A reductant aqueous solution mixing device interposed between a filter device that captures particulate matters in an exhaust gas and a selective catalytic reduction device disposed downstream of the filter device, the reductant aqueous solution mixing device adding a reductant aqueous solution in the exhaust gas, and the reductant aqueous solution mixing device comprising:
- an elbow pipe attached to an outlet pipe of the filter device, the elbow pipe changing a flow direction of the exhaust gas flowing from the filter device;
- a straight pipe connected to a downstream side of the elbow pipe, the straight pipe extending in a direction intersecting an axial line of the outlet pipe of the filter device;
- and
- an injector attached to the elbow pipe, the injector injecting the reductant aqueous solution into an inside of the elbow pipe toward the straight pipe,
- wherein:
- the elbow pipe is provided with an injector attachment on which the injector is attached by a bolt,
- the injector attachment has an attachment face for the injector to be attached thereon, the attachment face being substantially flush with an end of an injection nozzle of the injector,
- the injector attachment is provided with a recess at which the end of the injection nozzle is exposed, the recess enlarging toward the straight pipe,
- a heat-insulation layer located near an outer periphery of the recess is provided inside the injector attachment,
- an end of the bolt penetrates the injector from an outside to reach the heat-insulation layer in the injector attachment,
- the injector attachment comprises a base plate on which the attachment face is provided and a sub-plate bonded to the base plate on a side near an inside of the elbow pipe,
- the heat-insulation layer is provided in a closed space defined by bonding the base plate and the sub-plate,
- an injection opening for exposing the end of the injection nozzle to the inside of the elbow pipe is provided to the injector attachment,
- a gasket is interposed between the injector attachment and the injector,
- the gasket comprises (i) an inner plate that is in contact with the attachment face of the injector attachment and has an inner opening corresponding to the injection opening, (ii) an outer plate that is in contact with the injector and has an outer opening corresponding to the injection opening, (iii) an annular outer periphery support ring held between outer peripheries of the inner plate and the outer plate, and (iv) an annular inner periphery heat-insulation ring held by a periphery of the inner opening of the inner plate and a periphery of the outer opening of the outer plate,
- a gasket-side heat-insulation space covered with the inner plate, the outer plate, the outer periphery support ring and the inner periphery heat-insulation ring is provided inside the gasket,
- an annular abutment portion to be in contact with the gasket is provided at a position of the injector close to an outer periphery of the injector and spaced away from the end of the injection nozzle,
- an injection-nozzle-side heat-insulation space opened toward an inside of the straight pipe through the injection opening is defined between the end of the injection nozzle and the abutment portion, and
- the injection-nozzle-side heat-insulation space is covered with the gasket.