Anthony Fahme

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 Solars 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. NO X and CO emissions have been consistently <15 ppmv and <10 ppmv, respectively. Maximum test durations of 15,144 h and 13,937 h 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 12,582 h. 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 Ml and CVI CMCs. Results to date indicate that oxide/oxide CMCs with protective FG1 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.

Ceramic Stationary Gas Turbine Program: Combustor Liner Development Summary

Under the Ceramic Stationary Gas Turbine Program sponsored by the U. S. Department of Energy, Solar Turbines Incorporated has successfully designed and developed ceramic combustor liners. Their potential for low emissions has been demonstrated in five field-engine tests for a total duration of over 30,000 hours, with over 13,000 hours on EBC protected liners in one engine test. The ceramic combustor development under the CSGT Program (1992–2000), including design, material selection, testing and evaluation are discussed.Copyright

Combined Back-Side Cooled Combustor Liner and Variable Geometry Injector Technology

The need to evolve next-generation ultra-lean premixed systems with advanced air management and improved liner cooling strategies have led Solar to develop a pre-production combustion system for its C50 class engine. The system uses an Augmented Backside Cooled/Thermal Barrier Coated (ABC/TBC) combustor and Variable Geometry injectors. The technology reduces both NOx and CO emissions, while improving part-load cycle efficiency.The ABC/TBC combustor technology eliminates quenching of the reaction at the walls typically found in combustors using film-cooling techniques. Eliminating this quenching effect is not only conducive to reducing CO emissions, but it also enables the operation of the combustor primary zone at low temperatures to produce minimum thermal NOx. Coupled with a set of variable geometry injectors, the system manages air more effectively to extend the combustor operating range under which emissions and stability limits are maintained. The injectors enable the control of air entering the combustor as a function of engine load and ambient temperature. Such ability reduces the need to bleed high-pressure compressor air at part-load, thus enhancing the engine cycle efficiency.The pre-production combustion system is currently undergoing field evaluation to assess long-term durability, characterize system performance, and develop optimum control algorithms. The development methodology and experience for this system is discussed in this paper.Copyright

Back Side-Cooled Combustor Liner for Lean-Premixed Combustion

This paper describes the design and initial testing of a second generation, lean-premixed combustor for a 6100 horsepower industrial gas turbine. The full scale, prototype combustor liner employed augmented backside cooling (ABC) as a means of reducing NOx and CO emissions. A thermal barrier coating (TBC) was applied on the liner hot side to reduce thermal flux from the flame zone. The goal of the effort was to demonstrate that the avoidance of film-cooling for the combustor liner would allow emissions reductions in a lean-premixed combustion system.Testing of the combustor was conducted in both low and high pressure environments. The testing demonstrated that the use of trip-strips for backside cooling provides an effective means of reducing CO emissions. The lower CO levels can be exploited by lowering flame temperatures to achieve lower NOx emissions. Reaction quenching associated with film cooling is indicated as the cause of the higher CO emissions in more conventional liners. Cyclic rig testing showed the TBC to have good short-term durability. Long-term field testing is getting underway.Copyright