Ceramic Applications in Turbine Engines

Abstract

The objective of the CATE program is to apply ceramic components in a highway vehicle gas turbine engine and thus reduce engine fuel consumption. Ceramic components permit increased engine operating temperatures which improve engine cycle efficiency. An initial program milestone has been achieved as ceramic components are operating over the road in a gas turbine powered truck which is available for demonstration. In preparation for this demonstration, the silicon carbide nozzle vanes and aluminum silicate regenerator disks were operated in a turbine powered truck over city streets, interstate highways, road hazards, Belgian block and rough road courses. Both components emerged from this testing in completely serviceable condition. Overall, a total of 4484 operating hours have been accumulated in this program, representing nearly 250,000 miles of vehicle operation at 1900°F turbine inlet temperature. Included are over 400 hours of successful transit coach durability subjecting silicon carbide vanes and alumina silicate regenerator disks to far more accelerations/decelerations (thermal shocks) than the composite truck cycle used for the other engine durability testing. Alumina silicate regenerators experience now totals 4484 hours and reaction bonded silicon carbide vanes 1829 hours. Design of the 2070°F engine continues with the ceramic gasifier nozzle, turbine tip shroud and gasifier turbine blades already being fabricated. Supporting this design and fabrication, has been process development using a prototype blade and compliant layer testing using a ceramic coupon duplicating the blade attachment. Materials characterization activities have resulted in initial design data definition of reaction bonded silicon carbide, reaction bonded silicon nitride, sintered alpha silicon carbide and sintered silicon nitride. Further, the design to be used with ceramic materials has been defined including analysis techniques and statistical treatment of materials strength data. Evaluation of second and third generation ceramic parts and test bars has indicated that process development activities are increasing the realizable strength of ceramics. Testing of several abradable layer samples has been very encouraging with parts now being fabricated for full scale evaluation. Oxidation resistance tests have been initiated on candidate materials for 2070°F operation indicating operation to be feasible without application of resistant coatings.