Half a croissant, on a plate, with a sign in front of it saying '50c'
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Two stroke four stroke hybrid

Best of both worlds
  [vote for,

This idea would be applied to single cylinder motocross bikes where space and weight are of large importance. I won't go into great detail on the drawbacks of each engine unless someone needs me to for understanding. The main drawbacks of two-stroke engines are the mixing of exhaust and intake gases, as well as the effective stroke being shorter than the actual stroke of the piston due to the exhaust port being in the cylinder. The main drawback of a four stroke is that intake only occurs for 180 degrees of the total 720 degrees of the engine cycle.

My engine uses case reed induction like a two stroke, but instead of the gas/oil/air mixture going up through the cylinder transfer ports into the combustion chamber, the mixture goes from the crankcase to a chamber near the intake valves in the head. The cylinder head would be much like a current four stroke head, of course doing away with poppet valves and using a rotary setup similar to the Coates engine (see link). This engine would still be a four stroke, but you're using the underside of the piston and the crankcase as a positive displacement supercharger. You would need another reed valve between the intake chamber and the crankcase to prevent backflow. This engine would undergo intake for 360 out of 720 degrees of the cycle. This won't necessarily be more efficient than a normal four stroke due to increased pumping losses, but it will definitely yield more power per cc of displacement compared to either a four stroke or two stroke. Even if the peak hp numbers are a little shy of the same displacement two stroke, the powerband will be much wider and it will burn cleaner due to isolation of the intake and exhaust gases. This is better than an external supercharger or turbo due to being lighter and more compact. Motocross bikes have to be light and well balanced and there just isn't any room for a conventional turbo or supercharger. I hope my explanation is clear enough for everyone to understand.

scarecrow, Jan 13 2004

Coates engine http://www.coatesengine.com/
Rotary valve head [scarecrow, Oct 04 2004]


       I don't see how this differs from a conventional four-stroke engine with rotary valves.   

       How do you get 360 degrees of intake? Does it intake on both downstrokes or on one downstroke and one upstroke?   

       Could you re-write this as:
Upstroke 1: (stuff happens)
Downstroke 1: (stuff happens)
Upstroke 2: (stuff happens)
Downstroke 2: (stuff happens)

       Also, the underside of the piston cannot act as a supercharger. If the piston moves down to increase the volumn of the combustion chamber by 10cc, the volumn in the crankcase under the piston will have been decreased by 10cc.
GenYus, Jan 13 2004

       I still think a supercharger is needed, so I'll hold my croissants and fishbones for a little longer...
croissantz, Jul 18 2004

       I believe a direct-injection 2-stroke solves this problem.
whlanteigne, Sep 26 2005


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