Some readers may be a bit hazy regarding constant flow nozzles, so here's the short version...
The restrictor is a precision orifice. This is the part we swap for slightly smaller or larger diameters to achieve a small GAMI spread, i.e. to make all the EGTs peak at the same time when leaning.
The nozzle body has a passage somewhat larger than the restrictor ID. There is an air bleed hole in the side of the body. The restrictor shoots a stream of solid fuel into the passage, where it mixes with air from the bleed. The result breaks up more readily in the intake port, in particular at part throttle.
A standard nozzle body has a simple guard shroud and screen to keep the bugs and trash out of the bleed hole. The air source is upper cowl pressure, which is usually higher than manifold pressure, even at full throttle.
The variables here are (a) pressure loss through the intake system and (b) upper cowl pressure recovery, i.e. how much of the available dynamic pressure was converted to increased static pressure in the upper cowl. An installation with great intake tract performance (ram, no filter, big throttle throat, etc) and lousy cooling pressure will have poor bleed air delta. A system with uneven upper cowl pressures will have unbalanced bleed air supply; the nozzles may flow different quantities of bleed air, and the proportions may change at different airspeeds.
A turbocharged installation has a more significant problem; manifold pressure is routinely higher than upper cowl pressure. Obviously that would make the bleed air holes flow backwards. So, a sealed shroud is installed over the nozzle body, and air is piped to the nozzles from a source near the turbocharger outlet. That keeps the bleed delta positive.
Assume (or suspect) a normally aspirated engine shows symptoms of poor or uneven bleed pressure. We can install the sealed shroud turbo nozzles, and supply them with a pitot tube (usually in the cowl inlet) to capture total pressure, the sum of static and dynamic. The result should be higher bleed pressure, equal at connected nozzles, thus better atomization in the nozzle passages. At least that's the theory.
The plot in the previous post was a sample from a live measurement of bleed air delta with turbo nozzles. In the photo below, you can see the pitot opening feeding bleed air to cylinders 2 and 4, and a black hose connecting the pitot tube to the cyl #2 nozzle shroud.
Do you need a setup like this? Maybe, maybe not. Note available dynamic pressure, a function of velocity and density, drops with altitude gain. There is less bleed air pressure to entrain air in the nozzles, so at low flow rates (think LOP and WOT cruise at 10.5K) the nozzle delivery into the port is more blobby, for lack of a better term. Higher, or more uniform bleed air pressure may improve LOP smoothness due to better atomization. Again, so sayeth the theory.
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