Alternative Power sources - highway vs. city mileage, was: 100 MPG??

Author

highway vs. city mileage, was: 100 MPG??

danny burstein

2005-09-30, 11:21 pm

In <quGdnanxBN-HpareRVn-pg@golden.net> "Solar Flare" <sflare@hotmail.com> writes:

>Lesser efficiency on the highway? I wonder why that is? Perhaps the engine
>is less efficient at higher horsepowers and could be factory tuned or
>selected by user for specific usage personality?

Not quite. It's simply a matter of mpg vs. speed. As you move
faster and faster (i.e. highway speeds) you run into an
exponential increase in air resistance.

So... all things being equal (which they're not, see next parag) you'll
get _zero_ mpg when stopped in traffic maybe 10 mpg moving at 5 mph
(you're using up plenty of fuel just keeping the engine running) perhaps
60 mpg when going 40 mph
.. and ..
drop a bit to 50 mpg when going 60 mph.

Now those figures are kind of back of envelope,
but the progression is correct. Your best mileage
will be at something like 40 mph.

Now for the hybrid trick... the better designed
ones do an "idle shut off" so when you're stopped
at a traffic light, you're _not_ burning/wasting fuel.
[color=darkred]

Nah. They do better. At least the properly
designed ones.

A typical US gasoline car uses an engine that's way
over powered for cruisig speeds. While this gives
you the ability to rapidly come to speed at a highway
entrance, it's a big waste once you're up to that 70 mph.

(The physical size and weight of the engine means you
have to burn quite a bit more fuel tha you would
with one that didn't have all that extra horsepower).

So... a well designed hybrid, like the Honda Insight,
uses a smaller gasoline engine that's just large
enough for cruising (well, somewhat bigger than that,
but not as horrendous as standard), thus saving
you all that extra, wasted, fuel. When you're on that
highway "on ramp", (or passing a truck, etc.) and
push the accelerator pedal, the electric motor
kicks in and gives you that extra horsepower.

As to weight? The battery pack and motor plus circuitry
add about 125 pounds to the car. A lot of that is saved
by using a smaller egine. And, again, the physical
engine size/mass is smaller, thus saving fuel right there.

fyi, my own Insight mileage (auto transmission) is
about 55-60 on the highway, and 35-40 in NYC traffic.

(I'd do better in the City except that my idle
shut-off isn't working. I'll fix it RSN)
--
_____________________________________________________
Knowledge may be power, but communications is the key
dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]
--
_____________________________________________________
Knowledge may be power, but communications is the key
dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

Tom

2005-10-04, 9:21 am

Typical road load HP on an average size vehical at 60 MPH is in fact
around 12 to 15 HP. That assumes not much wind and flat road. I
know this becuase I work with vehicals on dynomometers.

On Sat, 1 Oct 2005 02:06:49 +0000 (UTC), danny burstein
<dannyb@panix.com> wrote:

>In <quGdnanxBN-HpareRVn-pg@golden.net> "Solar Flare" <sflare@hotmail.com> writes:
>
>
>Not quite. It's simply a matter of mpg vs. speed. As you move
>faster and faster (i.e. highway speeds) you run into an
>exponential increase in air resistance.
>
>So... all things being equal (which they're not, see next parag) you'll
>get _zero_ mpg when stopped in traffic maybe 10 mpg moving at 5 mph
>(you're using up plenty of fuel just keeping the engine running) perhaps
>60 mpg when going 40 mph
> .. and ..
>drop a bit to 50 mpg when going 60 mph.
>
>Now those figures are kind of back of envelope,
>but the progression is correct. Your best mileage
>will be at something like 40 mph.
>
>Now for the hybrid trick... the better designed
>ones do an "idle shut off" so when you're stopped
>at a traffic light, you're _not_ burning/wasting fuel.
>
>
>Nah. They do better. At least the properly
>designed ones.
>
>A typical US gasoline car uses an engine that's way
>over powered for cruisig speeds. While this gives
>you the ability to rapidly come to speed at a highway
>entrance, it's a big waste once you're up to that 70 mph.
>
>(The physical size and weight of the engine means you
>have to burn quite a bit more fuel tha you would
>with one that didn't have all that extra horsepower).
>
>So... a well designed hybrid, like the Honda Insight,
>uses a smaller gasoline engine that's just large
>enough for cruising (well, somewhat bigger than that,
>but not as horrendous as standard), thus saving
>you all that extra, wasted, fuel. When you're on that
>highway "on ramp", (or passing a truck, etc.) and
>push the accelerator pedal, the electric motor
>kicks in and gives you that extra horsepower.
>
>As to weight? The battery pack and motor plus circuitry
>add about 125 pounds to the car. A lot of that is saved
>by using a smaller egine. And, again, the physical
>engine size/mass is smaller, thus saving fuel right there.
>
>fyi, my own Insight mileage (auto transmission) is
>about 55-60 on the highway, and 35-40 in NYC traffic.
>
>(I'd do better in the City except that my idle
>shut-off isn't working. I'll fix it RSN)
>--
>_____________________________________________________
>Knowledge may be power, but communications is the key
> dannyb@panix.com
>[to foil spammers, my address has been double rot-13 encoded]

danny burstein

2005-10-05, 10:21 pm

In <rrr4k15kkj5tpk2266s1481qh2omvr5n3t@4ax.com> Tom <tgiorgi1REMOVE@nycap.rr.com> writes:

>Typical road load HP on an average size vehical at 60 MPH is in fact
>around 12 to 15 HP. That assumes not much wind and flat road. I
>know this becuase I work with vehicals on dynomometers.

As you're measuring this on a dynamometer, is that 12-15 hp
just rolling resistance or are you somehow figuring out
the air resistance as well?

Thanks

--
_____________________________________________________
Knowledge may be power, but communications is the key
dannyb@panix.com
[to foil spammers, my address has been double rot-13 encoded]

nospam.clare.nce@sny.der.on.ca

2005-10-06, 12:21 am

On Thu, 6 Oct 2005 00:50:05 +0000 (UTC), danny burstein
<dannyb@panix.com> wrote:

>In <rrr4k15kkj5tpk2266s1481qh2omvr5n3t@4ax.com> Tom <tgiorgi1REMOVE@nycap.rr.com> writes:
>
>
>
>As you're measuring this on a dynamometer, is that 12-15 hp
>just rolling resistance or are you somehow figuring out
>the air resistance as well?
>
>Thanks

Electric vehicle experience has shown a 96 volt motor will draw
between 300 and 400 amps at 60MPH in a Chevette sedan. 400 amps is
38.4KW - which in the real world is 35 HP, more or less.

At 37MPH, a 72 volt system draws about125 amps (9hp +/-). 43 MPH
draws 175 amps.(aprox 13HP)
28 MPH is only 80 amps.( less than 6 HP) This is on a 2990 lb EV.
This is also running relatively high pressure fabric radials.

From other data, using a Fiat 128 sedan at 40MPH, wheel torque of 76.5
ft lbs at 936 revs per mile translates to 10 HP. Car weight is 2900
lbs.

60 MPH requires 125 ft lbs.which translates to just under 25 HP.

That is theory.
Real world experience with a 48 volt motor on MY Fiat 128 L coupe was
top speed of 50MPH at 400 amps. That's 19.2KW. The motor I was running
was roughly 82% efficient, according to specs I was given (Converted
B52 generator) My Fiat was about 2255 lbs plus passengers.

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