Accord 04 mileage improved if in-coming air is heated?

I think that the confusion is that, when I speak of aircraft
performance I am speaking of its ability to climb which is improved by
denser air(colder and/or lower altitude.) This is true for all
aircraft with the possible exception of high performance military
aircraft which are almost rockets. Light aircraft are definitely more
fuel efficient at higher altitudes although they generally aren't
flying above 10,000 feet because that requires supplemental oxygen for
the pilot and passengers. Their performance (rate of climb) at higher
altitudes (or higher temperatures) is compromised not only by reduced
engine power but by reduced ability of the wings to generate lift in
less dense air. By 20,000 feet their performance (rate of climb) is
essentially zero. Turbocharging or supercharging will restore the
engine's power and allow them to climb further but the rate of climb
will still be much less than at sea level.

By the measure of true airspeed the picture is mixed. Reduced air
density reduces parasitic drag but also reduces engine power (in
atmospheric engines) so the net effect on true airspeed is not very
large. Fuel economy does improve however. Adding a turbo will make
the aircraft faster at high altitudes and it will still be more fuel
efficient than at sea level.

To bring it back to cars; increased air density will definitely
increase fuel consumption at higher speeds. Sea level air density at
0F is about 20% higher than at 80F and wind resistance would be
proportionately higher as well. Since wind resistance is the major
factor in fuel consumption at high speeds, it is obvious that highway
fuel economy will suffer significantly for this reason alone when the
temperature is cold. Warming the intake air will not help this.

 

This is the real point. Wintertime gas mileage is not appreciably
affected by engine performance. It's all about drag.

It would be interesting to check gas mileage between winter and summer
on a car that never gets on the highway. Anybody here drive around on
the streets without ever going more than 40 MPH?

 

But in a car, the fuel-air mixture is harder to ignite,
among other adverse consequences of cold air car engine
operation.

 

Air density should be roughly a function of
Pressure/Temperature. How much do weather variations cause
air pressure to vary? 10% or so? On an absolute temperature
scale, any city's temperature varies maybe 15% or so. But
pressure and temperature are in constant interplay.

Fuel mileage is certainly a function of car speed in
general, with wind resistance being the main explanation for
why fuel mileage drops off as one increases one's car's
speed.

You're entitled to your opinion, but my own is it's not 'all
about drag.' Drag plays a role, but gasoline engine
performance on cars is in fact worse for several reasons in
cold temperatures.

45-50 mph. Mileage goes down by I'd say 5-10% in the winter.

 

"Harder to ignite"???

 

You don't know what I mean? Then you shouldn't be posting to
this thread.

 

I hope the net cops don't arrest me for posting inappropriately. Hey, I
should introduce you to Daniel J. Stern on the Chrysler group. You two
could have a "who is more arrogant" contest... that is, if you aren't
the same person in disguise.

Anyway, do you mean that the fuel-air mixture is harder to ignite in the
winter than in the summer? If so, why would that be? And don't tell me
that if I don't know, then I should take a remedial course. You're the
one who brought it up.

 

eh? i'm not saying /anything/ about oxygenation - i'm talking about
WINTER fuel. that's the paragraph _above_ oxygenation, in case you'd
missed it. sheesh. shame on me for bothering with a citation if you
won't take the time to read or can't understand it. especially since
it's been quoted here before.

 

may be true, but is the cause of the poor fuel atomization cold air,
cold gasoline or a combination? I live in central Minnesota. At -30F my
fuel injected engines will start but the old '81 F150 floods easily at
-20F. I believe lower fuel economy in cold weather is due more to
vehicle warm-up than anything else, and my proof is that when my
vehicles are parked in my heated garage the mpg remains the same in the
winter as the summer months but when they are parked outside (due to my
garage being full of pointless projects) then I noticed a 10% to 15%
drop in mpg. Rolling resistance is also a factor to consider when it is
cold. The wheel bearings can get so stiff that when the car is jacked up
the wheel is extremely hard to spin by hand. Also the transmission and
final drive get very "stiff" and don't "limber up" until several miles
have been driven.

 

inappropriately.

Not to worry. People will just think you're a weenie.

People who drive Fords, GMs, etc. are bilious. I do not
associate with them on Usenet and certainly try to avoid
them offline as well.

You brought it up. Do you know what "harder to ignite" means
or not? I simply don't understand what you're asking here.
If you want to learn something new, and you reach a
stumbling block, you have to identify what the confusing
point is. Or stay ignorant. And don't mess with me: I am a
former highly esteemed engineering educator with a gift for
teaching. Except I have no patience anymore.

A fuel air mixture does not all ignite in the same
"instant." It burns, and expands, at a certain rate. Some
fuels burn slower than others. Temperature of the fuel air
mixture will affect the rate at which it combusts (or burns
or ignites yada). At lower temperatures, the mixture doesn't
burn as readily. Combustion is a chemical reaction that
requires a certain temperature for ignition etc. Higher
temperatures promote better ignition.

Google for more. I don't say that to be mean. (Well, I am
mean, but I don't say it here to be mean.) I say it because
I'm sure there are some very polished sites that explain it
better than I am willing to do here in a few minutes.

This discussion is also overshadowing other things that
contribute to worse engine performance at cold temperatures.
I don't care to be backed in a corner like this is the only
aspect of worse engine performance. As I posted originally,
the greater resistance to ignition of the cooler fuel-air
mixture is but one example of the adverse effects of colder
temperatures on gasoline engines. Google is your friend.

Elle
I welcome being killfiled by both the depraved and the
ignorant

 

Density is proportional to barometric pressure. Outside of a tropical
depression/tropical storm/hurricane, barometric pressure at sea level
typically ranges from 29.80 to 30.20 inches Hg. That's a little over
1% - not very significant.

Absolute humidity also has a small affect, about 1%, at warmer
temperatures with higher humidity reducing air density. At cold
temperatures, absolute humidity has almost no effect because the air
holds very little moisture even at 100% RH.

Here is a fun calculator you can play with:

http://wahiduddin.net/calc/calc_da_rh.htm

Of course, performance (power output) of gasoline engines improves
with cold temperatures due to higher air density. This is a well
known phenomenon.

I assume that you mean that cold weather causes poorer fuel economy
for reasons related to engine operational issues. We have noted
severe warm-up cycles and maintenance of optimum running temperature.

 

cold air,

Well, I didn't say anything about atomization, but I think I
know what you're getting at.

I'd just argue for now both contribute to the fuel being
more resistant to ignition. I guess one could say many more
parts of air are req'd per part of gasoline, so the air
dominates in its effects, but I don't want to spout bs off
the top of my head. Plus, I haven't studied up on
atomization in a million years. (Really these days the only
thing I lose sleep over is why I am such a weenie over
trying to change my clutch. Not that it's due. It's just
something I doubt I'll ever try.)

Good anecdote, particularly for relatively young "I know
everything" whipper-snappers like me who have seen darn
little of carbureted engines.

Depending on the driver and car model, absolutely vehicle
warm up is a factor, though "warm up" can mean different
things, as I reckon you know. E.g. there is the warm up
whereby people let the car idle until the defroster has
melted the 1 mm yada of ice on the windows. Then there is
the warmup that the car goes through even at very balmy
temperatures, where the car's computer revs the idle high to
bring it up to temperature faster.

I'm not pretending to be an authority here or anything,
arrogantly ruling on whose answer is best. I'm just
reporting based on my own reading and my own experience
driving, throwing in a bit of mechanical engineering
background, but just a bit. And I'm not always right, but I
try to indicate when I'm posting an opinion rather than
assserting something as fact.

Absolutely. That is discussed on the net, IIRC. People can
hear it and feel it, probably, too. Of course the engine
lube oil's higher viscosity at lower temperatures has a
similar deleterious effect. Hence up north, aren't those
little oil dipstick heaters popular?

Absolutely.

There is no one cause that I would say is the greatest for
every car. Even for one particular car and driving style, I
wouldn't try to separate the several variables (by size)
that are likely to contribute to reduced mpg at colder
temperatures. To me, the variables that seem important, in
no particular order, are:

-- computer set to run the car at higher fuel flow at cooler
temperatures, yada
-- higher viscosity of engine oil
-- higher air density, producing greater wind resistance
-- lower heating value yada gasoline used in some parts of
the country
-- more cautious driving style in worse weather
-- yahoos forgetting that their tire pressure will go down
as temperatures fall, messin' with that rolling resistance
yada
-- yahoos not keeping their coolant topped off, since the
coolant helps warm up the engine in cold temperatures.

 

Are you /sure/ Gordon??

Absolutely really really sure that you nailed this issue?

Profound. So you're saying "air" is not like a homogenous
compound, with a constant molecular weight yada.

Wow. You're really smart. If only Google were this smart.

Shall I cough up ten more?

No wait. That might insult your intelligence.

Are you still /sure/ Gordon??

Not "of course."

temperature.

Assume away. It's not healthy but people don't really
change.

Killfile my addie, hon. I want intelligence.

 

"You're thinking of, for example, certain diesel designs that
cool the intake air so as to pack more in for each cycle.

What you say above is not so for automotive engines."

If it is true for diesels, why not for spark ignition engines?

 

A little bit of engineering education and no practical experience is a
dangerous thing, isn't it?

 

it /is/ true for si engines as well as diesels - that's why turbos
usually have intercoolers for both types of engine.

 

engines?

For one thing, the way the fuel is ignited is different.
Spark ignition vs. compression ignition. That topic alone
would reveal a lot about why diesel engines are so different
from gasoline engines.

I do think there is some misreading going on here. Off the
top of my head, 'cause I don't feel like doing a thorough
review of the diesel cycle vs. gasoline yada cycle: Of
course it's true that cooler air is more dense and so, for
the same volume, one could pack more air, and so fuel, into
each cycle, be it a gasoline cycle or diesel cycle. So in
theory, by cooling intake air, one can get more power out of
such engines. Indeed, this is so for diesel engines.

Leaving theory now and going to what is practical and
actually done, as you are probably aware, some diesel
engines do have intercoolers precisely for cooling the air
and so increasing the engines' power. But the gasoline cycle
has limitations that preclude using intercoolers yada. My
recollection is this has a good deal to do with the
ignitability, if you will, of gasoline vs. diesel (which is
partly why gasoline has an octane number, but diesel has
another metric to indicate how well, if you will, it burns).

Sorry I don't feel like digging thoroughly and regurgitating
it here. I'm not trying to force anyone to believe me. I'm
stating what I recollect about gasoline engine design vs.
diesel design, design relying of course on both theory but
also practical implications that the theorist simply can't
disregard if s/he actually wants something to work well in
everyday living.

 

Government mandated gasoline reformulation is to blame for your lower gas
mileage. Heating the air is not going to help.

 

Tee hee. Yeah, we could all tell that you are or were deeply involved
with institutionalized education. It's all about what you have read,
where you read it, and the fact that everybody else is helplessly stupid
compared to you. Typical university crap. And yes, I've seen the
inside of a university. That's how I know. Real cars don't work that
way, though.

You really do have an amazing talent for packing huge amounts of
arrogance into so few words. If you don't have time to explain and
share your incredible gifts of intelligence with us, why do you bother
wasting your time here in the first place?

And yes, we all know about the famous "flame front", the lack of which
causes knocking in your engine. In other words, gasoline is formulated
to not burn as well as it could. Funny, that. In your extensive
reading on the subject, did you come across the revolutionary gadget
called the thermostat? It maintains a nearly constant head
temperature. Leaving aside the extreme climates and just sticking
between 0 and 100 where most normal folks live, gasoline is really
pretty easy to ignite once it gets all squished down and hot in that
little bitty combustion chamber. You probably wouldn't recognize the
cold air any more. Cold starts notwithstanding of course.

I'm sure that it just makes you feel more important when lesser folk
can't stand to be around you. But some of us can see right through the
argument style. When "backed into a corner" you might actually have to
start saying something substantial rather than simply posting links and
implying that everybody else ought to read more. That's why
enthusiastic arguers try not to actually say anything.

Come to think of it, I might just be almost as stupid as you probably
think I am. After all these years I should have learned better. I come
to groups like this to ask a real Honda mechanic with years of
experience what might be a good place to start looking for the cause of
my problem, and I end up hanging around and getting into these
ridiculous discussions with folks who should have been lawyers (the
primary requirement for being a lawyer is a love of arguing above all
else) and have probably never diagnosed an engine problem more severe
than an an empty gas tank.

Anybody can learn to lay bricks, but when you want it done right, and
done right now, you call a guy who has been doing it for years.
Likewise, I'll come back when I need more advice from a real Honda
mechanic. Thank you to the guy who told me about the water temperature
sensor, it worked like a charm. And to the fellow who wants to find out
about heating the intake air, go for it if you want to take a whack at
it. But if you want to know about engine performance in different
temperatures, ask somebody involved in car racing.

 

I hope this is Laura talking.

Lord no, but you have a right to your opinion.

Much university work is crap, true. But most of my teaching was not at
research institutions and was very hands-on-ish oriented engineering.

I still can't hold a candle to many of the regulars here when it comes to
certain areas of car repairs and diagnosis.

Oh dear. An inferiority complex.

Lose that.

As I have said here a few times, most auto technicians (amateur or
certified) or smarter than most lawyers and doctors.

snip, because egos are likely going to preclude a meaningful exchange at
this point

I know nothing about "flame fronts," though this might be a factor here. I
don't feel like googling.

I agree that colder air often means denser air and it will have an effect on
fuel mileage, based on some reading and the reasonableness of the argument.
I of course also feel there are other factors that reduce mpg in colder
weather as mentioned before blah blah.