Cold weather...worse MPG?
11-20-2008, 01:56 PM
#32
AudiWorld Super User
You obviously know a good amount about fuelling but mixtures are overly....
enriched to ensure the cat heats up more rapidly than if it were to just receive the amount of HC's remaining in the exhaust gases.
It is a case more fueling actually reduces the overall polution and ensures our cars acheive about 5 mpg for the first 1/2 mile or so of driving.
Why do you think the 2.7 has an auxiliary air pump?
It is a case more fueling actually reduces the overall polution and ensures our cars acheive about 5 mpg for the first 1/2 mile or so of driving.
Why do you think the 2.7 has an auxiliary air pump?
11-20-2008, 04:46 PM
#34
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You could read through this paper, which has these guys reason for increased fuel at startup.
They wouldn't buy your use more fuel to decrease time to cats working properly I don't think. The air pump is to add o2 to the exhaust to help get the cats operating correctly because the extra fuel is slowing down the process. The extra fuel is added to help with ignition of the fuel in a cold combustion chamber.<ul><li><a href="http://www.uctc.net/papers/505.pdf">http://www.uctc.net/papers/505.pdf</a</li></ul>
11-21-2008, 01:23 AM
#35
AudiWorld Super User
Interesting stuff. I think my information about extra enrichment for aid the cat warm up is from a..
Technical manual about petroleum fueling systems by Probst, I read a few years ago whilst researching for a project I was working on.
It is now an old book but the principles remain the same.<ul><li><a href="http://www.bizrate.co.uk/miscellaneousbooks/oid705060156.html">http://www.bizrate.co.uk/miscellaneousbooks/oid705060156.html</a</li></ul>
It is now an old book but the principles remain the same.<ul><li><a href="http://www.bizrate.co.uk/miscellaneousbooks/oid705060156.html">http://www.bizrate.co.uk/miscellaneousbooks/oid705060156.html</a</li></ul>
11-21-2008, 03:37 AM
#36
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My worst gas mileage ever was driving at -25 degrees
thru North Dakota and eastern Montana. In the last 5 years of owning my car I haven't seen mileage like that again.
11-21-2008, 06:12 AM
#38
Dude - if you hook up an engine in a lab somewhere and feed it cold intake air, then I accept your
argument that the MPG will stay the same - we understand that the stoichiometric ratio doesn't change due to temperature. In the real world, an automobile driving on the road gets less MPG when it is 30 F outside versus 70 F for many reasons. You have to draw a box around the entire system, not just the MAF and injectors, to do the energy balance.
11-21-2008, 09:23 AM
#39
As an adder - if engines get better mileage running 5w-20 oil than 5w-30 oil, how can a car not get
worse MPG running in winter vs summer? The oil is typically slightly colder during the winter than in summer, even at steady state at cold enough temperatures.
11-21-2008, 11:59 AM
#40
If you play golf, you know that the ball travels farther in 80 F weather than in 50 F weather due to
air density differences. The frontal area of a car magnifies this effect. It doesn't take 250+ mph to have this phenomenon translate to higher wind resistance and therefore decreased MPG in the real world.