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Car Forum / Honda Cars / November 2005Accord 04 mileage improved if in-coming air is heated?
My accord 04 4 cyl mileage drops by 10-15% in winter time and I have measured that miticulously. If I can somehow warm up likely through passive means not by 12V) the incoming air before the airfilter, will that improve mileage? I am talking about temp around 30 F or 0 C only and it is very obvious. My 99 accord did the same thing. Any input from this NG is appreciated. Daniel >My accord 04 4 cyl mileage drops by 10-15% in winter time and I have >measured that miticulously. [quoted text clipped - 8 lines] > >Daniel The phenomenon of reduced milage in cold weather is well documented, but you will gain little or nothing by this scheme. For one thing, most cars already have a mechanism for warming intake air, although not for this reason. It is to prevent carburetor (now intake) icing which can occur in humid weather. If warming the air in winter gave better milage, manufacturers could easily adjust the system to achieve that. Perhaps to some extent, they do. Lower fuel economy in cold weather is due to a number of factors. Much of it is due to colder engines/longer warm-up when the engine is first started. Warming the intake will have little effect on this. Another factor, often overlooked, is that the denser air increases wind resistance. This is a very significant factor on the highway. (Any pilot will tell you about the huge increase in performance of an aircraft going from 70F to 0F. They will also tell you about the increased economy of flying at higher altitude where air density - and aircraft performance - is reduced.) Obviously, heating the intake air will do nothing to help you there. Warmer intake air will be less dense and the FI will reduce the amount of fuel delivered to compensate. Sounds good except that performance will be less and you will compensate by opening the throttle further. That might increase milage due to increased volumetric efficiency (decreased pumping losses) which means that the engine isn't working as hard to suck air through the restricted intake. That might offset some of the above efficiency losses, but only at the expense of a reduction in maximum power available. >>My accord 04 4 cyl mileage drops by 10-15% in winter time and I have >>measured that miticulously. [quoted text clipped - 21 lines] > Much of it is due to colder engines/longer warm-up when the engine is > first started. ok. > Warming the intake will have little effect on this. not true. increasing intake temp at this time /can/ decrease warmup time. > Another factor, often overlooked, is that the denser air increases > wind resistance. true. > This is a very significant factor on the highway. > (Any pilot will tell you about the huge increase in performance of an > aircraft going from 70F to 0F. doesn't this contradict your air density statement? > They will also tell you about the > increased economy of flying at higher altitude where air density - and > aircraft performance - is reduced.) Obviously, heating the intake air > will do nothing to help you there. dude, you're all over the shop. density increases as temperature drops. density decreases as you increase altitude. that's not the same thing. by your rationale, air would be denser as you go higher because of the decreased temperature. economic flying at higher altitude is because the skin of the plane has less friction, not because the engine is finding it easier to suck in air. in fact, the opposite is true. that's where turbos & super charges come from - the need to increase air volume in aero engines at high altitude because air density is too low to produce needed power. > Warmer intake air will be less dense and the FI will reduce the amount > of fuel delivered to compensate. Sounds good except that performance > will be less and you will compensate by opening the throttle further. ok > That might increase milage due to increased volumetric efficiency > (decreased pumping losses) which means that the engine isn't working > as hard to suck air through the restricted intake. That might offset > some of the above efficiency losses, but only at the expense of a > reduction in maximum power available. eh? increased volumetric efficiency as manifold pressure decreases? wow. bottom line, no, there are two factors against high air temps for cars. 1. higher temp is lower density. lower density = less oxygen to burn gas. 2. higher temp is higher viscosity. higher viscosity makes it harder to ges the air into the cylinder. that's why turbos have intercoolers. http://www.ce.utexas.edu/prof/kinnas/319LAB/Book/CH1/PROPS/dynviscgif.html and regarding lower mileage in the winter, one of the biggest factors is a change in gas formulation. "winter" grades of gas have lower calorific content. > and regarding lower mileage in the winter, one of the biggest factors is > a change in gas formulation. "winter" grades of gas have lower > calorific content. You have referred to this often. I finally googled. Does this web site and its accompanying sites discuss what you mean? http://www.epa.gov/oms/rfg/whereyoulive.htm If so, the part of the country that uses this lower calorie fuel is extraordinarily geographically small. It's certainly not nationwide. Aside: Your refusal to snip posts to which you are replying and so repeat ad nauseam is rude. Very. >>and regarding lower mileage in the winter, one of the > [quoted text clipped - 15 lines] > fuel is extraordinarily geographically small. It's certainly > not nationwide. it's nationwide and seasonal. "The heating value of winter gasoline is about 1.5 percent lower than summer gasoline because winter gasoline contains more volatile, less dense hydrocarbons." http://www.chevron.com/products/prodserv/fuels/bulletin/motorgas/1_driving-perfo rmance/pg4.asp#power i've cited this before. > Aside: Your refusal to snip posts to which you are replying > and so repeat ad nauseam is rude. Very. go forth and multiply. a logical argument requires retention of relevant points. it's pathetic how frequently and how telling is the snippage of detail from those seeking to avoid a point that contradicts them. i'm surprised you're not top posting in protest. >For what it's worth, I drive in those temperatures a lot in the >winter, as well as 100+ in the summer. I don't notice what you are >seeing. 1999 and 2003 Accord V-6's, as well as a 1993 Jeep Grand >Cherokee. >Dick I saw that in my 99 and 04 accord both 4 cyl I could hardly see that in my 94 intrepid 6 cyl. Likely it is a honda design . You are right. Honda engineer would have dealt with that if simple preheating intake air would cure it. I am located in toronto really not an extremely cold area at all. Daniel > Elle wrote: > > [quoted text clipped - 19 lines] > > it's nationwide and seasonal. Baloney. Your own citation below does not say it's nationwide. It indicates some areas use it: "Oxygenated gasolines, which are required in some areas of the U.S.(see Chapter 4, Oxygenated Gasoline), have lower heating values... " Further along, it hints that it may be used elsewhere, at best. You should be saying that local use of oxygenated gasoline in some areas of the U.S. /may/ reduce fuel mileage. > "The heating value of winter gasoline is > about 1.5 percent lower than summer gasoline because winter gasoline > contains more volatile, less dense hydrocarbons." http://www.chevron.com/products/prodserv/fuels/bulletin/moto rgas/1_driving-performance/pg4.asp#power > i've cited this before. > > Aside: Your refusal to snip posts to which you are replying > > and so repeat ad nauseam is rude. Very. > > go forth and multiply. a logical argument requires retention of > relevant points. You include non-relevant points routinely. You also presume people are incapable of looking back. Do whatever. Along with your refusal to use caps so a reader can easily discern sentences, your posts are a pain. Whatever. Be an arse. >>>>and regarding lower mileage in the winter, one of the >>> [quoted text clipped - 40 lines] > You should be saying that local use of oxygenated gasoline > in some areas of the U.S. /may/ reduce fuel mileage. er, the section on fuel economy has 3 paragraphs on factors that effect economy, starting with calorific value and how calorific value is seasonally adjusted. it /then/ goes on to discuss additional factors such as oxygenation. such a device of argument is called "logical progression". >> "The heating value of winter gasoline is >>about 1.5 percent lower than summer gasoline because [quoted text clipped - 26 lines] > > Whatever. Be an arse. er, i leave relevant commentary in the name of logical progression... ever heard of it? [rhetorical] > >>>>and regarding lower mileage in the winter, one of the > >>> [quoted text clipped - 46 lines] > such as oxygenation. such a device of argument is called "logical > progression". You're being non-responsive, and when it comes to logic, you don't know what you're talking about. You should be saying that local use of oxygenated (yada) gasoline in some areas of the U.S. /may/ reduce fuel mileage. > > You include non-relevant points routinely. You also presume > > people are incapable of looking back. Do whatever. Along [quoted text clipped - 5 lines] > er, i leave relevant commentary in the name of logical progression... > ever heard of it? [rhetorical] Jim, I don't think you have a mind that thinks entirely logically. Or it's just incredibly poor writing on your part. Elle No need to bother snipping response to Jim's posts. Let him suffer. >>>>>>and regarding lower mileage in the winter, one of the >>>>> [quoted text clipped - 77 lines] > gasoline in some areas of the U.S. /may/ reduce fuel > mileage. 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. >>>You include non-relevant points routinely. You also > [quoted text clipped - 23 lines] > No need to bother snipping response to Jim's posts. Let him > suffer. >> Another factor, often overlooked, is that the denser air increases >> wind resistance. [quoted text clipped - 6 lines] > >doesn't this contradict your air density statement? No. Unlike cars, airplanes use air for lift. Greater air density = greater performance. The engine also develops more horsepower with denser air. >> They will also tell you about the >> increased economy of flying at higher altitude where air density - and [quoted text clipped - 3 lines] >dude, you're all over the shop. density increases as temperature drops. >density decreases as you increase altitude. Right. > that's not the same thing. >by your rationale, air would be denser as you go higher because of the >decreased temperature. The air does tend to be colder as altitude increases, and that does make it denser than it would be if it were warmer. But the bigger factor is that air density decreases with altitude, as you point out. > economic flying at higher altitude is because >the skin of the plane has less friction, not because the engine is >finding it easier to suck in air. If I was unclear on that, I apologize. The greater economy is due to decreased air resistance. The engine does develop less power but the main reason performance decreases is that lift decreases due to thinner air. > in fact, the opposite is true. >that's where turbos & super charges come from - the need to increase air >volume in aero engines at high altitude because air density is too low >to produce needed power. The turbo will help the engine overcome the loss of power, but aircraft performance will still decrease due to the thinner air. It may have higher true airspeed due to lower air resistance but a lower rate of climb compared to sea level. > (Any pilot will tell you about the huge increase in performance of an > aircraft going from 70F to 0F. They will also tell you about the > increased economy of flying at higher altitude where air density - and > aircraft performance - is reduced.) This is a very unclear statement. There is a curved graph for aircraft efficiency that takes into account temperature and altitude. As altitude increases, air density decreases. Also, the temperature decreases, except above around 30 to 40 thousand feet, at which it stays almost constant at -65 F until there is not enough air to run an engine. Starting at sea level, it is more efficient to fly an airliner the higher you go because of decreased temperature and density until you get to 30,000 feet. Any higher than that is less efficient because of decreased density with no further decrease in temperature. This is why airliners fly at or near 30,000 feet. Obviously this altitude is above the max altitude attainable by small piston powered airplanes and the altitude/efficiency factor is therefore not relevant in the same way. When you simply say "airplanes" you confuse the issue. Most small airplanes don't have turbochargers, intercoolers, superchargers, or whatever, although they all have heated intakes to prevent ice. Lots of older large planes with radial engines have superchargers built into the back of the engine to pack in more air, as well as a heated intake to prevent ice. Apparently the resistance of denser air, as another poster mentioned, is not a problem. Incidentally, the ice forms as a result of the venturi effect, where the air speeds up and experiences decreased pressure and lower temperature as it goes past the carburetor venturi and draws gasoline into the intake. Jet engines really don't care about ice. They suck in a ton of air and use turbine blades to squish it down into an extremely small space, causing it to get very hot, and then the fuel is injected. Most of these factors affecting airplanes relate in no way to a car engine. Neither do altitude and efficiency and their effect on aircraft performance. The altitude, temperature and density that a car deals with is only the tip of the airplane iceberg. After all of that I forgot to say what I think we can discern from aircraft performance that does relate to cars. The greatest factor affecting airplanes at ground level (the realm of the automobile) is air temperature. It affects the takeoff performance of airplanes so drastically that air crews have to use charts to tell how much weight to allow on the aircraft. In places that get really hot, sometimes they don't even take off because they can't carry enough people and baggage to make it worth the trip. The engines run great in any case, with a small enough variance in performance that it's not really a factor. But the density of the air has such a drastic effect on wings and propellers that it becomes a safety issue. As this relates to cars, I would guess that the greatest single factor affecting the efficiency of winter driving would be incerased wind resistance. Driving in snow probably doesn't help much either. But I wouldn't expect that cold air would be a problem for the engine. In fact, engines tend to produce more power in cold weather because they take in more air. Not that this would affect a car engine because you never run them at max power anyway. "In fact, engines tend to produce more power in cold weather because they take in more air. Not that this would affect a car engine because you never run them at max power anyway." Also produces more torque, which always matters. > "In fact, engines tend to produce more power in cold weather because > they > take in more air. Not that this would affect a car engine because you > never run them at max power anyway." > > Also produces more torque, which always matters. That's a good point. > In > fact, engines tend to produce more power in cold weather because they > take in more air. But in a car, the fuel-air mixture is harder to ignite, among other adverse consequences of cold air car engine operation. > > In > > fact, engines tend to produce more power in cold weather [quoted text clipped - 4 lines] > among other adverse consequences of cold air car engine > operation. "Harder to ignite"??? > Elle wrote: > > [quoted text clipped - 8 lines] > > "Harder to ignite"??? You don't know what I mean? Then you shouldn't be posting to this thread. > > "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. > Elle wrote: > [quoted text clipped - 4 lines] > > I hope the net cops don't arrest me for posting inappropriately. Not to worry. People will just think you're a weenie. > 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. 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. > 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. 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 > > Elle wrote: > > [quoted text clipped - 35 lines] > former highly esteemed engineering educator with a gift for > teaching. Except I have no patience anymore. :-) 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. > A fuel air mixture does not all ignite in the same > "instant." It burns, and expands, at a certain rate. Some [quoted text clipped - 9 lines] > I'm sure there are some very polished sites that explain it > better than I am willing to do here in a few minutes. 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. > This discussion is also overshadowing other things that > contribute to worse engine performance at cold temperatures. [quoted text clipped - 7 lines] > I welcome being killfiled by both the depraved and the > ignorant 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. > Tee hee. I hope this is Laura talking. > 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. Lord no, but you have a right to your opinion. > Typical university crap. 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. > And yes, I've seen the > inside of a university. That's how I know. Real cars don't work that > way, though. 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 > 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 [quoted text clipped - 3 lines] > And yes, we all know about the famous "flame front", the lack of which > causes knocking in your engine. 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. snip > 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. snip +++++++++++++++++++++++++++++ I was going ot avoid jumping in but I just can;t keep my fingers still. I have a 1991 MT Honda Civic. In an attempt to improve my understanding of modern engine control systems I built and added a PWM to the both injectors. I have a dual point so my car has a primary and secondary, AKA main and aux. I have watched as the dwell time of the injectors increased as cooler, then cold weather arrived. I decided to try a siple experiment last week when the temps got down to 20F. I added a piece of flex tubing to restrict the inlet air to air warmed by the radiator. Guess what, the injector dwell time went back down to the lower values of mid summer. I also have a g-meter, accelerometer so I can make some estimates better then WAGs about performance. Get into 2nd at 15MPH and floor it.Very revealing. The increase due to cold is on the order fo 10 to 15%. So I have to conclude that cold air hurts millage, but I agree it does boast performance. Like many things in life, kind of pardoxical. Terry Terry AFAIC, these are wonderful experiments. From them, I gather the intake air temperature signal to the engine computer tends to dominate, compared to the coolant temperature signal. So if I have it right, in cool weather, the injector duration ordinarily is higher than in hot weather, and so more fuel per cycle is dumped into each cylinder in cool temperatures. I presume this is to bring the engine up to normal operating temp, and maintain it there, quicker. With cooler and so denser air, more air is packed in as well. So one gets more power, but as you imply, more power doesn't necessarily translate to greater efficiency miles per gallon-wise. Something like this... Note for those new to the thread: Below I actually meant the higher wind resistance in winter, due to more dense air, will decrease fuel mileage, as will other things. > Elle wrote: > snip [quoted text clipped - 35 lines] > > Like many things in life, kind of pardoxical. >>Tee hee. > [quoted text clipped - 20 lines] > > Oh dear. An inferiority complex. It's not a complex with some. <>snip "Robbie and Laura Reynolds" <robbie@kcnet.com> wrote > Elle > I welcome being killfiled by both the depraved and the > ignorant Great sig, okay if I use it? > > Elle > > I welcome being killfiled by both the depraved and the > > ignorant > > Great sig, okay if I use it? No problem. > But in a car, the fuel-air mixture is harder to ignite, 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. "High" <789@123.456> wrote E babe wrote > > But in a car, the fuel-air mixture is harder to ignite, > > may be true, but is the cause of the poor fuel atomization cold air, Well, I didn't say anything about atomization, but I think I know what you're getting at. > cold gasoline or a combination? 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.) > I live in central Minnesota. At -30F my > fuel injected engines will start but the old '81 F150 floods easily at > -20F. Good anecdote, particularly for relatively young "I know everything" whipper-snappers like me who have seen darn little of carbureted engines. > I believe lower fuel economy in cold weather is due more to > vehicle warm-up than anything else, 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. > and my proof is that when my > vehicles are parked in my heated garage the mpg remains the same in the [quoted text clipped - 3 lines] > cold. The wheel bearings can get so stiff that when the car is jacked up > the wheel is extremely hard to spin by hand. 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? > Also the transmission and > final drive get very "stiff" and don't "limber up" until several miles > have been driven. 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. >> (Any pilot will tell you about the huge increase in performance of an >> aircraft going from 70F to 0F. They will also tell you about the [quoted text clipped - 32 lines] >performance. The altitude, temperature and density that a car deals >with is only the tip of the airplane iceberg. 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. > To bring it back to cars; increased air density will definitely > increase fuel consumption at higher speeds. Sea level air density at [quoted text clipped - 3 lines] > 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? > Gordon McGrew wrote: > > To bring it back to cars; increased air density will definitely [quoted text clipped - 7 lines] > This is the real point. Wintertime gas mileage is not appreciably > affected by engine performance. It's all about drag. 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. > 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? 45-50 mph. Mileage goes down by I'd say 5-10% in the winter. >> This is the real point. Wintertime gas mileage is not >appreciably [quoted text clipped - 5 lines] >scale, any city's temperature varies maybe 15% or so. But >pressure and temperature are in constant interplay. 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 >Fuel mileage is certainly a function of car speed in >general, with wind resistance being the main explanation for [quoted text clipped - 5 lines] >performance on cars is in fact worse for several reasons in >cold temperatures. 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. > On Mon, 21 Nov 2005 01:13:07 GMT, "Elle" <honda.lioness@earthlink.net> > wrote: [quoted text clipped - 10 lines] > > Density is proportional to barometric pressure. Are you /sure/ Gordon?? Absolutely really really sure that you nailed this issue? > 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. At sea level. Ur killin' me. > 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. 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. > Here is a fun calculator you can play with: > > http://wahiduddin.net/calc/calc_da_rh.htm Shall I cough up ten more? No wait. That might insult your intelligence. > >Fuel mileage is certainly a function of car speed in > >general, with wind resistance being the main explanation for [quoted text clipped - 9 lines] > with cold temperatures due to higher air density. This is a well > known phenomenon. Are you still /sure/ Gordon?? Not "of course." > 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. Assume away. It's not healthy but people don't really change. Killfile my addie, hon. I want intelligence. >> On Mon, 21 Nov 2005 01:13:07 GMT, "Elle" ><honda.lioness@earthlink.net> [quoted text clipped - 17 lines] > >Absolutely really really sure that you nailed this issue? Yup. PV = nRT >> Outside of a tropical >> depression/tropical storm/hurricane, barometric pressure [quoted text clipped - 10 lines] >killin' >me. What do you want? Obviously barometric pressure will vary with elevation (as opposed to altimeter and barometer settings which are based on the corresponding pressure at sea level). Assuming that you are not changing elevation/altitude radically, meteorological changes in barometric pressure are pretty negligible for the purpose of approximating air density. If you are driving from New York to Denver, or climbing from sea level to 5000 feet MSL, it will be a factor. What is your point? >> Absolute humidity also has a small affect, about 1%, at >warmer [quoted text clipped - 14 lines] > >Shall I cough up ten more? Only if they give different results from this one. Otherwise it would be superfluous. >No wait. That might insult your intelligence. You were the one claiming that weather fluctuations (other than temperature) are going to affect air density by 10%. I am merely pointing our that you are off by an order of magnitude. Live with it. >> >Fuel mileage is certainly a function of car speed in >> >general, with wind resistance being the main explanation [quoted text clipped - 18 lines] > >Not "of course." Really? It is what I and many others have learned through logic, training and direct experience. It is hardly a secret except maybe to you. >> I assume that you mean that cold weather causes poorer >fuel economy [quoted text clipped - 5 lines] >Assume away. It's not healthy but people don't really >change. I was giving you the benefit of the doubt that you aren't so stupid that you think cold air decreases engine performance. Perhaps I was wrong to do that. >Killfile my addie, hon. I want intelligence. I would recommend you get some then. Usually, the mileage goes up, not down when the temperature drops. That is because there is an increase in volumetric efficiency. I.E. the air is more dense. I think I would look at other factors. Do you warm the car up before driving? (shouldn't do that.) Do you drive through a lot of snow and ice? Are you driving at the same speeds? Etc. For what it's worth, I drive in those temperatures a lot in the winter, as well as 100+ in the summer. I don't notice what you are seeing. 1999 and 2003 Accord V-6's, as well as a 1993 Jeep Grand Cherokee. Dick >My accord 04 4 cyl mileage drops by 10-15% in winter time and I have >measured that miticulously. [quoted text clipped - 8 lines] > >Daniel > Usually, the mileage goes up, not down when the temperature drops. > That is because there is an increase in volumetric efficiency. I.E. > the air is more dense. 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. Several people have already identified several of the reasons why fuel efficiency in automotive designs is lower at lower ambient temperatures. For my part, I'm partial to the fact that the engine has to combust more fuel to achieve the same temperatures everywhere, yada, all per the car's engine control computer directions. But then too is the fact that the oil is denser, and this has an effect on efficiency. Another poster talked about wind resistance being worse, since the ambient air is denser, and I'm inclined to buy that, also. Wind resistance has the greatest effect on fuel efficiency. "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? > "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? > "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? it /is/ true for si engines as well as diesels - that's why turbos usually have intercoolers for both types of engine. > "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? 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. >Leaving theory now and going to what is practical and >actually done, as you are probably aware, some diesel [quoted text clipped - 5 lines] >partly why gasoline has an octane number, but diesel has >another metric to indicate how well, if you will, it burns). http://wwwrsphysse.anu.edu.au/~amh110/Intercooler/volvo_intercooler.htm >>"You're thinking of, for example, certain diesel designs > [quoted text clipped - 27 lines] > and so increasing the engines' power. But the gasoline cycle > has limitations that preclude using intercoolers yada. eh? that's totally untrue. you want a list of si turbo engines with intercoolers? > 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). you're confusing mixture with air intake. > Sorry I don't feel like digging thoroughly and regurgitating > it here. you should. that way you'll stop making mistakes. > 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. wishy washy nonsense. > My accord 04 4 cyl mileage drops by 10-15% in winter time and I have > measured that miticulously. Probably winter/oxygenated gasoline formulations. >> My accord 04 4 cyl mileage drops by 10-15% in winter time and I have >> measured that miticulously. > >Probably winter/oxygenated gasoline formulations. Good point. I forgot about that one. > >> My accord 04 4 cyl mileage drops by 10-15% in winter time and I have > >> measured that miticulously. > > > >Probably winter/oxygenated gasoline formulations. > > Good point. I forgot about that one. Also, cold fuel is denser and harder to vaporize. David > My accord 04 4 cyl mileage drops by 10-15% in winter time and I have > measured that miticulously. [quoted text clipped - 8 lines] > > Daniel ------------------------------ Start the car, brush off the snow, get in and drive like a 'little old lady' for the first two minutes. Don't install a remote starter. Like someone else pointed out, winter gas is also poor for mileage. :-( 'Curly' >My accord 04 4 cyl mileage drops by 10-15% in winter time and I have >measured that miticulously. [quoted text clipped - 3 lines] >My 99 accord did the same thing. Any input from this NG is >appreciated. Government mandated gasoline reformulation is to blame for your lower gas mileage. Heating the air is not going to help. -------------- Alex |
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