Warmer Weather, Higher Mileage?
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Super Member
Joined: May 2004
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From: Warren, NJ
'05 E320 CDI;'04 S2k;'94 Supra TT;'10 QX56;'38 Buick;98 Port City Offset Late Model
Warmer Weather, Higher Mileage?
Ok, is a little warmer...40s and 50s. Farenheit. And the car has around 9000 miles.
Mixed driving. Suburban commute. Two trips to the dreaded New York City. 572 miles 19.2 gallons of diesel. 29.8 mpg? Average?
All winter we saw 30-31mpg has a high average on highway trips. This commute closer to 27.5-28mpg. Now nearly 30?
Is this correct?
Mixed driving. Suburban commute. Two trips to the dreaded New York City. 572 miles 19.2 gallons of diesel. 29.8 mpg? Average?
All winter we saw 30-31mpg has a high average on highway trips. This commute closer to 27.5-28mpg. Now nearly 30?
Is this correct?
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Joined: Sep 2004
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From: In the shadow of D.C. (No.Va.)
'05 E320CDI, 1987 300E, Vanagon Syncro, Turbo Arrow III
In warmer weather the "density altitude" is higher, due to some combination of higher temperature and higher relative humidity. This generally requires that the engine run leaner in order to burn at peak efficiency.
This is particularly obvious in aircraft, where the operator still often has a "mixture" control, but the concept is the same for automobile engines. The ECU simply does the adjusting for you.
This is particularly obvious in aircraft, where the operator still often has a "mixture" control, but the concept is the same for automobile engines. The ECU simply does the adjusting for you.
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Joined: Sep 2004
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From: Virginia
2005 Carlsson CD32 E320 CDI Inline-6
Turbo/ Intercooled setup contributes...
Because the car is intercooled, it gets a much colder, denser charge of air in the winter, thus the engine is operating at a higher volumetric efficiency.
The ECU compensates by pouring on more fuel to maintain stoichiometry, result is higher mileage despite the richer mixture because more torque is being produced at a lower RPM, propelling the car forward at the desired pace without more RPM's, and/or ending the "acceleration" phase sooner and laying back to cruise power sooner.
For a leadfoot, the cold air can have the opposite effect. If you go around flooring it always using max or even 50% power, you will actually use more fuel in cold air because max power is greater, more air can be stuffed into the engine (Recall pv=nrt) and thus more fuel will be added to the available air.
In airplanes, even though it is colder "up there" I think (may be wrong) mixture is leaned at higher altitude because less oxygen is available?
KB
The ECU compensates by pouring on more fuel to maintain stoichiometry, result is higher mileage despite the richer mixture because more torque is being produced at a lower RPM, propelling the car forward at the desired pace without more RPM's, and/or ending the "acceleration" phase sooner and laying back to cruise power sooner.
For a leadfoot, the cold air can have the opposite effect. If you go around flooring it always using max or even 50% power, you will actually use more fuel in cold air because max power is greater, more air can be stuffed into the engine (Recall pv=nrt) and thus more fuel will be added to the available air.
In airplanes, even though it is colder "up there" I think (may be wrong) mixture is leaned at higher altitude because less oxygen is available?
KB
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From: Longmont, CO
04 E320 4 Matic, 95 Audi S6, 99 Carrera 4 Cabrio, 12 Fiat 500 Sport, 00 BMW R1200C 10, BMW R1200R
Originally Posted by cdiken
Because the car is intercooled, it gets a much colder, denser charge of air in the winter, thus the engine is operating at a higher volumetric efficiency.
The ECU compensates by pouring on more fuel to maintain stoichiometry, result is higher mileage despite the richer mixture because more torque is being produced at a lower RPM, propelling the car forward at the desired pace without more RPM's, and/or ending the "acceleration" phase sooner and laying back to cruise power sooner.
For a leadfoot, the cold air can have the opposite effect. If you go around flooring it always using max or even 50% power, you will actually use more fuel in cold air because max power is greater, more air can be stuffed into the engine (Recall pv=nrt) and thus more fuel will be added to the available air.
In airplanes, even though it is colder "up there" I think (may be wrong) mixture is leaned at higher altitude because less oxygen is available?
KB
The ECU compensates by pouring on more fuel to maintain stoichiometry, result is higher mileage despite the richer mixture because more torque is being produced at a lower RPM, propelling the car forward at the desired pace without more RPM's, and/or ending the "acceleration" phase sooner and laying back to cruise power sooner.
For a leadfoot, the cold air can have the opposite effect. If you go around flooring it always using max or even 50% power, you will actually use more fuel in cold air because max power is greater, more air can be stuffed into the engine (Recall pv=nrt) and thus more fuel will be added to the available air.
In airplanes, even though it is colder "up there" I think (may be wrong) mixture is leaned at higher altitude because less oxygen is available?
KB
One thing that you also need to keep in mind is that running the a/c compressor when it gets even hotter will also contribute to lower MPGs.
Steve
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Joined: Sep 2004
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From: In the shadow of D.C. (No.Va.)
'05 E320CDI, 1987 300E, Vanagon Syncro, Turbo Arrow III
Originally Posted by cdiken
Because the car is intercooled, it gets a much colder, denser charge of air in the winter, thus the engine is operating at a higher volumetric efficiency.
The ECU compensates by pouring on more fuel to maintain stoichiometry, result is higher mileage despite the richer mixture because more torque is being produced at a lower RPM, propelling the car forward at the desired pace without more RPM's, and/or ending the "acceleration" phase sooner and laying back to cruise power sooner.
For a leadfoot, the cold air can have the opposite effect. If you go around flooring it always using max or even 50% power, you will actually use more fuel in cold air because max power is greater, more air can be stuffed into the engine (Recall pv=nrt) and thus more fuel will be added to the available air.
In airplanes, even though it is colder "up there" I think (may be wrong) mixture is leaned at higher altitude because less oxygen is available?
KB
The ECU compensates by pouring on more fuel to maintain stoichiometry, result is higher mileage despite the richer mixture because more torque is being produced at a lower RPM, propelling the car forward at the desired pace without more RPM's, and/or ending the "acceleration" phase sooner and laying back to cruise power sooner.
For a leadfoot, the cold air can have the opposite effect. If you go around flooring it always using max or even 50% power, you will actually use more fuel in cold air because max power is greater, more air can be stuffed into the engine (Recall pv=nrt) and thus more fuel will be added to the available air.
In airplanes, even though it is colder "up there" I think (may be wrong) mixture is leaned at higher altitude because less oxygen is available?
KB
In airplanes, the mixture is leaned at altitude due to the lower partial pressure of O2, but is also leaned on the ground when it is hot or humid. If it is both hot and humid, it may be necessary to lean dramatically, just to keep an (reciprocating) engine running, otherwise they run quite rich.
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Joined: May 2004
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From: Warren, NJ
'05 E320 CDI;'04 S2k;'94 Supra TT;'10 QX56;'38 Buick;98 Port City Offset Late Model
Thanks for all you input. However, the trouble is that we are talking about constant power and about consumption rate, not air/fuel ratio.
First, a note on ratio. Reducing fuel flow (smaller jets) at higher altitude or increasing it a lower temperatures (bigger jets) is to match the change in air density. The ratio should remain consistent. These are common adjustments on carbureted engines. Closed loop systems adjust based on the ratio. Mass Air Flow sensor work based on density.
Second, the amount of power is determined by the amount of fuel burned. Is the combustion process less efficient from a 5% drop in absolute temperature?
Do the lower temperatures increase vehicle drag from the higher air densities? Is something else at work?
First, a note on ratio. Reducing fuel flow (smaller jets) at higher altitude or increasing it a lower temperatures (bigger jets) is to match the change in air density. The ratio should remain consistent. These are common adjustments on carbureted engines. Closed loop systems adjust based on the ratio. Mass Air Flow sensor work based on density.
Second, the amount of power is determined by the amount of fuel burned. Is the combustion process less efficient from a 5% drop in absolute temperature?
Do the lower temperatures increase vehicle drag from the higher air densities? Is something else at work?
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From: NW Ohio
2008 335 vert, 2004 MDX
Engine efficiency is increased when the outside air is colder all else being constant. If I remember there's a relationship to the temperature difference between combustion temperature (relatively constant) and temperature of the air. Hey, I'm an MD, physics was a long time ago. Any engineers out there?
(Holy crap, pv=nrt! I just heard some static way in the back of my brain.)
(Holy crap, pv=nrt! I just heard some static way in the back of my brain.)
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From: Christchurch, New Zealand
17 E220D, 11 E350 CDI(sold), 06 CLS320 CDI (sold), 05 Cadillac DeVille (gone), 04 E320 CDI (sold)
Although I know that theoretically, and certainly in aeroplanes, engine efficiency is better in cold weather, the opposite seems to be true with my car.
I have always assumed that this is because I mostly use it on shortish trips and that the engine is spending longer running below temperature. In winter the car has barely warmed up by the time I get to work, and this must cause extra fuel to be used.
I imagine that on a long trip, the theoretical benefits would emerge.
I have always assumed that this is because I mostly use it on shortish trips and that the engine is spending longer running below temperature. In winter the car has barely warmed up by the time I get to work, and this must cause extra fuel to be used.
I imagine that on a long trip, the theoretical benefits would emerge.
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Posts: 314
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From: In the shadow of D.C. (No.Va.)
'05 E320CDI, 1987 300E, Vanagon Syncro, Turbo Arrow III
Originally Posted by johna1
Although I know that theoretically, and certainly in aeroplanes, engine efficiency is better in cold weather, the opposite seems to be true with my car.
