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A combustor, in which a flame holding region is formed at a location distant from a pilot burner to avoid burnout of the pilot burner and in which flame holding capability is increased to use a lean pre-mix gas for reducing NOx emission, is provided. The combustor includes a combustion liner having

A combustor, in which a flame holding region is formed at a location distant from a pilot burner to avoid burnout of the pilot burner and in which flame holding capability is increased to use a lean pre-mix gas for reducing NOx emission, is provided. The combustor includes a combustion liner having a cylindrical side wall that defines a combustion chamber; and a main burner positioned at a top portion of the combustion liner for injecting an annular pre-mix gas into the combustion chamber to form a reverse flow region at a downstream portion thereof, which region is oriented towards the top portion of the combustion chamber along a longitudinal axis. In this combustor, a pilot burner is arranged at the top portion for injecting a mixture of fuel and air only in a direction confronting the reverse flow region.

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1. A combustor comprising: a combustion liner having a cylindrical side wall that defines a combustion chamber inside thereof;a main burner positioned at an inlet end of the combustion liner for injecting a pre-mix gas as a flow swirling about a longitudinal axis of the combustor in an annular shape

1. A combustor comprising: a combustion liner having a cylindrical side wall that defines a combustion chamber inside thereof;a main burner positioned at an inlet end of the combustion liner for injecting a pre-mix gas as a flow swirling about a longitudinal axis of the combustor in an annular shape into the combustion chamber to thereby form a reverse flow region at a location downstream with respect to flow of the pre-mix gas, in which at least a portion of the flow of the pre-mix gas flows in an upstream direction from a downstream location within the combustion chamber towards the inlet end of the combustion chamber along a longitudinal axis of the combustion chamber; anda pilot burner arranged at the inlet end for injecting a pre-mix gas of fuel and air in a single direction confronting the portion of the flow of the pre-mix gas flowing in the upstream direction within the combustion chamber;wherein the pilot burner injects the pre-mix gas at an initial velocity higher than a velocity of propagation of flame so as to form a flame holding region, at which the velocity of flow of the pre-mix gas is reduced down to a value equal to the velocity of propagation of flame, at a location spaced from the pilot burner in a direction axially of the pilot burner, andwherein the pilot burner includes a pilot nozzle formed in a most downstream end thereof and having an inner peripheral wall flaring axially outwardly in a direction downstream thereof, and a porous member, provided at an upstream end portion of the pilot nozzle, in the shape of a plate having a multiplicity of pores defined therein and is operable to inject the pre-mix gas of fuel and air through the porous member. 2. The combustor as claimed in claim 1, wherein the pilot burner includes a pre-mixing member provided in a pre-mix gas passage defined in the pilot burner and having a multiplicity of pores defined therein for facilitating mixing of fuel and air to create the pre-mix gas of fuel and air injected through the porous member. 3. The combustor as claimed in claim 2, wherein the pilot burner includes a support rod arranged on a longitudinal axis thereof and the plurality of pre-mixing members are mounted on the support rod so as to be positioned spacedly from each other in a direction axially of the pilot burner. 4. The combustor as claimed in claim 1, wherein the main burner has a first pre-mix gas passage defined therein that accommodates the pre-mix gas, and a second pre-mix gas passage of the pilot burner that accommodates the pre-mix gas of fuel and air is arranged inwardly of an inner periphery of the first pre-mix gas passage of the main burner. 5. The combustor as claimed in claim 1, wherein the pilot burner includes a pilot nozzle for guiding an injection gas therefrom in a direction towards the combustion chamber. 6. The combustor as claimed in claim 1, further comprising: a first fuel supply system that provides fuel to the main burner to create the pre-mix gas; anda second fuel supply system that provides fuel to the pilot burner to create the pre-mix gas of fuel and air;wherein the first fuel supply system and the second fuel supply system supply fuel to the main burner and pilot burner, respectively, independently of each other; andwherein the first fuel supply system and the second fuel supply system are configured to adjust a concentration of the fuel provided to the main burner and the pilot burner, respectively, independently of each other. 7. The combustor as claimed in claim 1, wherein the pilot burner includes a backfire preventing structure for preventing flame from penetrating from the combustion chamber. 8. The combustor as claimed in claim 7, wherein the backfire preventing structure is formed by a porous member having a plurality of throughholes defined therein. 9. The combustor as claimed in claim 1, wherein the pilot burner includes an introducing port defined at an upstream end of the pilot burner for introducing a fuel and an air thereinto, a pre-mix gas passage formed on a downstream side of the introducing port for pre-mixing the fuel and the air and a pre-mix gas injecting unit formed on a downstream side of the pre-mix gas passage for injecting the pre-mix gas through a porous member having a multiplicity of pores defined therein.