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Ultra Micro Gas Turbines
Roberto Capata
Department of Mechanical and Aerospace Engineering, University of Roma 1,
Faculty of Engineering, Roma
Italy
1. Introduction
1.1 State of art
Object of the present work is the detailed study, in every its aspect, of Ultra-Micro-Gas-
Turbine Generator, that is a power device with high power density. These generators,
although the covered power range oscillates between 100 and 500W, is characterized by
very reduced overall dimensions: this introduces complications in the design and, above all,
the realization of the mechanical components who represents the greater difficulty to
exceed. The advanced searches in this field preview the realization of the characteristic
structures of the machine with high tech systems:
• the impellers, both turbine and compressor, can be manufacturing with silicon,
titanium or special alloys micro laser techniques (figure 1);
• the combustion chambers can be obtained in toroidal spaces with the possible lowest
volume: this involves the necessity to construct fuel injection device technologically
complicated, inside the same combustion chambers; a different model is constituted, in
some NATO devices, by a 2-D geometry combustion chambers (an example is visible in
figure 2);
• the electrical generators are constituted by a highest number of polar braces due to high
rotational speed of the machine (> 100 000 rpm). Their realization is realized by micro
manufacturing of planned rings that have been inserted in the case (for the statoric
part), and the other ring is located on the faces the rotor impeller (usually the
compressor, to avoid the high temperatures problems);
• the rotational speed is within 150 000 ÷ 350 000 rad/s (in some cases > 500.000)
a) b)
Fig. 1. Typical compressor a) and b) turbine D geometry [Epstein 2003]
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