Quote:
Originally Posted by milt
Exhaust gas turbo charging on a 2-cycle would not be efficient. I wonder if a mechanical blower would be good.
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I've looked into this in the past. Turbocharging a conventional 2 stroke gasoline engine would be very difficult.
Both theoretically could be made to work but both would have engineering limitations.
An exhaust driven turbo on a 2 stroke could pose problems due to back pressure, but it's all relative. Delta P.
the intake charge forces the exhaust out of the cylinder. Increase the intake pressure and it mostly compensates for the increase in back pressure.
If you increase the intake pressure that would also help to evacuate the exhaust overcoming the resistance from the turbo.
The problem with that would be the turbo efficiency. Most turbo compressers are only about 55% efficient. So if it was putting out 7 psig boost, it could take up to 10 psig of exhaust pressure to spin it. that means the cylinder would not be evacuated very well.
A 2 stroke diesel works because of the very high compression and boost levels, and having some left over exhaust in the combustion chamber actually helps ecomony and the dieseling process. Sure it robs horsepower but as long as it is controlled it is an accepted trade-off. Conventinal intake valves also help.
Serious port timing modifications would be necessary on both types of systems to prevent large amounta of unburned air/fuel from going out the exhaust and it might require computer-controlled variable exhaust ports to make it work well (slide valves) but it is do-able.
The other issue would be sealing the case.
Most two stroke cases are not designed to contain positive pressure (above atmospheric). That would have to be addressed, a mechanical seal on the crankshaft would probably take care of that.
The reed valves would probably have to be modified also.
It would definately not be a bolt on type of thing.