Pezhman Akbari

A Review of Wave Rotor Technology and Its Applications

The objective of this paper is to provide a succinct review of past and current research in developing wave rotor technology. This technology has shown unique capabilities to enhance the performance and operating characteristics of a variety of engines and machinery utilizing thermodynamic cycles. Although there have been a variety of applications in the past, this technology is not yet widely used and is barely known to engineers. Here, an attempt is made to summarize both the previously reported work in the literature and ongoing efforts around the world. The paper covers a wide range of wave rotor applications including the early attempts to use wave rotors, its successful commercialization as superchargers for car engines, research on gas turbine topping, and other developments. The review also pays close attention to more recent efforts: utilization of such devices in pressure-gain combustors, ultra-micro gas turbines, and water refrigeration systems, highlighting possible further efforts on this topic. Observations and lessons learnt from experimental studies, numerical simulations, analytical approaches, and other design and analysis tools are presented.

Review of Recent Developments in Wave Rotor Combustion Technology

For some decades, efforts have been made to exploit nonsteady combustion and gas dynamic phenomenon. The theoretical potential of nonsteady-flow machines has led to the investigation of various oscillatory flow devices such as pulse detonation engines, wave rotors, pulse jets, and nonsteady ejectors. This paper aims to provide a progress review of past and current research in developing a particular combustion concept: the wave rotor combustor. This pressure-gain combustor appears to have considerable potential to enhance the performance and operating characteristics of gas turbine and jet engines. After attempts in the mid-twentieth century were thwarted by mechanical problems and technical challenges identified herein, recent successes in Switzerland and efforts in the United States benefited from design expertise developed with pressure-exchange wave rotors. The history, potential benefits, past setbacks, and existing challenges and obstacles in developing these nonsteady combustors are reviewed. This review focuses on recent efforts that seek to improve the performance and costs of future propulsion and power-generation systems.

Preliminary Study of a Novel R718 Compression Refrigeration Cycle Using a Three-Port Condensing Wave Rotor

Using a novel 3-port condensing wave rotor enhancing the turbocompression in a R718 refrigeration cycle, which uses only water as a refrigerant, has been introduced. The wave-rotor implementation can increase efficiency and reduce size and cost of R718 units. The condensing wave rotor employs pressurized water to pressurize, desuperheat, and condense the refrigerant vapor—all in one dynamic process. The underlying phenomena of flash evaporation, shock wave compression, desuperheating, and condensation inside the wave rotor channels are described in a wave and phase-change diagram. The thermodynamic process is shown in pressure–enthalpy and temperature–entropy diagrams. A computer program based on a thermodynamic model was generated to evaluate the performance of R718 baseline and wave-rotor-enhanced cycles. The effect of some key parameters on the performance enhancement is demonstrated as an aid for optimization. A performance map summarizes the findings. It shows optimum wave rotor pressure ratio and maximum relative performance improvement of R718 cycles by using the 3-port condensing wave rotor. DOI: 10.1115/1.1850503

UTILIZING WAVE ROTOR TECHNOLOGY TO ENHANCE THE TURBO COMPRESSION IN POWER AND REFRIGERATION CYCLES

The objective of this paper is to review and suggest wave-rotor applications in power generation and refrigeration systems. The emphasis is on recent investigations performed by the authors for a microturbine (30 kW) and a novel enhancement of a state-of-the-art water (R718) compression refrigeration cycle. The results of thermodynamic analyses performed for the small gas turbine topped with a 4-port wave rotor show that engine overall efficiency and specific work may increase by up to about 33% without changing the compressor. Expecting similar advantages, it is suggested to use wave rotors in novel R718 compression refrigeration systems. This also introduces a new concept of a condensing wave-rotor that employs pressurized water to both (1) additional rise the pressure of the vapor and (2) desuperheat and condense it, all in one dynamic process. Adding the condensing wave-rotor to the refrigeration cycle allows for a lower pressure ratio of the compressor, which is crucial for the R718 chiller technology. Some structural and economic advantages of the proposed system are mentioned.Copyright

Performance Enhancement of Microturbine Engines Topped With Wave Rotors

Significant performance enhancement of microturbines is predicted by implementing various wave-rotor-topping cycles. Five different advantageous cases are considered for implementation of a four-port wave rotor into two given baseline engines. In these thermodynamic analyses, the compressor and turbine pressure ratios and the turbine inlet temperatures are varied, according to the anticipated design objectives of the cases. Advantages and disadvantages are discussed. Comparison between the theoretic performance of wave-rotor-topped and baseline engines shows a performance enhancement up to 34%. General design maps are generated for the small gas turbines, showing the design space and optima for baseline and topped engines. Also, the impact of ambient temperature on the performance of both baseline and topped engines is investigated. It is shown that the wave-rotor-topped engines are less prone to performance degradation under hot-weather conditions than the baseline engines.

Implementation of 3-port condensing wave rotors in R718 cycles

The use of a novel 3-port condensing wave rotor is suggested to enhance the turbocompression in a refrigeration cycle that works only with water (R718) as a refrigerant. Although the implementation of such a wave rotor essentially reduces the size and cost of R718 units, their efficiency may also be increased. The condensing wave rotor employs pressurized water to pressurize, desuperheat, and condense the refrigerant vapor, all in one dynamic process. The underlying phenomena of flash evaporation, shock wave compression, desuperheating, and condensation inside the wave rotor channels are described in a wave and phase-change diagram. The thermodynamic process is shown in pressure-enthalpy and temperature-entropy diagrams. Based on the described thermodynamic model, a computer program was generated to evaluate the performance of R718 baseline and wave-rotor-enhanced cycles. The effect of some key parameters on the performance enhancement is demonstrated as an aid for optimization. A performance map summarizes the findings. It shows optimum wave rotor pressure ratio and maximum relative performance improvement of R718 cycles by using the 3-port condensing wave rotor.

Performance improvement of small gas turbines through use of wave rotor topping cycles

Results are presented predicting the significant performance enhancement of two small gas turbines (30 kW and 60 kW) by implementing various wave rotor topping cycles. Five different advantageous implementation cases for a four-port wave rotor into given baseline engines are considered. The compressor and turbine pressure ratios, and the turbine inlet temperatures vary in the thermodynamic calculations, according to the anticipated design objectives of the five cases. Advantages and disadvantages are outlined. Comparison between the theoretic performance (expressed by specific cycle work and overall thermal efficiency) of wave-rotor-topped and baseline engines shows a performance enhancement by up to 33%. The results obtained show that almost all the cases studied benefit from the wave-rotor-topping, but the highest gain is obtained for the case in which the topped engine operates with the same turbine inlet temperature and compressor pressure ratio as the baseline engine. General design maps are generated for the small gas turbines, showing the design space and optima for baseline and topped engines.Copyright

PERFORMANCE INVESTIGATION OF SMALL GAS TURBINE ENGINES TOPPED WITH WAVE ROTORS

A performance analysis is performed for a small turbojet engine topped with various wave rotor cycles. Five different advantageous implementation cases for a four-port wave rotor into the given baseline engine are studied. The compressor and turbine pressure ratios, and the turbine inlet temperatures vary in the thermodynamic calculations according to the anticipated design objectives of the five considered cases. Advantages and disadvantages are outlined. Comparison between the theoretic performance results of wave-rotor-topped engines and the baseline engine shows a significant performance enhancement for almost all the cases studied. The highest gain is obtained for the case in which the topped engine operates with the same turbine pressure ratio, inlet temperature and the same physical compressor like that of the baseline engine. A general design map is generated showing the design space and optima for the baseline and topped engines.

An Application of Wave Rotor Technology for Performance Enhancement of R718 Refrigeration Cycles

** § A number of technical challenges have often hindered the economical application of refrigeration cycles using water (R718) as refrigerant. The novel concept of condensing wave rotor provides a solution for performance improvement of R718 refrigeration cycles. The wave rotor implementation can increase efficiency and reduce size and cost of R718 units. The condensing wave rotor employs pressurized water to pressurize, desuperheat, and condense the refrigerant vapor - all in one dynamic process. In this study, the underlying phenomena of flash evaporation, shock wave compression, desuperheating, and condensation inside the wave rotor channels are described in a wave and phase-change diagram. A computer program based on a thermodynamic model is generated to evaluate the performance of R718 baseline and wave-rotor enhanced cycles. The detailed thermodynamic approach for the baseline and the modified cycle is described. A generated performance map summarizes the findings.

Gas dynamic design analyses of charging zone for reverse-flow pressure wave superchargers

The paper is focused on a comprehensive and systematic gas dynamic analysis of the high-pressure phase (charging zone) of pressure wave superchargers. The procedure is documented for a four-port reverse flow (RF) wave rotor, the typical configuration for engine wave superchargers, also named Comprex. A one-dimensional analytical gas dynamic model is employed to calculate flow characteristics inside the channels. Existing normal shock wave equations along with isentropic relations for expansion waves are used for calculations. Useful design parameters such as cycle timing and port widths are determined by formulating traveling times of the waves inside the channels. The gas dynamic study of the internal wave process demonstrates its fundamental dependence on the externally imposed compression ratio of the pressure wave supercharger.Copyright