exhaust gas heat exchanger

have a look at these links:
http://www.ejbowman.co.uk/pdf/ExhaustGas.pdf
http://www.polarpowerinc.com/products/heat_exchanger/heat_exchanger.htm

try and follow me here, I am assuming that there is about 5' -8' of dry exhaust before the exhaust gas enters a wet exhaust: Install this Bowman heat exchanger as the first part of the exhaust system (just after the engine), then let the raw water pump circulate the sea water though it (heats up the water and cools the gas), and then let the hot water flow to the standard wet exhaust for further cooling.

My thinking is that this double heat extraction will reduce the temperature of the exhaust gas (by heating the sea water and extracting it over board), and also reduce the noise in the engine room.

An additional benefit would be the reduced insulation work around the dry section of the exhaust.

Would this be an overkill?

 

That may be useful for engines without water cooled exhaust manifolds. I use Bowman's manifolds with integrated heat exchanger, where the exhaust temperature is already that low it impairs the performance of the turbo chargers.

 

Thanks, this engine is naturally aspired and does it not have a water cooled manifold. Hense the dry section folled by a wet exhaust

Would it reduce the noise compared to the standard 5-8 feet dry exhaust followed by a wet exhaust?

 

It might be a little quieter but wouldn't a good lagging job accomplish the same thing. Then you wouldn't have to worry about the thing leaking internally and ruining your engine. Same goes for the water cooled sections. Many builders will wrap the water cooled sections of exhaust tubes to reduce the sound coming through.

 

I doubt that it will make much difference. The dry part is a metal tube and should stay that way because the exhaust gases after the heat exchanger will still be too hot for a rubber hose.
The metal pipe amplifies exhaust sound.

To change that, water must be injected directly behind the exchanger, which is only possible when there is protection against water entering the engine i.e. a riser or the exhaust pipe is sloped downward from the engine to the stern.

 

I think that it will work as a silencer, with the added benefit of removing heat. The polarpowerinc might be a better system though since the heat exchanger can run dry (the other one must have water in it) -this means that it must be insulated as well (so no benefit there).
Also, the remaining temperature after the Polarpowerinc is about 90-130 Degree F - this should be cool enough for exhaust hose.

 

No, that isn't true unless you're in a polar region and pump enormous quantities of water through the exchanger.
The datasheet says the exhaust gas is up to 100 F. above the output water temp. and doesn't specify engine hp.

In their examples 12 hp is used, which may not be what you have in mind.

 

good point.
But the exhaust gas heat exchanger will still reduce the heat-load and noise in the engine room since the heat is taken away so close to the engine. The point was also to let the exhaust gas and water meet again in the wet exhaust to take away the last heat.

 

My idea has just been shot down by an old boatbuilder, he said the weldings would rust through within 5 years...That is a show stopper.
thanks

 

Tell your mate you will cast it from inconel...that will last a bit longer

 

Excellent advise....................!