The C-BRAHMS Project

Bononia University Press; 88-7395-155-4;Peer reviewe

Process development of silicon-silicon carbide hybrid structures for micro-engines (January 2002)

MEMS-based gas turbine engines are currently under development at MIT for use as a button-sized portable power generator or micro-aircraft propulsion sources. Power densities expected for the micro-engines require very high rotor peripheral speeds of 300-600m/s and high combustion gas temperatures of 1300-1700K. These harsh requirements for the engine operation induce very high stress levels in the engine structure, and thus call for qualified refractory materials with high strength. Silicon carbide (SiC) has been chosen as the most promising material for use due to its high strength and chemical inertness at elevated temperatures. However, the state-of-the art microfabrication techniques for single-crystal SiC are not yet mature enough to achieve the required level of high precision of micro-engine components. To circumvent this limitation and to take advantage of the well-established precise silicon microfabrication technologies, silicon-silicon carbide hybrid turbine structures are being developed using chemical vapor deposition (CVD) of thick SiC (up to ~70µm) on silicon wafers and wafer bonding processes. Residual stress control of thick SiC layers is of critical importance to all the silicon-silicon carbide hybrid structure fabrication steps since a high level of residual stresses causes wafer cracking during the planarization, as well as excessive wafer bow, which is detrimental to the subsequent planarization and bonding processes. The origins of the residual stress in CVD SiC layers have been studied. SiC layers (as thick as 30µm) with low residual stresses (on the order of several tens of MPa) have been produced by controlling CVD process parameters such as temperature and gas ratio. Wafer-level SiC planarization has been accomplished by mechanical polishing using diamond grit and bonding processes are currently under development using CVD silicon dioxide as an interlayer material. This paper reports on the work that has been done so far under the MIT micro-engine project.Singapore-MIT Alliance (SMA

An assessment of the aerodynamic, thermodynamic, and manufacturing issues for the design, development, and microfabrication of a demonstration micro engine

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Aeronautics and Astronautics, 2000."September 2000."Includes bibliographical references.Silicon microfabrication is an established technology for the manufacture of integrated circuits and microelectromechanical systems (MEMS) devices such as pressure transducers and accelerometers. Recent advances in silicon microfabrication technology allow the possibility of designing high-precision mechanical devices for power conversion. Micro gas turbine engines (microengines) are one particular application of this technology. These tiny jet engines have immediate application as propulsion systems for Micro UAVs Other envisioned applications include portable electrical power generation for commercial, consumer, and military uses A microengine-based power or propulsion system could offer more than 10x the performance of a battery of the same weight. This would make it an enabling technology for longduration portable computers, high-power mobile phones, and other portable power applications. This thesis describes an assessment of the aerodynamic, thermodynamic, and manufacturing issues associated with the design, development, and microfabrication of an all-silicon demonstration microengine. The design goal is the simplest feasible engine that can demonstrate the micro gas turbine engine concept. This demo microengine integrates high-speed, low Reynold's number turbomachinery, high-speed micro gas bearings, a compact hydrogen combustor, and an innovative turbine cooling scheme into a quartersized turbojet engine with a target thrust of 10 grams. Due to the scale of the device and the nature of the microfabrication process, the engine components are tightly coupled and the design involved a number of system trades not normally encountered in conventional engines. This thesis addresses several of these key design trades and identifies thermo-structural design and manufacturing constraints as the two principal limitations on current microengine design. The thesis also discusses the fabrication development effort and results culminating in a micro turbocharger that has been tested to speeds of up to 30,000 RPM. Rotor imbalance was identified as the probable limit on current operation. Recommendations for future work include development of advanced turbine cooling schemes to improve device efficiency and development improved fabrication capabilities to reduce rotor imbalance.by Jonathan M. Protz.Ph.D

Aero-acoustic performance comparison of core engine noise suppressors on NASA quiet engine C

The relative aero-acoustic effectiveness of two core engine suppressors, a contractor-designed suppressor delivered with the Quiet Engine, and a NASA-designed suppressor was evaluated. The NASA suppressor was tested with and without a splitter making a total of three configurations being reported in addition to the baseline hardwall case. The aerodynamic results are presented in terms of tailpipe pressure loss, corrected net thrust, and corrected specific fuel consumption as functions of engine power setting. The acoustic results are divided into duct and far-field acoustic data. The NASA-designed core suppressor did the better job of suppressing aft end noise, but the splitter associated with it caused a significant engine performance penality. The NASA core suppressor without the spltter suppressed most of the core noise without any engine performance penalty

Definition study for variable cycle engine testbed engine and associated test program

The product/study double bypass variable cycle engine (VCE) was updated to incorporate recent improvements. The effect of these improvements on mission range and noise levels was determined. This engine design was then compared with current existing high-technology core engines in order to define a subscale testbed configuration that simulated many of the critical technology features of the product/study VCE. Detailed preliminary program plans were then developed for the design, fabrication, and static test of the selected testbed engine configuration. These plans included estimated costs and schedules for the detail design, fabrication and test of the testbed engine and the definition of a test program, test plan, schedule, instrumentation, and test stand requirements

Look Out! The Biggest Library Problem

Libraries may lose control of the support, operation, and direction of their institutions because of the popularization of information and accompanying political wrangling. To a large extent, it will be their activism that will determine their viability going forward. If they fail to deal with this situation they may lose control of their destinies. Will we continue to expand and prosper? Case studies

Small Engine Component Technology (SECT) study

Small advanced (450 to 850 pounds thrust, 2002 to 3781 N) gas turbine engines were studied for a subsonic strategic cruise missile application, using projected year 2000 technology. An aircraft, mission characteristics, and baseline (state-of-the-art) engine were defined to evaluate technology benefits. Engine performance and configuration analyses were performed for two and three spool turbofan and propfan engine concepts. Mission and Life Cycle Cost (LCC) analyses were performed in which the candidate engines were compared to the baseline engines over a prescribed mission. The advanced technology engines reduced system LCC up to 41 percent relative to the baseline engine. Critical aerodynamic, materials, and mechanical systems turbine engine technologies were identified and program plans were defined for each identified critical technology

Technology transfer methodology

Information on technology transfer methodology is given in viewgraph form. Topics covered include problems in economics, technology drivers, inhibitors to using improved technology in development, technology application opportunities, and co-sponsorship of technology