Shock-Expansion Wave Engines — New Directions for Power Production

Abstract

For decades large amounts of money and effort have been spent on conventional turbomachinery development. Initially improvements in performance were rapid. However, in the last two decades better performance of these machines has slowed considerably. Compressor efficiencies have been near their present limits of 88% to 92% for many years. High pressure ratios required of high performance engines are not efficiently produced in the conventional turbomachines. High pressure ratios for high cycle efficiency require many stages of conventional compression. Compressors, especially in small turbomachines, decrease in efficiency as the number of stages increase due to the large amounts of surface area and relatively large leakage passages in the higher pressure stages. The requirement for many stages of conventional compression also results in heavy machines. If high compressor pressure cannot be attained the turbine exhaust gas temperature may be considerably above the compressor discharge temperature; a regenerator or recuperator is then required for acceptable cycle efficiency. This results in considerable complication and high engine weight. Maximum turbine inlet temperatures in conventional machines have also been near their limit for many years. High temperatures and high pressures required for light weight, high efficiency machines are inconsistent with the requirements for high strength materials. To increase permissable turbine inlet temperatures compressor discharge air is used for blade cooling. Use of this air soon reaches its limit because the high pressure cooling air is then not available for power production. Engine power and cycle efficiency begins to decrease and a limit on turbine inlet temperature results. Consequently, new concepts in power and thrust production are required. One class of machines which may alleviate many of the above described problems are the wave rotors or engines (1 thru 15). These operate with time dependent flow in the moving rotor blade passages and steady flow in the stator parts.