Fuel injection plugs

[Greg Hermann]

>What is the point of direct injection?  All it does is make the operating
>conditions on the injector more severe.  Direct injection requires injecting
>only during the intake stroke.

Orbital injects during the compression stroke, during the lower part of it,
over only about 30 to 50 crank degrees. They use air to inject and atomize
the fuel from a very small pre chamber, which is, in turn, fed by a
conventional fuel injector.

This provides some time for mixing during
>compression.

The finer atomization (under 10 micron average droplet size) given by the
air allows good dispension of the fuel during the remainder of the
compression stroke. Timing of injection AFTER closing of the intake valve
would certainly avoid having the fuel displace any oxygen!

 That would be a lot of gas injected in a very short time.
>Less than 180 degrees of crank, probably less than 100 deg.

As stated above, 50 degrees or less.

 The gaseous
>fuel would take up volume the same as if it were carbureted.

Not if injected after the intake valve is closed, as is the case with
Orbital style injection timing.

It might be possible to inject liquid --not gaseous--propane directly , and
dispense with the air boost, if one had injectors that would stand high
enough pressure AND if you could keep the liquid propane below its critical
temperature (206 degrees F.).
This would take rather trick injectors, and quite likely, refrigeration of
the liquid fuel. With reliably cold liquid fuel, the pressures would be
within the capabilities of current injectors.

BUT--it COULD work, and work well!

Orbital also plays some games with their injection timing (as well as
aiming) at light loads so to stratify the charge and gain some part
throttle efficiency.

Regards, Greg