1. Field of the Invention
The present invention relates to a combustion apparatus for use in a boiler or the like and, more particularly, to a combustion apparatus equipped with a pilot burner and a main burner.
2. Description of the Related Art
As a known example of the combustion apparatus of a boiler formed so as to burn a gas fuel to obtain steam and hot water, there exists one equipped with a pilot burner and a main burner (see, for example, JP 10-196942 A).
Here, the “pilot burner” is a burner provided to function as an ignition means for igniting the main burner, and is provided adjacent to the main burner. The “main burner” is a burner formed so as to be capable of supplying a gas fuel required in the boiler, and can be switched between low combustion and high combustion as needed. Pilot burners of different combustion types are known, for example, one that is extinguished after the ignition of the main burner or one that continues to burn together with the main burner.
The combustion apparatus as disclosed in JP 10-196942 A has a main burner and a pilot burner positioned beside the main burner, and a gas fuel is supplied to the main burner and the pilot burner through piping branched off from a gas supply pipe. After the ignition of the pilot burner has been confirmed, the gas fuel is supplied to the main burner, and the ignition of the main burner is effected by using the flame of the pilot burner. In this prior-art technique, to reduce the possibility of defective ignition, a plurality of pilot burners are provided for one main burner.
The combustion apparatus according to the above-described prior-art technique has a blower for supplying combustion air, and combustion air is supplied to the pilot burner and the main burner from a single blower. In the combustion apparatus, constructed as described above, the pilot burners are extinguished after the ignition of the main burner. That is, after the ignition of the main burner has been confirmed, no gas fuel is supplied to the pilot burner.
However, in the prior-art technique, even after the supply of gas fuel to the pilot burner has been stopped, the combustion air from the blower continues to be supplied thereto. Thus, air that has passed by way of the pilot burner is also supplied to the portion in the vicinity of the main burner, which makes the combustion state of the main burner rather unstable and adversely affects the combustion.
To be more specific, the air from the pilot burner is blown against the flame formed by the main burner, so the flame temperature is locally reduced, resulting in generation of CO and unburned substances.