Ahmed Ibrahim


Recently, immense research work was done on the thermoacoustics power converters for their great potential in generating electricity by different types of heat sources, including solar energy, waste heat as well as conventional fuels. This work studies the performance of the linear alternator which is the part responsible for converting the acoustic power generated by the thermoacoustic engine into electric power. This work encompasses three parts: the first part is an analytical model that consists of algebraic equations that estimate the main acoustic, mechanical and electrical performance indices of the linear alternator and the relationships between them under linear loading case. These equations are experimentally validated under different conditions. These equations are used to analyze the effects of the operation conditions such as operation under mechanical resonance and electrical resonance, the values of linear alternator parameters and the load parameters on the performance of the linear alternator. This part of work introduces the relationship between the effective inductance of the linear alternator and the mechanical stroke. Additionally, this part introduces an optimization for the piston area to achieve the minimum sum of the mechanical motion loss and the Ohmic loss and an optimization for the load resistance to achieve the maximum electric power in the load and to achieve the maximum acoustic-to-electric conversion efficiency. The second part of this work is an experimental parametric study using an experimental setup that was built for testing the linear alternator over a wide range of the thermoacoustic-power-conversion conditions that cannot be experimentally achieved in the case of testing the linear alternator with thermoacoustic engine. The parametric study covers the performance of the linear alternator under linear loading case and non-linear loading case. The effects of operating frequency, input dynamic pressure ratio, mean gas pressure, gas mixture, electric load value and the value of the power-factor-correcting capacitor on the performance indices are studied under the two types of loads. The results of the parametric study in the linear load case are compared to results of the analytical model and DELTAEC simulations and good agreement was found. The third part of this work is a sensitivity analysis that utilizes design-of-experiment methodology to estimate how the factors and their combined interactions affect the performance indices of the linear alternator under linear loading. The results of the study build a comprehensive study about the linear alternator performance under thermoacoustic-power-conversion conditions. The result are useful to properly select a linear alternator for an existing engine, or vice versa and to match the resulting system to an electric load. The results can be used to select the operating conditions that result in large generted power and or large efficiency. The results can be used to control the operating conditions in the correct proportions to achieve a certain required performance index, while observing the effects on other indices.


Mechanical Engineering Department

Degree Name

MS in Mechanical Engineering

Date of Award


Online Submission Date

November 2018

First Advisor

Abdel-Rahman, Ehab

Committee Member 1

Serag Eldin, Mohamed Amr

Committee Member 2

Essawey, Abdelmaged

Document Type



167 p.


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The work that this thesis encompasses was made possible with the support of many individuals and organizations. First of all, I would like to thank my advisor Prof. Ehab Abdel-Rahman the head of the Thermoacoustics research team who provided me and the rest of the team with the needed scientific guidance and advanced facilities in the Thermoacoustic Research Lab throughout many years of research. Thanks also to my advisor Prof. Mohamed Amr Serag-Eldein who helped me a lot with his long and strong experience in the renewable energy field to produce this thesis work. For sure I would like to thank my advisor Dr. Abdelmaged H. Ibrahim Essawey whose experience, flexibility, technical guidance, and day-to-day follow up helped me produce the results of this work and made it easier to get over the many barriers in the field of the Thermoacoustics and linear alternators. I also have a great deal of gratitude for Prof. Steven Garrett (Penn State University) and Dr. Kai Wang (Imperial College) whom knowledge and experience in thermoacoustic engines and their applications are great. Their prompt replies on my questions enabled me to significantly enhance the analytical model. Additionally, for sure I would like to thank Prof. Gregory W. Swift (Los Alamos Labs) for his great help in the modeling of the load resistance and the power-factor-correcting capacitor in DELTAEC software. I am very thankful to John Corey, Phillip Spoor and Gordon Miller of Q-Drive (Rix Industries, Chart Industries in the past) for the technical support they provided on many aspects of linear alternators. For sure, I would like to thank Dr. Islam Ramadan who assisted on the numerical simulations using DELTAEC software, Eng. Moamen Bellah Abdelmawgoud who built the initial form of the experimental setup, and Eng. Khaled El Beltagey who assisted in the development of the experimental setup along the years. I am also thankful to every member in the thermoacoustic research team for the fruitful discussions, technical support, and the great time I had during this research period. The American University in Cairo provided access to numerous scientific resources, a research grant, and two conference grants that enabled me to greatly develop this work and assisted in the building, continuous and smooth running of the experimental setup and presenting nine publications in international conferences and meetings. This work was possible with the financial assistance of the European Union. The contents of this document are the sole responsibility of the master student and can under no circumstances be regarded as reflecting the position of the European Union. I am very thankful for the Egyptian Academy of Scientific Research and Technology which partly funded the development of the initial form of the experimental setup used. This work is a new step of my research work in the space systems field that I have started under supervision of Dr.Mohammed Khalil Ibrahim, Prof. Atef Omar Sherif, Prof.Bahy-El Dein Argon and Dr.Ayman Kassem in Space Systems Technology Laboratory (SSTL), aerospace engineering department-Cairo University. I would like to thank all of these professors and the previous leader of this laboratory Eng.Samy Amin (Avelabs). Many thanks go to my parents (Dr.Yassin Ibrahim and Mrs.Hanim El Saadany) who give me all what they have of love and support.