this method, however, is that the measurement method has a high susceptibility to error, since the determination of the conductivity is dependent on the exact known geometry of the electrode arrangement, and deviations from the ideal air ratio when setting the air-gas mixture can occur dependent on an imprecisely measured ionization current.
German Patent Document DE 198 38 361 A1 also discloses that the gas composition of a mixture supplied to a gas burner be identified by a sensor arranged in the gas conduit, particularly in the form of a metal oxide sensor. The gas composition identified in this way is then used for determining the calorific value of the combustion gas and for setting a corresponding Wobbe index for the gas mixture by varying the mixture composition. A disadvantage of this method, however, is that expensive sensors must be employed in order to achieve an adequate measuring precision in the determination of the gas composition, and the determination of the caloric value involves complicated conversions that can be affected by errors. Moreover, additional inserts are provided in the gas burner, which increases the design outlay for the device.
German Patent Document DE 199 08 885 A1 discloses a method for the operation of an energy converter supplied with combustion gasses with varying composition. It is provided in this method that the combustion gas is heated in a lockable measuring chamber, and the dependency between the heat quantity supplied to the measuring chamber and the rise in pressure and/or temperature in the measuring chamber is used in order to set the combustion gas composition to a rated value. A disadvantage of this method, however, is that additional inserts are provided and the measurement method is imprecise and susceptible to disturbance due to the determination of the supplied heat quantity that is sensitive to change in the environmental conditions.
German Patent Document DE 199 21 167 A1 discloses a method and an arrangement for measuring the calorific value and/or the Wobbe index of combustion gasses, particularly natural gas. In this method, the speed of sound or the density of the combustion gas is measured, the combustion gas is exposed to an infrared radiation, the part of the infrared radiation absorbed by the combustion gas is measured, and the calorific value and/or the Wobbe index is obtained from these two measured signals. A disadvantage of this method, however, is that it also is technologically complicated and susceptible to malfunction.
German Patent Document DE 197 50 873 A1 discloses a method for the control of an atmospheric gas burner for heating units, particularly water heaters. In order to adapt the starting gas quantity to various environmental conditions, it is proposed that the starting gas quantity be increased time-depen
Rusche Stefan
Schreiner Thomas
Rational AG
Schiff & Hardin LLP
Yeung James C.
LandOfFree
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