Air Injection System: Operation
This system uses a jet valve that is used along with intake and exhaust valves. Jet valve is used for pulling out jet air (super lean mixture) in combustion chamber.
Jet valve assembly consists of the jet valve, jet body and spring. Jet valve assembly is screwed into jet piece which is press fitted in cylinder head with jet opening toward spark plug.
A jet air passage is provided in carburetor, intake manifold and cylinder head. Air flows through 2 intake openings near primary throttle valve of carburetor.
Air flows through passage in intake manifold and cylinder head, flows through jet valve and jet opening into combustion chamber. Jet valve is actuated by same cam and rocker arm as intake valve.
Jet and intake valve open and closes almost simultaneously. On intake stroke air/fuel mixture flows through intake valve port into combustion chamber.
At the same time, jet air is forced into combustion chamber from the pressure difference between jet air intake openings in carburetor throttle bore and jet opening of jet piece as piston moves down. See Fig 1 .
When throttle valve opening is small during idling or light load, a large pressure difference is produced. As piston moves down, it causes jet air to flow into combustion chamber rapidly.
Jet air flowing out of jet opening expels residual gases around spark plugs creating a good ignition condition. When throttle valve opening is increased, more air/fuel mixture is pulled in from intake valve port so that pressure difference is reduced and less jet air is forced in.
The jet air swirl diminishes with increased throttle valve opening, but intensified inflow of normal intake air/fuel mixture can satisfactorily promote combustion.