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Ultra-High-Energy-Density Converter for Portable Power

B. Schneider, M. Bruderer, D. Dyntar, C. Zwyssig, M. Diener, K. Boulouchos, R. S. Abhari, L. Guzzella and J. W. Kolar Swiss Federal Institute of Technology Zurich Physikstrasse 3, 8092 Zurich, Switzerland

Tel +41-44-6322837, Email zwyssig@lem.ee.ethz.ch

Abstract

Mesoscale gas turbine generator systems are a promising solution for high energy and power density portable devices. This paper presents an overview of a two-stage system with a power output of 100 W. There is a need for catalytic combustion and new ceramic materials. An existing turbine expander and a compression system are downscaled and a high-speed test-bench setup for the electrical system has been built. A simulation toolbox for small thermal machines and model-based control and diagnostics are developed.

1. INTRODUCTION

The increasing need for high energy density portable power devices has led to intense research and development efforts on mesoscale systems with power outputs up to a hundred Watts [1]. Gas turbine generator sets offer advantages over battery based portable power systems due to the higher chemical energy density of fuel. In contrary to other international mesoscale gas turbine projects the basic setup of the envisaged system has two compressor/turbine stages. A configuration with two shafts has the advantages of a higher possible pressure ratio than with a single shaft system, which improves the overall efficiency of the system. With an increased efficiency and a fixed total system mass (including fuel) the allowed mass of the machine increases and compensates for the drawback of a more complex system. Assuming a total system mass of one kilogram the relationship between overall system efficiency and the maximum possible machine mass (system mass without fuel) for butane fuel is shown in Figure 1. If the system has a total efficiency of 8% then the required fuel for the 10 hour operation of the machine already takes up the whole weight – therefore nothing is left for the machine itself. The gradient of

the available machine mass is very high in the 10% to 20% efficiency region – even very small gains in the system efficiency give room for a much heavier machine design.

This paper presents the considerations for a two stage gas turbine system according to Figure 2. The goal is an integrated system with an electrical power output of a hundred Watts over ten hours in a volume of one litre and a mass less than one kilogram, including fuel. The paper identifies challenges in the five areas combustion, compressor and turbine design, materials, control and modelling and electrical system design. Furthermore, a model library for predicting pressures, efficiency and temperatures is presented.

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Figure 2.

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Figure 1. Trade-off between overall efficiency and available mass for the machine for a fixed total system mass of 1 kg and butane fuel.

Setup of a two-stage gas turbine system.

Centrifugal Compressor

Image | Ultra-High-Energy-Density Converter for Portable Power



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