Aircooled manifold, water cooled exhaust?

Discussion in 'DIY Marinizing' started by DennisRB, Dec 10, 2016.

  1. DennisRB
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    DennisRB Senior Member

    Waterpumps and exhaust elbows are easy. Building a watercooled manifold is much harder. Has anyone tried using a fan forced ducted cooling system for a manifold, then just injected water into the exhaust?

    In a car there is no cooling, so the manifold does not need it. But in a boat the heat needs to be taken away from the engine compartment. Some simple shielding and a pressurised fan and ducting system may suffice?
     
  2. gonzo
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    gonzo Senior Member

    The heat that the air can take is much less than what water can. The ratio is about 4.3. Also, you need to consider how to circulate the air in and out of the engineroom without letting the heat transfer into the compartment.
     
  3. DennisRB
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    DennisRB Senior Member

    The shielding would be an insulator, the air would just be forced through enough to keep the shielding temp acceptable to prevent excessive radiation. The only way I can see it working is that the ducting would exit to the exterior of the boat, air would enter the same way as it would for the running of the engine so it would present little extra issue.
     
  4. DennisRB
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    DennisRB Senior Member

    What I am in fact proposing is functionally the same as a water cooled manifold but the cooling medium is air. A containment vessel will be built around the manifold just like a water cooled one, air will be forced to flow through it, then exit the vessel. Very similar to a water cooled version.

    It will be easily made from sheet aluminium or similar, require no welding, be light weight and use a simple fan. It does not need to be water tight. Fabrication would be trivial and cheap compared to watercooled for a DIY marinization.

    Water moves a lot more heat yes, but think of the tiny water flow rate used. The fan can pump massive amounts more so will make up for it. The shielding properties alone would be a massive help even with no airflow.

    Ideally a heat tolerant fan could be used on the suction side to draw air in through any gaps in the shielding. Any plastic fan could be used on the intake with more attention to minimizing gaps that would allow hot air to escape under pressure compared to a vacuum system.
     
  5. Carioca
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    Carioca Junior Member

    I fabricated cooling jackets from SS, which enclose the turbo charger units on my twin-diesel set up.

    Engine water (closed-circuit) circulates through these cooling jackets and helps to transfer the heat irradiated by the turbo chargers, which would otherwise heat the surrounding space.

    I know of a person who enclosed the exhaust manifold on his Cummins 6BTA in a similar way....never had a problem, though he does have a wet exhaust elbow.

    Not a simple feat when both the admission as well as the exhaust manifold are on the same side of the engine.

    Bear in mind that a water-cooled exhaust manifold usually increases the heat load on the heat-exchanger, while decreasing the power available for the turbo to offset pumping losses.

    Having a water-jacket around your manifold - containing and conducting irradiated heat as it were - will keep your engine compartment cooler, while also reducing the fire risk, should fuel spill on a hot, bare exhaust manifold.
     
  6. DennisRB
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    DennisRB Senior Member

    Do you have pics of the cooling jackets of the turbos? Is the water in contact with the turbine housing in your method? That would lower the boost threshhold, but that probably does not matter in a boat where surplus power is always available in the lower RPM range due to the way a propeller requires exponentially less power at low RPM.

    I have been involved in custom turbocharging and have many a debate on the matter. In short, reducing available heat by cooling the exhaust gasses wont loose you any peak power or efficiency as long as the turbine still gets enough energy to produce the required boost pressure. Adding more exhaust energy if that boost target is met only means the wastegate needs to open further to waste the extra unnecessary excess energy. But it cooler gasses will mean less boost at lower RPM which may matter in many applications such as acceleration (not as important in a boat as a car)

    But I digress. I would just have the turbine housing and manifold ceramic coated and use shielding containment and air pumping in the method that I want to discuss in this thread.

    Freshwater cooling? That would require the same effort as a raw water manifold, but I think its a good idea if water cooling is what you want.

    Absolutely, but why cant a similar air jacket with forced air cooling have a similar acceptable effect if correctly designed and implemented?

    I agree, the risk of fire will be less with water as the the whole entire thing needs to be 100% water tight and the air cooled version does not.

    To put this into perceptive we are talking sailing AUX engine here maybe 100hp available (as you cant find anything with less power than that in a car to marinize), but hardly run anywhere near that HP, so the exhaust temps would be low anyway. I was thinking a petrol car engine like from a small Toyota. 37% thermal efficiency, light weight 100kg engine of 1500cc capacity. Easy and cheap to find spares for. There are next to no small diesel engine here in AU to use. They are all rare, expensive heavy, and have much more power than required so will probably not be more efficient than a modern engine from a Toyota Yaris or similar anyway.
     
  7. tom kane
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    tom kane Senior Member

    Complete Auto engines are great in boats and have a lot of advantages some good thinking going on here just a matter of getting the right design sorted designing the boat to suit.
    But watch out for those regulatory requirements they may trip you up.
     
  8. Carioca
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    Carioca Junior Member

    The whole idea is related to the KISS principle !

    Do you have fresh-water engine cooling on board ? Make avail of this facility for any extra cooling/heating applications in your boat.

    Fresh-air cooling will require air pumps. The rest is for you to decide.
     
  9. DennisRB
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    DennisRB Senior Member

    There is no boat to speak of right now. Just wanted to discuss this idea.

    A cooling fan isvery cheap and simple. Building a water cooled manifold is much harder, even though I am capable of that.

    There would be a heat exchanger for fresh water cooling. Probably a titanium pool heat exchanger requiring no fabrication, just plumbing.
     
  10. Carioca
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    Carioca Junior Member

    Enclosing the OEM exhaust manifold with a water-cooled metal shroud - painted lamp black on the surface facing the former, to enhance absorption (black-body radiator/absorber)- is much, much simpler than designing and manufacturing a water-cooled one-off exhaust manifold.

    And choice of the latter will see your heat-exchanger requirements getting more demanding ( you will pick up conducted heat, not just radiated heat)

    You are obviously going to need some kind of a heat-exchanger, be it a keel-cooler sort - a couple of copper pipes, one 'out', the other 'in' that circulate engine water beneath the hull to cool it, availing of underwater currents and/or boat dynamics - or a more elaborate and costly option, such as a shell-and-tube heat exchanger installed on baord.

    Your engine water-pump will be doing the job of circulating the closed-circuit cooling water in any of the two alternatives selected above. The more elaborate option would require purchase of a sea-water pump driven off the engine crankshaft.

    So if you go the metal shroud route, it will be one less item to purchase and to maintain in good running order, even if it is a simple air fan ! Obviously, you will need to exhaust hot air from your bilge !

    Keep in mind that if your engine outputs 30 HP at the crankshaft (roughly 23 kW)...imagine at least 23 x 1 kW electric heaters in your bilge from just cooling the engine block if you scrap the idea of a heat-exchanger and decide to use a standard auto-type air-cooled radiator....and that too, excluding the water-cooled metal shroud over the exhaust manifold.
     
  11. DennisRB
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    DennisRB Senior Member

    I certainly think a rawwater/freshwater heat exhanger will be worth it. Something like this titanium heat exchanger. http://www.ebay.com.au/itm/Titanium...873516?hash=item3ab2714f6c:g:LMUAAOSwKIpWA0ju

    A raw water pump could be electric. I like the idea of items like this being modular. They are connected only by pipes. So when they need replacing an exact version will not be required and the job will be done on minutes.

    http://www.ebay.com.au/itm/12V-24V-...677392?hash=item2ef4084190:g:ZrIAAOSwGtRXzlkq
    http://www.ebay.com.au/itm/40L-Min-...309078?hash=item41b2c7be56:g:WJkAAOSwxg5X1e~B

    They are so cheap you would use 2 at once even if only one is required and carry a few spares. I have not ascertained required flow rates, merely that you can buy this stuff.

    Your water cooled shroud does seem like an OK idea, but the fan forced version would still be simpler, lighter and cheaper.

    I would love to see some pics. Do you have any?
     
  12. tom kane
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    tom kane Senior Member

    Aircooled manifold,water cooled exhaust

    Why would anyone not want all of the advantages present in a modern auto engine in their boat, a 6 speed auto would be great,even a three speed manual box is good.
    the air conditioner can cool boat cabin and help the engine cooling at a small power loss to transmission.
    Auto engines do not have water cooled exhausts so don`t put water into your boat engine.except at the extreme exit but preferably water jacket the exhaust.

    All engines have an optimum operating temp and keeping an auto engine at right temp in a boat is not difficult.
    Oil pan does not need cooling but an oil cooler can be fitted simply.
    Auto or manual G/Box can be easily cooled.
    Crank case fumes can be burned.
    The list goes on, I love easy to maintain auto engines in a boat.
     

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  13. DennisRB
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    DennisRB Senior Member

    High Tom. I'm fairly sure only 2 of the forward gears are of any use. With 1st being a little too short, probably good for going against strong winds and chop. Second is kind of an overdrive. Reverse seems too short, but acceptable. The rest are almost unusable, maybe 3rd if you are lucky. Obviously prop dependant.

    ZF6 speed.
    1st gear ratio 4.17
    2nd gear ratio 2.34
    3rd gear ratio 1.52
    4th gear ratio 1.14
    5th gear ratio 0.87
    6th gear ratio 0.69
    Reverse 3.4

    As for the comments about "auto" engines not putting water into the boat? What does the transmission have to do with that? This is just a problem with marinizing that they don't in fact do this. We need to figure out how to cool stuff down for boat use. You can even fit a cooler thermostat which may decrease the thermal efficiency by a % or 2. Modern car engines run at very high temps, around 100 deg for efficiency. Heat exchangers and exhaust cooling are issues needing solving. I would still want a raw water cooling system for a heat exhanger, and that water would be dumped into an mixing elbow at the exhaust collector. Without this you have a very hot and noisy dry exhaust.

    My propsal for keeping heat down for the manifold was over and above a heat shield by providing targeting air cooling and removal of that hot air from the engine compartment. I dont think a regular automotive heat shield will be enough. Carioca has said you can just build a water cooled heat shield instead of a full blown water cooled manifold.

    In a boat we can eliminate the Torque Converter as the prop acts like one anyway. The TC is the major power loss in an auto trans. Once that is gone it is not much less efficient than a regular trans. Just about all auto TCs have a "lock up" clutch in them which stops slip anyway. But from experiance I think they will not be up to the task and fail. In a car, the ECU enguages this lockup under cruise. In a marine application there may be too much power for this small clutch to hold all day everyday. Oil coolers are easy with an auto as they already have an oil pump. With no torque converter they would not need a lot of cooling.

    Using the standard car AC is also opens up a few possibilities of course :) Like cabin AC and eutectic plate refrigeration etc. I would probably have it set up for a large day ice chest for parties, big fishing trips etc where the regular fridge is too small.
     
  14. tom kane
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    tom kane Senior Member

    DennisRB. I suggested against having any water cooling inside the exhaust for obvious reasons preferably a water jacketed exhaust, and modern mufflers make autos very quiet. I prefer exhaust to go straight up from the boat not out the back as the fumes circulate back into the boat. This can be raw water cooled where necessary, at hot spots.
    (Auto engines do not have water cooled exhausts so don`t put water into your boat engine.except at the extreme exit but preferably water jacket the exhaust.)
    Having played with G/Boxes in boats you may be surprised what having a choice of gears is when you can switch your drive from a subsurface drive to s/p drive by having a retractable shaft drive.
    It`s a different world between the two and lots of scope for different propeller diameter and pitch and gearing.
    As you say gears definitely have their uses in a boat and torque converters make changing quick and easy..slip into reverse or any gear is a must for my type of boating.
    One of my first boats had a three speed box and it was pleasant to be able to run the engine fast but go slow in unknown waters in a rough and windy sea.

    Added image.nice easy control for a boat?
     

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    Last edited: Dec 12, 2016
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  15. DennisRB
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    DennisRB Senior Member

    Nice Tom. :) But I am still very confused by your continual talk of Autos and thier connection with dry exhausts. I still can't fathom what the heck an automatic transmission has to do with an exhaust system. All engines from cars won't have a water cooled exhaust. What does the gearbox have to do with it?

    I intend this for a light weight minimalist live aboard motorsailer catamaran. So no need for crazy gear shifting when the prop becomes surface piercing! But I can see how awesome the extra gears might be on a fast "hoon" boat.

    I would want watercooling for the exhaust. The engines (or maybe only one internal combustion engine) will be in a fairly tight compartment of a PVC hull. For other applications I would think a dry exhaust would be a good option though, in which case I would try to also use a regular automotive radiator plumbed to a suitable area elsewhere on the boat.

    The engine I would use is the smallest common gasoline car engine you can get. That way it will cost near nothing to maintain and replace. The toyota yaris engine has 100hp and weighs 100kg. It has an alloy block, thermal efficiency of 36% and is only 1500cc. The same cubic capacity of a regular yanmar 50hp engine. The newer versions actually have an integral exhaust manifold to the head so you will struggle to water cool the manifold.
     
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