Ceramic Matrix Composite Combustor Liners: A Summary of Field Evaluations

Abstract

Solar Turbines Incorporated, under U.S. government sponsored programs, has been evaluating ceramic matrix composite combustor liners in test rigs and Solar’s Centaur® 50S gas turbine engines since 1992. The objective is to evaluate and improve the performance and durability of CMCs as high-temperature materials for advanced low emissions combustors. Field testing of CMC combustor liners started in May of 1997 and by the end of 2004, over 67,000 operating hours had been accumulated on SiC∕SiC and oxide∕oxide CMC liners. NOx and CO emissions have been consistently <15ppmv and <10ppmv, respectively. Maximum test durations of 15,144h and 13,937h have been logged for SiC∕SiC liners with protective environmental barrier coatings. An oxide∕oxide CMC liner with a Friable Graded Insulation coating has been tested for 12,582h. EBCs significantly improve SiC∕SiC CMC liner life. The basic three-layer EBC consists of consecutive layers of Si, mullite, and BSAS. The durability of the baseline EBC can be improved by mixing BSAS with mullite in the intermediate coating layer. The efficacy of replacing BSAS with SAS has not been demonstrated yet. Heavy degradation was observed for two-layer Si∕BSAS and Si∕SAS EBCs, indicating that the elimination of the intermediate layer is detrimental to EBC durability. Equivalent performance was observed when the Hi-Nicalon fiber reinforcement was replaced with Tyranno ZM or ZMI fiber. Melt infiltrated SiC∕SiC CMCs have improved durability compared to SiC∕SiC CMCs fabricated by Chemical Vapor Infiltration of the matrix, in the absence of an EBC. However, the presence of an EBC results in roughly equivalent service life for MI and CVI CMCs. Results to date indicate that oxide∕oxide CMCs with protective FGI show minor degradation under Centaur® 50S gas turbine engine operating conditions. The results of, and lessons learned from CMC combustor liner engine field testing, conducted through 2004, have been summarized.

Advances in SiC/SiC Composites for Aero‐Propulsion

“…This effect, which can be severe for all silicon-based ceramics, is typically due to the water vapor formed in the combustion process, which reacts with the oxides, such as silica, that continually form on the ceramic surface, causing them to volatilize. For industrial gas turbines, these EBCs have been very instrumental in extending the life of SiC/SiC CMC combustor liners and shrouds at temperatures up to ∼1250 • C [43], but little experience exists for using EBCs under more aggressive engine conditions. To minimize this effect, environmental barrier coatings (EBCs) have been developed for both Si-based monoliths and composites [41,42].…”

Degradation of Nextel™ 610‐based oxide‐oxide ceramic composites by aluminum oxychloride decomposition products

“…Oxide‐oxide CMCs that rely on matrix porosity for damage tolerance are in production for the fluted mixer for the GE Passport Business jet engine . They are in development for nozzles and cowling for several Boeing airframes, and for combustor liners for industrial gas turbines . Oxide‐oxide CMC characteristics are reviewed elsewhere …”

“…2 They are in development for nozzles and cowling for several Boeing airframes, [2][3][4] and for combustor liners for industrial gas turbines. [4][5][6] Oxideoxide CMC characteristics are reviewed elsewhere. 1,[7][8][9] Oxide-oxide CMCs that do not rely on a porous matrix for damage tolerance have been demonstrated.…”

Low‐Temperature Oxidation Embrittlement of SiC (Nicalon™)/CAS Ceramic Matrix Composites

“…C ontinuous fiber‐reinforced ceramic matrix composites (CMCs) are promising candidates for a number of advanced structural applications, including use in gas turbine engines, automotive brakes, and heat exchangers 1–6 . While there are now several classes of these materials, developed with both dense and porous matrices, the majority of prior work has explored the development and mechanical assessment of materials with compliant interphases between the fiber and matrix.…”

“…C ONTINUOUS fiber-reinforced ceramic matrix composites (CMCs) are promising candidates for a number of advanced structural applications, including use in gas turbine engines, automotive brakes, and heat exchangers. [1][2][3][4][5][6] While there are now several classes of these materials, developed with both dense and porous matrices, the majority of prior work has explored the development and mechanical assessment of materials with compliant interphases between the fiber and matrix. For nonoxide composites, these interphase layers are required to lower the interfacial fracture energy and allow fiber-matrix debonding, and are typically based on the use of materials such as carbon or boron nitride.…”