Cruise Control Freeway Mileage in 06HCH (Experiment)
#51
12-05-2005, 11:07 AM
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Re: Cruise Control Freeway Mileage in 06HCH (Experiment)
Originally Posted by ElanC
There's no need to guesstimate. The aerodynamic drag force increases with the square of speed.
If you get 52 mpg at 60 MPH you should get, according to the formula, 38 MPG at 70 MPH, and 29 MPG at 80 MPH. The reason the drop isn't so bad, probably, is that there are other drag forces such as road friction and drivetrain friction that don't increase with the square of speed but more linearly with speed. And the energy spent to climb a hill, for example, is the same regardless of speed.
If you get 52 mpg at 60 MPH you should get, according to the formula, 38 MPG at 70 MPH, and 29 MPG at 80 MPH. The reason the drop isn't so bad, probably, is that there are other drag forces such as road friction and drivetrain friction that don't increase with the square of speed but more linearly with speed. And the energy spent to climb a hill, for example, is the same regardless of speed.
#52
12-05-2005, 11:30 AM
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Re: Cruise Control Freeway Mileage in 06HCH (Experiment)
Originally Posted by CGameProgrammer
Right. According to your figures, going from 60 to 70 results in a 14 mpg drop, and going from 70 to 80 results in a 9 mpg drop. The FE decrease becomes less severe each time your speed goes up.
1.92 Gallons per 100 mi @ 60 MPH.
2.63 Gallons per 100 mi @ 70 MPH.
3.45 Gallons per 100 mi @ 80 MPH.
So from 60 to 70 you use another 0.71 gallons per 100 miles.
from 70 to 80 you use another 0.82 gallons per 100 miles.
(from 60 to 80 your fuel consumption almost doubles)
#53
12-05-2005, 11:50 AM
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Re: Cruise Control Freeway Mileage in 06HCH (Experiment)
It's not a fully linear drop with speed though because generally the engine has a higher volumetric efficiency at higher load factors, although that drops off as RPM goes up beyond the maximum efficiency range.
#54
12-05-2005, 12:00 PM
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Re: Cruise Control Freeway Mileage in 06HCH (Experiment)
Originally Posted by ElanC
Yes, but it's a bit of an optical illusion because the MPG drop between 70 and 80 is from a much lower starting point. I think looking at the inverse measure - Gallons per 100 miles - will illustrate my point. The numbers I gave translate to -
1.92 Gallons per 100 mi @ 60 MPH.
2.63 Gallons per 100 mi @ 70 MPH.
3.45 Gallons per 100 mi @ 80 MPH.
So from 60 to 70 you use another 0.71 gallons per 100 miles.
from 70 to 80 you use another 0.82 gallons per 100 miles.
(from 60 to 80 your fuel consumption almost doubles)
1.92 Gallons per 100 mi @ 60 MPH.
2.63 Gallons per 100 mi @ 70 MPH.
3.45 Gallons per 100 mi @ 80 MPH.
So from 60 to 70 you use another 0.71 gallons per 100 miles.
from 70 to 80 you use another 0.82 gallons per 100 miles.
(from 60 to 80 your fuel consumption almost doubles)
#55
12-05-2005, 12:51 PM
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Re: Cruise Control Freeway Mileage in 06HCH (Experiment)
Originally Posted by CGameProgrammer
Yes, that's all true, but if you remember the way this conversation started, it was because NASA got a 7 mpg drop going from 60 to 70 but a 9 mpg drop going from 70 to 80, which I argued was a result of the cold or other factors because it should have resulted in less than a 7 mpg drop. You are agreeing with me.
That's -
1.93 G / 100 mi @ 60
2.23 G / 100 mi @ 70
2.78 G / 100 mi @ 80
So it does look like the deterioration of FE from 70 to 80 was more, compared to 60-70, than we'd expect from aerodynamic drag.
Yes, I agree.
It could be a temprature change, or it could be a 10 MPH head wind that he'd hardly notice.
#56
12-05-2005, 08:25 PM
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Re: Cruise Control Freeway Mileage in 06HCH (Experiment)
xcel asked me to post something from the chatroom tonight in this thread, so here it is:
on a 4 mile long slight downhill, i can use FAS on my 04 hch cvt for the entire route, @35-45 mph
on the same 4 mile route, if i try to enter ev-mode on my 06 hch without using any assist, the 06 hch slows down and cannot keep going as the 04 hch did in FAS.
xcel says this is due to rotational frictional losses, even if the valves are sealed in the 06 hch.
however, i pointed out that it was possible to go the whole 4 miles on ev mode, if i used assist in ev-mode, up to 5 bars (50% assist). that way, i still used 0 gallons of gas for the whole 4 miles, in both cars. at the end of the route, i can recharge the battery again by braking for a stop sign to turn left on.
End report.
on a 4 mile long slight downhill, i can use FAS on my 04 hch cvt for the entire route, @35-45 mph
on the same 4 mile route, if i try to enter ev-mode on my 06 hch without using any assist, the 06 hch slows down and cannot keep going as the 04 hch did in FAS.
xcel says this is due to rotational frictional losses, even if the valves are sealed in the 06 hch.
however, i pointed out that it was possible to go the whole 4 miles on ev mode, if i used assist in ev-mode, up to 5 bars (50% assist). that way, i still used 0 gallons of gas for the whole 4 miles, in both cars. at the end of the route, i can recharge the battery again by braking for a stop sign to turn left on.
End report.
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