Geo Au and MIT
The physics of injecting into an atmosphere that is light vacuum is somewhat different from that of the combustion chamber with the piston up. Light vacuum is instead 180psi, the temperature is also elevated from the compression, although that wouldn't impact the physics as much as the turbulence probably would. Plus, we really don't know anything about the air-assisted injector they used (was it as effective at "shearing" the fuel into fine atomization as OCP is?). BUT THE KEY POINT is that the fuel is being drawn into the cylinder as the piston drops. This exposes the mixture to the entire surface of the cylinder bore instead of the just the combustion chamber and piston top. Not only is the surface area comparatively huge, but the time duration is long, giving the fuel plenty of time to form a film on the cylinder bore. Which is then wiped upwards by the piston ring, essentially "pushing it all together" into a virtual "puddle" caught in the gap between the piston and bore atop the top piston ring. This accounts for the opportunity for the fuel to be later "swept out of the cylinder as hydrocarbons out the exhaust". Immediately following the "power" stroke, which follows combustion, is the exhaust stroke. And this is when some trapped fuel that was not burned has an opportunity to be pushed out as the piston rises with the exhaust valve open.
I wouldn't expect an air assisted injector to perform radically different from a convention one when fitted in the conventional intake manifold configuration. DFI is just radically different from EFI. With DFI, the injector has little time to act, firing with the piston approaching TDC, not with it dropping during the air intake stroke. The other key difference is that DFI injectors are of course exposed to the violence of combustion. The physics of that environment isn't pleasant. Designing an injector to tolerate that is much more difficult, especially if it has to pass emissions 100,000 miles later without service. This is why OCP's injector self-cleaning cycle is important. |
