The wave rotor is a device capable of increasing the pressure of a fluid by deploying shock waves in a transient process. The operation principle is based on the shock tube where shock waves, rarefaction waves and contact waves result from the mixture of fluids with different levels of total pressure. The incorporation of a wave rotor into a gas turbine increases the machine thermal efficiency and reduces fuel consumption, thus allowing the development of new environmentally friendly technologies. The preliminary design of a wave rotor can be achieved by following two fundamental steps. Firstly, it is necessary to carry out a thermal analysis of the cycle in order to obtain the fluid state at each port of the device, secondly to track the different waves generated during the process in order to determine the dimensionality of the wave rotor. The thermal analysis can be accomplished if the performance of the wave rotor is predicted in advance, to set the trajectory of the cycle. The performance prediction can be obtained from the analytical solution of the one-dimensional equations used to describe compressible flow, in a gas dynamic evaluation. Among the available alternatives to perform the gas dynamic analysis, this work considers the algorithm of Weber, because it has proven to be robust by ensuring the mass balance across all the device ports, and also as this technique has not been used previously to evaluate the performance of propulsion gas turbines. In this study, four thermal cycles of gas turbine with a double expansion through-flow wave rotor were considered. These configurations come from changes of some processes in the thermal cycle to a turbofan implemented in business jets, which is set as the baseline engine. In each cycle the wave rotor is exposed to different velocities, expressed as Mach numbers, of the injected air that comes from the compressor, as well as different temperature ratios between this air and the gases that come from the combustion chamber in order to evaluate changes in the overall efficiency of the cycle and the specific thrust. The results obtained from this study show that not all the possible cases can be implemented in propulsion gas turbines, and none of the cases that prove to be suitable has a single point of operation. Rather they have a range of operations with maximum specific thrust and minimum specific fuel consumption, located at different operation conditions.
Gas-Dynamic Analysis of Processes in a Small-Sizes Two-Stroke Combustion Engine
