Heat output of engine

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

  1. ErikdeJong
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    ErikdeJong Junior Member

    I'm not sure how the cooling is divided over exhaust and cooling system.

    based on the assumption that a kg of diesel gives 11.7 kWh of energy and that the engine is running at 190 gr/kWh, we "use" 35kW mechanical power and therefore 39 kW of heat is produced while running the boat on cruising speed in flat sea and no wind.

    I reckon that the heat output of the exhaust is similar to the heat subtracted by the closed circuit cooling system. Let's for now assume that therefore 50% of 39kW (=19.5kW) is available at the exhaust as well as at the closed circuit cooling.
     
  2. WestVanHan
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    WestVanHan Not a Senior Member

    As mentioned before,different salt mixtures melt at different temperatures. Buying all these eutectic salts is not cheap,however one can buy the salts on their own for cheap and get the melting point data easily.

    I looked into the salts for my cabin BUT I have the space and having a huge plastic tank filled with salt water cost me $50.

    BTW VW was going to do a small version of this in their diesel cars,so as to have almost instant warm-up to reduce emissions.I think they figured a way to remap the fuel/spark instead.
     
  3. WestVanHan
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    WestVanHan Not a Senior Member

  4. DCockey
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    DCockey Senior Member

    That would be the amount of heat energy of the exhaust gasesrelative to the heat energy of the exhaust gases and coolantat ambient temperature.

    However the theoretical maximum amount of heat energy available to be transfered with simple heat transfer is the the difference between the heat energy of the hot exhaust gases and the heat energy of the exhaust gases at the temperature of the substance to which the heat is being transfered to. Considerably more heat energy will be available to heat salt water or other substance to 70C than to heat salts to 300C.

    One way to get around the limit of the amount of heat which can be transfered is to use a heat pump, which is less than 100% efficient and adds mass and cost.
     
  5. Submarine Tom

    Submarine Tom Previous Member

  6. Submarine Tom

    Submarine Tom Previous Member

    I don't follow your numbers EJ.

    What output do you run at when cruising?

    If you're 70hp max then 45 perhaps?

    So, about 34kw which is at the shaft.

    Applying the 1/3 mechanical,

    1/3 wasted heat,

    and 1/3 coolant heat leaves ~1/2 of ~34kw could be recovered from the coolant.

    ~17kw available

    Well, lookie there, our numbers are actually pretty close to each other.
     
  7. jonr
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    jonr Senior Member

    Diesel fuel is 9.7 kWh/l.

    6.5 l/h (consumption rate) = 63 kW. Say 55%* of that goes to heat, so 35 kWh/h is available from the exhaust, the coolant and heat left in the system when it is shut down. I'll agree with 17 kW from the coolant alone.

    * - based on .190 gm/kWh, which may be optimistic unless you are operating right at the optimal load and rpm.
     
  8. FAST FRED
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    FAST FRED Senior Member

    Engines use about 1/3 of the heat generated to move the boat , 1/3 goes out the exhaust the rest out the cooling system.

    Capturing the coolant heat is simple .

    An exhaust stack can easily have a tank welded that would capture the exhaust heat.

    Since it will probably be above the internal capture tank , a pump will be required to push the hot water down into the hull tank.

    No big deal .

    Remember your engine OFF will be a heat source for a while (1000lbs+ of warm iron).

    Not in your league , but on our bus camper we have a "box heater" that is used when operating down the road.
    The same 12V circ pump is used to "steal" heat after shut down.
    At almost 2500lbs for an 8V71 we get warm evenings for "free".

    Use both exhaust stack and circ water for heat, why not?
     
  9. ErikdeJong
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    ErikdeJong Junior Member

    1/3 th of the diesels energy is usually used for mechanical energy, however, industrial slow running diesels get as far as 50% mechanical efficiency.

    When I do my math, I always want to be on the save side of things. For engine calculations, that would mean in a normal case that you assume a lower efficiency, but: since I want to use the "waste" I will calculate with an efficiency on the HIGH side of the spectrum to remain on the conservative side.

    As for heat storage in salt, I was looking into the zeolite linked earlier in this topic. It only stores 4 times more energy and a maximum DetaT of factor 3 more than water. All together, Zeolite would be capable of storing 12 times more heat energy than seawater, ohja, Zeolite is not on the marked yet.

    I did find some phase changing salts, but non of them can store more than twice the amount of energy compared to water according to the specs given by the sales persons. This salt also has a lot higher density than water and therefore is not saving weight and comes at great cost.

    Did I miss something here? Where did the factor 80 come from, none of the sales persons that I talked to this morning has ever heard of such high numbers. Factor 5-7 would be considered extremely high and more than that potentially dangerous.

    I think I will run my tests with seawater from the coolant first and see how far it brings me. When I need more heath, I will look into the salts and the exhaust pipe again and make it a separate heat source.

    In a few months/years the zeolite will become available. I will modify the system in that case completely and will use the zeolite.
     
  10. ErikdeJong
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    ErikdeJong Junior Member

    I will, but I will start with the circulation water and will add the exhaust heat storage later to make it two independent systems.

    How would you solve the vaporizing problem when doing that? if I will circulate water around a 300 degrees celcius exhaust pipe, I will start boiling the water or coolant at some point changing it into a gas and make it not work any more, or worse.

    The rest heat of the engine is already in use. I have an air heat exchanger with a fan mounted on the steel engine room compartment. I do not take it directly from the block, but I am using the radiation heat for as long as it is available.
     
  11. WestVanHan
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    WestVanHan Not a Senior Member

    I looked into this before for my cabin and high numbers stuck in my head...quickly googled' it and thats what I read-up to 80x
     
  12. philSweet
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    philSweet Senior Member

    This is nonsense as far as operating in the arctic is concerned. What decreases is the peak power capability of a normally aspirated engine. We are measuring fuel consumption in grams, not volumetrically in liters. The stuff expands when heated, so volumetrically, less heat capacity as a fuel. But you still have the same weight of fuel on board. The fuel is pretty darn hot when it enters the engine. It gets heated by the engine if was cold to start with.

    Using your fuel tanks as a heat sink is a perfectly good idea if they are located inside the insulated envelope. They already get return fuel that is warm. Using diesel as a working fluid makes pretty good sense in a passage maker, even if it is confined to a separate loop.
     
  13. jonr
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    jonr Senior Member

    > water around a 300 degrees celcius exhaust pipe..start boiling

    Not if you circulate enough water. Doing so will cool the exhaust to below 100C.

    Be careful with the corrosive condensate.
     
  14. Frosty

    Frosty Previous Member

    Warm diesel is perfect to culture cladesporium resinea--the blag bug.
     

  15. TeddyDiver
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    TeddyDiver Gollywobbler

    warm diesel tanks doesn't condensate water so that's bad for the blag bug.
     
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