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Insulating Fuel Distribution Lines

Low Pass

Low Pass

Well Known Member
Friend
Trying to correct the popping and irregular idle on an IO-360 (Bendix system), I am to the point that I believe insulating the distribution lines would help. Since I believe this is occurring as a result of the fuel in the lines flashing and pushing fuel into the cylinders at a sporadic and high rate, insulation seems to be the next step.

However, I have heard here and there, that this is not recommended. Why? Mine are braced very well using at least two points of attachment though the run. So I can't see the added mass being a dynamic issue.

If it's about inspecting for damage/cracks, etc., this can be done occasionally if the insulation is made removable (gotta figure that one out).

If anyone has info or experience with this, can you please pass it along?

Thanks,

Bryan
 
I'm curious as well on doing this. I'm not able to get a smooth idle at all when the engine is hot. I have Airflow Performance FI with the purge valve, so at least I can cool down the fuel lines forward of the injector lines. I've done all the usual checks for leaks and have set the idle mixture correctly. I have to keep the engine spinning at 1000 RPM or it will die taxiing off the runway. This forces me to use my brakes excessively during taxi.

I'm thinking of putting some Heat-Reflective Wrap-Around Sleeving from McMaster-Carr on the lines to see if that might have any difference. The other thought would be to add a cooling shroud around the fuel pump on the engine with a dedicated blast tube.
 
May not be pertinent to your case, but ....

... many of us with cooling plenums, S James or otherwise, believe the problem is exacerbated. During idle and taxi modes, when OATs are above 80-85F, the vaporization problem is most pronounced. That plenum that works so well during flight modes offers a smaller area/space for dissipation of heat during lo speed ops.
If possible, going to smaller injection restrictors raises the back pressure in the lines and helps a little bit, but does not cure the problem. (Don at AirFlow Performance has been very helpful with this.) My IO-320 came with .028 restrictors normally installed on IO-360s; with Don's advice I downsized them all to .022 - which helped quite a bit.
 
This is pretty common on all mechanically injected engine installs, even certified ones. You'll see it on M20J's a LOT as well as Dimondstars. The question I have for you is why you are defining this as a 'problem' as opposed to a normal operation for the system you have.

The "fix" is an electronic FI system or carburetor. Insulating the fuel lines won't make a difference at all from my limited experience. But once again, it's a characteristic of the system you have, not a problem.
 
I do not believe insulating the lines will help. The fuel pressure in these lines is very low and the entire area is heat soaked metal.
My solution is to get air borne ASAP.
 
Rupester said:
... many of us with cooling plenums, S James or otherwise, believe the problem is exacerbated
Click to expand...

The plenum lid doesn't allow post-shutdown ventilation via the oil door (4-cyl models), but would have no effect when running. Size of the chamber is moot. The issue is heat transfer rate from the local environment to the fuel, which is always being replaced in any given line with fresh fuel.

Three possible solutions; slow the heat transfer rate, increase the fuel flow rate, or increase the fuel pressure. Insulation slows transfer. More throttle increases flow rate and pressure. Smaller nozzles increase pressure.
 
David-aviator said:
I do not believe insulating the lines will help. The fuel pressure in these lines is very low and the entire area is heat soaked metal.
My solution is to get air borne ASAP.
Click to expand...

To add to my thoughts on the subject, if the lines are insulated they will also be insulated from air flow heat transfer once off the ground.

Dan Horton has a better understanding of heat transfer than do I so I agree with his conclusion. There is no easy complete solution to the problem on the ground with a hot engine. Its been that way since fuel injection was invented with these engines.

I do not consider it a big deal once you understand what the issue is. Increasing flow rate by higher engine rpm, smaller nozzle size, and insulation will help but the best solution is WOT and getting off the ground. I would not want the flow divider lines insulated in flight.
 
David-aviator said:
To add to my thoughts on the subject, if the lines are insulated they will also be insulated from air flow heat transfer once off the ground.

Dan Horton has a better understanding of heat transfer than do I so I agree with his conclusion. There is no easy complete solution to the problem on the ground with a hot engine. Its been that way since fuel injection was invented with these engines.

I do not consider it a big deal once you understand what the issue is. Increasing flow rate by higher engine rpm, smaller nozzle size, and insulation will help but the best solution is WOT and getting off the ground. I would not want the flow divider lines insulated in flight.
Click to expand...

I fully understand the variables and heat transfer conditions involved. As for being typical, this is not true. Six months ago I switched from an IO-320 to IO-360. I had a Silver Hawk system on the -320 that idled beautifully - very smooth with no issues. This one's Bendix.
 
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Low Pass said:
I fully understand the variables and heat transfer conditions involved. As for being typical, this is not true. Six months ago I switched from an IO-320 to IO-360. I had a Silver Hawk system on the -320 that idled beautifully - very smooth with no issues. This one's Bendrix.
Click to expand...

Doesn't this mean that there is a calibration solution as opposed to a design solution? I am just recalling some previous posts that mentioned a method (spring) to increase the pressure to the distribution block (spider) that largely eliminated this issue? It seemed to be the drain back diaphragm spring in the distribution block that gave higher pressure drop and therefore higher liner pressure up to the block.

Maybe the question should be: How is the Bendix design/calibration different that it presents this behavior?
 
Low Pass said:
Trying to correct the popping and irregular idle on an IO-360 (Bendix system), I am to the point that I believe insulating the distribution lines would help...

...If it's about inspecting for damage/cracks, etc., this can be done occasionally if the insulation is made removable (gotta figure that one out)...
Click to expand...

2 random thoughts:

1. They make fuel line insulation blankets for race cars that simply slip over the line and is velcro'd in place. Check with Summit Racing, et.al.


2. There are many Bendix equipped airplanes that idle (relatively) fine. I've had 3 in a row now and I've never had any die at a low idle. I'd be looking hard for any problems specific to your aircraft before trying somewhat "unconventional" fixes.
 
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Interesting discussion!

I have often wondered why the fuel injection system is mounted on top of the engine and not on the bottom where it would be cooler when the engine is stopped. Has there been any thought towards this? Just assumed there is a good reason seeing how all engines are set up the way they are.
 
Toobuilder said:
2 random thoughts:

1. They make fuel line insulation blankets for race cars that simply slip over the line and is velcro'd in place. Check with Summit Racing, et.al.


2. There are many Bendix equipped airplanes that idle (relatively) fine. I've had 3 in a row now and I've never had any die at a low idle. I'd be looking hard for any problems specific to your aircraft before trying somewhat "unconventional" fixes.
Click to expand...

Good information and points - thank you! Mine doesn't die. It idles a little inconsistently and pops/backfires occasionally.

Update - I found a similar product that is much cheaper. Will give it a shot and see. Can't see a downside. The point here, as I see it, is to buy some time between start-up and takeoff *after start up and the engine is already warm/hot*. (The time when the problem is pronounced.)

My hope is that this product might keep the lines from heating as quickly while the engine goes from warm to much hotter, taxiing for takeoff. If not - I'm out $25.

http://www.amazon.com/Thermal-Zero-Temperature-Exhaust-Aluminized/dp/B006TIOEGS/ref=sr_1_1?s=automotive&ie=UTF8&qid=1412720000&sr=1-1&keywords=1%2F2+aluminized+sleeve
 
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BillL said:
Doesn't this mean that there is a calibration solution as opposed to a design solution? I am just recalling some previous posts that mentioned a method (spring) to increase the pressure to the distribution block (spider) that largely eliminated this issue? It seemed to be the drain back diaphragm spring in the distribution block that gave higher pressure drop and therefore higher liner pressure up to the block.

Maybe the question should be: How is the Bendix design/calibration different that it presents this behavior?
Click to expand...
Maybe the IO-320 had fuel injection nozzles with smaller orifices then the ones on the IO-360 . The smaller orifices would require higher fuel pressure in lines to produce a given fuel flow, and the higher fuel pressure would increase the temperature required to boil the fuel.

The downside of smaller nozzle orifices is that they limit the maximum fuel flow, so while they might be a solution on an IO-320, they are less workable on engines that require more fuel flow for take-off.
 
I'd be nervous about the insulation introducing new vibration modes, which could be mischievous. An 1/8" OD tube vs an insulated diameter of perhaps 3/8" to 1/2" is a big difference. It's pretty windy in there...

As others have mentioned, investigate if you system will still deliver full fuel flow at WOT, but with smaller restrictors in the nozzles. Consult with the system manufacturer to get their opinion on what restrictors they may suggest would work. If you go to smaller restrictors, verify that WOT fuel flow is unchanged.

It is also not clear if leaning or full rich is better for idle, there are arguments for each being a better choice, depending on what is causing the idle problem.

I just ignore idle problems, which for me generally only show up in ~80F or warmer days, after landing. Sometimes I'll have to occasionally "goose" the throttle to clear things when taxiing in.

Fixing ground idle is not worth adding any additional risk to flight.
 
AlexPeterson said:
I just ignore idle problems, which for me generally only show up in ~80F or warmer days, after landing. Sometimes I'll have to occasionally "goose" the throttle to clear things when taxiing in.
Click to expand...

Well, here in sunny SoCal, it has been over 80F every day since February. :)

I went up again today and after taxiing in the engine stopped again on the ramp when my idle dropped below 900 RPM. It took two tries to get the engine running again just to get off the taxi way. I had the wheel pants off this weekend and the brakes seem to be wearing OK, but I doubt if I will get more than a couple hundred hours on them at this rate.
 
Toobuilder said:
2 random thoughts:

1. They make fuel line insulation blankets for race cars that simply slip over the line and is velcro'd in place. Check with Summit Racing, et.al.


2. There are many Bendix equipped airplanes that idle (relatively) fine. I've had 3 in a row now and I've never had any die at a low idle. I'd be looking hard for any problems specific to your aircraft before trying somewhat "unconventional" fixes.
Click to expand...

A friend and I tried insulating the fuel lines on his airplane and found it did NOT help, if anything it made the problem worse. So we removed the insulation. My theory is it also insulated the lines from the little bit of airflow they have. I mean when you think about it you have metal injectors screwed into 300 degree plus cylinders and the spider bolted to the case all of which are absorbing a lot of heat.
 
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bruceh said:
Well, here in sunny SoCal, it has been over 80F every day since February. :)

I went up again today and after taxiing in the engine stopped again on the ramp when my idle dropped below 900 RPM. It took two tries to get the engine running again just to get off the taxi way. I had the wheel pants off this weekend and the brakes seem to be wearing OK, but I doubt if I will get more than a couple hundred hours on them at this rate.
Click to expand...

Having it die is another matter all together. Do you have a low-inertia prop? Still, it should idle down to at least 600 or so. I'm wondering if you don't have another problem, like a bad flow divider.
 
I have the Sensenich Ground Adjustable composite prop, which is lightweight.

I also have the .022 injector nozzles for the AFP FI on the IO-320. It runs smooth as silk above 1000 RPM cold or hot.

At 1000 RPM taxiing, I'm moving pretty fast! This is the main issue -- having to ride the brakes a lot to slow it down.
 
Don Jones said:
A friend and I tried insulating the fuel lines on his airplane and found it did NOT help, if anything it made the problem worse. So we removed the insulation. My theory is it also insulated the lines from the little bit of airflow they have. I mean when you think about it you have metal injectors screwed into 300 degree plus cylinders and the spider bolted to the case all of which are absorbing a lot of heat.
Click to expand...
Interesting. Thanks.
 
WE built some -4 hoses for a customer several years ago with firesleeve. Electronic injection, but never the less, it was insulated. Pretty cool looking.
Tom
 
Another direction

I hate problems like this. Hard to figure out why it's happening!

Two issues that I've encountered that caused back-firing that may be worth considering:

1. Small intake leak
2. Timing slightly off
 
Fuel divider

I also had the same problem with rough idle after landing on hot days.
What made an improvement on my I0-360 was changing the spring in the Flow divider to a stronger one. I was told that the Cessna sky-masters changed these springs on the rear engine because of the lack of cooling. I believe it allows the pressure to build in the lines and help prevent this problem.

This made a noticeable differance in my idling on hot days. I still get some But not as bad.
 
Not hard at all

I hate problems like this. Hard to figure out why it's happening!
Click to expand...

None of this is a mystery.
It is simply a fuel system installation with too many components and fuel hoses too close to heat sources. Often a gascolator unnecessarily added FW
to make matters even worse.
Among the fixes suggested, I believe a fuel system installation with as many components as possible installed aft of the firewall "cool side" is the best general approach to a trouble free fuel delivery system.
I am aware that this method of fuel system installation is not popular with everyone but it works for me.
I did also install a constant flow return line to ensure a constant flow of "cool" fuel supplied to the fuel controller. Again, not popular with too many people but highly effective, very simple, almost no cost and needs no attention nor does it rob you of speed or horsepower.
My IO-540 runs very smooth at 600 RPMs hot or cold anytime with avgas or
91 octane mogas E10.
I may not have the engineering credibility of some but I do have the proverbial
" proof in the pudding" with my installation.
BTW, my RV-8 had the same installation and never coughed or sputtered hot or cold or any other time.
 
Ernst,

My post must have struck a nerve with you. Sorry about that.

I've always been of the opinion that when troubleshooting a problem, never rule out things until you know for sure they're not the issue. Kinda like your tag line in your signature, "don't believe everything you know".

My suggestions were probably off the mark, but easier to rule out than some other theories.

Keith
 
Sorry Keith

Did not mean to sound the way it did, my apologies.

Certainly does not hurt to check everything, especially intake leaks which I think go untreated in many cases due to the nature of intermittent rough running especially at low RPMs.

What is apparent to me is that a fairly large number of Rvs exhibit the symptoms of fuel boiling and most likely because the airplane is already built
and running, redesigning a fuel system is not on the top of anyone's list.
Other fixes usually somewhat cure the problems and all is well or so it seems.
 
Don Patterson said:
I also had the same problem with rough idle after landing on hot days.
What made an improvement on my I0-360 was changing the spring in the Flow divider to a stronger one.
Click to expand...

Where did you go to find out which spring was appropriate for your installation? I have similar behavior in an IO-540.
 
Been through this recently on a 375. Worked with Airflow Performance, who was most helpful. The condition was mitigated, not cured, though.

It's overheated fuel vaporizing, and for me it happens in the servo. Using clear tubing segments for viewing, clear fuel in, bubbles out of the servo. Perhaps the spider runs also added to the problem, but the bubbles already existed so the engine ran very rough. Heavily insulating the very short fuel lines FWF did no good. Even shunting around the hot engine pump direct to the servo didn't help. Nor did shunting around the high pressure aux pump direct to the engine pump. It's the huge 10:1 pressure drop between the servo inlet to the outlet that sets you up for bubbles with very slight heating. I installed the 4lb spring (2 is standard), but no obvious improvement, but it can't hurt, either.

And all servos are not created the same. The initial installation was a Bendix RSA. That thing would bubble if you looked at it wrong. AFP exchanged it for a Silverhawk - which is the same design - and now operations are usually smooth unless it's more than five minutes from touchdown to shutdown, or >15 minutes idling from cold (such as leaving OSH).

AFP swears they can set their calendar by the phone calls about rough running when spring turns to summer. The entire situation is a good reason for using a carb if you don't want to put up with it for whatever perceived advantages FI means to you.

John Siebold
 
John,
Does your system have a purge valve ?

I ask because if you do, you could very easily plumb a constant flow return line into it.
Tee'd out of your mechanical fuel pump outlet and return fuel via the purge return line.
For the cost of a hose and a T with an orifice the size of a #65 drill hole you can see if this would solve your problem. It's worth a try and if it does not work for you can easily restore the system to its current configuration.
 
Fuel injection

Tim,

I ordered the spring from a guy that rebuilds Bendix fuel injected systems in Illinois a few years ago. Don't know if there are stronger springs for the system or was the spring in my system just not strong enough any more. I have an older Bendix system.

Don
 
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