Explain semi direct injection

[Polarice]

I believe that I understand how a 2 stroke works. Oil, gas, and air are sent into the bottom and forced into the top, burned and shot out of the exhaust. Some of the air, gas, and oil mix is not burned but still shot out the exhaust.

A direct injection is shooting just air and oil into the bottom end. Gas alone is sent to the top only. Very little oil is used to lubricate and therefore very little makes it to the top.

How does the SDI work? Is gas, oil, and air sent into the bottom and gas also sent to the top?

 

[snake]

direct injection is injected directly into the combustion chamber(into cylinder/on top of piston) semi is in the intake and has to go thru the case and transfer ports. not sure about "sdi" ski doos,but I'll bet there is no "direct injection" at all.generally direct injectors create a lot more fuel pressure on their own,where as normal injectors do not create pressure(fuel pump and regulator). an engine is basically just an air pump=suck,squish,bang,blow. hmmmm,bet I'll get some comments on that last line!!

 

[Polarice]

Polaris Cleanfire is also an SDI.

You say semi is in the intake or are you referring to a regular 2 stroke?

 

[srt20]

The injector is in the side of the cylinder. It sprays into the transfer port. Poo CFI.

The doo DI has the injector on the top of the cylinder and sprays on top of piston. Etec.

Poo oils the bottom end then gets pushed up the transfer port and burned into combustion chamber.
The doo oil doesn't have to oil the some (all?) of the crank bearings so it needs less oil. Gets pushed up the transfer port and burned.

New cats are different yet, but closer to poo than doo in design.

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Btw it's not that the charge doesn't get all the way burned then shoved out the exhaust, it's that the new fresh charge coming into the cylinder pushes the old burned charge out and some of that new fresh charge goes out the exhaust with the old.