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Boat Forum / Building / July 2006Converting air cooled to water cooled...maybe
I just joined this group and have a dilema to present: My boat has a large engine room and I want to add a genset to it. BUT it must be diesel as I dont want any gasoline aboard. I can buy a new marine diesel gen set with warer cooling for $7,000 or so. I dont have that kind of money to spend. But I can buy a new diesel, AIR COOLED, getset for under $1000. With the gen set in the engine room I will either have to supply a MINIMUM (probably more) of 1000 CFM of cool air and exhaust it as well. This is not altogether too dificult, BUT that air I am supplying will be SALT air and will promote corrosion in the new gen set, I am sure. So I am wondering about the possibility of converting the air cooled diesel to a water cooled diesel with a salt to fresh water heat exchanger. I read somewhere once that someone did this by coiling copper pipe around the head of the engine for the fresh water part and used a wet exhaust to cool the exhaust. But with no details of how the fresh water cooling was actually constructed on the engine, and my limited imagination in this area, I dont see how it could work. I think it would take more than cooling the head alone. Does anyone have any ideas along these lines?? > I just joined this group and have a dilema to present: > [quoted text clipped - 18 lines] > > Does anyone have any ideas along these lines?? I wouldn't waste my time on this, it's not worth it, your just looking for trouble and the gen set will not be CG approved. If you have a problem, fire, CO gas, ect, your in trouble, your insurance won't cover it. And the boat will never pass a survey. >I wouldn't waste my time on this, it's not worth it, your just looking >for trouble and the gen set will not be CG approved. If you have a >problem, fire, CO gas, ect, your in trouble, your insurance won't cover >it. And the boat will never pass a survey. I agree. Probably your best bet is to find a good used "takeout". Check with one of your local Kohler or Onan dealers, they may have some laying around. Also check on EBAY. You don't want gasoline because it is too dangerous....and you want to jury rig cooling of a stay ashore generator???? Must be a troll. >I just joined this group and have a dilema to present: > [quoted text clipped - 18 lines] > > Does anyone have any ideas along these lines?? No, not a troll. And NO, I dont want to "jurry rig." I want to do it right the first time. I see no reason why ducting air to an air cooled device is jurry rigging. After all we duct sea water to a fresh water cooled engine to cool the fresh water and we dont call that "jurry rigged". If any thing is a Rube Goldperg design, fresh water cooled engines are!!! Sure, if one does not prepare for all the challanges, it would be jurry rigged. With propper sensing on engines we prevent destructive failures. Why cant we assume the same for an air cooled system? I would use temperature sensing to make sure there was no fire hazard etc. > You don't want gasoline because it is too dangerous....and you want to jury > rig cooling of a stay ashore generator???? Must be a troll. [quoted text clipped - 20 lines] > > > > Does anyone have any ideas along these lines?? Jim, Sorry, but changing the mode of cooling for an engine without proper engineering *is* jury rigging. Not at all the same as just using a water-to-water heat exchanger. If you're worried about "salt" air, and you're running in cold water, put a de-mister coil in the air duct and pipe sea water through it chill it and pull the moisture out of the air. Now that's a Rube'd device that would actually work. Bear in mind though that by the time you buy all the required equipment to make the aircooled unit functional and long-lived, you'll have a bunch more into it than the $1K, and you'll have a less fuel-efficient unit. Keith Hughes > No, not a troll. And NO, I dont want to "jurry rig." > [quoted text clipped - 35 lines] >>> >>>Does anyone have any ideas along these lines?? > Jim, > > Sorry, but changing the mode of cooling for an engine without proper > engineering *is* jury rigging. I didnt say I wanted to do it "without proper engineering." That is why I am here, to get information on how to properly engineer it. I am an engineer so with proper input I think this can be done. As you say, it may not be economical, but to reject it out of hand is shortsighted. I always like to point out to young engineers that if we didnt try what couldnt be done, nothing would ever be accomplished. Almost any engineering project has never been done before or it wouldnt be in the engineering department, the technicians in the lab would have looked it up and done it by now. >>Jim, >> >>Sorry, but changing the mode of cooling for an engine without proper >>engineering *is* jury rigging. > > I didnt say I wanted to do it "without proper engineering." OK, but 'wrapping copper tubing around the cylinders' doesn't sound like an approach resulting from much engineering analysis. > That is why I am here, to get information on how to properly engineer > it. I am an engineer so with proper input I think this can be done. Well then, surely you must know that you first need the designed combustion chamber temperature range and the thermal conduction profile for the cylinder sleeve (top to bottom), to properly size the multiple, vertically segmented, cooling loops you'll require. You could estimate the vertical temperature cline by analyzing the relative fin surface areas, air flow rates, and standard thermal conduction value (F sub r, U sub L as ASHRAE defines it) and the emissivity of the fin material. And that just gets you the info you need to design the heat exchange process. You need to go through the same exercise with the copper tubing with the bonding method, heat transfer characteristics, mass flow requirements, baffling to ensure turbulent flow, etc., etc. Not a trivial exercise. > As you say, it may not be economical, but to reject it out of hand is > shortsighted. As you seem to have rejected, out of hand as you say, the most simple way of achieving your stated goal? I.e., not air cooling with "salt" air. Properly trapped (i.e. collection drain) demisters are the standard method for achieving these results. Used all the time to pull moisture from ductwork. > I always like to point out to young engineers that if we didnt try what > couldnt be done, nothing would ever be accomplished. You might also want to point out that trying to create novel designs and implementations when existing designs *meet all customer requirements* results in nothing but higher development costs and, typically, unnecessary process complexity. This, IME, is the biggest failing of most engineers (excepting R&D of course). And, I might point out, this thread epitomizes that situation; trying to redesign the end point of the process (i.e. the engine) instead of addressing the problem earlier in the process (i.e. the cooling air supply) where it can be solved easier, cheaper, and with less complexity. > Almost any > engineering project has never been done before or it wouldnt be in the > engineering department, the technicians in the lab would have looked it > up and done it by now. Well, sorry but that's just ridiculous. Virtually all day to day engineering projects are varying implementations of basic systems/processes that are done all the time. The vast majority of engineers are not involved in R&D work; they're doing practical process applications using basic engineering principles. I'm not trivializing the Engineering process. The most difficult engineering exercise, IME, is taking an existing process or piece of equipment and implementing that process or equipment into a specific/unique application and achieving a result that is timely rugged, efficient, cost-effective, and meets the specific needs of the end user. If you can do all of those five, you're a damn fine engineer. Keith Hughes This has degenerated from a discussion of possibilities into what I would expect in a board meeting, not in an engineering lab. So I am bailing out to look elsewhere. By the way, I didnt reject air cooling, only expressed my concern that it could cause corosion. BTW, thanks for those comments, they WERE valuable. > >>Jim, > >> [quoted text clipped - 63 lines] > > Keith Hughes > This has degenerated from a discussion of possibilities into what I > would expect in a board meeting, not in an engineering lab. So I am [quoted text clipped - 3 lines] > it could cause corosion. BTW, thanks for those comments, they WERE > valuable. Don't bail out too soon, there will always be more 'you can't do that' types than 'that sounds interesting, let's have a think around the problem' types. Adrian Smith. > Don't bail out too soon, there will always be more 'you can't do that' types > than 'that sounds interesting, let's have a think around the problem' types. > > Adrian Smith. I will continue to look at the problem, not bailing out yet. I dont have a metal hull anymore. My current boat is Fiberglass. The last one was steel but I sold it. However, my research seems to indicate that I need about 1500 cfm and that shouldnt be too hard to get. >> Don't bail out too soon, there will always be more 'you can't do that' >> types [quoted text clipped - 10 lines] > However, my research seems to indicate that I need about 1500 cfm and > that shouldnt be too hard to get. How did you arrive at 1500cfm? (Asking cause I just guessed.) I used an oversized fan, linked to a temperature controlled speed controller, with auto shut down should things get too hot. Even at full tilt, 3 KW, the cooling fan never reaches anywhere near full speed. Adrian Smith >> That is why I am here, to get information on how to properly engineer >> it. I am an engineer so with proper input I think this can be done. [quoted text clipped - 11 lines] >requirements, baffling to ensure turbulent flow, etc., etc. Not a >trivial exercise. You could always just measure the temp of the head and block in different locations and under different loads. Knowing the difference in block temp at idle and full load would be very useful. Using a thermocouple(s) to measure the block temp between the fins would be a good start. It may be the fins are designed to give a fairly even temp throughout the block itself. Some slightly oversized copper tube that's squashed to give an interference fit between the fins should give good conduction, if not enough then use more than one layer. In testing the thermocouple could be used to monitor the block temp under water cooling, to ensure it's within the same values as for air cooling. One issue with copper is that it may fracture through vibration if not supported properly, so stainless may be better for some parts. A tank, manifold, thermostat, pressure relief, and raw water heat exchanger would also be needed. Also a thermal cutout if the cooling fails. Different temps at top and bottom of block could be accomodated by different thermostats. Doing some practice on an old engine might give some useful lessons. cheers, Pete. > No, not a troll. And NO, I dont want to "jurry rig." No, but you want to "warer cool". Judge not, lest ye be judged. Sounds like a troll to me. You could try this. A fan sucking from a long duct inside the hull. If the hull is steel or aluminum, it would be quite effectively cooled air from the sea water. The duct plays over the cylinder then exhaust manifold. Brian Whatcott. >No, not a troll. And NO, I dont want to "jurry rig." > [quoted text clipped - 34 lines] >> > >> > Does anyone have any ideas along these lines?? > You could try this. A fan sucking from a long duct inside the hull. > If the hull is steel or aluminum, it would be quite effectively cooled > air from the sea water. The duct plays over the cylinder then exhaust > manifold. > > Brian Whatcott. I have actually done this with excellent results. Basically, I contained the diesel generator in a soundproofed box and sucked air out of the box. The air inlet sucked air that was first passed over a large area of the steel hull. The incoming air being specifically directed at the cylinder head area. As a finishing touch I installed a fire detector and two heat sensors both of which can independently cut the engine and fuel in the event of the compartment overheating. Hope this helps. Adrian Smith. |
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