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Turbo Nozzle Shrouds

dpansier

Well Known Member
I have seen Turbo Nozzle Shrouds on a few non turbo, fuel injected engines. The owners I asked could not provide any definite answer on the advantages as they did not build the aircraft.

Appears the 2 or 3 shrouds are connected to a ram air tube extending centrally in the cowling inlet, one ram tube for each side. I assume this modification is used to provide more uniform pressure to the nozzle / restrictor assemblies.

Anyone have them installed and can explain the benefits?
 

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air moves from high pressure to low pressure. Std injector is vented (need air to atomize the fuel spray) outside of the intake plenum as it comes out of the restrictor. In normally aspirated engines, the cowl air the same or higher pressure as the intake chamber, so air and fuel flow naturally from the inj to the intake chamber. In a turbo engine, the pressure in the intake chanber is higher than the cowl pressure (in most cases), so a std injector wouldn't want to flow air / fuel into the intake chamber (instead it would be trying to push the air fuel out of the inj vent), so they send pressurized air from the turbo to the inj body to make sure the pressure is not lower at the injector body than it is in the intake chamber. Not sure what advantage these would bring to a NA engine, but doubt it is significant if it exists. One might assume that ram air adds a bit of pressure to the plenum, but have my doubts that this pressure rise is any higher than the upper cowl, which also is getting ram air. Dan is the pressure expert and may have greater insight into that. Auto injectors operate at MUCH higher fuel pressures and therefore do not need an air mix to atomize effectively.

Larry
 
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Don, I've been flying them for a while, and have recorded deltaP for bleed air pressure vs intake port pressure across 720 degrees of crank rotation.

Specific to your question, bleed air feed rails with the intake right up front in the cowl intake can offer more consistent pressure, as well as higher pressure at the rear cylinders. That said, I did not make "before" measurements, so I can't quantify any improvement.
 
Don, I've been flying them for a while, and have recorded deltaP for bleed air pressure vs intake port pressure across 720 degrees of crank rotation.

Specific to your question, bleed air feed rails with the intake right up front in the cowl intake can offer more consistent pressure, as well as higher pressure at the rear cylinders. That said, I did not make "before" measurements, so I can't quantify any improvement.

Hi Dan
So did your investigation imply higher ram air / intake pressure than upper deck at all in the cycle?
3/6 of my injectors have fuel staining and clearly leak a lot of fuel (even have staining on my plenum inside).
I have the showplanes cowl and that intake seems very good from a ram perspective.
I really battle getting smooth LOP at altitude (subject of another thread coming) and I’m running out of possibilities. This is one a few people have suggested for me.
Cheers
 
I appreciate the info Larry and Dan.

Digging into this further (RV10 List) I found reports where several RV10 owners reported difficulty running lean of peak with the James Plenum, the solution they found was to run the turbo nozzles with a ram air tube. Not sure why it was unique to the RV10 / 6 cylinder and not reported with the other RV’s.

Some of the participants in the RV10 List discussion 10 -15 years ago are still active on this forum, hopefully they will respond to fill in the gaps.
 
Hi Dan
So did your investigation imply higher ram air / intake pressure than upper deck at all in the cycle?
3/6 of my injectors have fuel staining and clearly leak a lot of fuel (even have staining on my plenum inside).
I have the showplanes cowl and that intake seems very good from a ram perspective.
I really battle getting smooth LOP at altitude (subject of another thread coming) and I’m running out of possibilities. This is one a few people have suggested for me.
Cheers

Bleed pressure was higher than port pressure during all but a small portion of the 720 degree cycle.

I'm currently off on a flying trip, and the graphing is on my home computer. Remind me next week?
 
I appreciate the info Larry and Dan.

Digging into this further (RV10 List) I found reports where several RV10 owners reported difficulty running lean of peak with the James Plenum, the solution they found was to run the turbo nozzles with a ram air tube. Not sure why it was unique to the RV10 / 6 cylinder and not reported with the other RV’s.

Some of the participants in the RV10 List discussion 10 -15 years ago are still active on this forum, hopefully they will respond to fill in the gaps.

I know little about the james cowl, but suppose it may have a design flaw that results in areas where upper plenum pressure drops a bit. In my 10 w/ stock cowl and no plenum, I have 0 issues running LOP and can easily go 100*+ LOP, but most typically fly 50-70 LOP. I suppose some folks could have more issues with air distribution and have poor gami spreads that were not dealt with and maybe the turbo nozzles helped in some way that is not obvious.

Larry
 
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Hi Dan
So did your investigation imply higher ram air / intake pressure than upper deck at all in the cycle?
3/6 of my injectors have fuel staining and clearly leak a lot of fuel (even have staining on my plenum inside).
I have the showplanes cowl and that intake seems very good from a ram perspective.
I really battle getting smooth LOP at altitude (subject of another thread coming) and I’m running out of possibilities. This is one a few people have suggested for me.
Cheers

I struggle to see enough pressure differential to push fuel out of the inj screens on most engines. While I do agree that having ram air feeding turbo nozzles can only provide goodness, I am not convinced that you will have meaningfull problems without them. The std injectors are used on 10's 1000's of planes without much issue and there is no evidence to indicate that it is a flawed design. Fuel staining could be as simple as not installing the inj with the bleed hole pointed up (boiling fuel pushes towards inj at shut down and will drain out of the bleed hole if pointed down). There are several reasons for not being able to run smoothly LOP and I would put traditional nozzles pretty low on that list.

If there is truly blue staining all over the place, that implies excessive pressure in the intake chamber and may be best to start with diagnosing why that is, as it may also be the source of your issues running LOP. Several things can cause that, but top of the list would be int valves not fully seating (bad valve job being a target suspect with a 50% problem rate). This could cause pressure spikes that will push fuel/air from the intake chamber out of the inj vent on the compression stroke. This also has a leaning affect for that cyl. Also need to be certain that these are not leaks in fittings or soldered joints in the fuel lines.

Larry
 
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Showplanes or Sam James cowl.

The aircraft you have seen them on most likely had a Sam James or Showplanes cowl. The problem is that the velocity of the air coming in the small opening is quite high, which drops the pressure, especially for the number 1 and 2 cylinders. I had this problem (I have a RV10 with the Showplanes cowl) so I put in the injectors designed for turbocharged engines and fed ram air the the injectors with a 3/8 tube at the front of the cooling opening. It made a huge difference in how well the engine ran LOP. Don Rivera at Airflow Performance provided me with the necessary parts.

If you want photos text me at 702-521-1840.
 
One explanation

I’ve recently learned why one individual put the turbo shrouded injectors on his N/A engine. He didn’t like the fuel stains caused by fuel boiling and dribbling at his injectors. The shrouded turbo injectors eliminated the issue. His engine stays spotless!


Bill
 
The aircraft you have seen them on most likely had a Sam James or Showplanes cowl. The problem is that the velocity of the air coming in the small opening is quite high, which drops the pressure, especially for the number 1 and 2 cylinders.

My understanding also, and very likely. Recall a small inlet area generally means a inlet high velocity ratio and internal diffusion. If the inlet duct doesn't expand sufficiently prior to the front cylinders, velocity will still be high at the nozzle bleed. Some of the earlier James plenum inlets are like that, with long narrow necks.

I've been flying turbo nozzles several years now. This cowl is a low Vi/Vo system, so velocity near nozzles 1 and 2 should be low, but I was still curious to see if I could get a little further LOP if I balanced bleed air pressures front to rear. The kicker was that Don was curious about bleed air pressure vs manifold pressure. So, each side got a rail with a pitot entry, tying a pair of nozzles together. Tapping the aft end of one bleed air rail provided a relatively stable measurement source. The other side of the Honeywell pressure sensor was connected to the primer port of #1. Analog sensor output went to a Dataq https://www.dataq.com/products/di-1100/ and my laptop. Flight engineer was a teenager in the back seat. None of my older airport buddies seemed to be able to run the software ;)

Ran another channel to pick up the #1 spark, providing a reference marker for event timing.

Collected a lot of data at different power settings and altitudes. As I'm sure you've heard, real time manifold pressure isn't the steady value you see on your cockpit MP gauge. It oscillates considerably due to wave activity and valve action, which is why we wanted to see what deltaP looked like across 720 degrees of crank rotation. I've attached a sample below.
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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.

Education and recreation.
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I’ve recently learned why one individual put the turbo shrouded injectors on his N/A engine. He didn’t like the fuel stains caused by fuel boiling and dribbling at his injectors. The shrouded turbo injectors eliminated the issue. His engine stays spotless!


Bill

Thanks Bill - I don't like the stains either, even if mine are not blue. Not to mention the smell of fuel after shutdown.

Anyone know if these shrouds can be retrofit?

@DanH - thanks for the explanation and graphs - very interesting if these shrouds have even more than the cosmetic benefit. Any concerns about bugs flying into the pitot?
 
@DanH - thanks for the explanation and graphs - very interesting if these shrouds have even more than the cosmetic benefit. Any concerns about bugs flying into the pitot?

I have considered installing screens on them, but it has gone quite a while without trouble.
 
Bit of follow up...

I like a reality check when collecting data. For example, look at underlying principles (the laws of physics don't vary for anyone), or compare with measurements from other sources.

Below I've aligned two intake port pressure plots. The upper plot was taken from an old CAFE report (EPG Part IV, IO-360 angle valve on a Mooney), the lower from my own records (IO-390 angle valve on an RV-8). The intake tracts are similar, the differences being recording method, RPM, and density. The CAFE plot was taken at 2700+ near sea level, while mine was at 2400, at altitude. The difference shifts the wave shapes and timing a bit, but still, the correlation is obvious.

BTW, in considering the desired length and diameter of the intake tract, those 1960's Lycoming guys did OK. Ignore the left side, when the intake valve is closed. Our interest is high port pressure at valve opening, to get the flow moving into the cylinder, and again as the valve closes, to shove in the last bit even as the piston is beginning to rise from BDC.
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Dan thanks for the information! I am right in the decision state with my IO-540, 9:1, Barrett CAS. I just can't get LOP without a rough engine. Don at AFP suggested I go to Turbo Injectors and based on your analogies looks like that be best for me.
My question to you is getting away from bugs why not pick up Pressure in the Air Plenum?
 
By "air plenum", do you mean a pickup location somewhere above the engine but further aft, not in the inlets?

The tube in the inlet is a total pressure pitot, the sum of both static pressure and whatever dynamic pressure remains in the inlet velocity. A unidirectional source somewhere in the aft cooling plenum would be exposed to flow without much velocity, i.e. less dynamic pressure.
 
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Don, remember, even a pressure tap in some out of the way location with no direct exposure to ram air is still an inlet and thus remains subject to bug ingestion. Needs a screen regardless, unless inside an air filter, which would mean even more pressure loss.

That said, a pressure tap from an airbox would provide relatively steady pressure, a plus if your real problem is turbulent flow around #1 and #2. Although not as high as the delta between total pressure and port pressure, it would provide a delta near that of the induction tract loss. That would be around 14" H20 for my horizontal Lycoming sump with an FM200, and range from something higher for an updraft sump, to almost none for a recently measured Sky Dynamics manifold.

Try it if you want. Can't hurt.
 
A follow up in this from me.
I test flew my turbo nozzle setup today.
Chalk and cheese. Can comfortably get to 80LOP now.
Whereas before it started becoming unhappy as soon as all cyls were lean with around a 0.5 GPh GAMI spread.
I’ll still aim to improve my spread. I have a collection of restrictors. Maybe there’s a little more I can eke out.
To recap:
Showplanes cowl, 9:1, CAI, 1 mag, one surefly, AFP with FM300. 0.026 restrictors (-/+ 0.0005)
Thanks to all for pointing me in the right direction. I’m much happier now.
 
Hi Richard, did you get the new nozzles from AFP? Can you briefly describe what you needed to do? Thanks!
 
Hi Richard, did you get the new nozzles from AFP? Can you briefly describe what you needed to do? Thanks!

Yes 6 new nozzles and 2 rails plus assorted adel clamps and hardware. Kept my original restrictors.
Replace original nozzles with turbo nozzles. Install rails and plumbing.
Probably about 3-4h work all up for a 540.
I’ll post some more pictures when I get a free minute
 

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Yes 6 new nozzles and 2 rails plus assorted adel clamps and hardware. Kept my original restrictors.
Replace original nozzles with turbo nozzles. Install rails and plumbing.
Probably about 3-4h work all up for a 540.
I’ll post some more pictures when I get a free minute

Thanks Richard - that's helpful.
 
FWIW, I have turbo nozzles on a plastic plane with an IO550N.
At idle, it sounded like an old school drag racer popping and spitting somewhat, but ran great at higher power settings. One bank appeared to be running quite rich on the ground with a black tail pipe while the other bank was fine.

It took a long time to figure out that the 1/4” air lines feeding the nozzles were too small. The rich side had a slightly longer supply tubing run, and must not have been getting enough air to properly atomize is the fuel on the ground.
I increased the air supply tubing to 3/8 inch and problem solved. I do however miss that drag racer sound a little bit…. Something to explore if you have similar symptoms (or just use larger lines to start with)

Unfortunately, like Dan H, I don’t have before and after data but the set up works great.
 
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Yes 6 new nozzles and 2 rails plus assorted adel clamps and hardware. Kept my original restrictors.
Replace original nozzles with turbo nozzles. Install rails and plumbing.
Probably about 3-4h work all up for a 540.
I’ll post some more pictures when I get a free minute

That is a nice-looking rail. Did Don at Airflow Performance supply that rail, with the welded tube stubs for each cylinder? And there are threaded bosses on the cylinders to screw those nut launchers-ahem-Adel clamps down to?
 
That is a nice-looking rail. Did Don at Airflow Performance supply that rail, with the welded tube stubs for each cylinder? And there are threaded bosses on the cylinders to screw those nut launchers-ahem-Adel clamps down to?

Yes Don supplied the rails.
The Adel clamps are stacked to mount the tubes to the pushrod covers.
I’ve got my safety wire Adel clamp method down to a fine art now so there was only minimal cursing.
Not my photo but mine looks exactly the same as this photo.

I may yet relocate the rail outboard of the spark plugs.
The bend in the stiff short hoses places a twisting moment on the shrouds on the nozzles. The o-rings and spring setup appears to tolerate this but a straight hose I think would be better. I’ll ask AFP.

Picture 1.jpeg
 
Yes Don supplied the rails.
The Adel clamps are stacked to mount the tubes to the pushrod covers.
I’ve got my safety wire Adel clamp method down to a fine art now so there was only minimal cursing.
Not my photo but mine looks exactly the same as this photo.

I may yet relocate the rail outboard of the spark plugs.
The bend in the stiff short hoses places a twisting moment on the shrouds on the nozzles. The o-rings and spring setup appears to tolerate this but a straight hose I think would be better. I’ll ask AFP.

View attachment 50424

I'll bet these guys can come up with a good hose for that application.

https://www.aircraftspecialty.com/

The rail and the hose look great for a turbo installation, but for just providing ambient air pressure, looks like a simpler, lighter solution could work.
 
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