Exhaust Insulation Wrap

[Guest Maj Millard]

Would I be right in suggesting a larger capacity oil cooler with larger air exposure area for the Jabs. A larger oil cooler also gives you increased oil capicity, to absorb and transfer heat, so things would have to cool down a bit. Has this been tried ?.

 

 

[Guest Lucifer]

Exhaust Insulation Wrap - first hand report

 

Hi Jack,

 

For what it is worth, I wrapped the home-made SS exhaust headers on my Rotax 912 and never had an overheating problem in 11 years, including a trip around the Top End - or corrosion for that matter.

 

The pipes weren't thin-wall, so that may have helped, but I would not wrap mild steel pipes for any extended period due to rusting. Prior to wrapping the 912 pipes, i was involved in some motorcycle dyno testing, and wrapping the first 18 inches of the header pipes gave 2 hp increase. Not enough reason to do it on an aircraft, but certainly for a competition machine. The other alternative is to coat the headers ( Jet-Hot or HPC) but they should be coated inside as well as outside ! The theory for either system is that by keeping the exhaust gas temp up, flow is increased, and consequently scavenging of the burnt gas from the cylinder is improved. But I did it to help keep under cowl temps down - this helps engine cooling as well as component life ( seals, rubber hoses, ignition etc )

 

It worked for me and I have done the same on my Lycoming -powered RV. I wrapped the induction pipes as they are close to the exhaust, as well as the first foot of the SS headers. The engine runs very low CHT and I have to cover up part of the oil cooler to keep oil temps up, and this is in Queensland.

 

So here is another first-hand account that may help.

 

Cheers

 

Martin

 

 

[Vev]

Hi Martin,

 

 

Thanks for the feedback and your insight into exhaust wrap, particularly with your 11 years + 2 aircraft experience… I don’t feel like Robinson Crusoe in trying this after hearing your account.

 

To be honest I’m not completely sure about the metallic composition of the headers on the Jab, although I’m almost certain it’s not mild steel … may be someone out there will know off the top of their head?

 

 

I do like your thinking in terms of the positive impact on other ancillary components such as rubber and seals etc. I hadn’t thought about this outcome but it will be a nice bonus if I can replicate this in the Jab too.

 

 

Like you, I have so far seen a reduction in temps, which in my case are quite acceptable levels, but as I have already said, I won’t be surprised if my oil temp get too low and I may need to reduce air flow over the oil cooler… I guess time will tell once I get a few more hours under the belt and experience different ambient temps.

 

 

Thanks again for the input.

 

 

Cheers

 

Jack

 

 

[GlennB]

Hi Jack,

 

Some work has been done along this line at The Oaks. Carried out on an LSA Jab.Did show improvement in warmer months but carby ice did rear it head on a number of occasions.After removal no more icing.

 

Cheers Glenn

 

 

[vk3auu]

Concerning the ratio of the size of the opening for outlet air compared to inlet air. The volume is proportional to the absolute temperatures in degrees K, not the degrees C, so that assuming a cold day with inlet temp of Zero degrees C and outlet temp of say 80 degrees C, the outlet would only need to be about 353/273 = 1.3 times the area of the inlet. Any bigger would just be causing unnecessary drag.

 

David

 

 

[Ross]

When a local engineering shop was about to weld the pipe socket to the exhaust header pipe of my Jabiru J160 serial #14 to fit an exhaust temp probe as supplied by the Jabiru factory the engineering shop thought that it was not manufactured in stainless steel (the pipes are a dull brownish colour).

 

They thought that it was Titanium!!

 

Maybe I should find some one else to do that kind of work!

 

So I rang Rod Stiff at Jabiru who verified that the exhaust header pipes were definitely stainless steel.

 

Regards

 

 

[Vev]

Hi Ross,

 

Thanks for the update on the header materials ... I guess this should put the oxidation concern to bed. I will however still undertake a high frequency inspection progamme until I'm convinced there's no harm re cracking etc.

 

Cheers

 

Jack

 

 

[Ross]

The whole formula is

 

P1.V1/T1 = P2.V2/T2

 

where the full stop indicates multiplication and the / indicates division.

 

P1 indicates the starting Pressure

 

V1 indicates the starting volume

 

T1 indicates the starting temp in degrees Kelvin.

 

Kelvin degrees = (degrees Celcius +273)

 

etc etc

 

So it all depends where you want to start the calculations because the finished gas mix out the exhaust pipe is not the same material as what entered the air intake and the formula above assumes that no material has been added or subtracted or changed composition from the original compounds by chemical action like burning fuel.

 

That is as far as I want to go in the discussion! (in other words that's all I know)

 

Regards

 

 

[vk3auu]

Ross, I think we may be talking at cross purposes. My comments were regarding the air under the cowl where the pressure is not too much greater at the inlet than it is at the outlet, so that the P term can almost be ignored. There are some people who make the inlet hole larger than the outlet in the mistaken belief that this will increase the air flow, but at the end of the day it has to be the other way around. Just putting a lip under the exit hole can only be marginally effective too, if the ratio of outlet to inlet is not large enough, just creating drag, but no extra air flow.

 

David

 

 

[Ross]

Yes I'm with you now. I must have been half asleep or just plain dumb.

 

The air going through the motor cooling system for oil cooler and cylinders etc has to put heat into that air.

 

This increased heat content of that air will cause it to expand and/or increase the pressure. Increasing the pressure is not acceptable as it will reduce the flow rate of incoming air and therefore the capacity of the air to remove heat.

 

So it has to be allowed to expand by increasing the exit hole cross sectional area making sure that the shape of that exit does not cause exit problems as well.

 

Some of the heat load could be removed by insulating the exhaust header pipes or the muffler (thus sending more of the the heat out of the cowl area via the exhaust pipes rather than in the cooling air) providing that does not also cause problems as pointed out in earlierr posts on some Jabs by causing excessive carbie ice or reducing engine oil temperature too much.

 

A kit J170 at Mildura suffered excessive oil cooling so the owner mounted a butterfly flap in the mouth of the oil cooler air inlet so that he could adjust it in flight.

 

 

[Vev]

Hi Ross & et'al,

 

May be a dumb question... but why would insulation on the exhaust headers cause carbie icing??? The carbie sit directly over the muffler (which is not in scope for insulation) and intake air is drawn from outside the cowl, therefore I presume no more hot or colder than before?

 

Cheers

 

Jack

 

 

[Ross]

I presume insulating anything to do with exhaust gases must reduce the heat loss from the exhaust gases into the steel of the exhaust header pipes or the exhaust muffler and then into the air and/or the other metal parts under the cowl by way of conduction and/or radiation.

 

To continue evaporation of the fuel in the venturi of the carburettor, it needs heat from from the incoming air and the surrounding air and metal etc otherwise it will get colder and colder.

 

If part of the heat supply is removed by insulating the muffler or the exhaust header pipes this could cause the fuel air mix to now fall below the freezing point of water where it did not previously get that cold.

 

If the relative humidity is high enough so that water will condense out of the incoming air it may possibly freeze up in the carburettor throat causing the motor to stop.

 

It might not have stopped if it were in a normal throttle position.

 

The minimal throttle setting aggravates the trend for the carburettor to ice up.

 

I think climbing up past cloud base could result in carburettor ice as the air gets more humid as you climb towards cloud base also depending on air temperatures etc.

 

Yet above cloud tops the risk of carb ice is probably less until you start to descend again.

 

 

[Vev]

Hi Ross,

 

 

Thanks again for the feedback … Whilst your post make sense of the probable cause, in my case, I don’t feel that carbie icing is anymore likely than before as the heat generated around the carbie and the intake manifolding is exposed to quite warm surrounds. The muffler is uninsulated and contains hotter gases, as there has been less heat loss through the headers, which sits directly below the carbie … to be honest I was more concerned about too much heat around the carbie as the heat has increased.

 

 

Just as an update … I’ve now done 8 hrs over the weekend and tried every combination to get the CHT to get past 300 deg F (on the gauge, 288 deg corrected) and it just won’t go beyond that mark. In cruise it is sitting around 275 deg (264 deg corrected) … my oil temp is sitting on 75 deg C in climb and 70 in cruise. All in all these seem to me to be acceptable numbers and feel that the exhaust wrap is doing what I had been looking for and has significantly reduce my operating temps.

 

 

Best regards

 

Jack

 

 

[Ross]

Hi Jack

 

I am very interested in your results as I near eventually getting my #14 kit J160 into the air.

 

A lot of the engine problems seem to be associated with running the engine too hot so my interest in these posts particularly for the J160.

 

Just a few minutes ago I got an email from AircraftSpruce advising of the consignment of my order for a parcel of exhaust wrapping from the USA!

 

Regards

 

 

[Steve Donald]

Hiya Ross, i have heard as well the wrap makes a huge difference to temps as well as reducing the heat that transfers to the induction pipes and leak out that occurs here, this heat on the induction does richen the mixture further but unevenly and only in the hot induction areas, causing a hotter CHT as well to an individual cld. So i wouldn't mind betting there would also be a slight performance improvement as a bonus, as cooler air induction is the first step in any performance mod, i don't have any temp issues with my aircraft but i would like to reduce the heat directly on the induction pipes to balance mixtures evenly has to be better, at full power fuel flow on the 4 cld is about 20 ish ph so that needs to mix with a correct volume of air hot air less volume cooler air more volume, the carb can only pull whats there even though the carb auto compensates it can only use what is available, more oxygen in the cooler air= better burn, i will post my findings whatever they are. induction icing is not an issue, this is caused by the atmospheric conditions on the day, it is good to be aware of conditions that exacerbate icing. it is a good idea as a check that you are not overlean just add some carb heat, now if the RPM increases i would suspect you are to lean and would recomend you get a L2 to check it out if you are not familiar with jetting ect. also dont chase economy bug, it will cost ya more in the end, burn the fuel 15/16 ph in the 4cld is good 2850 to 3100 rpm cruise the engine will love it

 

 

[Ross]

Hi Steve I think that I will try and prevent some radiant heat from reaching the oil cooler from the muffler. It is so easy to overheat the engine in that initial climb from the take off where you are rather busy.

 

I will either fully wrap or partially wrap the muffler with exhaust tape or just put a radiation shield between the muffler and the oil cooler like the one that reduces radiant heat getting to the carburettor from the muffler.

 

So I will probably do one of those alternatives before I fly it and then suck it and see.

 

I am still waiting on the muffler tape but have decided to do some more on the tyres again to get them in balance and to replace the liners.

 

 

[Vev]

Hi Ross,

 

 

Where is your oil cooler located?

 

 

It sounds like you must have a different set up to my 160 … mine hangs off brackets in front of the sump and fits snugly into the air intake, which is quite some distance from the muffler and therefore I think not effected by radiated heat.

 

 

Regards

 

Jack

 

 

[Ross]

20081214 Hi Jack the oil cooler & muffler are only 50 mm apart with the air inlet side of the cooler only a few mm from the cowl air inlet. It is bounded by a sock of made of Neoprene sheeting pop-rivetted to the opening to keep the incoming air going to the cooler radiator. See attached pic.

 

I can always remove any muffler shielding if it runs too cold.

 

From what I remember of oil theory is that the oil temp maximum generally recommended was the temperature at which the oxidation rate of the oil became unacceptable becoming a major factor in the life of the oil and therefore also a major factor in the life of the motor.

 

For good lubrication, the oil temperature does not have to be near the maximum.

 

When the oil is oxidised it forms very abrasive and corrosive products. The abrasive ones do obvious wearing damage and the corrosive ones should be neutralised by the additives that come the oil but eventually are all used up. The hotter the oil runs the faster all these events take place. When the additives are used up neutralising the corrosive products the corrosion becomes quite dramatic on some parts of the motor particularly some bearing materials.

 

[ATTACH]6934.vB[/ATTACH]

 

When I eventually fly it that will tell me what is going on if my gauges work and I look at them but I do not want a cooked motor on a test flight or shortly after. That would seem easy enough to do without trying going by at least three examples nearby two of which were Jabiru 3000 motors. The third was not a Jabiru.

 

The exhaust spring and lock wire are temporarily removed. Gotta go. A thunder storm.

 

Regards

 

 

 

[Vev]

Hi Ross,

 

 

For what it’s worth, I have the same brackets and cooler as you but it sits 180deg to your set up with the brackets turned around and facing fwd. This allows my cooler to fit snugly into the air intake without the sock, which means it’s quite some distance from the muffler. I wonder if this is why I hear from time to time some jabs having an oil temp problem, which I have never experienced???

 

 

Cheers

 

Jack

 

 

[Ross]

Hi Jack

 

I don't think I could turn my brackets around with the supplied bottom cowl. I actually had to remove some fibreglass off the back of the air cooler intake as it was touching the oil cooler in the present configuration.

 

This cowl is substantially different from the original and has much more bottom lip than the original to help the air flow presumably.

 

If you could do a pic or two it might be helpful at least to see what I am missing.

 

If I picture it in my mind correctly you also probably get more airflow over the bottom of the sump as it leaves the oil cooler.

 

Regards

 

 

[Vev]

Hi Ross,

 

Will do some pics but won't be able to do until the weekend. I think you're right in terms of my configeration re air flow over the sump... I'm quite sure the fitment I have will provide very good oil cooling.

 

Regards

 

Jack

 

 

[Steve Donald]

hiya Ross i just wrapped my pipes this morning, also put a heat mat in front of the carb and the face of the air filter box as a thermal barrier, i had no temp issues before but runs about 5 deg less cht, but i did pick up about 50 rpm static, I am sure this due to an improved mixture due to cooler induction pipes, any gain is worth the effort to balance mixtures i am happy with the result

 

 

[Vev]

Hi Steve,

 

This sounds like an excellent outcome.

 

When you say 5 deg lower CHT is this F or C???

 

Regards

 

Jack

 

 

[Steve Donald]

hiya Jack, it is Celsius what i did forget to mention is the cowl underbonet temp i put a remote sensor near the battery it read 12C less with the wrap on, has to be better for all of the electrics as well battery, i used the black graphite bandage 50mm wide, most ignition and other electrical components fail due to heat,or a much shorter life span, the exhaust are stailess so corrosion wont be a prob, and cracking i would suspect would be less an issue as the wrap creates a damping force assorbing resonance and vibration, time will tell i guess

 

 

[Geoff]

Hi Ross, if you wrap the muffler were will you get the heat for the carb?