Combustion – Burner having electrical heater or igniter – Igniter in shelter chamber
Reexamination Certificate
1999-09-17
2001-11-27
Lazarus, Ira S. (Department: 3743)
Combustion
Burner having electrical heater or igniter
Igniter in shelter chamber
C431S158000, C431S353000, C060S039821
Reexamination Certificate
active
06322353
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an ignition appliance for a heat generator, comprising a fuel gas supply passage, an air supply passage, a flame tube and an igniter, the igniter being arranged in an ignition space through which flow occurs and which is spatially remote from the flame tube, which ignition space opens into the flame tube.
2. Discussion of Background
The ignition of flames in heat generators, as for example in gas turbine combustion chambers, can take place for example by means of an igniter plug or a glow plug, as described inter alia by A. Lefebvre in “Gas Turbine Combustion” (Arthur H. Lefebvre:
Gas Turbine Combustion,
Hemisphere Publishing Corporation, 1983).
An obvious precondition for the function of the ignition appliance is that conditions are present at the igniter which are essential for a stable and sufficiently powerful ignition flame to occur in the first place. In this connection, particular mention should be made of the setting of the fuel/air ratio at the igniter and of an appropriate flow velocity in the region of the igniter.
These requirements can often only be satisfied by the employment of special ignition burners, particularly in the combustion chambers of gas turbines. Placing the igniter directly in the combustion space is intrinsically ruled out by the criteria mentioned above. The igniter is therefore frequently accommodated in a small ignition space so that only a small volume has to be ignited by the initial ignition. A stable ignition flame occurs in succession in a flame tube located downstream of this ignition space. Even then, satisfactory results are often only obtained with substantial complication, for example by the employment of ignition gas supply systems fed with propane gas.
If, on the other hand, direct ignition is to take place with natural gas or even with low calorific value gases, the range of fuel/air ratios in which a reliable function is ensured is very tightly limited. The gas supply and air supply to the igniter must correspondingly have very tight tolerances and the upstream gas pressure must be carefully matched.
Under the conditions which are present in the combustion chambers of modern gas turbines, the ignition systems demand a high level of maintenance in order to maintain their reliable function over a long period of time.
SUMMARY OF THE INVENTION
The invention is intended to provide help on this point. Accordingly, one object of the invention is to ensure good ignition conditions, even without ensuring compliance with very close tolerances in the supply ducts for fuel gas and air, in the case of an ignition appliance for a heat generator, comprising a fuel gas supply passage, an air supply passage, a flame tube and an igniter, the igniter being arranged in an ignition space through which flow occurs and which is spatially remote from the flame tube, which ignition space opens into the flame tube.
In accordance with the invention, this object is achieved by having the fuel gas supply passage and air supply passage open into the flame tube, and by the ignition space being connected by at least one connecting duct to the fuel gas supply passage and the air supply passage.
By means of this embodiment, the air and fuel supply to the igniter itself can be effectively decoupled from that of the overall ignition device because if the cross sections of gas lines and air lines are selected to be sufficiently large, the result is a small respective pressure drop between the supply lines and the flame tube and ignition space. Because of this, however, the pressure drops over the connecting ducts between the ignition space and the supply passages for air and fuel gas are also almost equal, and small. Because of the small pressure drop, the cross sections of the connecting ducts can be selected to be large without the flow velocity in the environment of the igniter increasing to more than a permissible and desirable amount. As a consequence, the sensitivity of the mass flows transmitted to manufacturing tolerances is reduced. Because the pressure drops over all the connecting ducts are not significantly different, on the other hand, the fuel/air ratio in the ignition space is essentially determined only by the ratio of the cross sections of the connecting ducts for air and fuel gas.
The possibility of influencing the flow through the ignition space on a sustained basis by means of a nozzle-shaped or diffuser-shaped geometry of the openings for the fuel gas supply passage and the air supply passage can be readily implemented by the specialist.
The flow of air and fuel gas around the igniter is effectively decoupled, from parameters such as pressure in the combustion space and the upstream pressure of air and fuel gas, by the embodiment of an ignition device according to the invention. In consequence, good ignition conditions can be ensured immediately at the igniter over a wide operating range of the ignition device.
It should also be noted that the igniter itself only has to ignite a small volume of mixture. In consequence, the minimum energy needed for reliable initial ignition is reduced. The pilot flame occurring in this way emerges from the ignition space into the flame tube, where it ignites the fuel/air mixture present there so that, finally, the actual ignition flame for the complete combustion space is generated.
The intensity of the pilot flame can, in addition, also be influenced by a corresponding shaping of the ignition space and the connecting ducts to the same, as is explained in the following embodiment example.
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Stalder Marcel
Sybon Günter
Asea Brown Boveri AG
Burns Doane Swecker & Mathis L.L.P.
Cocks Josiah C.
Lazarus Ira S.
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