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| Author |
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| 25 new of 81 responses total. |
senna
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response 50 of 81:
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Apr 30 01:16 UTC 2002 |
I enjoy five speeds myself. There's a nice hill on Liberty that I can coast
down for close to a mile on my way home with barely any speed loss, one of
the best parts of that particular commute.
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russ
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response 51 of 81:
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Apr 30 06:02 UTC 2002 |
Re #46, #47: I was using the Tzero as an example for the economics
of cogeneration, not as a practical all-purpose vehicle. (The lack
of doors and a real heater makes it a toy.) On the other hand, there
is no reason why a similar drivetrain couldn't be supplemented with
a 30 horsepower sustainer engine and stuck in something like a Mustang
or a Chrysler Sebring. That would give you up to 90 miles of range on
batteries, plus cruising at up to about 75 MPH for as long as you can
keep the fuel tank full. At 2 lb/hp plus 5 gallons of fuel, you'd be
talking maybe another 95 pounds added to the car; no big penalty.
How many people drive more than 90 miles a day? How much of most
people's oil consumption would be eliminated if even the first 50
miles every day used no oil? This requires no new tech, folks.
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gull
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response 52 of 81:
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Apr 30 13:09 UTC 2002 |
Nope, no new tech, but the economics won't support it yet. Gas is still so
cheap that you'll never make up the difference in cost between a hybrid and
a conventional car. There doesn't seem to be much interest in any sort of
government incentive, either. In fact, Oregon decided that people who buy
hybrids aren't paying their fair share of fuel taxes, and is now requiring
them to pay double the normal registration fee.
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drew
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response 53 of 81:
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Apr 30 20:41 UTC 2002 |
I'd like transcontinental range. Could one of these ultra-high MPG vehicles
be fitted with a normal or slightly extra-large (20, maybe even 30 gallon)
fuel tank?
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gull
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response 54 of 81:
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Apr 30 23:51 UTC 2002 |
Sure, you *could*. It'd cut down on the gas milage, due to the extra
weight, though. It might be hard to find the extra space, too, and it
probably wouldn't be all that safe.
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mdw
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response 55 of 81:
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May 1 01:01 UTC 2002 |
Weight has almost no effect on highway mileage. What matters there is
wind resistance, rolling resitance, etc -- none of which are directly
related to weight. For wind resistance, the most important component is
the square foot area of the vehicle from the front. Length is
relatively unimportant, it's "almost" free.
If installed right, an auxillary gas tank could actually *improve* wind
resistance -- for instance, many sedan have a double deck rear. The
notch for the rear window causes boundary separation, and the trunk adds
insult to injury. What is actually far better is a station wagon or
even better a flat hatchback design - the body should smoothly come to a
slight taper, and if a sharp tip is not possible, it should come back to
one blunt edge. So, an auxillary gas tank installed in the "notch" of a
sedan, and properly smoothed into the body contour so there are no edges
or creases, should significantly decrease wind resinstance of a typical
sedan -- at the cost of visibility, safety, and probably adversely
affecting the center of gravity when full.
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scott
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response 56 of 81:
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May 1 01:36 UTC 2002 |
Weight does indeed affect highway mileage, at least in states like Colorado.
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russ
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response 57 of 81:
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May 1 02:09 UTC 2002 |
Re #52: It's half economics and half political will. Either one could
change overnight. For instance, if Saudi Arabia asked the USA to leave
the peninsula and Iraq invaded all the way down to their oilfields, the
world price of oil would make it economically attractive. If the Saudis
turned blatantly anti-American, it would be politically attractive. (Then
there's the scenario that our trade partners decide to do something
because we haven't signed on to the Kyoto agreement...)
I don't think either of these is a terribly low-probability event. I
just wish we had the political will to shift our system (and keep all
that money at home), then tell OPEC they can keep their oil; that would
completely shaft *all* the oil dictatorships including Iraq without a
shot fired, and deflate the Wahhabist attempt to convert the whole world
to their radical sect (it's hard to buy influence when you're broke).
Oregon is quite "green". I doubt that the higher hybrid taxes are
going to survive very long.
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mdw
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response 58 of 81:
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May 1 05:50 UTC 2002 |
Well, in states like Colorado, the weight penalty climbing hills turns
into the weight advantage descending those very same hills. The main
difference at the end of the day will be the gain or loss in potential
energy due to any net gain or loss of altitude, +/- any intermediate
inefficiencies. I suspect air friction will be more important in most
cases. Now, in start/stop city traffic, weight is much more of a
penalty, particularly since it's hard to use regenerative braking at low
speeds (and the regenerative equipment itself will cost weight.)
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gull
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response 59 of 81:
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May 1 13:09 UTC 2002 |
Most cars sold in the U.S. seem to be designed to have a range of 300 to 400
miles between fill-ups, except for some pickup trucks with dual tanks. I'm
not sure how that figure was settled on.
Adding a second fuel tank to a modern car is actually pretty non-trivial.
Presumably you'd need a second electric fuel pump, and a pair of valves (one
for the fuel supply line, one for the fuel return line.) Another
possibility would be to provide a way to pump fuel from the new tank into
the stock one. I've heard of this being done with auxiliary tanks for small
aircraft. No matter what you do, the new tank is unlikely to have the vapor
collection systems the stock tank has, so you'll be venting fuel vapors into
the air and contributing to photochemical smog.
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mdw
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response 60 of 81:
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May 2 03:15 UTC 2002 |
If the 2nd tank is above the 1st tank, gravity feed will do. No reason
to have dual fuel return loops -- the one that's there will do fine;
mainly the loop is there so that the fuel injection system doesn't get
vapor lock. It's certainly true that unless you bother (and most people
probably wouldn't), the auxillary fuel tank wouldn't have fuel venting.
Of course, that's probably still true for all the gasoline bought for
lawnmowers.
There's probably a sort of equilibrium between the distance of fuel
stops out in the country, and the maximum fuel range of automobiles.
Although there's probably also a wide safety margin there. Motorcycles
typically have a shorter range (down to about 100 miles in some cases),
and that that can be a hazard sometimes out in remote areas.
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gull
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response 61 of 81:
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May 2 13:49 UTC 2002 |
Hmm...my point about dual fuel returns is that if you run the engine off the
second tank (instead of just using it to fill the first), you'll definately
need to switch both the intake *and* the return to it. (Think about what
would happen if you ran off the second one while the first one was full,
otherwise.)
I'm actualy not sure how a modern EEC system would react to you tapping into
the fuel system to add a gravity-feed tank. They rely on having a partial
vacuum in the tank to make the vapor recovery system work. This is why the
CHECK ENGINE light will come on in newer cars if the fuel cap is loose.
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drew
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response 62 of 81:
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May 2 18:26 UTC 2002 |
It's more like area times drag coefficient; that is, the shape is as important
as the size. And I've found experimentally that vehicle weight via tire
resistance does contribute significantly to overall drag.
However, 30 gallons of gasoline at around 0.75 s.g. mass about 180 lbs, which
is about the mass of a typical passenger, and less than 10% of the mass of
the smaller of my cars.
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gull
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response 63 of 81:
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May 2 19:10 UTC 2002 |
That'd be a little over 20% of the usable load of my car.
(By usable load I mean GVWR - curb weight)
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russ
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response 64 of 81:
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May 3 00:24 UTC 2002 |
Re #58: The "weight advantage" just means that you have to dump more
energy in the brakes. Lots of mountain passes have 6% grades on both
sides, and enough curves that the speed limits are as low as 25 MPH.
Hauling weight up that slope just means you have to brake it coming back
down, and if you can't store the energy you have to burn fuel for the
next hill too.
Interesting points of fact:
1.) An 85,000 pound truck climbing a 6% grade at 25 MPH is using 340
horsepower to raise mass against gravity.
2.) The energy for an 80,000 pound truck to climb 2000 feet is about
81 horsepower-hours; at 0.35 lbm/hp-hr (typical of a diesel) this
requires about 28 pounds of fuel, or about 4 gallons. A regenerative
braking system could thus save about that much fuel for every
2000 foot climb.
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gull
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response 65 of 81:
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May 3 03:41 UTC 2002 |
Interesting, though around here there aren't many 6% grades. A more
useful calculation would be to figure out how much fuel it takes to
accellerate a loaded truck from 0 to 60 mph. Regenerative braking should be
easy to get truckers to use -- they're already familiar with compression
brakes, so the concept is familiar.
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scott
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response 66 of 81:
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May 3 13:22 UTC 2002 |
It's one thing to talk about how to handle kinetic energy in Colorado, it's
another thing to drive on I-70 west from Denver into the mountains and see
how much vertical distance you'd have to plan for. It's something like 4-5%
minimum for 30 or so miles up to the Eisenhower Tunnel (through the pass),
and once on the other side you've got twisty freeways going long distances.
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gull
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response 67 of 81:
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May 3 13:59 UTC 2002 |
I really don't think climbing mountains is a big win for a hybrid, for the
simple reason that you can't store enough energy. (One complaint about the
Insight is that it runs out of battery charge on long grades, forcing you to
rely on the gasoline engine alone.)
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russ
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response 68 of 81:
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May 27 04:10 UTC 2002 |
Re #65: I've seen plenty of 6% grades in Washington, Idaho, Oregon,
Nevada, Utah, Colorado, Montana, Wyoming and Arizona. Logging trucks
in the PNW may be going up and down such grades at relatively low
speeds much of the day. This is ideal for hybrids.
The energy of an 85000 lbm vehicle moving at 60 MPH (88 ft/sec) is
about 10 million foot-pounds, or about 5.2 horsepower-hours. At
.35 lbm/hp-hr, it takes about 1.8 pounds of fuel to accelerate to
that speed. That's roughly a quart of diesel fuel.
Use of compression brakes is prohibited in many places, but an electric
dynamic brake would be noiseless (quieter than even the wheel brakes).
Electric acceleration would be very quiet, as well as producing much less
exhaust. I can see hybrid rigs being used for local service in order to
comply with noise or pollution restrictions. Electric assists would
probably be faster than the combustion engine (little or no time wasted
in shifts), allowing the trucks to move faster in traffic. Enough of that
could pay for itself. Being able to charge from grid electricity at
freight stops might displace expensive diesel fuel and save even more money.
Re #67: The batteries of the Insight and Prius are very small and
light. If the batteries amounted to 7-10% of the vehicle weight you'd
see a lot more climbing ability. Here's a BOTE calculation:
15 WH/lb (33 WH/kg) battery (lead-acid batteries run 10-20 WH/lb).
Battery amounts to 10% of vehicle mass (total stored energy 3.3 WH/kg).
80% efficient converter/motor: total energy for climbing = 2.64 WH/kg.
At 9.81 J/kg-meter, the vehicle could climb 2.64*3600/9.81 = 969 meters
(about 3180 feet) on battery power alone.
You're not going to climb Vail Pass on a small battery, but you could
definitely run up and down smaller hills with a reasonable hybrid and
still use relatively little fuel. If you bump the battery size up to
30% of the vehicle mass or use something better than lead-acid, you can
tackle even larger hills without turning lots of energy to waste heat.
Charging that battery from the grid would allow running short trips
entirely without fuel, too.
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gull
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response 69 of 81:
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May 28 14:57 UTC 2002 |
The problem with the "use bigger batteries" approach is that the
limiting cargo factor for trucks is often the gross weight the state
department of transportation allows them to have. More batteries means
less weight available for cargo.
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russ
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response 70 of 81:
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May 29 04:07 UTC 2002 |
Re #69: True, so far as that goes. However, weight limits and
requirements for weight distribution can be changed. Adding another
axle to carry the weight of the batteries could address the road-wear
issue. And even without that, if fuel to run up and down hills is
a large enough fraction of the operating cost, reducing the payload
may still make economic sense if it saves even more expense in fuel.
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gull
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response 71 of 81:
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Jun 21 13:27 UTC 2002 |
The Free Press reviewed the new Honda Civic hybrid yesterday. They
tested the automatic CVT version. (There's also a five-speed available.)
I got the impression the reviewer really wanted to like this car, but
ultimately he panned it. He felt that the $21,000 price was too high.
You'd have to drive it for something like 13 years to make up the price
difference between it and a gasoline Civic in fuel savings. He also was
disappointed by the fuel economy -- he only got 37 mpg in mixed driving,
compared to the 48 city/47 highway Honda advertises. (For comparison,
my 1994 Civic Si gets about 30 mpg in city driving and 38 mpg on the
highway, in my experience. That's a relatively light 2-door hatch,
though; the Civic Hybrid is a 4-door sedan.) On the other hand, this is
a much better packaged car than the Insight. The price premium aside,
you can drive it around and use it for everything you would normally use
a four-door Civic for, with no real compromises.
I think either the price of gas needs to triple, or the price premium of
hybrids needs to come down, before they're going to be big sellers. I
do think Honda is making a good move, though. By getting these cars out
early, they'll gain valuable experience in producing them and hopefully
develop a reputation for building good, reliable hybrid vehicles. That
will give them a big head start over other car makers if gas prices
spike in the future. (Personally, I think that's inevitable.)
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brighn
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response 72 of 81:
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Jun 21 15:38 UTC 2002 |
Civics seem remarkable in how long they maintain their gas mileage. My 91
Civic was still getting over 30MPG the day it was totalled in '01. (My new
'01 Civic gets around 33 or so, mostly commuting.)
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gull
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response 73 of 81:
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Jun 21 15:57 UTC 2002 |
That reminds me, one thing I forgot to mention is that pretty much all
cars get better gas milage once they're broken in. If the reviewer's
Civic Hybrid was factory-fresh, it's not unreasonable to expect its
milage to improve by 4 mpg or more after its got a thousand or so miles
on it. New engines have more internal friction because the rings are
still being seated.
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lynne
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response 74 of 81:
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Jun 21 20:35 UTC 2002 |
<my '91 corolla also still gets fantastic gas mileage. can't afford a new
car, much less a hybrid, so old Japanese manual transmission seemed like the
way to go.
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