Ceramic Matrix Composite Combustor Liner Research Articles

Durability of Oxide/Oxide Ceramic Matrix Composites in Gas Turbine Combustors

An integrated creep rupture strength degradation and water vapor degradation model for gas turbine oxide-based ceramic matrix composite (CMC) combustor liners was expanded with heat transfer computations to establish the maximum turbine rotor inlet temperature (TRIT) for gas turbines with 10:1 pressure ratio. Recession rates and average CMC operating temperatures were calculated for an existing baseline N720/A (N720/Al2O3) CMC combustor liner system with and without protective Al2O3 friable graded insulation (FGI) for 30,000-h liner service life. The potential for increasing TRIT by Y3Al5O12 (YAG) substitution for the fiber, matrix, and FGI constituents of the CMC system was explored, because of the known superior creep and water vapor degradation resistance of YAG compared to Al2O3. It was predicted that uncoated N720/A can be used as a combustor liner material up to a TRIT of ∼1200 °C, offering no TRIT advantage over a conventional metal + thermal barrier coating (TBC) combustor liner. A similar conclusion was previously reached for a SiC/SiC CMC liner with barium strontium aluminum silicate (BSAS)-type environmental barrier coating (EBC). The existing N720/A + Al2O3 FGI combustor liner system can be used at a maximum TRIT of ∼1350 °C, a TRIT increase over metal + TBC, and uncoated N720/A of ∼150 °C. Replacing the Al2O3 with YAG is predicted to increase the maximum allowable TRIT. Substitution of the fiber or matrix in N720/A increases TRIT by ∼100 °C. A YAG FGI improves the TRIT of the N720/A + Al2O3 FGI by ∼50 °C, enabling a TRIT of ∼1400 °C, similar to that predicted for SiC/SiC CMCs with protective rare earth monosilicate EBCs.

Ceramic Matrix Composite Combustor Liners: A Summary of Field Evaluations

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.

Development of a Combustor Liner Composed of Ceramic Matrix Composite (CMC)

The Research Institute of Advanced Materials Gas-Generator (AMG), which is a joint effort by the Japan Key Technology Center and 14 firms in Japan, has, since fiscal year 1992, been conducting technological studies on an innovative gas generator that will use 20 percent less fuel, weigh 50 percent less, and emit 70 percent less NOx than the conventional gas generator through the use of advanced materials. Within this project, there is an R&D program for applying ceramic matrix composite (CMC) liners to the combustor, which is a major component of the gas generator. In the course of R&D, continuous SiC fiber-reinforced SiC composite (SiCF/SiC) was selected as the most suitable CMC for the combustor liner because of its thermal stability and formability. An evaluation of the applicability of the SiCF/SiC composite to the combustor liner on the basis of an evaluation of its mechanical properties and stress analysis of a SiCF/SiC combustor liner was carried out, and trial SiCF/SiC combustor liners, the largest of which was 500-mm in diameter, were fabricated by the filament winding and PIP (polymer impregnation and pyrolysis) method. Using a SiCF/SiC liner built to the actual dimensions, a noncooling combustion test was carried out and even when the gas temperature was raised to 1873K at outlet of the liner, no damage was observed after the test. Through our studies we have confirmed the applicability of the selected SiCF/SiC composite as a combustor liner. In this paper, we describe the present state of the R&D of a CMC combustor liner.