October 2007
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The Jet-powered Car

I had a really long discussion about car engines with my co-worker today. He has tons of information locked in his head about internal combustion design. We touched on valve and cylinder design, compression ratios, cam design. Discussed all the ways that race teams have tried to optimize fuel delivery, from alternative valve designs (rotary, spinning cylinder, spinning disk with holes, solenoid, etc..) so that standing waves in the spring don’t float the valve, and so that space isn’t wasted on the valve stem, and so that timing can be made more computerized (independent control for each cylinder) by removing the mechanical linkage to the cam shaft. It turns out that they shape the delivery tubes so that the compression/rarefactions that propagate through the inlet and outlet system are designed so that just when one delivery valve has to open up, a compression wave is standing right behind it pushing that fuel/air into the chamber, and just when an exhaust valve needs to open up a vacuum is being pulled by the exhaust from a separate cylinder. I think that all this design gets frighteningly complicated.

Finally I decided that the internal combustion engine just has way too many parts and too high tolerance, and requires too much active control to keep running optimally. So I think that vehicles should have an engine with continuous burn. This comes in two popular camps: the Jet Engine, the Steam Engine, and the Stirling Engine.

Now since a steam engine requires a working fluid and all sorts of other stuff (boiler, radiator if water is to be recycled, pistons or steam turbine, etc..) it quickly becomes just a complicated as the internal combustion. Plus, I think the fastest you could get the car warmed up and running would be about 30 seconds. (which you should be doing anyway on cold, winter days).

The Stirling Engine is good but it’s primary usefulness is for really low temperature differentials. And it would also require a trapped working fluid and some pistons. Too many working parts.

The Jet Engine has gotta be the way to go. They unfortunately like to spin at really high rpm (80,000) and so have tolerance and balance issues. But, if you could make a lower rpm version (10,000) then attach that to a good generator, then the car on could run solely on electric motors. This has all the advantages of electrical power distribution: extreme and perfect acceleration, drive by wire, rapid response to traction control, regenerative breaking, etc… Also, jet engines can be made really quiet by ducting the exhaust through a manifold. All it requires is that air move smoothly through the engine at a fairly good clip. The most complex part about the entire car would then be the fan assembly, and computers/sensors take care of everything else. Also, the engine could be run at optimal fuel efficiency all the time, and isn’t as sensitive to the type of fuel. As a bonus, the generator could probably be made to double as the starter-motor.

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