| Author | Message | ||
     Cochise |
Oh yeah, well, I am a water boy. Here is my Question. You have a 1 million Gallon water tank and a 100,000 gallon water tank, each tank has 50 ft of water, which tank has a higher water pressure? | ||
| Crusty |
Which is heavier; a pound of lead or a pound of feathers? | ||
| Blake |
Joe, I used to think I was smart until I wised up. Same pressure.  | ||
| Blake |
Mike, Cold air is denser and so presents more aerodynamic drag compared to warmer less dense air. Also, an air-cooled engine's steady state operating temperature decrease significantly on a cold day and thus result in cooler more viscous oil; same for the tranny. More viscous oil will hurt engine/tranny efficiency. So... cold air is more of a drag, and cooler (not as hot) engine and tranny oil is more viscous, thus a more voracious parasitic consumer of engine power. Please note that at a given vehicle speed, an engine only requires enough fuel to maintain that speed. If the air is denser, the throttle will not need to open as much to generate the same power level compared to if it were in less dense air. But if you are doing a lot of drag racing type riding at WOT, then yes, the cooler/denser air will dictate a comparable increase in fuel at WOT. Zat make sense? | ||
| Rocketman |
Blake, that does make sense but tell me this. I would say that two vehicles of mine feel like they exhibit a definite increase in performance if I use them late into the evening and early hours of the morning during summer, if it's a cold night. One is my S1W. The other is my TVR. Both n.a engines of course. So accordingly, more performance = more power. Denser air means more fuel = more power. What say you, because for me agreeing with your above analysis seems completely contradictory? Rocket | ||
| Buellbozo |
Rocket: I'm too new here (and too stupid) to take on Blake,but you've got my proxy! lol!! Especially with a digital FI system... If the magic box is always striving to maintain 14.2/1 mix,if there's more o2 per given volume, it's gonna add fuel.It's gonna run stronger. There seems to be some semantic confusion here between "more power" and "more efficient". Don't try to lay no BOOOOGIE WOOOOOGIE on the King of Rock and Roll  | ||
| Iamike |
I see this more with my cars than the bike (since I don't ride much once it gets below 40). On the cars it is usually about 2-3 mpg (about 10%). I guess the density of the air would make sense because I also notice a slight increase in mpg while in the mountains. I would also watch my instantaneous mpg meter while driving in the mountains. On the uphill climbs it would drop down to 10mpg but then would max out at 99 on the descent. I figured that the average would have to go up then. | ||
| Rocketman |
Do remember though, Blake said, if the air is denser, the throttle will not need to open as much to generate the same power level compared to if it were in less dense air. This comment supports my findings for the S1W and TVR in the scenario I mentioned above. But it contradicts Blake's aerodynamic drag and oil viscosity suggestions. Unless the power balance is adjusted that much more in cold dense air it overrides whatever drag from dense air or thicker oil is present? Rocket | ||
| Buellbozo |
I don't know just what we're missing here, but... For years,rsce pit crews chilled the fuel before stops.Why? so more would fit in the tank. Everything-not just air-is denser when it's cold. Let's say the amount of fuel in a single intake stroke is constant...If the incoming air is denser-more o2 molecules are available to combine with more of the existing fuel molecules. I suspect the increase in power is because more of the normally unburnt fuel molecules find o2 to bind with and ignite. Or not. WWKCS...What would Kevin Cameron say? | ||
| Timbo |
Rocket, Is there a chance there is more moisture in the air during the hours you describe? Moisture in the air will effectively raise the compression ratio of your motor, as water does not compress, combined with the cooler, more dense air makes a great combination. This often makes your motor feel "stronger". I always love an early morning ride when the air is moist and cool. Feels awesome. Timbo | ||
| Chasespeed |
Blake, Back to seriousness. One thing that has puzzled me is why does the fuel efficiency of an engine go down in the winter? I can understand in a carbureted engine that the atomization isn't as good but injected engines lose too. I would think that the cold air is denser and would expand more when ignited and that should give better efficiency, not less. Our power plants spend an awful lot of effort cooling the steam back to water for the pressure needed to run a big generator. Actually, whomever mentioned the a/f ratio, woudl be correct. Even the most basic of FI systems, strive to maintain a 14.7: a/f ratio. Either using teh O2 sensor alone, or combining that with an IAT sensor, Mass air, MAP sensor, etc.. So correspondinly, when teh air is more dense, teh ECM, is pump more fuel in there, to keep it from running leaner than its parameters are set... On teh flip side, this will result in a somewhat better increase in performance, usually throttle response it eh most noted increase. Basically, think in terms of forced induction, teh more air in, the more fuel needed to maintain Stoich..that simple... N/A racers dont just chill the fuel..if they are going to those lengths, look at the motor, they are usually icing the intake as well(N/A motors, are the most common)..BUT, if you look closer, they have a can, taht the fuel goes into, the fuel line wraps around ont eh inside or it, and it can be filled, with ice, dry ice, etc..again, keeping the fuel cooler,(especially alky, and nitro methynol, creates a denser mix, if only slightly...but, in a sport where every thousnadth of a second counts.. SO, you could conclude that the density of the air, and fuel would NOT result in a decrease in mpg..BUT... Air and fuel become more dense are different rates, and temps, thus they will NOT be symetrical. In the case of gasoline, though I dont remember what is freezing point is, I KNOW its lower than 0* F. The closer you get to its freezing point, the more dense it will become(as when its frozen, its as dense as it will get)... All that, just so racers can squeeze a little more bang into the compression chamber. Now, dont ask where I learned all this, BUT, it should be pretty self explainitory, especially looking at my s/n... NOW, I have a question for ya'll, and sorry, no door prizes for the winner... DOES, air velocity INCREASE or DECREASE with lower temps... get as technical as anyone chooses..pretty simple...(though, relooking this thread, this may have already been dicussed, but answer away).... NO CHEATING...lol What do ya'll think? Anyway, I will work on that equaiton later hopefully, proving my daughter stays alseep, she isnt feeling too well... Chase} (Message edited by chasespeed on January 28, 2006) | ||
| Gentleman_jon |
Blake, I would be very interested to see an informed discussion of the BMEP on the XBRR in comparison to Japanese in line four 600's and the Standard race kitted XB engine. I am sure that there are at least three or four other brothers who would enjoy reading it too. May be six. Who knows:-) Thanks for all the work you do on the board, it really is a very important part of my Buell life. Number one after my bike, (and eBay, of course:-) | ||
| Blake |
Rocket, There are two scenarios, one of acceleration and one of steady state cruise. Cooler/denser air makes for more WOT power to accelerate more rapidly as it allows more fuel to be burned. Acceleration at WOT is governed by the engine's power and the total mass being accelerated (rider plus motorcycle) with little affect from aerodynamic drag until higher speeds are reached, especially on a faired motorcycle. Just guessing for a faired motorcycle, I'd say that aerodynamic drag probably doesn't become the governing factor wrt the rate of acceleration until around 100 mph or more. For the case of steady state cruising the engine needs to expend more fuel to generate more power in order to push through denser air. Engine power and aerodynamic drag both increase when the air temperature turns cold. The result is more power and more drag. More power governs the acceleration scenario; increased aerodynamic drag governs the fuel mileage at cruise scenario. It ain't one or the other, it is both. Did I do better explaining that this time? | ||
| Blake |
Gregory (Buellbozo), Pretty sure that fuel doesn't change volume to any significant amount when chilled. Pretty sure drag racers chilled fuel in order to prevent the higly volatile and expensive racing fuel from evaporating so much prior to entering the combustion chamber. The amount of fuel charge increases right along with air density, even in carburetted engines, but the EFI systems these days do an even better job at maintaining the optimum desired A/F ratio. | ||
| Mr_grumpy |
Ah yer all dummies EVERYONE knows what sfc stands for............ Southern Fried Chicken. (but did it come before the Southern Fried Egg?) | ||
| Blake |
Timbo, Great to see you engage in this fun discussion. You know anything about going fast in thin air? Warmer air generally carries more moisture than cooler air. Example... When warn humid air contacts a cold surface, moisture will condense since the chilled air reaches its saturation point wrt water vapor, meaning that at the lower temperature it cannot carry any more water in gaseous/vapor form, so some precipitates (condenses) out in liquid form. Automobile air conditioner evaporators are a great illustration of this. Home air conditioner evaporators also exhibit this dehumidifying effect and so must provide a way for that same condensation/precipitation to drain away, else it will collect and make a wet mess inside the house. Condensation of the outside of a cold drink container... same-same. To put it another way, cold air at 100% relative humidity might hold the same amount of moisture as warm air at 50% relative humidity. Seems backwards to me too. It's a good thing though, not sure it would ever rain (precipitation) if the situation was reversed. Just thought of another example; engine exhaust on a cold day is very visible due to the large amount of rapidly condensing water vapor. In general, hydrocarbon (fuel molecules composed of hydrogen and carbon) plus oxygen plus ignition yeilds water (H2O) plus CO2. On a warm day, the large amounbt of water vapor in the exhaust never condenses, remaining in gaseous/vapor form as it is absorbed by the warmer air and thus the exhaust is virtually invisible. Same-same with your breath on a cold day. If it's really cold... It was so cold one Winter in NW PA that it made for a very strange and disturbing phenomenon. It was so wickedly cold that certain highly concentrated vapors were sublimating directly from vapor to solid crystaline form. We had to remove our boots outside and be sure to shake the crystals out of them to keep from polluting the air inside the house. | ||
| Mr_grumpy |
During the later part of WWII, fighter aircraft, notably the F4U Corsair, had a water injection system to boost high speed performance for short periods. Based on the same principle, an optimum mixture ratio is around 16-1 by weight, or mass if you prefer, if you make the air denser by injecting water, you can inject & burn more fuel, thus giving greater power. This was being done over 60 years ago! Ain't much new in the internal combustion world, just the ways of controlling things. | ||
| Mr_grumpy |
Cochise, it depends on the spigot size. (or so my wife tells me) | ||
| Buellbozo |
Blake: Not just exotic mix race fuels.I remember in distant past even stock car crews keeping fuel cans iced down until the pit stop. If you fill a 1 gallon can to the top-no air- and seal the lid at an ambient temp of ,say,40 degrees, and set it in the sun,what happens? The fuel expands and the can swells. From what I remember,the reason the nascar boys did it-and nascar banned the practice- was that it enabled them to put more fuel in the tank than the the tank would hold if the fuel was at ambient temp. I think. Maybe. Disclaimer:My remaining brain cells bring new meaning to the term "random access memory." | ||
| Buellbozo |
Mr. Grumpy, sir... Main purpose of water injection was to control detonation. See above disclaimer. | ||
| Blake |
Right on the water injection to prevent detonation. I had water injection on my turbocharged 1970 Chevelle SS so that I could run higher boost on pump gas. Worked great. Keeps the intake charge cool by absorbing a bunch of the heat. It takes alot of heat to convert water into steam. I'd have to disagree on the fuel can expanding though. If there is no vapor present, the fuel can will not exhibit any expansion. However, it doesn't take much to create a pocket of vaporized fuel in what was previously all liquid fuel. Some racing fuel will practically boil at ambient temperatures, meaning it will produce vapor in a sealed container where there was none before. Stock cars run racing fuel. Racing fuel is much more volatile than pump gas, way more volatile than pump gas. It will boil off at surprisingly non-extreme temperatures. Heck some of the more volatile hydrocarbon molecules in pump gas will begin to boil off at just 80oF. You may have a point wrt the amount of fuel, but it would be due to the vapor pressure generated by warm racing fuel, not that cold fuel takes up less volume than warm fuel. | ||
| Reepicheep |
You sure they dont just try and cool the fuel to try and get cooler (and thus denser) intake charges? Like icing down the manifold for a drag racer? | ||
| Buellbozo |
Gee,This is fun... I don't have a scanner or know how to post a link to this,but... Cycle World, July 2003,Kevin Cameron's column. Can anybody post this? Quote: "Peak power comes when intake air picks up JUST enough heat to evaporate the fuel-no more and no less." I wish could type well enough to slog through more. So,if you start with cooler air... | ||
| Rocketman |
Timbo's scenario makes a lot of sense, in theory. But is it really happening in the real world? If it is, that contradicts Blake's scenario. Who and what should I believe? I'm familiar too with water injection, from the 1977 Saab 99 Turbo's. Saab dealers sold the kit over the counter back then. I also believe there's gains in what Grumps says even if that doesn't nail the real purpose of water injection. This is all confusing and highly contradictory, but I'm with Timbo 110%. I always love an early morning ride when the air is moist and cool. Feels awesome. I always do my best to please the girl too though  Rocket | ||
| Iamike |
Mr Grumpy's water injection jogged my memory. Our gas turbine generators use water injectors in the summer. They have spray nozzels at a faily high pressure that spray the water at the air intakes. I can't remember the exact amount of generation gain there is but I was thinking that it was 2-10%. That was with turbines and not piston engines so I don't think that detonation was the issue. | ||
| Bluzm2 |
Mike I think the turbines get the additional boost from the water flashing to steam and providing additional exhaust density to spin the turbine blades on the way out. Just a guess, but it makes sense. | ||
| Blake |
Clarification: Liquid water does not compress. Water vapor (a gas) does compress almost infinitely so just like any other gaseous matter. Humidity is water vapor, gaseous water. | ||
| Timbo |
Timbo's scenario makes a lot of sense, in theory. But is it really happening in the real world? If it is, that contradicts Blake's scenario. Not necessarily. While temperature differences will create condensation, it doesn't automatically mean that there is more moisture in warm air than there is in cool air. For instance, take extreme examples, there is much more moisture in the air on a cool foggy morning than there is on day with Santa Ana wind conditions here in Southern California (very hot and dry). On the foggy morning it feels like your bike is on steroids, on the Santa Ana wind day it almost feels like your bike is wheezing and out of breath in comparison. Just my unscientific observations, but I do believe that higher moisture content in the air will result in a higher effective compression ratio. That combined with the cool morning air makes for a great combination. At least that's been my experience over the years and that's what I was referring to. Timbo | ||
| Diablobrian |
I don't think the change in gasoline formulation in the winter months has been mentioned yet, This too can impact your fuel economy. | ||
| Newfie_buell |
Rocket, I can understand Blake's reasoning with the oil and viscosity. I guess if the oil and gear box oil is cold then it takes more power to turn everything therefore burns more fuel. However, once the oil/gearbox oil is warmed up to operating temperature I bet the cool dense air does indeed increase the power or response. Being in a climate where the temp can go from 25 celsius in the middle of the day to 5 celsius in the evenings I have noticed the S1 being more responsive when the air is much cooler. All this is "Inconceivable" |
