Water Cooled Exhaust Manifolds

[cmn8226]

Hey guys, hope this is the right forum to ask my question:

I am currently in the process of building a Zone 2 compliant engine. One of the requirements is that any surface in contact with the surrounding air is under 200C. The exhaust gases reach temps up to 300C under our running conditions.

We are having to build a custom manifold with an integrated water jacket to ensure the surface temps do not reach over 200c.

My question is, we are going to use an external independent radiator with a fan for cooling the water circulating in the exhaust manifold, which is a water glycol mixture of 70-30. This loop is driven by an external water pump.

My question is, IF the pump fails, the water temp will shoot up to 300C and immediately turn to steam. In order to avoid this and keep the water in the liquid state we have to design the loop to withstand the saturation pressure of water at 300C (which is 1250psi if I am not mistaken) and run the system at those pressures? this seems very high.

I am in the correct on the above? This is my first time with an independent cooling loop to cool exhaust gases at that temps.

Any other ideas on how to achieve cooling the exhaust manifold at 300C to under 200C surface temps would be great

 

[Compositepro]

You need an expansion tank in you cooling loop. This will compensate for thermal expansion of the fluid and will control and limit the loop pressure. Boiling may occur if the pump fails. This is good and will provide cooling. Design the piping right and you will get cooling flow by thermosiphon effect with no pump running. Just remember that a pot of water on a gas stove still takes time to boil, and the flame is hotter than your exhaust.

 

[cmn8226]

Thanks for the quick response.

My area is not thermal nor cooling, hence why I am trying to get some feedback on the system design.

I am still unclear on how exactly to achieve this:
These are the facts

1. Independent cooling loop with water cooled exhaust manifold to ensure the surface temperatures at the exhaust is under 200C
2. Exhaust gases are at 300C
3. Loop consist of external centrifugal pump, radiator, fan, expansion tank and cooling manifold
3. Manifold has 2 chambers. 1 chamber is for exhaust gases in and out. Second chamber is for cooling water in and out.
4. Design Criteria for the loop is:
*Hot water out of manifold: 58C
*Cold water in to manifold: 54C
*Flow Rate: 16GPM
*Exhaust Gas temps 300C
*Mixture water-glycol 70-30
*Exhaust Gas flow rate: 175 kg/hr (Standard Diesel exhaust composition

Need to ensure that the system can handle immidiate water temps of 300C on the hot water out, in case of pump failure.

I have a high pressure switch for shutdown for the first line of defense and a steam vent valve in case pressure build up over a set pressure as the second line of defense.

What else should I consider?

 

[MikeHalloran]

If your base engine is available in a marine version, you may be able to just buy the manifold you need, since marine engines are now required to have water cooled exhaust manifolds.



Mike Halloran
Pembroke Pines, FL, USA

 

[amorrison]

I would check out what can be done with ambient air cooling.

Forced cooling (fan(s)) will get you 5-10X heat transfer for a given Delta T.

Fins (all along the exhaust manifold +/-) might get you an
another multiple of 5-10X of heat transfer for a given delta T.

So now what is the delta T required to get the heat out.

The best machines have no moving parts.

 

[MikeHalloran]

Yabbut... zone 2 means (I think) that flammable gases are assumed to be present, so you _really_ don't want ignition sources available. ... and even a hurricane of air might not keep the surface under that 200C limit.

Come to think of it, marine manifolds might not even be adequate. They're typically cast iron, but the flanges are solid and uncooled, and I think I've seen them glow a little on turbo Diesels that were really spooled up, even with cold seawater flowing through the manifolds.

I.e., the manifolds may require hollow/jacketed flanges. Now there's a fabrication challenge.




Mike Halloran
Pembroke Pines, FL, USA

 

[amorrison]

OP - Can you supply Internet sources for Zone 2 requirements in detail.

 

[osoloco]

cmn8226
Something else to ponder: Unless you are willing to use exotic materials do not allow the inside wall temperature to reach the dew point temperature of the exhaust stream. If this occurs you will get condensation on the exhaust pipe wall. This is very corrosive and WILL lead to failure of the exhaust pipe allowing the coolant to enter the exhaust pipe. If the exhaust points up then fluid will enter the engine at which point things get messy.
The calc's are a bit involved... My heat transfer & thermo texts are in another country or I would help more... good luck

 

[cmn8226]

thanks for the feedback guys. Deffo some good points to consider. I had not even thought about manifold getting rusted and coolant entering the exhaust piping.

Zone 2 requirements are based on the BS EN1834 standards. I am going to grab a copy and type of the most relevant section of it.

Ambient Cooling may not be the best way because it gets to 40C outside where the platform is, as well as 100% RH. Cooling might not be effective at those ambient conditions, specially if the exhaust is at 300C.