Research Papers: Gas Turbines: Microturbines and Small Turbomachinery

Design Overview of a Three Kilowatt Recuperated Ceramic Turboshaft Engine

[+] Author and Article Information
Michael J. Vick

Vehicle Research Section, Code 5712, U.S. Naval Research Laboratory, Washington, DC 20375michael.vick@nrl.navy.mil

Andrew Heyes

Department of Mechanical Engineering, Imperial College London, London SW7 2AZ, UKa.heyes@imperial.ac.uk

Keith Pullen

School of Engineering and Mathematical Sciences, City University London, London EC1V 0HB, UKk.pullen@city.ac.uk

J. Eng. Gas Turbines Power 132(9), 092301 (Jun 07, 2010) (9 pages) doi:10.1115/1.4000585 History: Received March 20, 2009; Revised August 18, 2009; Published June 07, 2010; Online June 07, 2010

A three kilowatt turboshaft engine with a ceramic recuperator and turbine has been designed for small unmanned air vehicle (UAV) propulsion and portable power generation. Compared with internal combustion (IC) engines, gas turbines offer superior reliability, engine life, noise and vibration characteristics, and compatibility with military fuels. However, the efficiency of miniature gas turbines must be improved substantially, without severely compromising weight and cost, if they are to compete effectively with small IC engines for long-endurance UAV propulsion. This paper presents a design overview and supporting analytical results for an engine that could meet this goal. The system architecture was chosen to accommodate the limitations of mature, cost-effective ceramic materials: silicon nitride for the turbine rotors and toughened mullite for the heat exchanger and turbine stators. An engine with a cycle pressure ratio below 2:1, a multistage turbine, and a highly effective recuperator is shown to have numerous advantages in this context. A key benefit is a very low water vapor-induced surface recession rate for silicon nitride, due to an extremely low partial pressure of water in the combustion products. Others include reduced sensitivity to internal flaws, creep, and foreign object damage; an output shaft speed low enough for grease-lubricated bearings; and the potential viability of a novel premixed heat-recirculating combustor.

Copyright © 2010 by American Society of Mechanical Engineers
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Figure 1

Efficiency as a function of pressure ratio for simple and recuperated cycles at high and low turbine inlet temperatures

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Figure 2

FEA results for first principal stress distribution at design point for high-pressure (gas generator) turbine

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Figure 3

Turbine velocity diagram

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Figure 4

Engine assembly. See Table 2 for meaning of numeric labels.

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Figure 5

Compressor shaft assembly

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Figure 6

Complete heat exchanger assembly. Cool air flows radially inward, entering through spaces between outer tubes and leaving through spaces between interior tubes. Hot exhaust enters interior tubes in the axial direction, turns 90 deg, flows radially through internal channels, and turns another 90 deg to leave recuperator flowing axially through ends of outer tubes.

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Figure 7

Geometry of a heat exchanger sector

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Figure 8

Simplified heat exchanger geometry: a stack of annular plates. Air and exhaust flow radially inward and outward, respectively, between alternating plate pairs.

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Figure 9

Computational domain

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Figure 10

Results from finite difference model

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Figure 11

Coupled CFD/thermal-FEA model results




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