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Old 09-18-2017, 04:57 PM   #1
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Dry riser question

All

I have had a new riser manufactured for my new engine install. My question is while it comes with a blanket the connection flanges are not covered is this a issue. How would they best be insulated if it's important.

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Old 09-18-2017, 06:51 PM   #2
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You have the water injection elbow bolted to the dry riser, so I don't think you need to worry much about a fire. Although it might be hot enough to burn you if you touch that. Probably could wrap it with header heat tape like used on cars.

example
https://shop.advanceautoparts.com/p/...E&gclsrc=aw.ds
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Old 09-18-2017, 09:04 PM   #3
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Just wrap with fiberglass bandage tape. That is all we used for the entire riser - no blanket.
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Old 09-18-2017, 11:36 PM   #4
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Any part of the exhaust system not water cooled needs to be wrapped in some form of insulation both from a safety point of view but as importantly keeping the temperature in your engine room at a cooler temp not just for your main engine requirement but as importantly for other engine room items such as and FIRE safety.

1) Generators -out put goes down they hotter they run, damage to wiring
2) Any electronics mounted in the engine room
3) Batteries if mounted in Engine room
4) As much as two thirds of all fires on board ships start in the engine room
5) The larger part of these are initiated by oil reaching a surface of a temperature above the auto-ignition point of the oil
6) For most oils such a critical temperature is just above 250C. SOLAS regulations therefore require insulation of all hot surfaces with a temperature above 220C, providing a "comfort zone" between the two temp's
7) Even if the insulation of an exhaust channel is of a good appearance, there may be hidden inadequately insulated areas and smaller open hot spots which could start a fire if in contact with oil.

If you dont think your exhaust gets this hot take a look at the below thermo picture of a exhaust partially wrapped

Cheers Steve
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Old 09-18-2017, 11:45 PM   #5
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Forgot to say, it looks like your new system is in Stainless Steel? if so dont forget the 300 series of stainless steels retain more heat than mild steel @ approx 219% more!

Not a lot of average boaters realize that?

Cheers Steve
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Old 09-19-2017, 12:00 AM   #6
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If still a non believer below picture is from a cummins engine with a non water cooled Turbo -running @ 3/4 to WOT throttle, we did for an owner that didn't understand what reality looked like, he changed his mind shortly after our engine survey - main complaint was regularly failing gen set bearings!!,- this engine room due to lack of a correctly fitted blower/ventilation system was at the staggering temp of 70 C
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Old 09-19-2017, 05:15 PM   #7
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Hmmmm, that last turbo picture looks a lot like one on this page....

https://www.honeywell.com/newsroom/m...urs-of-le-mans

Also, something a friend pointed out (he designs exhaust systems for diesels) pointed this out....

'The thermal conductivity of 300 series stainless is 1/3rd to 1/4 that of mild steel ... that means less heat moves through it to the outside. The specific heat (the amount of heat per pound required to raise its temperature 1 degree F - which can be described as how much heat it "holds") is actually less than mild steel, not enough for a boat owner to even measure.

http://www.engineersedge.com/properties_of_metals.htm

The fact that a stainless exhaust system uses thinner and lighter material than a steel system means that there is less heat retained in the piping and the fact that stainless conducts less heat than mild steel means more of the exhaust heat goes out with the exhaust then with a mild steel system."
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Old 09-19-2017, 11:03 PM   #8
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Originally Posted by psneeld View Post
Hmmmm, that last turbo picture looks a lot like one on this page....

https://www.honeywell.com/newsroom/m...urs-of-le-mans

Also, something a friend pointed out (he designs exhaust systems for diesels) pointed this out....

'The thermal conductivity of 300 series stainless is 1/3rd to 1/4 that of mild steel ... that means less heat moves through it to the outside. The specific heat (the amount of heat per pound required to raise its temperature 1 degree F - which can be described as how much heat it "holds") is actually less than mild steel, not enough for a boat owner to even measure.

Thermal Properties of Metals, Conductivity, Thermal Expansion, Specific Heat | Engineers Edge

The fact that a stainless exhaust system uses thinner and lighter material than a steel system means that there is less heat retained in the piping and the fact that stainless conducts less heat than mild steel means more of the exhaust heat goes out with the exhaust then with a mild steel system."

Hmmm, you know what the last turbo picture looks like the original post as:

https://www.sbmar.com/articles/propp...exhaust-leaks/

As images are posted on the WWW there's no end to who and how they are used after insertion??????

Perhaps there's just to much book work here, above arguments just prove the point that , What many operators and builders DO NOT understand is the approx 1/3 of the total energy (heat) that comes from the fuel that is consumed by a diesel engine is expelled as heat thru the exhaust system, and this heat must be contained and then exit the vessel safely.


Current REGULATIONS

1) The design of all exhaust systems must ensure minimum risk of injury to personnel. Protection must be provided in compliance with 177.970 : at such locations where persons or equipment might come in contact with an exhaust pipe.(What the original post was about)
2) If it passes through a combustible bulkhead or partition, be kept clear of, and suitably insulated or shielded from, combustible material.

In closing: Dry exhaust systems (especially close to the engine) can run @ 1200 f this means special lagging/insulation needs to added for the protection of people and surrounding area's/structure.This is the biggest area to come to grips with if using a dry or partial dry system.

You can ignore the following as it's only for the Book worms

1)Thermal conductivity is a materials ability to conduct heat through itself over a temperature gradient (temperature difference). The specific heat is the amount of energy required to change the temperature of a material a specific amount.

2)Stainless steel, has by definition a minimum of 10.5% chromium(normally 18%) added to it which gives it its non-corrosive properties. But chromium atoms that are mixed in with the iron have the added effect of making the material worse at conducting heat than mild steel.


Cheers Steve, Chief Marine Eng (I love it when engineers nerd out over such fun things! Fun to read and a nice little metals )
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Old 09-20-2017, 06:28 AM   #9
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Seems like 2 different views on why stainless could/should be used or not in marine exhaust systems. Its how the system is dealing with the heat in the exhaust gas.

Of course aside from corrosion.
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Old 09-20-2017, 07:19 AM   #10
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Quote:
All diesel engines, by design, lose about 33% of all the energy made (heat) burning fuel out the exhaust… So if you are burning 20 gallons per hour, that means the crankshaft is putting about 400 HP into the prop to move your boat forward, and about 400 HP thru the exhaust.
https://www.sbmar.com/articles/propp...exhaust-leaks/

Sad, very sad waste of heat energy is an internal combustion engine.

Someday we will have diesel fuel cells that heat the diesel and turn it into electricity more efficiently and electric drives. No transmissions needed.

I imagine this is still a few decades away for common use.
There would be no attempts at fuel cells unless exists significantly increased efficiency. Practically no moving parts too.
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The system is designed for the use in truck, recreational vehicle and yacht applications. It generates up to three kilowatts electrical power but can easily be modified for larger power ranges. Therewith enough output is available to run electric and electronic small consumers as well as „power guzzlers” like for instance air conditioning or refrigerators.
https://www.imm.fraunhofer.de/en/pre...fuel-cell.html
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To extract the hydrogen, which is needed for the fuel cell, out of the Diesel, the Diesel fuel in the tank is converted into a hydrogen-rich gas by autothermal reforming. This process was developed at Forschungszentrum Jlich and has already proven its high stability for a duration in the range of 10,000 hours. Carbon monoxide which is also generated by the reforming process is initially converted to a remaining low concentration (< 10 ppm) by means of further reactors (plate heat exchangers by Fraunhofer ICT-IMM) being part of the fuel processor. This is also valid for the sulfur which is contained in the fuel in minor amounts. The resulting gas is primarily composed of hydrogen, carbon dioxide and steam of which the hydrogen is processed in the fuel cell to generate electricity.
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Old 09-20-2017, 08:16 AM   #11
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Now, back to the question asked. Yes, wrap the exhaust up to the point the water injection elbow is placed. When in doubt, get your IR gun out to check for wrap integrity and missed spots.
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Old 09-20-2017, 08:59 AM   #12
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Originally Posted by psneeld View Post




The fact that a stainless exhaust system uses thinner and lighter material than a steel system means that there is less heat retained in the piping and the fact that stainless conducts less heat than mild steel means more of the exhaust heat goes out with the exhaust then with a mild steel system."
careful. Thinner means more heat conduction, all else being equal. You have "less conductive material that is thinner". May or may not be more heat transfer.
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Old 09-20-2017, 09:33 AM   #13
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Just going by what a patented diesel systems designer passed along.

Less heat transfer to the piping, less retained...somehow like lots of engineering ideas...2 ways to look at it from my less than tevhnical petspective.

Ultimately, practicality fits in a bit also....
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Old 09-20-2017, 10:04 AM   #14
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The specific heat and the thermal conductivity of the tubing do not really matter here. Conditions are pretty steady state once at a certain power setting, so temperatures will not be changing. It is thin walled stuff so not much of a temperature gradient in the material.

What does matter is the quality and fit of the lagging. Blankets can be ok, but also prone to poor fit which leaves "windows" with lots of radiative and convective heat transfer. If you do a blanket, it has to fit WELL.

If you do fiberglass wrap, that cures the gaps but also does tend to have higher thermal conductivity. It can do the job, but you have to be careful about anything combustible nearby.

Modern mixers have a dry section that is insulated then has some sort of hard coating applied. Not sure what the various materials are, but it works.
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Old 09-20-2017, 11:31 AM   #15
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Modern mixers have a dry section that is insulated then has some sort of hard coating applied. Not sure what the various materials are, but it works.

Yes. You want to approach the capability of what the space shuttle used for thermal tiles. Extremely low thermal conduction, high thermal withstand and amazingly low specific heat. You can bare hand a tile after being blasted with a torch. I will guess this hard coating is a ceramic.
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Old 09-20-2017, 01:10 PM   #16
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Cover the joint properly. Don,t fool around. Heat conduction rates are a nice ,pointless arguement here. Although not incorrect.
The part will get HOT.
Cover it.
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Old 09-21-2017, 05:47 AM   #17
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"this engine room due to lack of a correctly fitted blower/ventilation system was at the staggering temp of 70 C"

Another boat assembler needs to be shot.
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Old 09-21-2017, 06:54 AM   #18
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Dry riser question

This thread got me thinking...

My boat is more of a sailboat design than powerboat, with the 4 cylinder turbo Yanmar tucked into a compartment under a bunk. The compartment doesn't have a blower, and this thread got me thinking about ventilation and heat trapped in the compartment.

What is a good max temp to have in the engine compartment?

Should my compartment have a powered vent system? I'm sitting here thinking and can't figure out where the engine is getting fresh air from since it seems to be sealed up, but obviously it can't be totally sealed because it wouldn't run. It must be sucking air through the bilge somehow.
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Old 09-21-2017, 09:54 AM   #19
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Yes. You want to approach the capability of what the space shuttle used for thermal tiles. Extremely low thermal conduction, high thermal withstand and amazingly low specific heat. You can bare hand a tile after being blasted with a torch. I will guess this hard coating is a ceramic.
Dave,

Yep you are correct Ceramic here's a couple of points:

1) Best corrosion protection of any exhaust system coating
2) Tested to over 900F base metal temperature and 1200F exhaust gas temperature
3) Can be applied to any part that can withstand 500 cure temperature
4) Provides lifetime protection against rust
5) Can reduce engine temperature by 15 degrees or more less heat absorbed by nearby parts and surface helping to preserve engine electronics
6) Can provide a higher density fuel/air charge and more horsepower (horsepower gains have been reported of over 3%)
7) Ceramic coating normally runs between 2 and 4 mils thick and provides a hard finish which is resistant to rust and abrasion
8) Ceramic coatings can be applied over chrome, aluminum, carbon steel, stainless steel or cast iron. It is ideal for parts exposed to extreme temperatures (2,000F) such as exhaust pipes, headers, manifolds, turbo housings, intakes and brackets.

Cheers Steve
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Old 09-21-2017, 10:08 AM   #20
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Cardude,

Quoting Yanmar's Marine Installation Manual Volume 1:

The temperature of the engine intake air at the inlet of the air cleaner should not exceed 45C (113F).

At 29mm distance from alternator, the temperature should not exceed 60C (140F).

The required ventilation volume "Q" is: Q = 0.15 x Maximum output (hp) = m/min. It can be supplied by natural ducting or fans. For example: 100HP needs 15 m/min. or about 530 ft/min. of engine room ventilation at maximum power.

Cooler is better though because engine power begins to degrade with intake air temperatures over 30C (86F).
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