Quote Originally Posted by blackburn mark View Post
expansion chamber forms part of the exaust (the bulbus portion of a typical two stoke exaust) the inertia of the exaust gas (in the bulbus section) keeps its momentum forming somewhat of a vacume behind it drawing in the next charge
Traditionally a 2 stroke has the carburettor on the opposite side to the exhaust. The piston goes up producing a partial vacuum in the crank case, the bottom of the piston clears the inlet port and fuel air is sucked in . The piston descends and moments after the piston clears the exhaust it clears the fuel inlets which usually come up the sides connecting the crank case to the combustion chamber. You would think there would be enough heat to light the new fuel but I suppose the explosive decompression cools it somewhat and the mix doesn't really want to light until the pressure is up again. I'm actually rather surprised 2 strokes work at all, if they never existed and someone here came up with the design I'd probably pooh-pooh it.

I suppose you could use a supercharger to get the push, but you do need a push because the pressure must still be well high when the side inlets open.

Using exhaust to create a vacuum is steam locomotive technology but I'd say it could only ever be a helping hand in a 2 stroke, a bit of fine tuning, something to ease the back pressure, not enough to do the recharge.

In a steam train the exhaust comes up the blast pipe, into the smoke box, past the the ends of the fire tubes and up the funnel. What comes out the top is "steam" followed by smoke. What drives it is the valve gear shutting off the exhaust, the air simply doesn't want to stop so it carries on up the funnel drawing on the firebox. Unfortunately a funnel will only pull efficiently at one speed but the old boys knew that and filled the funnel with different size tubes to compensate.