Abstract This work focuses on studying the effect of welding heat input within the range from 1 to 5 kJ/mm on the microstructure and the corresponding mechanical and corrosion properties of dissimilar joint between su...Abstract This work focuses on studying the effect of welding heat input within the range from 1 to 5 kJ/mm on the microstructure and the corresponding mechanical and corrosion properties of dissimilar joint between superaustenitic stainless steel （UNS S31254） and Incoloy 28 （UNS N08028）. The two materials were butt-welded with ER NiCrMo3. The metallurgical changes associated with welding of SASS and Incoloy 28 were studied using optical microscope, SEM, and EDX. The mechanical and corrosion properties were investigated using tensile test, Vickers hardness test, and pitting and crevice corrosion tests. The weld metal microstructure showed precipitates with needle-like shape at 3 and 5 kJ/mm. Also, the microstructure showed unmixed zone （UMZ） at the fusion line of both SASS and Incoloy 28 sides at all the investigated heat inputs. The Mo microsegregation within UMZ at Incoloy 28 side increased as the heat input increased from 1 to 5 k J/ram but that in SASS increased with increasing heat input from 1 to 3 kJ/mm and then decreased with increasing from 3 to 5 kJ/mm. The ultimate tensile strengths for all specimens at all the investigated heat inputs are acceptable. The average hardness noticeably changed in weld metal as the heat input increased from 1 to 5 kJ/mm. Other zones such as HAZ or UMZ did not demonstrate marked changes in the average hardness. The pitting and crevice corrosion rates of the weld joint were found significant at l and 3 kJ/mm but insignificant at 5 kJ/mm according to ASTM G48.展开更多
NH_(3)has emerged as a promising candidate for low-carbon gas turbines,with NO_(x)emission issues being mitigated by air-staged combustion.However,the role of fuel/air mixing quality(represented by unmixedness)in NO_(...NH_(3)has emerged as a promising candidate for low-carbon gas turbines,with NO_(x)emission issues being mitigated by air-staged combustion.However,the role of fuel/air mixing quality(represented by unmixedness)in NO_(x)formation in NH_(3)systems remains poorly explored.In this study,the characteristics of NO_(x)formation under the effects of unmixedness have been numerically investigated using an NH_(3)/CH_(4)fired air-staged model combustor consisting of perfectly stirred reactors(PSRs)and plug flow reactors(PFRs),employing the 84-species,703-reaction Tian mechanism under H/J heavy duty gas turbine conditions.It was found that a primary-stage equivalence ratio of 1.2–1.5 corresponds to a low NO_(x)formation region under perfectly mixed fuel and air conditions.In this region,a relatively low NO_(x)formation is achieved when the unmixedness is less than 0.12 and NO_(x)formation exhibits low sensitivity to fuel/air unmixedness.Based on these findings and the fact that the air-staged combustion loses its advantage in reducing NO_(x)emissions when the unmixedness exceeds 0.12 across all equivalence ratios,recommended mixing quality thresholds for different equivalence ratios are proposed to guide combustor design and operation optimization.A parametric study of chemical reaction pathways at different unmixedness levels in the two stages demonstrates that NO_(x)is mainly formed in the main combustion zone of the secondary stage via the HNO pathway,which results in NO_(x)formation rising to thousand ppm when unmixedness exceeds 0.3,although NO_(x)reduction through NHi and N_(2)O pathways partially offsets contributions from the HNO and thermal NO_(x)pathways.To leverage the NO_(x)reduction potential of the NHi and N_(2)O pathways,the residence time in both stages should be carefully adjusted to help suppress NO_(x)to as low as 48 ppm.The results of this study are important for engineering applications,providing guidance for the design of NH_(3)fired combustors aimed at significantly reducing NO_(x)formation.展开更多
We know that the dimension for an irreducible ascending chain ASC is a crucial concept in Ritt-Wu’s constructive theory of algebraic geometry. We can also define the dimension for an arbitrary ascending chain similar...We know that the dimension for an irreducible ascending chain ASC is a crucial concept in Ritt-Wu’s constructive theory of algebraic geometry. We can also define the dimension for an arbitrary ascending chain similarly. But one may say that this definition has no geometric meaning. In this note, we shall show that the dimension of an展开更多
文摘Abstract This work focuses on studying the effect of welding heat input within the range from 1 to 5 kJ/mm on the microstructure and the corresponding mechanical and corrosion properties of dissimilar joint between superaustenitic stainless steel （UNS S31254） and Incoloy 28 （UNS N08028）. The two materials were butt-welded with ER NiCrMo3. The metallurgical changes associated with welding of SASS and Incoloy 28 were studied using optical microscope, SEM, and EDX. The mechanical and corrosion properties were investigated using tensile test, Vickers hardness test, and pitting and crevice corrosion tests. The weld metal microstructure showed precipitates with needle-like shape at 3 and 5 kJ/mm. Also, the microstructure showed unmixed zone （UMZ） at the fusion line of both SASS and Incoloy 28 sides at all the investigated heat inputs. The Mo microsegregation within UMZ at Incoloy 28 side increased as the heat input increased from 1 to 5 k J/ram but that in SASS increased with increasing heat input from 1 to 3 kJ/mm and then decreased with increasing from 3 to 5 kJ/mm. The ultimate tensile strengths for all specimens at all the investigated heat inputs are acceptable. The average hardness noticeably changed in weld metal as the heat input increased from 1 to 5 kJ/mm. Other zones such as HAZ or UMZ did not demonstrate marked changes in the average hardness. The pitting and crevice corrosion rates of the weld joint were found significant at l and 3 kJ/mm but insignificant at 5 kJ/mm according to ASTM G48.
基金supported by China Aeroengine University—Industry Joint R&D Projects(Grant No.HFZL2023CXY031).
文摘NH_(3)has emerged as a promising candidate for low-carbon gas turbines,with NO_(x)emission issues being mitigated by air-staged combustion.However,the role of fuel/air mixing quality(represented by unmixedness)in NO_(x)formation in NH_(3)systems remains poorly explored.In this study,the characteristics of NO_(x)formation under the effects of unmixedness have been numerically investigated using an NH_(3)/CH_(4)fired air-staged model combustor consisting of perfectly stirred reactors(PSRs)and plug flow reactors(PFRs),employing the 84-species,703-reaction Tian mechanism under H/J heavy duty gas turbine conditions.It was found that a primary-stage equivalence ratio of 1.2–1.5 corresponds to a low NO_(x)formation region under perfectly mixed fuel and air conditions.In this region,a relatively low NO_(x)formation is achieved when the unmixedness is less than 0.12 and NO_(x)formation exhibits low sensitivity to fuel/air unmixedness.Based on these findings and the fact that the air-staged combustion loses its advantage in reducing NO_(x)emissions when the unmixedness exceeds 0.12 across all equivalence ratios,recommended mixing quality thresholds for different equivalence ratios are proposed to guide combustor design and operation optimization.A parametric study of chemical reaction pathways at different unmixedness levels in the two stages demonstrates that NO_(x)is mainly formed in the main combustion zone of the secondary stage via the HNO pathway,which results in NO_(x)formation rising to thousand ppm when unmixedness exceeds 0.3,although NO_(x)reduction through NHi and N_(2)O pathways partially offsets contributions from the HNO and thermal NO_(x)pathways.To leverage the NO_(x)reduction potential of the NHi and N_(2)O pathways,the residence time in both stages should be carefully adjusted to help suppress NO_(x)to as low as 48 ppm.The results of this study are important for engineering applications,providing guidance for the design of NH_(3)fired combustors aimed at significantly reducing NO_(x)formation.
基金The work was supported in part by the Grant CIZR-8702108 of National Natural Science Foundation of China.
文摘We know that the dimension for an irreducible ascending chain ASC is a crucial concept in Ritt-Wu’s constructive theory of algebraic geometry. We can also define the dimension for an arbitrary ascending chain similarly. But one may say that this definition has no geometric meaning. In this note, we shall show that the dimension of an
