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Thread: EngMod2T Q&A

  1. #46
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    Released some small bug fixes today.

  2. #47
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    Has anybody played with Ethanol fuel in EngMod2T? I was doing some messing around and simulating E85 (85% ethanol/15% gasoline) with some interesting results. The sim was first run on Regular and Premium with squish and timing optimized to start seeing deto warnings. This is where things get interesting. I changed the fuel over to E85 and changed the AFR to maintain the same lambda as I was running on gasoline. Timing, squish, etc., besides compression ratio, were all left the same as the initial run on E85 (12.5:1 CR). There was a HUGE increase in power, especially below peak. Also interesting is how far TUbMax went down compared to the gasoline runs. Next I kept increasing compression ratio CR all the way to 15.5:1 and power kept going UP and UP below peak. This seems a bit like fantasy land to make such big leaps. What am I missing?

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    The other interesting thing is the power on E85 went right past the STA.

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  3. #48
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    I have no experience with either clean ethanol or with it blended with gasoline. My experience is limited to methanol. But some pointers:

    The biggest increase in power comes from the much bigger latent heat of evaporation (Gasoline~305kJ/kg, E85~836kJ/kg) and that causes two good things:

    1. The incoming charge density is increased by cooling it down during evaporation
    2. The temperature of the mixture in the cylinder at the start of compression is much less, leading to a lower maximum unburnt temperature during combustion and an effective anti-detonation result.



    E85 is used extensively by the drifter crowd as a detonation combatant when running high boost pressures.
    In a 2T engine we can increase the compression ratio quite a lot - clean ethanol has an effective octane number of 109.

    Currently there is no detonation checking for Ethanol or E0 to E100 built into EngMod2T, it is being rectified. We should verify this before analyzing the results.

  4. #49
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    Where does the E85 power come from? From internal cooling, yes. But also because with the amount of air that the engine inhales, you can burn much more E85 than regular petrol.
    I worked it out some time ago for my German mates and I have been planning to produce an English translation, but other things keep getting in the way, so here it is in its original form. Let's see how Google Translator will mutilate it.
    Click image for larger version. 

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  5. #50
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    Thank you, Neels and Frits!

    I do have some experience with E85 in forced induction 4T, so most of this makes sense. In full disclosure, I ran the sim comparison with all of the same temperature inputs. With all of the cooling from E85, this may be majorly wrong!

    Neels, any tips on where I can look in the sim outputs to figure out where things might be over optimistic? On E85 and much more compression, this pump gas engine went right past 200psi BMEP. Something can't be right.

    Frits, I think google translate did an OK job, at least the numbers make sense to me. I couldn't figure out the part about the wet candle towards the end. haha Great job breaking the numbers down for comparison! I really like the derivation down to 3.46x evaporative cooling. I knew it was a lot, but never realized it was that much!

    There is one statement in the EGT section that I noticed. "...because E85 probably burns a bit slower..." Everything I've known about E85 is that it actually burns FASTER (at comparable lambda). I think the faster/slower and more/less ignition advance story gets confused when we start talking about knock limited engines. Usually in the 4T world, the E85 discussion involves some forced induction. With forced induction, people are always talking about ADDING ignition advance. Well that is because pump gas ignition timing was way retarded and not anywhere close to MBT. So all things considered, a MBT tuned engine on pump gas would normally require LESS ignition advance on E85. No?

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    Here is one last thought on E85 in a 2T vs 4T. A 2T has much more surface area (crankcase, transfer ports, etc) to act on an probably more duration than a 4T (port injected EFI). Is it possible that a much more dense charge in the crankcase greatly benefits a transfer STA limited engine? In comparison, the 4T only has cooling at the very end of the intake tract and very short intake tract duration if the injection is spraying through an open valve.



    Google translated, below:

    Gasoline & E85 Frits Overmars

    Many motor sport regulations dictate that only fuels available at public gas stations
    may be used. Diesel is excluded because a larger diesel oil leak
    Racetrack could be unusable for a longer period. Thus remain gasoline and E85.
    Below, we compare the important properties of these two fuels.
    An air / fuel ratio, with each fuel molecule being just enough for its combustion
    The amount of oxygen molecules available is called a stoichiometric air / fuel ratio.
    It is indicated with lambda = 1.
    Lambda> 1 means an excess of air. e.g. Lambda = 2 means that twice as much air is present
    as theoretically necessary for complete combustion.
    Lambda <1, however, means a lack of air, or, in other words, a fuel surplus.
    In reality, racing engines never run with lambda = 1, but always fatter, because the mixture never exactly
    is homogeneous, and because unused oxygen from a performance point of view would be a waste.
    Optimal is lambda = 0.86. This optimum value applies to every fuel. However, the lambda actual value plays
    in the following comparisons between gasoline and E85 irrelevant and thus can be left out.
    One can calculate the fuel consumption for each type of fuel, if one considers the stoichiometric air / fuel
    Ratio of the respective fuel knows.
    Gasoline: 14.7; that means: to completely burn 1 kg of gasoline you need 14.7 kg of air.
    Ethanol: 8.4; that is, to completely burn one kilogram of ethanol requires 8.4 kg of air.
    Methanol: 6.5; that is, to completely burn 1 kg of methanol requires 6.5 kg of air.
    The amount of air that can suck a motor is not dependent on the fuel, but is determined by
    Displacement, speed, slot surfaces, timing and pressure differences.
    For our calculations, we assume that the engine draws in 1 kg of air per revolution.
    (In reality, that would be nice because air weighs 1.233 grams per liter, so 1 kg is 818 liters).
    For this supposed 1 kg of air the engine needs:
    1 / 14.7 = 0.068 kg of gasoline
    or
    1 / 8.4 = 0.119 kg of ethanol
    or
    1 / 6.5 = 0.154 kg of methanol
    If a fuel contains 85% ethanol and 15% gas, you need 1 kg of air for:
    (0.85 x 0.199) + (0.15 x 0.068) = 0.111 kg of fuel.
    This is 1.6 times the mass of the 0.068 kg of gas originally needed.
    When using E85 instead of gasoline you can burn 1.6 times as much fuel per kg of intake air.
    What does that do for performance? That depends on the combustion value expressed in MegaJoules per kg:
    Gasoline: 43.0 MJ / kg
    Ethanol: 26.8 MJ / kg
    Methanol: 20.1 MJ / kg
    1 kg of E85 contains 0.85 kg of ethanol and 0.15 kg of gasoline, and thus has a combustion value of
    (0.85 x 26.8) + (0.15 x 43) = 29.3 MJ / kg.
    E85 thus has a lower combustion value than gasoline. But because we use 1.6 kg instead of 1 kg of gasoline each time
    E85 can burn, the total released energy per kg of air but higher.
    Compared to 43 MJ / kg for 1 kg of gasoline stands 1.6 x 29.3 = 46.9 MJ for 1.6 kg E85.
    That means 9% more energy and thus 9% more power.
    Now there is the problem that the fuel quantity is generally not in kilos, but in liters
    is measured.
    1 kg of gasoline = 1.389 liters
    1 kg of ethanol = 1.267 liters
    1 kg of methanol = 1.266 liters
    1 kg E85 = (0.85 x 1.267) + (0.15 x 1.389) = 1.285 liters
    Instead of 1 kg of gasoline or 1.389 liters of gasoline, we need:
    1.6 kg E85 = 1.6 x 1.285 liter E85 = 2.056 liter E85. That's 1.48 times the volume.
    The consumption is 1.48 times higher: instead of 1 liter of gasoline now 1.48 liters E85.
    The capacity of the tank, and all flow areas in the entire spray system must
    therefore be 1.48 times larger. That means: All diameters must be 1.22 times bigger.
    The float chamber valve seat is often forgotten.

    Control:

    A Rennzweitakter needs about 7 cc of gasoline per hp per minute.
    The same engine With E85 would consume 1.48 times this amount of fuel, but it would also be 1.09 times
    deliver the original performance.
    Its consumption would be (1.48 x 7) cc per 1.09 hp per minute, or 9.5 cc / hp / min.
    With a measuring cup and a stopwatch, it is easy to determine whether the spray system is sufficient.

    Engine temperature:

    The specific evaporation value shows how much kiloJoule of heat needs to be added to fuel 1 kg
    evaporate.
    Gasoline: 380 kJ / kg
    Ethanol: 900 kJ / kg
    Methanol: 1100 kJ / kg
    1 kg of E85 contains 0.85 kg of ethanol and 0.15 kg of gasoline, and thus has a specific evaporation value
    of (0.85 x 900) + (0.15 x 380) = 822 kJ / kg.
    The specific evaporation value of E85 is thus 2.16 times higher than the specific evaporation value
    of gasoline.
    In addition, the engine now consumes 1.6 kg E85 instead of 1 kg of gasoline. The total evaporation required
    Heat for the aspirated air / fuel mixture is thus 1.6 x 2.16 = 3.46 times higher.
    This heat is removed from the sucked air. The mixture enters the engine much cooler.
    Thus, the internal cooling of the motor in E85 operation is considerably better, and the thermal load
    of the engine is lower, despite 9% more power than gasoline.
    Two-stroke engines react strongly to temperature differences. The cooler running E85 engine can do that
    even more than the 9% extra power calculated above, and also suffers less
    an increasing engine temperature during the race, especially in air-cooled engines too
    Performance loss would result.

    EGT:

    The exhaust gas temperature may be somewhat lower despite higher power than with gasoline operation.
    The engine will probably not turn quite as high as before.
    An attempt to correct that with lean spraying can easily backfire.
    Wrap the exhaust is better, but the first piece of the manifold, where purged fresh gas
    before it is pushed back through the exhaust shaft in the cylinder, must remain as cool as possible.
    How long this cool piece should be depends on the outlet channel diameter or the manifold
    Diameter off. Expect that the cool part of the exhaust system must be so long that it is a
    Volume equal to the displacement volume may contain; then it is definitely long enough.
    A second method of increasing the exhaust gas temperature is to fire the ignition later
    adjust. But you can not go too far with that, because E85 probably burns a bit slower,
    and therefore not less, but would require more pre-ignition.
    It would therefore be better if the maximum speed and the maximum speed had suffered too much,
    make an exhaust with smaller lengths and unaltered diameters. Only the tailpipe
    Bottleneck must be adapted to the additional power.
    Compression ratio:
    The compression ratio could be higher because E85 has a higher octane rating than gasoline,
    but that only makes sense in four-stroke engines. Especially turbo four-stroke will be quite lively with E85.
    In Rennzweitaktern but you should compact low. That promotes performance, bandwidth,
    The reliability, and if you do not have a strong spark, it also helps the ignition.

    Oil:

    Not every two-stroke oil mixes well with E85. Castor oil is already suitable.
    e.g. Maxima Castor927. Eleven 909 should also be usable.
    The oil / fuel ratio may be leaner compared to gasoline when using E85.
    For example, we take a mixture of 1 liter of oil to 20 liters of gasoline.
    When using E85, the engine consumes 1.48 x 20 = 29.6 liters of E85 instead of this 20 liters of gasoline.
    If we mix 1 liter of oil with this 29.6 liter E85, the engine gets the same amount of oil as before.

    Focus:

    Methanol, ethanol and E85 can attack various materials: copper, aluminum, magnesium,
    Plastic hoses, gaskets, o-rings, etc. And when plastic bearing cages are attacked,
    This can lead to major engine damage.
    It is therefore advisable to run the engine with petrol for a few minutes after using E85
    to let.
    Determining the spray on the basis of the candle image can be dangerous with alcohol-containing fuels.
    In methanol, I have found that the candle always stays wet. An attempt to thwart them
    getting dry can cost flasks.
    Sometimes you can also use a candle with a slightly lower degree of heat.
    All alcohols are hygroscopic: they attract water vapor from the atmosphere and dilute
    itself more and more.
    Always keep the fuel tank closed, and avoid draining the vehicle's fuel tank.
    Weighing is a better and safer way to determine fuel consumption.

  6. #51
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    Here is one last thought on E85 in a 2T vs 4T. A 2T has much more surface area (crankcase, transfer ports, etc) to act on an probably more duration than a 4T (port injected EFI). Is it possible that a much more dense charge in the crankcase greatly benefits a transfer STA limited engine? In comparison, the 4T only has cooling at the very end of the intake tract and very short intake tract duration if the injection is spraying through an open valve.
    Derek,

    Absolutely - transfer port and crankcase cooling gives measurable gains.

    I am adding the detonation feature for E0~E100 in EngMod2T, I will then have a better idea.

  7. #52
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    Here's one from the Aprilia RSA 125 sim... The blue line is the baseline from the sim found on this site (100 unleaded, 14.8CR). The fuel was then changed to 85% ethanol (lambda stayed the same), black line. Further runs showed increasing compression ratio, all else constant. Anyway, it looks like ~8.7% gain at 13,000rpm for 17.8CR. Make believe OR plausible?

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  8. #53
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    The trends are correct, with E85 creating more cooling which allows more compression. More cooling plus more compression will increase the power and move the whole curve to the left as is happening. While the trends are correct the magnitude is a bit suspect. I am suspecting the evaporation model and will investigate that further, it is not very sophisticated and might over predict the cooling.

    Is there anyone with actual measured performance and temperature data for a high performance 2T that is willing to share?

  9. #54
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    I did actually poke around at the Temperature traces (crankcase, transfers, etc.) and I didn't see a glaring obvious change from gas to ethanol. But, I should be clear that I didn't change any wall temperatures on the input side either. In fact, some of the ethanol runs had slightly higher temps, through the bottom end, than gasoline. It must be the cooling effects are all accounted for in the combustion chamber because that's where I saw a big difference in temps.

    I also looked at Mass Flow (air) all the way back to the intake and didn't see a clear trend vs power increase.

    One other thing that could be way incorrect is the Combustion Efficiency. I left this the same for gasoline vs ethanol. Maybe this needs to change as ethanol is added?

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