PURPOSE:To reduce satisfacorily thermal stresses and make the manufacture easy by providing at the air introduction port a pipe made of ceramics which has heat insulating and heat resisting properties with the outer circumferential face of the pipe arranged in circumferential contact with the inner circumferential face of the air introduction port. CONSTITUTION:On the outside of a combustion cylinder 1 that is formed of ceramics a metallic outer cylinder 3 is arranged so as to cover the outer circumference of the combustion cylinder 1 through a heat-resistant material 2. On the outer circumferential face of the combustion cylinder 1 a plurality of air introduction ports 4 are formed to introduce auxiliary air for combustion, and in each air introduction port 4 a pipe 5 made of a heat insulating and heat resisting ceramic material is arranged with its outer circumferential face in contact with the inner circumferential face of the air introduction port 4. Auxiliary air for combustion is, therefore, introduced into the combustion cylinder 1 through the inner side of a pipe 5. The pipe 5 made of ceramics is arranged with its outer circumferential face in contact with the inner circumferential face of the air introduction port 4 to make the temperature gradient near the air introduction port gentle.
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