Half a croissant, on a plate, with a sign in front of it saying '50c'
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I like this idea, only I think it should be run by the government.

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Dual-Purpose Valves

Same valves act as exhaust and intake
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In direct-injection engines, only air goes through the intake ports, and the fuel is injected inside the chamber.

Valveless pulsejet engines use the same pipes for inlet and exhaust, and rely on the elasticity of air to determine when it is flowing in or out.

It might be possible to use all the valves in the head of an engine for both intake and exhaust, if the pipes coming out were tuned properly.

I'm not sure what the advantages of this system might be, but it would be a cool engineering exercise and would allow for only one valve at the top.

discontinuuity, Oct 19 2005

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       It would be a modified 2-stroke?
Ling, Oct 19 2005
  

       No, this would be a four-stroke. Although you could probably make a two-stroke version too.
discontinuuity, Oct 20 2005
  

       I don't think this idea will result in greater fuel efficiency.
Cedar Park, Oct 20 2005
  

       Wouldn't you have trouble with ignition timing? All that fuel-air mixture flowing over hot exhaust valves would surely lead to some nasty pre-ignition.
Gordon Comstock, Oct 20 2005
  

       It's direct-injection, so you would only inject fuel when you wanted to have a power stroke.
discontinuuity, Oct 20 2005
  

       OK sorry missed that bit. But having heated (and thus expanded) air might not be such a good thing.
Gordon Comstock, Oct 24 2005
  

       On second thought, I don't think this would work at all. Or if it did, it would just be the same as a two-stroke, many of which use the elasticity of air to control exhaust flow.
discontinuuity, Mar 01 2006
  

       After reading this again, I realized that pulse jets really have no compression phase. If this was ever a well-though-out idea, I don't remember how it worked.
discontinuuity, Jan 24 2007
  
      
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