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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    Just park the car in the driveway in CHG mode with all accessories off. All of the gas use at that point is due to charge mode.
     
  2. MTN

    MTN Active Member

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    ...but people would prefer to test HV/CHG + EV, vs just HV
    There might be an incremental mpg cost for using CHG vs just HV while driving at higher speeds and it would be more efficient that simply getting 0 mpg while stationary and using CHG. That is what people would like to test.

    Basically you're altering the HV mode and forcing it to add to the battery for EV use later and seeing if that can be more efficient than HV alone. There's a good chance that doing so at higher freeway speeds and gaining EV miles for lower speed use, could prove more efficient than HV alone. If true and by how much is the questions to work out.
     
  3. PiPLosAngeles

    PiPLosAngeles Senior Member

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    That can be done mathematically because the only unknown variable is how much gas it takes the Prime to generate a unit of power. We already know the MPG in HV and miles/kWh in EV.
     
  4. Salamander_King

    Salamander_King Senior Member

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    A few problems. One how to measure the amount of gas used by the CHG Mode accurately enough to do this experiment? Also, how to measure the amount of electricity generated is not easily measured. If we assume 6.5kWh from the wall is needed to fill -- to 100% SoC, then 1kWh of electricity is about 15.4% SoC. But this is assuming 100% of wall electricity goes to the battery which certainly is not true. Moreover, trying to measure the accurate amount of gas used to generate that 15.4% SoC gain is not an easy task.

    I agree that driving conditions will affect the CHG mode efficiency. It is not a constant number of kWh generated per gallon of gas. We already know this because two data point one by me at 45mph and one by KYBlue at 75mph show wide differences in miles driven for gaining 1mile of EV range.
     
  5. PiPLosAngeles

    PiPLosAngeles Senior Member

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    That is the hard part. How accurate are the onboard diagnostics at measuring these values?

    CHG mode efficiency is constant. The variable is how much engine power is used for charging the traction battery vs. how much is used to propel the car. Of course the more power is needed to move the car the less will be available for charging. Since we already know how much engine and battery power it takes to move the car it's all the more reason to remove those variables from the experiment.
     
  6. Salamander_King

    Salamander_King Senior Member

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    With HA, I tried to measure the number of kWh used during EV mode drive, but the number did not match what was fed from the wall (read by kill-a-watt meter) and what is reported on the dash (SoC). In the end, I could not tell what number to believe. The gas used is more of a problem as you know ECU is very optimistic in calculating mpg. I don't know if I can believe that number either. I can no longer use HA on my 2021 PP. The app refuses to link to an adaptor. So I will not be able to play with HA app anymore.

    Even if the generator efficiency is constant, with other variables while operating CHG mode, the result would be totally different from one trip to another. Even if you can measure the precise amount of kWh generated with a precise amount of gas used when the car is PARKED, I don't know how you would use that number for the specific driving conditions without knowing how much change will occur under certain driving conditions compared to stationary CHG mode. Certainly, we are not expecting the CHG mode to generate the same amount of kWh of electricity from 1gal of gas used when comparing car stationery at 70F to the car going 75mph in sub-zero temp.

    In fact, I am not sure if the generator efficiency is really constant all the time. With your example of a portable generator generating 8 kWh using a gallon of gas, this must be a spec given under certain testing conditions not always a constant number. If you put a lot of load into the generator, it certainly uses more gas than just sitting and running without any load. At least that's what I have observed with my portable generator.
     
    #66 Salamander_King, Oct 20, 2021
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  7. PiPLosAngeles

    PiPLosAngeles Senior Member

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    Could engine load be a factor? Perhaps. If it takes ~40 minutes to generate 80% SOC, that's roughly 7 HP given some inefficiency. So no matter whether you're driving 5 mph or 85 mph, firing up the CHG mode is going to cause the car to call on 7 additional HP from the ICE. Whether that makes a big difference or not depends on the difference between the amount of fuel required to generate 7 additional horsepower under load vs. no load. Does anyone have any solid numbers on how much fuel it takes to generate 30 HP vs. 23 HP and 60 HP vs 53 HP?

    Either way, knowing how much the ICE requires to act as a generator with no other loads will be a valuable baseline to start with. That number can be used to make predictions that can be confirmed or disproved through experimentation.

    At a 12A load it will run ~8 hours on one gallon of gas. Is it 8:00:00 precisely? Probably not. But that doesn't matter a whole lot for our explorations here. It only matters if the margin of error is larger than needed to account for any MPG differences.
     
  8. MTN

    MTN Active Member

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    isn't the general theory of engines is that they are "air pumps"? and therefore more efficient at larger throttle openings?
    meaning CHG mode's 7HP requirement is less impactful to an engine operating at more load/throttle - again hwy driving vs city or idling.

    My theory is that if you're driving 65 mph + on the highway, adding a bit more fuel in CHG mode might be more efficient for overall mpg vs HV alone. I don't think you can tease this out with theoretical HP requirements for a stationary Prime ICE acting as a generator. I think you need to drive on the highway and get some results. If I had a routine commute, I'd be in. Walking to the living room requires zero EV and HV fuel use, though.
     
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  9. Salamander_King

    Salamander_King Senior Member

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    The amount of regen has to be taken into the consideration I would think. With stationary CHG mode, there would be no regen. If the CHG mode is turned on when the car is going downhill, you would have additional kWh produced. How much difference would it make, I have no idea...lol

    This I agree. Only if that is easily measured. But it's not. And extrapolating the data obtained from the stationary CHG mode to an actual real-world driving situation is going to be very difficult if not impossible. It is like EPA-rated mpg and EV range is a good starting point, but we all know that number does not apply to all driving situations in the real world.

    Cursory online search finds many generator data. I am not a generator expert, so I don't have any data to back up his claim. Here are some numbers on Honda portable generators. The amount of gallons of gas used/kWh generated under high and low load seems to be large enough to be concerned if applicable for CHG mode.
    Source: Generator Fuel Consumption Data - Thor Forums

    Honda Inverter Generators:

    900/1000 Watt Portable
    • .21 gallons / kWh at 100%
    • .38 gallons / kWh at 25%

    1800/2200 Watt Portable (New)
    • .16 gallons / kWh at 100%
    • .26 gallons / kWh at 25%


    2500/2800 Watt Portable
    • .16 gallons / kWh at 100%
    • .28 gallons / kWh at 25%


    2800/3000 Watt Portable
    • .17 gallons / kWh at 100%
    • .24 gallons / kWh at 25%
     
    #69 Salamander_King, Oct 20, 2021
    Last edited: Oct 20, 2021
  10. Salamander_King

    Salamander_King Senior Member

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    I am with you on this. What we need is more empirical real-world data just like the real-world mpg data on Fuelly. But the experimental drive does not need to be elaborate. All we need to know are two factors under various real-world driving conditions as I mentioned before. The driving conditions between reporters do not need to be identical. In fact, it is better to have a wider range of real-world variations. An experimenter just needs to make sure the comparison between CHG/EV and HV is driven under very similar conditions. The rests are calculatable with the assumption that CHG/EV driving is identical to HV driving conditions in every other variable that affects the overall mpg.

     
    #70 Salamander_King, Oct 20, 2021
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  11. PiPLosAngeles

    PiPLosAngeles Senior Member

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    Regen isn't relevant unless CHG mode causes you to have more or less regen than you would have without CHG mode. In other words, regen will generate y kWh going down that hill whether you have CHG mode engaged or not. Since it will be the same number under both cases it's irrelevant to the outcome of the equation.


    There are three variables involved in calculating whether it's more fuel efficient to drive in HV mode or to use CHG mode and EV mode: MPG, mi/kWh, and how much fuel the Prime uses to generate a unit of power. There's no need to extrapolate anything because we already know two of the three variables. The only unknown variable is how much fuel the Prime uses to generate a unit of power. The optimum experimental strategy is to eliminate potentially confounding variables. In this case, MPG and mi/kWh because they are both already known.

    It is possible that the Prime uses a different amount of fuel to generate a unit of power depending on other variables, but starting out with that assumption and taking the "shotgun" approach to experimentation is lengthy, messy, and prone to error. It's far simpler to eliminate the other variables and simply measure one. Then you use the observation to make a prediction. It only takes one trial to tell if the prediction is true or false.

    Just for simplicity let's say the Prime in the driveway burns 3/4 gallon of gas to generate 80% SOC (the limit of CHG mode AFAIK). We know that's about 4.8 kWh because we know a full charge is about 6 kWh in the battery. I already know I can drive ~40 miles on a charge, so 80% should give me ~32 miles. That works out to 43 MPG. No bueno. If the Prime's electrical generation efficiency gets worse under load, then the chances of HV+CHG being more efficient than HV are nil.

    I know I average about 65 MPG in HV mode. That means 2 gallons of gas can drive me 130 miles in HV mode. In HV+CHG mode 2 gallons will get me ~113 miles because 81 miles from gas in HV mode + 32 miles in EV generated by the other 3/4 gallon.

    If the Prime will vary the amount of ICE power used to generate electricity from 50-100% of the engine's total power capacity then I agree the difference could be significant. I'm betting that it never uses more than 5-6% of the ICE's total power capacity.
     
  12. PiPLosAngeles

    PiPLosAngeles Senior Member

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    In fact, there's an even easier way to answer the original question:
    Can using CHG Mode be more efficient?

    If I can drive ~130 miles on 2 gallons of gasoline in HV mode, I must be able to drive further than ~130 miles using a combination of HV and EV generated by CHG mode using the same 2 gallons of gas. To accomplish this feat I have to be able to generate 4.8 kWh using less than 1/2 gallon of gas.

    The math:

    130 HV miles - 32 EV miles = 98 miles. That means I have to drive 99 miles or more in HV mode before my 32 miles of EV driving can push me past 130 miles. 99 miles at 65 mpg requires a tad over 1.5 gallons. That leaves 0.5 gallons for CHG mode the generate the ~4.8 kWh I need to drive those last 32 miles. I won't say it's impossible, but it sounds like a very tall order. If the Prime can't do it in the driveway it's probably not going to be worth experimenting to see if it will do it on the highway.
     
    #72 PiPLosAngeles, Oct 20, 2021
    Last edited: Oct 20, 2021
  13. Salamander_King

    Salamander_King Senior Member

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    I think you are over-generalizing. Your miles driven, mpg and miles/kWh do not apply universally to everyone for every trip. And even for you, it is not a fixed constant number every day. You are also assuming the amount of kWh generated under CHG mode is constant which I really think will change depending on the driving conditions. The question is, assuming that you drove 130miles round trip all on HV mode at 65mpg, then can you drive the same round trip under similar conditions using CHG/EV mode and get an overall mpg better or worse than 65mpg, that is the ultimate question to be answered. If the number difference is small or results in flip-flop each time, or the number of trials is small, then it will not give a definitive answer but the number difference is large or it is always resulting in one being better than the other, then that would be a good indication there is a real difference.

    BTW, when your trip gets longer than 100 miles, the amount of HV portion increases if you restrict the distance of EV mode to only 80% of SoC. Therefore longer the trip, the less impactful the difference will be in either direction. To mitigate this problem you can keep repeating CHG/EV driving as many times as required to finish the travel without using any HV mode in the CHG/EV trip.

    Here is my formula-based calculation for that hypothetical trip using mpg factor=0.5, EV gain factor=1.00. As you can see, using these factors, the CHG/EV vs HV has no difference. This means if the 65mpg you can achieve on HV mode is reduced to 32.5mpg under CHG mode, but each mile you drive on CHG mode generates enough battery charge to be able to drive 1EV mile, then you do not gain or lose at all.

    upload_2021-10-20_19-59-13.png

    Now, change the factor to mpg factor=0.6, keeping the EV gain factor=1.00. This means from 65mpg HV mode is now 39 mpg on CHG mode, but 1 mile of CHG mode is able to produce 1 mile of EV mode repeatedly to get full 65 miles of EV drive. You see overall mpg is better under CHG/EV. Can I really do this? I don't know without trying, but since I have seen with my one trial that EV gain factor of ~1.0 and mpg factor of ~0.6, I think I can.
    upload_2021-10-20_20-0-0.png

    But if the factor is really like mpg factor=0.6, and the EV gain factor=0.5 the KYBlue has seen on his trip, then the overall mpg will be better on HV mode. This may be the case under certain driving conditions, but without actually doing this trip twice, you never know.
    upload_2021-10-20_20-16-45.png
     
    #73 Salamander_King, Oct 20, 2021
    Last edited: Oct 20, 2021
  14. PiPLosAngeles

    PiPLosAngeles Senior Member

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    Precisely. That's been my whole point. If I can drive in EV mode at 6 mi/kWh and HV mode at 65 MPG, that means in my particular driving style and conditions a kWh is equivalent to 0.09 gallons of gas - both will carry me the same distance. The only possible way for HV+CHG to be able to best 65 MPG is for the car to be able to generate more than 1 kWh for every 0.09 gallons of extra gas it burns. There's no other way because it has to net more than 65 MPG.
     
  15. PiPLosAngeles

    PiPLosAngeles Senior Member

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    It get even worse if you use the EPA ratings, which more closely resembles the experiences of people who don't hypermile. 55 MPG in HV and 4 mi/kWh means 0.07 gallons is equivalent to 1 kWh. The car will have to generate 1 kWh or more with 0.07 gallons of gas to best 55 MPG. That's almost double the efficiency of a Honda Eu2200i.
     
  16. Salamander_King

    Salamander_King Senior Member

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    Did you read my entire hypothetical trip calculation? You can repeat CHG/EV more than once to gain more EV range than single 80% SoC can supply. That alone will change your prospect. And again, the question is not specific to your trip alone. Maybe under your driving condition, it is not possible to get better efficiency using CHG/EV mode over pure HV mode, but that does not eliminate the possibility of CHG/EV mode getting better overall efficiency over pure HV mode driving under other conditions by other drivers. Again, just like Fuelly mpg collections, someone could get only 45mpg no matter how hard he/she tries does not negate the fact that someone else is getting 100mpg from the same make/model of car. And if we have enough people showing his/her own driving data, then we can get an overall average if in fact that CHG/EV mode can be more efficient than HV mode under certain circumstances.
     
    #76 Salamander_King, Oct 20, 2021
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  17. Salamander_King

    Salamander_King Senior Member

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    Try your calculation with 40 miles total distance of the trip. With that short distance, you do not have to drive on HV mode at all if ~20 miles of CHG mode can generate enough kWh to SoC ~80% to gain ~20EV miles at 4 miles/kWh efficiency. if the mpg drop is less than 50%, then overall mpg will be better with CHG/EV mode. This is easily testable unlike the measuring gas used and kWh generated under CHG mode either at PARK or DRIVE.

    upload_2021-10-20_22-0-43.png
     
    #77 Salamander_King, Oct 20, 2021
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  18. PiPLosAngeles

    PiPLosAngeles Senior Member

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    It doesn't matter if you engage CHG mode once or 6,000 times, if CHG mode is to best HV mode for efficiency the extra gas consumed by CHG mode must carry you farther than the same amount of gas would carry you in HV mode. Otherwise making the entire trip in HV mode would be more efficient.

    If we were to make that drive in HV mode it would require 0.72 gallons of gas (40 / 55 = 0.723).

    You're proposing that we can drive 20 miles of that trip under ICE power and 20 back in EV mode.

    The 20 mile leg fueled by gasoline will require at least 0.36 gallons of gas (20 / 55 = 0.364).

    If we're going to beat HV mode's 0.72 gallons for the whole trip we have less than 0.36 gallons left to generate 5 kWh. That's over 13.8 kWh per gallon.

    The only way the number in your chart are possible is if you used less gas on the first leg of the trip in CHG mode than you did on the same leg in HV mode. That means there's an external variable interfering.

    EDIT: I'll use the 55 mpg from your chart.
     
    #78 PiPLosAngeles, Oct 20, 2021
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  19. vvillovv

    vvillovv Senior Member

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    I did a 110 mile round trip a few days ago
    Winds of the west at 10 - 15 MPH -Temp 55 F - 55 miles each way 72 mph - (except on surface roads which added up to 10 miles in each direction and were driven all in HV mode except except last 5 miles of the second leg which was in Charge mode)
    First Leg:Traveling SouthWest 28 miles than Due West 17 miles at 72 MPH
    Second Leg: Traveling Due East 17 miles than NorthEast for 28 miles at 72 MPH
    Fist leg: in HV mode 54 MPG - 95% EV range left at the end of the first leg..
    Second leg: HV mode 5 miles to Hwy at 55 mph, than EV to 0% EV left, at 72 mph (around 17 miles),
    than Charge mode around 28 miles at 72 MPH than 5 miles at 35 MPH
    ending between 60 and 61 MPG.
    A mathematicians dream come true. :whistle:
    edit: one very noticeable geographical anomaly:
    200 ft incline within a 1/2 mile at 72 MPH in HV mode on first leg
    200 ft descent within a 1/2 mile at 72 MPH in EV mode of second leg
    edit2: ended with 60% EV showing
    edit3: first leg started in HV mode for 5 miles. the first 3 of 5 miles has an incline of 200 ft (humm, coincidentally) - second leg 200 ft descent for the last 5 in Charge mode
    elevation snaps taken from freemaptools
     
    #79 vvillovv, Oct 21, 2021
    Last edited: Oct 21, 2021
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  20. Salamander_King

    Salamander_King Senior Member

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    Yes, it matters. If the CHG mode can produce kWh of energy to carry the car further in EV mode than HV mode would by the excess amount of gas used under CHG mode, then more CHG mode is used further it goes on EV mode, thus more efficient mpg (higher). Of course, it is also true for the opposite direction as well. That is, if the CHG mode excess amount of gas used can not produce enough kWh of energy for EV mode to beat the regular HV mode efficiency, then more CHG mode used less efficient mpg (lower).

    However, all of this is assuming that the amount of kWh generated per gallon of gas used in CHG mode is always constant, which I really think is not the case. Also, the assumption is that EV efficiency and HV efficiency stay constant as well which is certainly is not the case. It simply depends on how much kWh CHG mode can produce under the driving conditions tested, and how far that kWh energy can carry the car on EV mode compared to HV mode used under the same condition. I think all three numbers, that is EV efficiency miles/kWh, HV efficiency mpg, and CHG mode generator efficiency kWh/gal are variables that change depending on the particular driving condition, thus can only be determined for a particular driver for a particular driving route and distance under particular condition by empirical testing.

    Your number is correct, but maybe you are underestimating the efficiency of the PRIUS generator. After all, it is the same generator for the regular Prius which has only HV mode for all practical purposes. You keep stating as if beating a small gas engine Honda generator efficiency is an impossible task. But my rudimentary understanding is that a small engine gas generator efficiency is very low even for a HONDA.

    1 gal of gas contains 33.70kWh equivalent of energy. 8kWh is only 23.7% efficiency. Isn't a larger electric generator much better than that? Again, I am not an expert in this area, so I might be way off, but maybe 13.8 kWh per gallon which is 40.9% efficiency isn't that hard to achieve? This may not apply to small engine generators, but I have read some articles saying over 90% efficiency is achieved by large industrial diesel engine generators.

    The only way to test it is just to do the actual drive and compare as I proposed, or do as you say to measure the CHG mode generator efficiency at PARK, if you find out ways to measure the gal of gas used under CHG mode and also measure the amount kWh of electricity generated. I think driving is the easier way of two and it is an empirical real-world result. Your CHG mode generator measurement only applies to the PARK condition, and if the amount of kWh generated per gallon under CHG mode is not a constant number, then it only gives some reference point that may or may not be applicable to all driving conditions.

    Try repeating the same condition drive with that segment you used CHG mode in HV mode and come back with mpg, Also, I need the miles of EV range gained for the total miles CHG mode you drove on this round. ;)
     
    #80 Salamander_King, Oct 23, 2021
    Last edited: Oct 23, 2021
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