Heat output of engine

Discussion in 'Diesel Engines' started by ErikdeJong, Sep 21, 2012.

  1. ErikdeJong
    Joined: May 2012
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    ErikdeJong Junior Member

    Hello All,

    I have a Ford Lehman 2713E in my boat. This is a 5.95liter 6 cilinder medium speed diesel engine of 70kW and built in 1979.

    I sail a lot in the arctic and want to make a heat buffer in my boat to use the heat to warm the cabin, even after the engine is turned off.

    1000 liter seawater can "store" about 75kW of heat energy which should be enough to keep the boat warm for 5-6 days.

    I want to use the hot water tap point on the engine to heat a 1200 liter tank that I can fill with seawater. To determine the efficiency of such a system, I need to figure out how long it would take the engine to heat the water to 85 degrees celcius.

    The documentation I have on the engine does not provide me any information on this, but extrapolation of the heating time for my 55 liter freshwater heather indicates that I will need about 3,5 to 4 engine hours to reach maximum temperature.

    Is it reasonable to use linear extrapolation between 55 liters and 1200 liters? or is there a better way to determine the time it would take to heat up the tank? Any rule of thumb indications on this matter?

    Based on 4 hours of heating time, I can reduce my monthly fuel consumption by 130 liters by using a heat buffer tank.
     
  2. jonr
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    jonr Senior Member

    Heat produced will be mostly proportional to fuel consumed, not hours. And of course insulation and air sealing would be the most important ways to retain heat. Heat stored in water is linearly proportional to the liters and to the change in temperature (assuming you aren't boiling or freezing it).
     
  3. ErikdeJong
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    ErikdeJong Junior Member

    Thanks Jonr,

    No, I have no intention of boiling or freezing the water.
    The fuel consumption at cruising speed is usually between 6 and 7 liters per hour. These are also the figures I used to determine the heat rising in the freshwater boiler for the shower.

    Insulation is a good point for the total heating time, I plan on insulating the tank with 2 inch thick insulation plates that are normally used to insulate roofs of houses. The rank will be in the accommodation area, any heat loss will be put to use immediately by rising the temperature in the cabin. When there is no cabin heating required, I intend to have the tank empty and the cooling water through the tank shut-off by means of a three-way valve and direct it through the regular cooling system. There is no sense in sailing around with 1200 kg of extra ballast if it cannot be put to use.
     
  4. Petros
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    Petros Senior Member

    You can also reduce your heating costs by insulating the cabin. The coolant in an engine is the waste heat need to keep the metal from getting too hot and melting. the higher the engine out put the higher the cooling load, direct proportional to the engine load (throttle setting). You are simply storing the excess heat energy in the water, if the water looses the heat to your cabin as it cools off it will keep the cabin warm. this would not be cost effective unless you have to run the engine daily anyway, but just running the engine up to warm up the water storage is a bad idea, it would be more cost effective to put a burner under the tank and use to it heat the water directly, that way you also take advantage of the exhaust heat of the burner as well (which you would not running the engine).

    If your plan is to heat the water when you have to run the motor for other reasons, it can be done if you have a closed loop cooling system on your engine. You have to place a water to water heat exchanger in your water tank and have some way of switching the engine coolant to another heat exchanger as your water tank heats up. this can be done manually with shut off valves, but if you forget you risk overheating the engine. A better set up would be rig a thermostat housing that switches engine coolant from the water tank cooling to seawater cooling as it heats up. If you create such a set up, use reliable components and keep an eye on it to make sure it operates as intended.

    Carrying all that water around just to store heat is also likely to add a lot of weight to the boat, so you might combine that with a water storage system of drinking water. No reason the potable water can not serve a duel purpose. Insulate the storage tank well and have it uninsulated on the side exposed to the cabin, best if it was located in the center of the cabin, or even under the floor boards.

    Good luck.
     
  5. ErikdeJong
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    ErikdeJong Junior Member

    Petros,
    Our boat is one of the best insulated boats in the world I dare say. I have built it with the dream in mind to spend a winter in the Antarctic, frozen in for 9 months. We have 15cm of high density 2comp foam till the floarboards and the floorboards have 5cm of roof insulation foam glued to their onderside. All the windows (very small in size) have double glazing and a perspex closing plate.
    We only need 2400W to maintain a 40 degrees difference between inside and outside temperature and that for a 52 ft boat.

    Currently we have a stand alone cabin heater (Dickinson) that consumes 6 liters of diesel per day. In addition we have a radiator where engine coolant runs through. This is great to heat the cabin, but it only works for 2 hours more after the engine is turned off. I was thinking of this heat buffer so that we can heat the cabin for extended period of time. It looks like that 20 minutes of engine time a day will be enough to keep the boat warm, or an hour every second/third day.

    I am not planning on using the engine to heat the boat, we have the stove for that, but literally throwing the heat overboard while using the engine is such a waste in my opinion. It is normal in the Arctic that once a week you need to cross an ice field, sailing is often not really doable, therefore the engine is used for several hours a week. If I could store the heat onboard, it would pretty much mean that the diesel heather can be off for most of the time. The saving here would be 6 liters a day for usually 4 months a year.

    I have been thinking of heating the fresh water as well, but since most of our water comes direct from natural sources like melt lakes, rain etc. I'm a bit hesitant to heat it up because of bacteria and algae growth.

    The boat is 23 ton at the beginning of the Arctic adventures and roughly 19 ton when we come back at the end of the season. 1.2 ton is not really making such a big difference in performance or stability. At the beginning and the end of the trip, heating is not really necessary and in those occasions the seawater will not be on board. Also the tank is indeed, as you mention, relatively centered in the vessel and the VCG will be roughly at loaded waterline level.
     
  6. jonr
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    jonr Senior Member

    There are some phase change materials like sodium sulfate that are very efficient at storing heat - but they aren't common or inexpensive.
     
  7. Submarine Tom

    Submarine Tom Previous Member

    Great idea EJ!

    It would be worth your while to do the math.

    It's not rocket science and you'll empower yourself hugely.

    You'll likely recover 40% or better of the output of your engine.

    You're only getting about 25% in mechanical energy.

    Water is a fantastic heat sink having one of the highest heat capacities of any material.

    Don't be distracted by those who love to argue, ridicule and split hairs poking wholes where ever they can for there own short sighted purposes.

    Enjoy the great white north my friend!
     
  8. Frosty

    Frosty Previous Member

    I would run a pipe around the entire hull --on the inside or even to domestic heating radiators. . Once you got it cooling sufficiently 100% of your thermal efficiency of the fuel will be used..

    You could Y valve it have a conventional type as well.
     
  9. WestVanHan
    Joined: Aug 2009
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    WestVanHan Not a Senior Member

    EDJ:

    I'm going out salmon fishing..not much time.

    A.-it's good to recover engine cooling heat,but what about the exhaust? Theres several hundred degrees flowing right out the pipe.

    B. Forget the water..use eutectic salts like jonr said...salts can be up to 80 c/g/d. so instead of a ton of water you'd need 20 liters to accomplish more storage IIRC.

    Potassium/calcium/sodium nitrates mixture melts at 250c and kept at 300c or so instead of 100 with water....then you could use your exhaust. Can handle 500-600C IIRC.

    Find a solar forum and pick their brains.

    Fish waiting..
     
  10. jonr
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    jonr Senior Member

  11. DCockey
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    DCockey Senior Member

    A very coarse approximation for automotive gasoline engines operating at a significant load was 1/3 of the energy produced by burning the fuel goes into mechanical power, 1/3 out the exhaust and 1/3 into the coolant.
     
  12. ErikdeJong
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    ErikdeJong Junior Member

    Thanks guy's I see some great ideas here.

    Jonr, I will definitely talk to the vendor of your link. Looking at the specifications of the different salt types, it seams like that 1200kg of salt can store about 6 to 7 times more energy than the same weight of seawater can, or I can do with 1 sixth of the weight for the same amount of energy storage. I do however see some complications here.

    First is the heat exchanger. The simplest method would be a box filled with salt through which the exhaust pipe goes. Except for a welded steel tank that is welded around the exhaust pipe as well, I don't think any material is capable of withstanding such high temperature differences without cracking or leaking. A steel tank will be heavy and has to be placed directly at the end of the exhaust manifold in order to function efficiently. This really limits my options in sizing the tank, It would need proper hanging and vibration dampening and will limit my excess for engine maintenance.

    Second, I'm a bit hesitant to have a big heavy box that is well over 300 degrees Celsius somewhere in the interior of the boat, you will always have to keep a sharp eye on the thing in order not to change it into a source for a fire.

    Third, this salt will always be carried around while I only need the heating capacity for a few months a year. In total 60-70% of all the miles we sail, we do not need cabin heating. We can easily pump seawater overboard when we do not use it, while the weight of the salt will always be there.

    Frosty, the system you describe is more or less what we currently have, but it only works when the engine is running plus a couple of hours after the engine is shut off. My idea is to store heat for several days till you have to use the engine again. Or do I misunderstand what you wrote?

    I will talk to some of the salt suppliers and see what they can come up with. Thanks for you input guys, I really appreciate that!
     
  13. DCockey
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    DCockey Senior Member

    Maximum cooling water temperature from the engine will be around 110C if you use a closed pressurized system. A non-pressurized system will be cooler. The maximum temperature for the storage system will be lower. I don't see how salts at 300C would work. The salts would never get anywhere near that warm. There are eutectic solutions with transition temperatures below 100C.
     
  14. ErikdeJong
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    ErikdeJong Junior Member

    The cooling water of our engine is not pressurized and reaches a maximum temperature of 90 degrees Celcius.
    But the part of the exhaust pipe between the exhaust manifold and the raw water injection point will easily reach 300 degrees Celcius. If you manage to exchange the heat of this piece of the exhaust pipe to the salt, it would theoretically be possible to get much higher temperatures.
     

  15. jonr
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    jonr Senior Member

    If you want a more radical idea, use a small standalone generator to run a heat pump to extract heat from seawater. You can exceed 100% efficiency (if you count the heat from the engine and the heat extracted). A small freezer is an example of a heat pump.
     
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