Can using CHG Mode be more efficient?

Discussion in 'Prime Technical Discussion' started by Salamander_King, Oct 8, 2021.

  1. PiPLosAngeles

    PiPLosAngeles Senior Member

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    The larger a generator gets, the less efficient it becomes in terms of kWh per gallon, in commercially available generators I can find anyway. 20% efficiency is pretty common for an internal combustion engine.
     
  2. Salamander_King

    Salamander_King Senior Member

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    I have read completely opposite of your statement. The larger the engine, the higher the efficiency. And maybe you can't compare the generator in Prius against a portable small engine generator.

    Here is one quote I found by Google search. Not saying this is the definitive proof or anything. But there are many search results saying a similar thing. And if you extend your search to any generator, you will find comments and articles with over 90% efficiency of generators.
    https://www.plantengineering.com/articles/large-engine-generator-sets-keep-getting-better/
     
  3. PiPLosAngeles

    PiPLosAngeles Senior Member

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    Larger engines can be more efficient when they're putting out more power, but that doesn't necessarily help us. A Diesel train locomotive is incredibly efficient when towing a 6,000-ton freight train. They can generally move 400 tons 1 mile on one gallon of Diesel. That's the equivalent of an ICE car getting 200 MPG or a 40-ton semi getting 10 MPG. Now use that locomotive to tow a single car and the efficiency is out the window.

    For example:
    • Briggs & Stratton 7000-Watt gas powered portable generator: ~1.6 gallons for a full Level 2 charge of a Prime (~4 kWh/gallon)
    • Champion 9375/7500: ~1.4 gallons for a full Level 2 charge of a Prime (~4.6 kWh/gallon)
    • Dewalt 8kW: ~1 gallon for a full Level 2 charge of a Prime (~5.9 kWh/gallon)
    • Honda 7000kW: ~1.2 gallons for a full Level 2 charge of a Prime (~5.5 kWh/gallon)
    We don't know what the Prime's charging limits are when in charge mode, but if it takes 40 minutes to charge from 0% to 80%, it looks to be roughly 7kW (typical Level 2 charge in many other EVs).

    The reason I think testing it in park will be the easiest is because that's when it's going to be most efficient. If the car can't best HV mode even when it's parked, the chances are slim that it will while driving.
     
  4. Salamander_King

    Salamander_King Senior Member

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    I don't know about this. If the larger gas engine generator is more efficient under load but not when low load. It seems to be related to gas being wasted when idling (low load). I can see a larger engine being more wasteful than a smaller engine if it is constantly idling. I think using CHG mode in PARK is similar to using a large gas engine generator under a very low load. The gas is being wasted for idling. I have no data or proof to support this but I have a feeling CHG mode is more efficient while driving than being stationary.
     
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  5. Salamander_King

    Salamander_King Senior Member

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    I have no training in this area to fully understand this paper. (full citation is posted below) But if my interpretation of the graph below is correct, then the highest efficiency of the Prius generator is 93% and it can be mapped at speed of ~250rad/sec and a Torque of ~100N.m. The lowest efficiency is 40% and it is at idling (speed=0).
    EDIT: I checked it online. 250 rad/sec is ~2400RPM

    upload_2021-10-23_22-4-13.png

    CITATION: Alzuwayer, B., Abdelhamid, M., Pisu, P., Giovenco, P. et al., "Modeling and Simulation of a Series Hybrid CNG Vehicle," SAE Int. J. Alt. Power. 3(1):2014, doi:10.4271/2014-01-1802.

    upload_2021-10-23_21-51-7.png
     
    #85 Salamander_King, Oct 23, 2021
    Last edited: Oct 23, 2021
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  6. MTN

    MTN Active Member

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    We're talking about the efficiency of an ICE - at idle it will be much less efficient than under load.
    ICE only cars achieve their best mpg at moderate speeds - in their highest gear and at an efficient part of the engine power curve, not at idle speed and before aero drag gets too high (~45 mph +/- depending on the vehicle).

    This makes the CHG mode while stationary a very poor way to test the theory of this thread. I don't think anyone thinks that idling your Prime in CHG mode and then driving HV + those EV miles, is somehow more efficient than HV only. This isn't a Volt with an ICE generator.
     
  7. PiPLosAngeles

    PiPLosAngeles Senior Member

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    There is no idling. The engine is powering a generator, presumably at the maximum allowable power since it doesn't need to power anything else. If you're driving the car under load and then add the generator load on top of that, I don't see how that could be more efficient. All combustion engines have a point where they're at peak efficiency in terms of loading. If the car is optimized to drive at peak efficiency it is reasonable to assume that calling for an addition 9-10 horsepower (10% of the ICE's total power capacity) may push it out of optimum load.
     
  8. PiPLosAngeles

    PiPLosAngeles Senior Member

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    Generating 7kW is putting the ICE under load. With 90% efficiency, 7 kW will require about 12% of full load.
     
  9. Salamander_King

    Salamander_King Senior Member

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    I still think engine running while driving will make it more efficient in generating the same amount of energy. Partially because I saw the graph I posted above. It is not about CHG mode on Prius Prime, but regular Prius has the same generator as far as I know, just not a big enough battery to put extra energy generated. The generator efficiency is the same whether it is for a small battery or for a large one.

    But that's enough arguments without any data. If you want to prove your hypothethis, now you would have to do two experiments, measure the use of gas and amount of kWh generated while PARK and while Driving. Please post when you have some data to share. I will go the empirical drive testing route and will post when the gas price becomes more reasonable or if I have to drive without EV range left in the battery.
     
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  10. PiPLosAngeles

    PiPLosAngeles Senior Member

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    As far as I know we can't directly get the gas consumption or electrical generation statistics from the car itself, but I think there's a little trick I can use. There's a stretch of road long enough to burn through all 80% of the EV generated by charge mode without any stop signs or traffic lights. I will be able to set cruise control and drive a fixed distance under two trials:

    1. I zero the trip meter and drive the route in all HV mode. At the end I record the distance and MPG as reported by the car.
    2. I zero the trip meter and start the car in CHG mode. I let it sit until the ICE turns off at 80% SOC. I drive the route in EV mode and record the distance and MPG as reported by the car.
    Yeah, the car is overly optimistic on MPG, but it will be equally optimistic on both trials so the difference will still be valid.

    EDIT - Got around to reading that paper:

    It seems to be a paper attempting to model the theoretical efficiency of a generator powered by an engine with specifications similar to a Prius and powered by natural gas. As far as I can tell there is no driving involved in this simulation.
     
    #90 PiPLosAngeles, Oct 24, 2021
    Last edited: Oct 24, 2021
  11. vvillovv

    vvillovv Senior Member

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    A couple of my numbers are off by 1 or 2 and I learned some new stuff besides while checking notes.
    If ya want / need anything else let me know....

    In the Driveway at the beginning of the trip
    16oct2021-driveway-start-DrPrius-P1010116.jpg 16oct2021-driveway-start-MFD-P1010117.jpg

    In the Driveway at the end of the trip
    16oct2021-driveway-end-P1010227.jpg 16oct2021-driveway-end-MFD-P1010228.jpg 16oct2021-driveway-end-Speedo-P1010230.jpg 16oct2021-driveway-end-1-minute-P1010235.jpg 16oct2021-driveway-end-2-minute-P1010236.jpg 16oct2021-driveway-end-BarGraph-P1010240.jpg 16oct2021-driveway-end-DrPrius-P1010255.jpg

    edits: my phones clock is 5 minutes slower than the clock in the car -
    A deer stacked and beat up on the car this morning.. I saw him/her a split second before I got rammed in the driver side front fender and rearview. I picked up part of the mirror off the road with some deer fur, but I have to go back and get the mirror glass. It was really dark and I'm supra glad I wasn't doin 55
     
    #91 vvillovv, Oct 24, 2021
    Last edited: Oct 24, 2021
  12. Salamander_King

    Salamander_King Senior Member

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    Well, you will also have to do the measurement of CHG mode generator efficiency while driving. @MTN already thinks the result will be in favor of HV only under your testing setting.

    Whatever the result, it only tells how efficient the CHG mode generator is while in PARK, and tells us nothing about how it behaves while driving. Nonetheless, it will be interesting to see what kind of results you get. If you have a stretch that long, then it would be easy to modify it so that you drive half the distance on CHG mode and rest on EV mode from the charge generated by CHG mode (plus HV mode if EV range is not sufficient to cover the half of the test course), and compare the overall MPG against all HV. You don't need to have a full 80% SoC to test the CHG mode efficiency. This is essentially what I am proposing to do on my regular commuting route of ~36 miles. Still, you need to perform the test more than once and average the results. More the batter.

    For the testing scheme that you describe, make sure to switch to EV mode immediately after CHG mode reaches the max EV SoC of 80%. I noticed this last time I did my experiment, the CHG mode did automatically stop at SoC80%, but the car stayed in HV mode. It may be because the car was in HV mode before starting the CHG mode. But I had to actively switch to EV mode to start driving on the traction battery.

    I also wonder what really happens to the mpg display during CHG mode at PARK and after you start driving on EV mode from the charge generated. I have never done it, so I don't know what happens, but while the car is in PARK and in CHG mode, the mpg will stay at 0 mpg. But in reality, it is actually using gasoline so the amount of gas on the denominator of the mpg calculator continues to be increasing. After you start driving on EV, the mpg display should start showing a positive number and keep increasing. Is that really what happens? If it is, and the mpg number does get up to mpg obtained by the HV mode before the end of the run, then CHG mode is more efficient, if it never gets to that mpg, then HV wins.

    Yes, I gathered that much. They are using Prius as a reference model for the simulation of the natural gas GENSET engine serial hybrid concept car because the Prius generator efficiency map (the figure I posted) was already known to the authors presumably from the previous testing done on Prius. I just don't understand all the formulas and equations in that paper.
     
  13. PiPLosAngeles

    PiPLosAngeles Senior Member

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    So do I, as stated earlier.

    For reasons I've already explained, I'm willing to bet a good chunk of change that Toyota's engineers didn't overlook a fairly obvious way to manipulate the Prime's drivetrain to squeeze out more efficiency.

    However, experimentation is always fun and sometimes leads to learning things you didn't even set out to learn. Times like these are when I'm glad to have a background in applied statistics. This sort of situation is perfect for null hypothesis testing. If we can find by experimentation that the mean MPG using CHG mode is 3 or more standard deviations above the mean MPG for the same trips in HV mode we can be fairly confident that the effect is real.

    Yes. I have seen this many times when I've sat in the car with the A/C running for an extended period of time. If you reset the trip meter before idling the display will stay at 0, but will climb very slowly as you drive. A drive that would normally read ~50 mpg might read 20 mpg because of the idling. I'm fairly confident the car is counting total gas consumption and dividing it by trip distance. I don't even know another way to calculate MPG since m/g is the literal definition of MPG.
     
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  14. Salamander_King

    Salamander_King Senior Member

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    If you know that the mpg indicator does keep track of the used gas despite the fact the car has not moved, then for the purpose of calculating the amount of gas used by CHG mode at PARK, you can simply drive the car 1 mile on EV mode after CHG mode is completed and record the MPG displayed number. If the number shown is, say 10.0 mpg when you drove only 1 mile on EV mode, then you know ~0.1 gal of gas was used by CHG mode. Again, this does not tell you anything about the amount of gas used during CHG mode in drive, which seems to change quite a bit depending on the driving condition.

    I just did very short (5 miles) drives on CHG mode. Although not identical 5 miles, the driving conditions and weather were similar. The first 5 miles produced 10% SoC and overall MPG 32.6mpg. The second 5 miles produced 20% SoC and overall MPG 34.6mpg. I think the low SoC produced in the first 5 miles is because there was no SoC left in the traction battery at the start. That is the EV range was - - miles. At that point, the SoC can be a negative number as low as 5% off. 10% SoC gain may be in reality a 15% SoC gain. But still, that is 25% less than 20% SoC generated in the second 5 miles of CHG mode.
     
  15. PiPLosAngeles

    PiPLosAngeles Senior Member

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    That's what I would expect if CHG mode put the ICE into its most efficient loading and then treated it as a constant source of power, i.e., the motor's output is constant and the motor's output is divided between motive force and electrical generation as needed. That way when you're stopped or coasting all of the ICE power is generating electricity and when you need engine power some or all of it is directed to the transmission.

    I think that's a very long way of saying it sounds like CHG mode is warmup mode with a SOC shutoff instead of coolant temperature.
     
  16. Salamander_King

    Salamander_King Senior Member

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    If I get a chance, I will try CHG mode at PARK to gain SoC 10% (but should not be done when the EV range is - -miles) before driving off my driveway. Then I will check the mpg at the 1-mile mark. I will try repeating it several times at, least 5 times but more the better, under similar temperatures and other environmental conditions. An 1 mile of drive from my driveway would be as constant as I can manage on any other road, so there should be very little variable for that 1 mile other than weather-related changes. It will be interesting to see if the number (mpg) I get is more or less constant. If this number varies widely from one testing to the next testing, then it will be very difficult to make a meaningful conclusion from the rest of the experiments.
     
  17. PiPLosAngeles

    PiPLosAngeles Senior Member

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    You should be able to eliminate most of the variation by driving that mile in EV mode and pressing the HV button right at the 1-mile mark. All the trip variation will be in the miles/kWh statistic and not affect MPG.
     
  18. Salamander_King

    Salamander_King Senior Member

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    Not sure what you mean by pressing the HV button. I am only interested in seeing the mpg display at the 1mile marker, not after the trip. Changing to HV mode at the 1-mile marker would slow down the climb of mpg numbers, but still, keep changing afterward. Also, if I do this test only once a day, then miles/kWh statistic can be looked at by checking the daily Eco log, but if I do it more than once on the same day, then there isn't an easy way to keep the miles/kWh statistic separated, that is unless I "reset" the EV efficiency for each trial. But I would like to keep my EV efficiency un-reset for the life of the car to keep the number going corresponding to ODO reading.

    One possible problem with this experimental procedure is that the frequency of the reading of the mpg monitor may be too low for a 1-mile trial. I know the mpg reading does not update every second. IIRC, it is more like every 30 sec or even longer. With a longer interval of update, it is likely that mpg reading right before and right after the update may show big differences.
     
  19. PiPLosAngeles

    PiPLosAngeles Senior Member

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    You drive from parked to 1.0 miles in EV, thus the only gas used was charging in the driveway. Boom! No variability in mpg. Pressing the HV button is to get the car to display MPG instead of miles/kWh.
     
  20. Salamander_King

    Salamander_King Senior Member

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    Well, the experiment is to test to confirm that there is No variability in mpg. Meaning, it is a test to confirm that gasoline used under CHG mode at PARK is constant (or at least very close each time). But if this number varies a lot, then the rest of the experiments are not very meaningful. And I will not be looking at the gauge next to the speedometer. That gauge up-and-down so rapidly, there is no way to pinpoint what the number (and there is no numerical display) the bar is indicating. Rather, I will be looking at the AVG MPG below the mile/kWh (or MPG) gauge.

    upload_2021-10-26_16-47-25.png
     
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