henry wrote: ↑
Fri Nov 09, 2018 10:37 am
hurril wrote: ↑
Fri Nov 09, 2018 9:56 am
gruntguru wrote: ↑
Fri Nov 09, 2018 6:15 am
At the beginning of the compression stroke the density in the cylinder (including the pre-chamber) is about 3 times atmospheric. At the end of the compression stroke the density in the combustion chamber (including the pre-chamber) is about 15 times that i.e. 45 times atmospheric. (assuming 15:1 CR). This means that 14/15 ths (93%) of the contents of the pre-chamber have flowed into it during the compression stroke and almost all of this 93% is fresh charge. The very worst case scenario where all the exhaust remaining in the pre-chamber at the end of the exhaust stroke stays there throughout the intake stroke, would still only allow 7% residual exhaust in the pre-chamber.
Right and this is a very good explanation. Why or how, though, would the mixture become denser within the shroud/ pre-chamber than it is without it? I take it this has to entail some vert intricate injector spray pattern and timing combined with some very precise fluid dynamics; because for a denser mixture to end up inside, it has to first form outside the pre-chamber.
If the mixture is not denser within the pre-chamber, then what does it buy? Is there more to having a shrouding or containment than its effect on the mixture? Does containment of the primary ignition event improve its triggering effect in a way that makes it ignite a homogenous mixture better?
So maybe they use fluidic diodes? This brief description http://www.fdx.de/en/products/fluidic-diode/
is for a device for gas turbines. So similar environment. Laminar flow in turbulent out, seems to match well with the needs to Turbulent
Jet Ignition. Maybe something as simple as a bell mouth in and sharp edge out on the orifices in the spark plug shroud.
In my mind, the orifices of the jet exits should be two circular drillings, about 15 degrees +/- from level, that are drilled at a tangent into the pre chamber cavity.
Thus, the exit orifices would look like a simple steak-knife blade serration (tooth) that would cause a twin, counter rotating vortex to emerge. If there were 6 of these around the nozzle, I would expect the rotations to actually ingest the unburnt mixture due to the pressure differential within each "slice" of the chamber.
So it would burn quickly, not by spreading the flame front, but by dividing the area into 6ths, then have one side of the pie slice at low pressure while the other at high to cause the unburnt mix to always be sucked into the flame.