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W. P. J. Visser

e-mail: wvisser@xs4all.nl

S. A. Shakariyants

e-mail: savad@mtt-eu.com

M. Oostveen

e-mail: mark@mtt-eu.com

Micro Turbine Technology MTT b.v., De Rondom 1, 5612 AP Eindhoven, The Netherlands

1 Introduction

During the last few decades, several attempts have been made to develop microturbines with efficiency levels close to those of larger gas turbines. Various interesting applications have emerged for both aircraft propulsion and power generation. Particularly for microturbines below 100 kW, many developments have failed to obtain sufficient efficiency, reliability, and cost effectiveness to be successful for the market. The major technical factors that chal- lenge microturbine development programs are the small-scale ef- fects:

• low Reynolds numbers in the turbomachinery flow passages causing relatively high viscous losses,

• relatively high tip clearances due to manufacturing toler- ances and bearing limitations

• large area-to-volume ratios resulting in high heat losses and inadvertent heat transfer to the compressor

• relatively high auxiliary system losses due to the low power output level

The turbomachinery dimensions for rated power levels lower than 10 kW become very small. When using the Balje 1 design rules for characteristic rotor speed and diameter, a 3 kW gas tur- bine optimal radial compressor would have a diameter in the order of 30–40 mm and a speed of several 100,000 rpm.

Another factor is costs. Development of efficient turbomachin- ery optimized for a particular cycle is very expensive and, in the micropower generation market, can only be justified with very large production volumes. An interesting opportunity to get around this cost problem is to use small automotive turbocharger components. During the last decade, small turbocharger turboma- chinery has become sufficiently efficient for gas turbine cycles and cost price is low due to the very large production volumes.

At MTT, a conceptual design study indicated that with the smallest off-the-shelf turbocharger turbomachinery, a 3 kW recu-

Contributed by the International Gas Turbine Institute IGTI of ASME for pub- lication in the JOURNAL OF ENGINEERING FOR GAS TURBINES AND POWER. Manuscript received April 13, 2010; final manuscript received June 1, 2010; published online November 22, 2010. Editor: Dilip R. Ballal.

perated microturbine with a thermal efficiency of at least 16% could be developed. If this concept can be mass produced at low prices corresponding to automotive parts, a very competitive op- portunity emerges in small-scale CHP combined heat and power applications.

2 Applications

The current development program focuses on a heat demand driven micro CHP system to replace heating boilers for house- holds and small businesses. During the development, large atten- tion is given to cost price, reliability and low maintenance costs. Domestic micro CHP offers significant energy saving potential. The system payback time target is 2–4 years depending on the user’s profile. Projected CO2 savings per installed system are up to 6 tons per year.

While natural gas is the initial fuel of choice for the domestic micro CHP application, liquid fuels such as heating oil or diesel are required for the CAP truck parking heater/APU application and for domestic micro CHP at locations without access to a natu- ral gas distribution grid. A separate development program has started for the development of a clean combustor for liquid fuels that will comply with future emission requirements.

3 Conceptual Design

Off-the-shelf turbocharger technology offers an interesting op- portunity to develop low-cost microturbines. The compressor, tur- bine, and sometimes bearing unit can be selected and matched without much modification. With the addition of a combustor, fuel system and control unit, a simple turbojet engine can be built. This concept is used for very small aircraft such as model planes. With a generator coupled to the shaft, a turboshaft engine is obtained for producing electrical power instead of thrust. With a recupera- tor, the efficiency of a turboshaft engine can be significantly in- creased, especially at the low cycle pressure ratios of turbocharger-based microturbines. This is due to the consequent relatively high turbine exit temperature providing good opportu- nity to recover heat. Off-the-shelf turbochargers are available for both petrol and diesel engines with rated air flows down to 30 g/s.

Laboratory condition tests have indicated turbine inlet tempera- tures up to 1000 ° C are feasible with the customary Inconel 713

Development of a 3 kW

Microturbine for CHP Applications

Combined heat and power (CHP) concepts for small-scale distributed power generation offer significant potential for saving energy and reducing CO2 emissions. Microturbines are an interesting candidate for small CHP systems with advantages in terms of perfor- mance, size, noise, and costs. MTT is developing a 3 kW recuperated microturbine for micro CHP applications for large households and for truck combined APU-heating sys- tems. To minimize costs, off-the-shelf automotive turbocharger technology has been used for the turbomachinery. During recent years, turbocharger turbomachinery performance and efficiencies have significantly increased, even for very small sizes. At the same time, efficient high-speed motor-generators have become available at relatively low prices. The development of a concept demonstrator started in May 2008. This program phase in- cluded a cycle analysis and component selection study around off-the-shelf turbomachin- ery, design of a custom combustor, recuperator and generator, and a test program. In this paper, results of the cycle definition, conceptual design and component matching study are presented. Next, the development of a detailed performance model is described and performance prediction results are given. Also, results of the test program and test analy- sis work are presented. Finally, from the conclusion of the demonstrator phase an outlook is given on the prototype design and performance, which will be the next phase of the development program. DOI: 10.1115/1.4002156

APRIL 2011, Vol. 133 / 042301-1 Downloaded 18 Feb 2011 to 131.155.56.82. Redistribution subject to ASME license or copyright; see http://www.asme.org/terms/Terms_Use.cfm

Journal of Engineering for Gas Turbines and Power

Copyright © 2011 by ASME

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