Can anyone suggest a topic for my mechanical engineering undergraduate thesis?

Question

the topic or study should be purely mechanical in nature please
and something that can be done with the a small budget if possible (something fit for an undergraduate student)

Answer 1

You should write it on something that you are interested in.
Where do your interest lie? in machine design; in metallurgy; in mechanical equipment like pumps, compressors, turbines, etc; in the HVAC field; in power plants?
Pick a subject, research it, and then write about and design it.
You could pick a power plant and describe the process including flow sheets, and then describe all the different types of equipment that are required and the advantages and disadvantages of different types of equipment.
Or you could pick a large commercial HVAC system and do the same thing.