Abstract: A combined plant is provided. The combined plant of continuously supplying hydrogen and nitrogen to an ammonia synthesis facility that continuously synthesizes ammonia from hydrogen and nitrogen, the combined plant including: a hydrogen production facility for acquiring solar energy and producing hydrogen by utilizing a part of the acquired solar energy; a nitrogen production facility for producing nitrogen from air and supplying the nitrogen to the ammonia synthesis facility; and a hydrogen storage facility for storing the hydrogen produced by the hydrogen production facility and supplying the produced hydrogen to the ammonia synthesis facility.

Abstract: An exhaust manifold comprising a plurality of exhaust pipes and a merging portion applies exhaust gas from each cylinder uniformly to an oxygen sensor in a merging portion at low speed thereby improving the durability of the oxygen sensor. A downstream forward end of each exhaust pipe of the exhaust manifold, when connected to an inlet wall of a merging case having the oxygen sensor mounted on a side thereof, is formed in the shape of a bell mouth for leading the exhaust gas to the oxygen sensor. Each exhaust pipe is fixedly welded to the merging case at a position upstream of the forward end of the bell mouth. An angle formed by lines perpendicular to tangential lines at starting and ending points of a curved portion of the bell mouth at the forward end of the exhaust pipe is set in the range of 45.degree. to 75.degree.. As a result, the bell mouth spreads over the whole interior of the merging case and reduces a flow rate of the exhaust gas, and part of the exhaust gas flows toward the oxygen sensor.