The Republic of Star Island - Solving the problems inherent with motorized vehicles

I am a big proponent of finding renewable sources of energy. I would wager that even in my envisioned car-free cities, there would be need for motorized vehicles to do important jobs, and they will need a portable source of fuel that may have to be liquid and combustible (i.e. gasoline). That is why I support the concept of algae gas. Algae gas is supposed to be carbon-neutral. This is how I envision that happening.

Exhaust would flow from your tailpipe into a compression chamber that you could buy and fit to your vehicle. When you stop for gas, you will then also have to empty the compression chamber. (It could ding to remind you, even!) The exhaust gases from your engine (mostly nitrogen, carbon dioxide, and water)  would be fed back into a system where algae are grown to produce more fuel. It's a much better idea than just letting the fumes go into the air and contribute to the depletion of the ozone layer and the changing of our climate.

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This is my concept for a mobile crane that would be used to help build skyscrapers. Instead of it being a massively tall structure itself, this machine would crawl up a building under construction, lift pieces to the top, and at the end of the day, use its hook to repel back down the building, sort of like how a spider uses its web lines to descend from its web. If it ran on liquid fuel, it would also have an emissions tank.