I don't know if I am just fooling myself or this is real, but as the temperature in Los Angeles has dropped, it seems like my car is much zippier than before. I seem like I have more power than before. I haven't made any engine mods lately, so I am wondering if the colder air is making a difference.<p>Suggestions?<p>Thanks,<br>Howard Kim<br>98 A4 1.8tms(neu)

nt<br>

nt<br>

Temperature AND humidity etc. have a clear difference in power as far as I can feel it. It is hard to say if it can be measured but the engine atleast feels different. A dry cool air seems best. Hot and humid makes my 1.8T feeling a bit tired both on stock and wett 1..0 bar.<p>Marko Litmanen<br>A3 1.8T Wett 1.0 bar K&N

Since no one really hit on this, I'll answer. Your engine burns the oxygen in the air that it takes in. The density of air increases as the temperature of it decreases. This means that you get more oxygen in the same volume of cold air than you would get from warm air. The more air you have, the more fuel you can burn, and thus, the more power your engine can produce.<p>This is also what an intercooler does. It cools the intake air to increase the density of oxygen for burning.<br>

ChemE's drool!

Yeah, but did he back it up with equations?<p>PV=nRT (or PV=znRT, to include slight compressibility if you want that extra decimal point of precision).<p>Rearrange a bit to get n/V = RT/P<p>Assume P is constant, R is a constant, therefore n/V (moles of air per unit volume, say) varies inversely with Temperature. (T up, n/V down or T down, n/V up).<p>Didn't mention ideal combustion, either:<p>4CxHy + (4x+y)O2 ----> 4xCO2 + (2y)H2O<p>O'course we could get hypertechnical and include incomplete combustion forming CO and smaller chain hydrocarbons; include sulfur containing compounds; the nitrogen and it's unfortunate conversion to NOx. Then continue into the catalytic converter where solving several simultaneous partial differential equations gives you both conversion versus length and conversion versus Temperature.<p>But I can't see throught this puddle of drool...so I'll stop<p>:)<br>steve

But thanks for playing along. However, I think you are getting overly technical. The question was simply whether the car feels more powerful at lower temperatures.<p>True, I didn't provide equations, but just to play along, here's your equation again with subscripting:<p>4CxHy + (4x+y)O₂ ----> 4xCO₂ + (2y)H₂O<p>The A4 Forum -- where cars, chemistry and HTML collide!<br>

<br>.. so, the cold air makes for an increased concentration of oxygen in the fuel/air mix. Besides hooking an O2 tank up to the air intake system, what are some other artificial ways to increase O2 concentration in the fuel/air mix?<p><br>tnx<br>-K.<br>

Turbochargers and superchargers force-feed air into the engine to get higher than atmospheric pressures, i.e. more air into the combustion chamber.<p>Intercoolers help this process by cooling the air.<p>Nitrous Oxide (N₂O, or is it NO₂??) provides a higher concentration of oxygen for combustion. This is usually used in short bursts for drag racing controlled by some sort of valve/switch setup. This is the tank you would hook up, not O₂ which I don't think you could get legally anyway.<p>Of course, if you're bringing more air in, then you need a greater capacity to get the exhaust out. So, you have to look at larger or less restrictive exhaust systems.<br>

OK, so my HTML skills need work, but to be overly picky:<p><p>4C_xH_y + (4x+y)O₂ ----> 4xCO₂ + (2y)H₂O<p><p>Oh! Oh! Mista Kotta!...Mista Kotta!<p>steve<br>:)<br>

Ha ha! Take this!<p><h1><br>4C_xH_y + (4x+y)O₂ ----> 4xCO₂ + (2y)H₂O<br></h1><p>Your superior intellect is no match for our puny weapons! *<p>Actually, your puny equation is no match for my monster equation!<p><font size=-1>* - stolen from a Simpson's Halloween episode with the aliens and the monkey paw.</font><br>

Have to be careful on this one. The overall concentration of oxygen does not change relative to, say, the concentration of nitrogen. As the total pressure increases, so does the partial pressure of oxygen and nitrogen (most of what air is). Cold air tends to hold less moisture, this makes it more dense (Mwt H2O = 18, N2 = 28, O2 = 32), i.e., one mole of gas is 22.4 liters, thus, a mole of water vapor is about half the density of a mole of O2. Also possible to use the old PV = nRT relation, or n/V = P/RT. Thus, as T decreases, density increases under isobaric conditions. So, for several reasons, cold air is more dense. Sound travels faster through a dense medium - the crack of a tree branch in winter v. summer. So, it's not so simple. Probably the biggest benefit comes from having dry air since water is a combustion product.

You missed it in the title. Its Mechanical Engineers to ponder. But they KNOW the answer. Yes, colder air gives better performance but not from density/O2 partial pressures. It is from the enthalpy difference and the electronic engine control not retarding the ignition timing. Its significant