Feasibility Study of Integrating Four-Port Wave Rotors into Ultra-Micro Gas Turbines (UMGT)

Abstract

Ultra-micro gas turbines (UµGT) have shown difficulties in obtaining high overall thermal efficiency and output power, resulting from miniaturization. Particularly, obtained compressor efficiencies have been as low as 40-50%, reducing optimum pressure ratios down to about 2. This work presents investigations of the feasibility and potential of integrating four-port wave rotors in microfabricated gas turbines to increase compression efficiency and optimum overall pressure ratio, hence increase overall cycle efficiency and power output. Practical implementation schemes and results of efficiency estimates are shown. The wave rotor efficiency is estimated first by simple extrapolation and then verified by a mathematical model. The model is based on gas dynamic equations for a moving normal shock wave in a channel and considers wall friction of the gas flowing through the channel. Knowing the inlet conditions and the pressure gain across the shock, the overall efficiency of the compression process in a wave rotor channel can be predicted. The results suggest that a compression efficiency in the range of 70-80% can be achieved in ultra-micro wave rotors. Based on thermodynamic cycle analyses a performance map was created that also gives optimum pressure ratios for a typical UµGT application.

Efficiency of shock wave compression in a microchannel

“…The wave rotor integration is most effective if the wave rotor compression and expansion efficiencies are greater than those of the turbomachinery components of the baseline engine. An initial study on the efficiency of the compression process in a wave rotor channel has suggested that values around 70% can be achieved at microscale (Iancu et al 2004). For large-scale wave rotors the value of 83% is consistent throughout the literature.…”

“…The entry data for the model have been introduced based on preliminary thermodynamic calculations of a wave rotor suitable for an UlGT (Iancu et al 2004) and initial thermodynamic parameters used by the MIT group (Kang 2001;Epstein 2004;Frechette et al 2005). The data are found in Table 2.…”

“…The UlGT are expected to be a power source for next generation devices with any number of applications from propulsion to power generation, from aerospace industry to electronic industry. Investigated by only a few research groups all over the world, MIT (Epstein 2003;Epstein et al 1997Epstein et al , 2000Fre`chette et al 2003;Spadaccini et al 2002;Zhang et al 2002), Stanford University (Johnston et al 2003;Kang et al 2004), Michigan State University (Iancu et al 2004), Warsaw University of Technology-Poland (Piechna 2005), ONERA-France (Dessornes et al 2003;Ribaud 2003), The University of Tokyo-Japan and Katholieke Universiteit Leuven-Belgium (Peirs et al 2004a(Peirs et al , 2004b the UlGT have yet to prove their utility. One of the main problems is their low overall thermal efficiency and output, and increased losses due to miniaturization.…”

Hybrid Wave Engine Concept and Numerical Simulation of Engine Operation

“…Many groups of researchers have focused their attention on the design of micro turbine engines in recent years [2,4,[6][7][8]16]. The recent trend towards miniaturization of thermal engines to the centimeter and millimeter scale shows, on the one hand, a high power density of such devices and, on the other hand, a reduction of efficiency due to the downsizing effect [23,25].…”

“…As a solution, the application of unsteady processes has been proposed [1,6,[17][18][19][20]. Closer investigations have shown the applicability of pure unsteady devices for gas compression, but it is also shown that they are practically not applicable for torque generation [21].…”