microturbines - kth 3.pdf · microturbine lecture, section 3, 2005-04-21, rolf gabrielsson...

Microturbines

2005-04-21Rolf Gabrielsson, Volvo Aero Corporation

Section 3

Microturbine lecture, section 3, 2005-04-21, Rolf Gabrielsson

Microturbines, section 3

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MEMS Gas Turbine Engines

• Micro-Electro-Mechanical-Systems (MEMS) or Ultra-microturbines.Ref.: Alan H. Epstein, ASME GT-2003-38866

• Microturbines 25 – 500 kW

• Small microturbines 1 – 10 kW Example: IHI remote application

• MEMS 10 - 100 W



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MEMS Characteristics

• MEMS based on manufacturing technologies developed by the semiconductor industry

• Diameters of millimetres rather than meters with airfoil dimensions in microns rather than millimetres

• Shirt-button-sized gas turbine



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User Pull - Market interest

• Small portable electronics - computers, GPS receivers, etc require compact energy supplies

• Mobile systems such as robots,air vehicles require increasingly compact power and propulsion

• Hydrocarbon fuels burned in air have 20-30 times the energy density of the best current lithium chemistry-bases batteries Modest system efficiency to compete with batteries

• Development started mid 1990´s

• Main player: MIT,USA



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Thermodynamic scaling• Air intake diameter:100 MW 1 meter100 W 1 mmHowever reduced pressure ratio (2:1 - 4:1), TIT and increases losses means reduced specific power

• Fluid viscous forces - IncreaseSurface area-to volume - IncreaseHowever, usable strength of material - Increase

• Manufacturing constraints means:- Reduced cycle efficiency Increased specific fuel consumption- But better thrust – to weight ratio. ”The cube-square law”



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Thermodynamic scaling

Ref.: Gong, Sirakov, Epstein, Tan “Aerothermodynamics of Micro-turbomachinery”, GT2004-53877, ASME Turbo Expo 2004, Vienna



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Mechanical scaling• Viscous forces larger

film heat transfer coefficient increases Temperature gradients in the structure reduced Helpful reducing stress but makes thermal insulation challenging

• Possibility to use ceramic materials due to size dependent fault-possibility

• Single-crystal semiconductor materials. Usable strength increase with reduced size

• Thermal shock resistance improvedRef: Epstein, ASME GT-2003-38866



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MEMS Gas turbine design for demo-MEMS

• Microturbine technology applies to Silicon, Si• Si loses strength above 950K• Fuel: H2

• Shaft power: 17 W• Design characteristics:Π = 2:1TIT = 950KDcompressor = 8 mmDturbine = 6 mmRotor speed = 1.2 Mrpm

Ref: Epstein, ASME GT-2003-38866



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MEMS Manufacturing

• Old-school designer ”Don´t let the manufacturing people tell you what you can´t do”MEMS design philosophy: ”Design for manufacturing”

• Primary fabrication processes:- Etching of photolithographically planar geometries- Bonding of multiple wafers

• Electronics, motors and sensors- Embedded sensors- Alternating insulation and conducting layers- Vapour deposition or sputtering approaches



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Manufacturing / complete stack




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Turbine design

• Si prototype turbine TIT < 950 K- (MIT has designed for 1600 K)

• Possible turbine performance- Π = 4:1- Tip speed = 500 m/s- Efficiency, total-to static = 50-60%

(compare Microturbine turbine efficiency approx = 85%)



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MEMS combustor


• Fuel : H2 (methane, propane)

• Reaction rate- H2 = 90%- Methane = 60%- Compare large Gt: 99.9%



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Bearings and rotor dynamics

• Electromagnetic and air bearings have been considered

• Electromagnetic bearings up to now not promising

• Gas bearings have advantages such as - No temperature limits- High load- Relatively simple manufacturing

• Gas bearings used in ”microturbines”in the range 30 – 70 kW and turbochargers. Also in gyroscopic instruments



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Examples of hydrodynamic and hydrostatic air bearings




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MEMS materials

Si SiC

Max temperature 950 K 1500 KCost 1 100



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MEMS GeneratorPermanent magnetic high speed generator




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Ongoing technical development

• No reported MEMS operations up to date

• Demonstration of component technology at MIT

• Possible improvements as recuperated cycles with heat exchangers

• MEMS performance:




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Economics and the future• What is required to make millimetre-scale turbines real?

Answer: - Technical feasibility - Must fulfil societal needs

• Power production in short term is aimed at portable applications due to:- Very much larger energy density of hydrocarbon fuel compared to lithium batteries

• In short term, 5 – 10% overall system efficiency is sufficient


microturbines - kth 3.pdf · microturbine lecture, section 3, 2005-04-21, rolf gabrielsson...

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