Evans Waterless coolant in V6/V8s?

Discussion in 'General Auto Conversion Discussion' started by pfarber, May 23, 2019.

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  1. Jul 6, 2019 #41

    pfarber

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    Please keep off topic remarks out of this. Can you do that?

    I'll take my free dig: RR was so smart that the early Merlins couldn't do negative G maneuvers. You would think a smart engineer, designing a FIGHTER, would know about negative G performance.
     
    Last edited: Jul 6, 2019
  2. Jul 6, 2019 #42

    BJC

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    Combat maneuvering by fighters, from WW I up to the present, involved / involve almost no negative g.


    BJC
     
  3. Jul 6, 2019 #43

    rv6ejguy

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    Engine dynos use cooling loops to dissipate engine heat loads.

    What would I find by pulling the thermostat?

    It seems you're saying that lower coolant mass flow will pull pull more heat from the engine? Am I understanding that right?
     
  4. Jul 7, 2019 #44

    mm4440

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    When we use the term liquid cooling, we tend to forget that the liquid is only a heat transfer fluid and we are in fact really air cooled. The reason for liquid cooling is the fact that air cooling directly has extreme difficulty keeping the hotspots in the cylinder head at reasonable temperatures. Of the practical cooling fluids water is the best. For use as a cooling fluid in internal combustion engines it has the unfortunate property of boiling, turning into vapor at a lower than desirable temperature. It additionally produces extremely large amounts of vapor when it does boil. This is great for powering a Rankin cycle, steam engine but can be deadly if it occurs in the cooling jackets of an internal combustion engine. In fact, steam cooling was researched and tested between the wars. It worked but was found impractical. I have given thought to single fluid cooled engine design using just motor oil. There are motorcycle engines that use additional oil flow to the hotspots in the cylinder heads to supplement air cooling. Oil is a great lubricant but really mediocre heat transfer fluid.


    I repeat, cooling problems are typically due to low airflow through the heat exchanger. There are some engines which have problems on the liquid side of the cooling system due to poor design of the water pump, plumbing or internal flow passages that produce dead spots with no coolant flow. Sometimes a better performing water pump will cure the problem. In the other cases the engines just are unsuitable for aircraft use. At low air speeds there is very little ram pressure to overcome the restrictions in the heat exchanger and therefore very little cooling capacity. Low speed cooling problems typically can be fixed by the addition of a cooling fan rather than screwing with the liquid side.


    In a high-power liquid cooled engine care must be taken to eliminate water vapor, steam and air from the cooling system. Steam blanketing must be prevented to avoid engine failure. Steam vent lines from high points in the cooling jacket and water pump are seen in racing engines. There are well-known techniques for increasing the boiling point of water-based coolants in engines; pressurized systems, restrictions on the outlet of the cylinder heads and the use of anti-freeze solutions.


    When cooling on the liquid side is marginal or fails, using an EG based coolant with no water may save the engine installation. This liquid side cooling failure may be caused by inadequate airflow through the heat exchanger as in some Rotax installations. In some cases, it may be a drop-in change but in others it may require increased coolant flow and elimination of restrictions in the cooling circuit to overcome the lower heat transfer capabilities of EG compared to water. Higher coolant temps can be used to reduce cooling drag but need careful testing.


    I have suggested using a heater core and blower for supplemental cooling and/or cabin heat and the use of the electric coolant pump in series with the mechanical pump if you are nervous about low RPM coolant flow or want redundancy but remember low-speed problems are typically on the air side and an electric fan might be in order.
     
  5. Jul 7, 2019 #45

    pictsidhe

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    Yes. There is a flow rate for maximum cooling, it isn't infinite.
    Try it sometime.
     
  6. Jul 7, 2019 #46

    pictsidhe

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    If your setup cools fine at high speed, but not at low speed, Increasing water flow will exacerbate the problem. Slowing the water pump may help a little. This would obviously be much easier with an electric pump. Increasing flow over the radiator is the usual fix, or fitting a more efficient radiator, which then means you can reduce high speed cooling air flow and get your low speed problem back ;). There are various ways to change low speed airflow. Many aircraft have variable ducts. the radiator exit flap would be opened all the way on the ground and until it wasn't needed. Many planes will overheat if asked to taxi or idle too long on the ground. They have sacrificed ground cooling for lower drag and weight.
     
  7. Jul 7, 2019 #47

    pictsidhe

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    A popular RAF WWII evasive manoeuvre was 'all in the left corner'. This was done when a pilot couldn't shake an enemy from his tail. Full throttle. The stick was pushed all the way forward and to the left. The left rudder pedal was also pushed all the way down. It was described as 'extremely unpleasant, but guaranteed to get the German off off your tail'.
     
  8. Jul 7, 2019 #48

    mcrae0104

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    pictsidhe, could you please explain your position that decreased flow rate increases cooling? In particular, please address Q/t = m/t c delta T.
     
  9. Jul 8, 2019 #49

    mm4440

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    The most challenging cooling problem is low speed, max power climb like with a STOL racer. With ram air there is very little pressure available no matter how good the baffling is to force air through the fins of an aircooled or the radiator of a liquid cooled engine. Full rich mixtures for fuel cooling is standard practice. Full rich is richer than best power for cooling. Engine survival is more important than max power. Water injection, ADI and fan cooling are proven. Spray water is common on unlimiteds. The liquid side is not often the problem.
     
  10. Jul 8, 2019 #50

    BJC

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    What is a “STOL racer”?


    BJC
     
  11. Jul 8, 2019 #51

    mm4440

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    Short take off and landing contests seemed to have originated in Alaska and have become a popular part of Oshkosh and other airshows in the lower 48 states. Check youtube, you'll be impressed.
     
  12. Jul 8, 2019 #52

    rv6ejguy

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    You can have multiple issues affecting the successful outcome of a liquid cooled engine in an aircraft. I've seen most of them on my 6A installation. The least of these worries is local boiling within the engine. The OEM engineers have already addressed this in their designs. All you have to do is not screw with the water pump flow, make sure no air remains in the system and keep the coolant temps below 220F or so. Case in point, I developed a 1.7L Toyota road race engine which eventually put out 5 times the original hp- all with stock water pump and no modifications to the engine part of the cooling system- simply a larger rad. 5 X the hp was 5 times the heat being developed yet there was never any issue with cooling and the engines were super reliable. Obviously no steam pockets or otherwise. Ran 50/50 EGW and a 17 psi cap. Nothing special. There are huge cooling margins within most engine designs, certainly lots for what we do with aircraft which are usually operated at less than the stock hp rating.

    Every Rotax installation I've seen has a poor radiator layout. Drag was the last concern in these designs. Non-aqueous coolant is simply a crutch for poor design in this case.

    I'd submit than any sound auto engine can be successfully used in an aircraft with a properly designed radiator system. I've never seen a case where an OEM water pump was not up to the cooling task at stock hp. Cooling fans on aircraft are a clear indication you didn't do something right. They should never be needed on tractor installation at least.
     
    Last edited: Jul 8, 2019
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  13. Jul 8, 2019 #53

    rv6ejguy

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    Can you explain the physics behind this statement?
     
  14. Jul 8, 2019 #54

    rv6ejguy

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    I've tried more things than you can imagine over the years and all were explained by physics in the end, even if I didn't see it at the time. Of course there is some point where increasing flow to get a 1F further temp drop wouldn't be worth it practically as far as pumping hp loss but physics tells us that pumping less coolant mass flow will always result in higher metal temps within the engine. If you can support your view with some math, please do so, since this counters basic thermodynamic laws.
     
    Last edited: Jul 8, 2019
  15. Jul 8, 2019 #55

    rv6ejguy

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    Stock pumps move lots of water at idle. All modern engines are validated for cooling performance from idle to maximum sustained output. Doesn't take much water flow to cool 5-10hp.

    I don't think you appreciate the significance of thermal conductivity in coolants. As you can see from the specs I published, Evans has MUCH worse TC than 30/70 EGW. This cannot be easily offset by increasing coolant flow.

    You'll have more weight with your plan. I stated the reasons why and you'll still need an expansion/ filling/ venting tank as this stuff expands when heated.

    Anyway, I say go ahead and experiment. It can work fine if you get the details right but it won't be lighter and it won't have as low drag as possible running 30/70 EGW with the mechanical pump.
     
  16. Jul 8, 2019 #56

    tspear

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    pfarber,

    I can see how converting mechanical energy to electrical back to mechanical (engine to alternator to electric pump) will never be as efficient as a straight mechanical pump. It also seems like it likely introduces new failure points; e,g, power failure in the alternator now will likely lead to engine failure.
    In your statements that electric saves a lot of weight, have you accounted for the extra battery and alternator power requirements?

    Also, do you have any data you can point too which shows mechanical pumps driving off the ICE are less reliable than electric pumps?

    Tim
     
  17. Jul 8, 2019 #57

    mcrae0104

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    ^This. aka Q = M c deltaT. If specific heat (c) goes way down, either mass flow or delta T need to go up. No getting around it.
     
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  18. Jul 11, 2019 #58

    Winginitt

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    Think of it this way. The purpose of using water is that it is capable of absorbing vastly more heat than air for a given sized area/time and it will follow irregular surfaces (at a reasonable flow rate) better than air. The problem is that the water will then require air to remove the absorbed heat, so we are back to square one in that we need air to now remove that same heat.from the water instead of the engine block.
    The beauty is that once we have quickly absorbed and moved the heat to a different location, we have more room to dissapate the heat.
    Yes, we can move the water too quickly to absorb enough heat to be effective. (Give me a moment here) Just as I mentioned in another defunct thread, I can move my finger across a recently welded part and if moving swiftly enough I will remove "some" heat from the part...
    but not enough to burn my finger and not enough to effectively cool the part any significant amount. Same thing with water, if its moved too quickly past the heated object it will not cool sufficiently. The fly in the ointment here is that in a cooling system, the water is a never ending supply being pumped in a circle rather than a limited amount moved one time past the heated surface. So within reason moving the water in a never ending circle, you basically will not hurt anything by increasing its speed....unless you begin to get cavitation from the mechanical aspects of the system. If you move the water too fast and cause cavitation you introduce air back into the system. Technically that is not the same as just considering the speed of the water, so other than being aware that cavitation caused by water speed CAN be a problem that needs to be dealt with, its not directly the same as too high a water speed.

    Going back to just the speed of the water traveling past the heated surface. I don't think the speed of the water in a continuous flow past a heat source can be too great and will not reduce the ability of the water to absorb heat.......provided that water can be consistently and continuously depleted of the heat in the air part of the system. That is where the idea that water can flow too fast rears its head. We are back at the point of AIR being needed to absorb the heat from the water. Now the water CAN move thru the radiator too fast.Given all the factors which affect the air's ability to remove heat (temp,density,speed) we can see that its a variable number. Something else we have to consider is the SIZE of the radiator. I think this is where the confusion exists. If we have a radiator that is capable of providing an average of say 100 btu of heat removal in 1 second but we have an engine that is producing 200 btu of heat every second, we can look at the solution multiple ways. The radiator is either going to have to take 2 seconds to contain the water, or the size of the radiator is going to have to be increased (doubled) in order to posess the capability to remove 200 btus every second.

    Looking at the first option, we could say that we are flowing the water TOO FAST through the radiator because if we slowed it down to a 2 second pass thru...it would cool the needed 200 btus

    We could also just say that the radiator is undersized for the system since we can't (or won't) change the flow rate.

    So, if we are moving the water thru the radiator in 1 second we ARE moving it TOO FAST for the radiators capability.

    I think that is where the crux of the disagreement about "too fast" lies.

    So "Yes" water can be moved too fast for a given sized system to expel its heat properly, but is the speed of the water the problem, or the size of the heat exchanger ?
     
  19. Jul 11, 2019 #59

    rv6ejguy

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    Cavitation is only a concern at the impeller, not in the rest of the system and is not caused by the speed of the water, rather the rapid drop in pressure at the impeller.

    Heat must transfer in 2 places- in the engine water jackets and again, out at the rad. The same physics applies in both cases. The higher the coolant mass flow, all other things being equal, the more heat we can sink off an item per unit time, mainly because Delta T is higher at the junction between the metal and coolant.

    In practical terms, if our system needs coolant flow of 50 gallons/ min. to remove the heat generated to keep the system in a safe state of thermal equilibrium at the worst case scenario (usually full power climb) it doesn't do us much good to double the coolant flow as that would just sap more power from the engine to pump that higher mass flow.

    But to say coolant can flow too fast to take in or give up its heat in an engine or rad is simply false and not supported by the physics. Feelings don't make facts.
     
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  20. Jul 11, 2019 #60

    pictsidhe

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    cooling_spreadsheet.png Did someone mention the P word?

    Well, if you insist, here's some actual physics rather than 'common sense'. With a spreadsheet and graph.

    Download the flagrant breaches of copyright quick before Topaz sees them. They are photos of pages 27-29 from Kays and London's 'Compact heat exchangers'. Less than 1% of the book...

    I used the following guesstimates:

    Hot side heat capacity is set at 1, the other capacities are relative to that. This is approximately the mass flow rate of air through the engine times it's heat capacity.

    Cold side heat capacity is going to be much higher than hot side, or our engine temp would be way higher. As a ballparking estimate, it is the ratio of cooling air flow to engine air flow. It is proportional to the air mass flow through the radiator. That increases with speed. I've given the spreadsheet two values, one for low speed cooling air flow, one for high speed cooling air flow. I still haven't worked out how to put labels on spreadsheet graphs...

    Since we are hoping to keep the temperature of the hot side heat exchanger (the engine block) constant, it's gas side thermal resistance drops out of our equations. It's liquid side thermal resistance will be minimal with Cl>>Ch. So Eh ~ 1
    Cold side effectiveness. This will vary a bit with cooling flow rate. With a decent radiator, it's probably between 0.5 and 0.7. You can play with the number. A larger radiator increases this. Max is 1

    The graph is total effectiveness. 1 is perfect. That would require an infinite radiator. We can do pretty well with a realistic one, though.

    Notice how the highest effectiveness is when the liquid capacity rate equals the cold capacity rate, whatever you do. Well, if you keep Cc>>Ch, which is required to avoid melting the engine.

    I was expecting a larger drop in effectiveness with increasing liquid flow rate, but the high ratio of cold to hot capacity will keep it reasonable.

    Edit: Bah, humbug! I managed to upload my spreadsheet, but the Gods at HBA decied to strip out the pretty picture. Screenshot now attached. The numbers in the E1 and E2 columns are the total effectiveness for cold rates 1 and 2.

    Edit 2. Found a spreadsheet filetype that HBA doesn't strip the graph out of, though it's lost the nice spline. Trying again with page 28 with an enlarged photo of the formulae. Photo resolution is limited on HBA to 360x600 now. They are just fine, until I upload them.


    20190710_203616.jpg 20190710_203700.jpg 20190710_203737.jpg cooling_spreadsheet.png
     

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