[DarthSurplus]

I am having problems accepting (b) and (c). I have been under the impression that the heat rejection (thermal losses) of the engine is a function of its power output, not the ambient air temperature. And that the thermodynamic efficiency of the engine is dependent upon the engine's temperature, not the ambient. And that cooler air and cooler fuel increased thermodynamic efficiency. But I struggle conceptually with several aspects of thermodynamics, even though I passed the courses. /ubbthreads/images/graemlins/shrug.gif /ubbthreads/images/graemlins/smirk.gif
.
.

 

[Believer45]

Fuel is blended regionally specific so you actually are getting winter blend fuel earlier than you expect. It may be a wimp answer as you say but it is also a correct answer.

Dave / Believer45

 

[DarthSurplus]

For the sake of a good pseudo-scientific discussion, /ubbthreads/images/graemlins/smirk.gif let's disregard the fuel blend variable, and presume that the engine is warmed up in route, with an initial idle time of two minutes or less, and negligible other idle time.

 

[MarkEkberg]

Still winter blend fuel has less potential btu's then straight #2.

I think that is why.

 

[frashdog]

I noticed a 2-3 mpg loss as soon as they started started with the blend up here, before it got cold, still in the 30-40 degrees! /ubbthreads/images/graemlins/rolleyes.gif I did not lose any more than another mpg when it got stupid cold like zero and 10 below degrees F.

Then I got a 2-3 mpg gain when they started to switch back, before it got really warm out, still a few 20-30 degree days around. Not too hard to figure that out.

Many people let there trucks run idle to warm up or stay warm in the winter at 0mpg, which yea it's not alot of fuel but its not going anywhere either.

Now I have read a few indepth posts/articles of the effects of temp, humidity, altitude, as to 02 content for the motor to use and the air density being on drag. I still "think /ubbthreads/images/graemlins/shrug.gif" the fuel is the biggest factor for our trucks.

 

[DENNY]

Question: Why do diesel-powered on-highway vehicles see reductions in fuel economy when the weather turns cold, even when consuming summer-blend fuel?

Answer: If it is truely #2 summer fuel. Than you should not see any loss and may even see a slight increase in MPG in cold weather due to colder air charge.
The fuel will have to be heated so it will not gell. Warmup and extended idleing should not be considered if you want true MPG testing.
You are putting in too many variables for it to be science. More like a SWAG.
DENNY

 

[hiall]

[ QUOTE ]
I have been under the impression that the heat rejection (thermal losses) of the engine is a function of its power output, not the ambient air temperature.

[/ QUOTE ]

It takes a lot more fuel getting up to operating temperature. This means you have lots of energy lost through the cylinder wall to heat the coolant. The less temp difference between the wall and head and combustion air, the less heat loss.

[ QUOTE ]
And that cooler air and cooler fuel increased thermodynamic efficiency. But I struggle conceptually with several aspects of thermodynamics, even though I passed the courses

[/ QUOTE ]

They do, the temp of the fuel is pretty irrelevant. It's not inejecting a large enough amount to make a signifigant in the temperature of cylinder. Fuel temp also does not fluctuate that much in the PSD so your injected quanity will not change much.


Timing is retarded slightly because of the cold temps, Ford's programming could overcome this, but the calibration isn't perfect...

 

[ChrisB]

I notice quite a few responses still focussing on differences in fuel chemistry even though you fairly clearly have asked us to disregard the lack of heat content that makes up the main reason why diesel fuel economy is reduced in the winter. This discounts the obvious factors such as, warm up time, increased aero drag, tire structural stiffness, even tire pressure as affected by heat, etc.

Some folks seem to still focus on and seem to be convinced colder induction air improves fuel efficiency. This has not been proven, and I believe quite a bit of evidence has been submitted in other threads to support this.

We need a vounteer who might be able to run a test using exacting fuel consumption calculations on flat roads in Minnesota or similar to run a test in cool weather and then another in a couple months in much warmer temps. Obviously the fuel should probably be the same warm weather blend if it's possible to come by. That vounteer needs to be as scientifically minded, particular, observant, and as unbiased as possibe.

 

[hiall]

If you look at a fuel consumption (BSFC) chart for an engine, you can see that the BSFC increases as air intake temps increase.

The reason for the drop in winter is taking longer to warm-up the engine and different fuel used.

I don't really notice this supposed drop in my personal truck.....

All my superduties have always gotten crap mileage regardless of what time of year it is.

 

[ChrisB]

I've never seen a BSFC chart referenced to inlet air temp. I'm not saying they're not out there, but please make one known to us.

 

[DarthSurplus]

[ QUOTE ]
This means you have lots of energy lost through the cylinder wall to heat the coolant. The less temp difference between the wall and head and combustion air, the less heat loss.

[/ QUOTE ]Yeah, that's how I first thought about it, too. Kinda like heating your house in winter, eh? /ubbthreads/images/graemlins/tongue.gif With your house, more energy is pulled through the wall insulation simply due to the greater temperature gradient between the inside and outside air.

This is a much different circumstance. And it's a seductive analogy. But it won't hold water, er, coolant. /ubbthreads/images/graemlins/wink.gif

Think of the heat transfer in terms of a flow rate, like water flowing through a pipe. The waste heat energy that is generated in the power cylinder is approximately proportional to the shaft energy being produced. The outside air has nothing to do with it. At a given shaft power output, the heat rejection (the flow rate of heat energy from the power cylinder to the coolant) should be the same, rain or shine. The coolant in the iron should be at the same temperature summer or winter, because it is controlled by the thermostat.

There should be no increase in temperature gradient from the cylinder wall to the coolant path with decreased outside air temperature, once the thermostat opens and the coolant gets moving.

That is my understanding of the situation. I might be missing something. I'm going to run this one by some coworkers to see if they can shed some light on it.

 

[ChrisB]

I believe Antagonist is correctly referring to this occuring only during warm up. As you state, if the cooling system is setup to maintain at or close to a specific temperature no matter the ambient temp, it will not matter much if at all. It's only during warm up that efficiency should be lower in cold ambient temps.

 

[roofeditor]

"the temp of the fuel is pretty irrelevant"

You're kidding? /ubbthreads/images/graemlins/shrug.gif

 

[hiall]

[ QUOTE ]
the temp of the fuel is pretty irrelevant"

You're kidding?



[/ QUOTE ]

You're adultering?

 

[hiall]

[ QUOTE ]
There should be no increase in temperature gradient from the cylinder wall to the coolant path with decreased outside air temperature, once the thermostat opens and the coolant gets moving.



[/ QUOTE ]

Darth, there was another thread in which we talked about cool and hot air and fuel economy....

I am wondering if on the Diesel engine, if colder intake air doesn't start to zap too much heat away from the cylinder walls?

I honestly do not witness a drop in winter fuel economy on long trips?

Short tripping I loose a lot.......

Consulting some truckers on this matter would be a good thing to do. I know they run shutters and aprons across their grills to keep the engine from getting too cold and loosing economy during the winter. Even with a thermostat, the engine still looses enough heat through the block surfaces so much so that they block off the grill.

Maybe this is why as the Dr Campbell was saying, hotter air increases economy in certain cirsumstances???

Thermodynamically hot air is bad, but maybe in real world applications during cold operation if your engine cannot be kept at operating temp, hotter air is better....

 

[roofeditor]

[ QUOTE ]
[ QUOTE ]
There should be no increase in temperature gradient from the cylinder wall to the coolant path with decreased outside air temperature, once the thermostat opens and the coolant gets moving.



[/ QUOTE ]

Darth, there was another thread in which we talked about cool and hot air and fuel economy....

I am wondering if on the Diesel engine, if colder intake air doesn't start to zap too much heat away from the cylinder walls?

I honestly do not witness a drop in winter fuel economy on long trips?

Short tripping I loose a lot.......

Consulting some truckers on this matter would be a good thing to do. I know they run shutters and aprons across their grills to keep the engine from getting too cold and loosing economy during the winter. Even with a thermostat, the engine still looses enough heat through the block surfaces so much so that they block off the grill.

Maybe this is why as the Dr Campbell was saying, hotter air increases economy in certain cirsumstances???

Thermodynamically hot air is bad, but maybe in real world applications during cold operation if your engine cannot be kept at operating temp, hotter air is better....

[/ QUOTE ]

Thermodynamically cold "fuel" is bad, but maybe in real world applications during "cold operation" if your engine cannot be kept at operating temp, hotter "fuel" is better....

 

[Dave Whitmer]

Actually, I think all five factors

1. Lower heating value of winter blend fuel
2. Increased thermodynamic losses due to cold induction air/fuel
3. Increased aerodynamic drag due to increased air density
4. Snow/ice
5. Sticky EBPV

have an effect. How much each one affects you depends on where you are and how you drive.

Winter Blend
This is a highly variable factor and it is almost entirely dependent on where you operate your truck. “Winter blend” is a mixture of No. 1 (kerosene) and No.2 diesel, just as jet fuel is. Winter blend can vary from 5% No. 1 (the lame stuff we get in central Indiana) to the 66% No. 1 mix (good for 40 below) you get on the Great Plains. I suppose folks in non-coastal Alaska use jet fuel which is about 85% No.1. No.1 has lower heating value than No. 2 – 120,000 Btu/gal vs 140,000 Btu/gal and winter blend is just a pro rata of these figures. High grade Nebraska winter blend has a heating value of about 127,000 Btu/lb. If that were the only factor a Nebraska panhandle truck would see a loss of about 9.3%. A 18 MPG truck would drop to about 16.3 MPG. Trucks operating in the heart of Dixie should see no MPG drop. But we know that Great Plains trucks lose more than 9% MPG and southern trucks do experience MPG drop in the winter, so winter blend is only part of the answer.

Thermodynamic Losses
The case for thermodynamic losses on short-run trucks is sound. School buses often run with their Cold Fronts completely zipped up because their stop-and-go operational pattern precludes them from ever really getting warm. Truly long-haul trucks always unbutton their cold fronts on long runs because the trucks get plenty warm due to road load. Class 7 and 8 trucks have staggeringly powerful (in terms of BTU/HP) cooling systems because of the prolonged high-load operation they face, so they do keep the front partially closed until the weather warms up. I think thermodynamic losses are important if you are making runs of less than 5 miles but beyond that the engines and fuel warms up to the point this factor recedes in importance as the trip gets longer.

Aerodynamic Drag
This factor affects everyone to varying degrees. A vehicle becomes a crude propeller because it pushes air out of the way as it moves along. The vehicle moves cubic feet of air, but the work necessary to move air depends on the weight of the air moved. A cubic foot of air at 18,000 feet MSL weighs half of what air does at sea level, so an airplane get better MPG at higher altitudes. Air at 85 degrees and 40% humidity (common Midwestern summer conditions) weighs roughly 0.055 lb per cubic foot. Air at 20 degrees and 50% relative humidity weighs roughly 0.063 lb/cubic foot. That is a 14.5% difference. Your 18 MPG truck (summer) should have its winter mileage reduced to 15.4 MPG if you do a lot of Interstate cruising.

Snow and Ice
Snow, in particular, imposes rolling resistance. How much varies according to the depth and type snow. Western powder and eastern slush would have different effects on MPG. Probably more important is how many days of it you get. Denver can get heroic amounts of snow in short periods, but it usually melts off in a few days. Buffalo gets hammered day after day for months on end, so the guy in Buffalo pays a heavier MPG price than the guy in Denver while the guy in Houston doesn’t understand. Deeper snow also may require use of four-wheel drive which imposes more mechanical friction.


EBPV
These trucks have a back pressure valve to enhance engine warm up. It imposes a heavy load on the engine. I noticed that no matter how clean I got my setup, the darned thing blew from October to May, so it got electrically disconnected. Bingo! I regained 1.5 MPG although the truck takes three times farther to warm up. Maybe a compromise would be to control the valve with a manual switch.

The Perfect Storm
All these factors can add up. My “Perfect Storm” scenario is a truck used for short runs in the Upper Peninsula of Michigan with a sticky EBPV. Very cold temperatures and strong winter blend at relatively low altitude and lots of snow. Such a truck may see it winter MPG drop to half or less of its summer value. The converse is also true. The guy in Houston (is it ever truly winter in Houston?) may only see a 13% drop due to cool temperature air.

 

[hiall]

[ QUOTE ]
Thermodynamically cold "fuel" is bad, but maybe in real world applications during "cold operation" if your engine cannot be kept at operating temp, hotter "fuel" is better....


[/ QUOTE ]

Explain....

 

[roofeditor]

[ QUOTE ]
[ QUOTE ]
Thermodynamically cold "fuel" is bad, but maybe in real world applications during "cold operation" if your engine cannot be kept at operating temp, hotter "fuel" is better....


[/ QUOTE ]

Explain....

[/ QUOTE ]

It's much harder to fully atomize very cold fuel compared to warm fuel. I am referring to extremes. Very cold like 0 (C) or less.

 

[roofeditor]

[ QUOTE ]
Actually, I think all five factors

1. Lower heating value of winter blend fuel
2. Increased thermodynamic losses due to cold induction air/fuel
3. Increased aerodynamic drag due to increased air density
4. Snow/ice
5. Sticky EBPV

have an effect. How much each one affects you depends on where you are and how you drive.

Winter Blend
This is a highly variable factor and it is almost entirely dependent on where you operate your truck. “Winter blend” is a mixture of No. 1 (kerosene) and No.2 diesel, just as jet fuel is. Winter blend can vary from 5% No. 1 (the lame stuff we get in central Indiana) to the 66% No. 1 mix (good for 40 below) you get on the Great Plains. I suppose folks in non-coastal Alaska use jet fuel which is about 85% No.1. No.1 has lower heating value than No. 2 – 120,000 Btu/gal vs 140,000 Btu/gal and winter blend is just a pro rata of these figures. High grade Nebraska winter blend has a heating value of about 127,000 Btu/lb. If that were the only factor a Nebraska panhandle truck would see a loss of about 9.3%. A 18 MPG truck would drop to about 16.3 MPG. Trucks operating in the heart of Dixie should see no MPG drop. But we know that Great Plains trucks lose more than 9% MPG and southern trucks do experience MPG drop in the winter, so winter blend is only part of the answer.

Thermodynamic Losses
The case for thermodynamic losses on short-run trucks is sound. School buses often run with their Cold Fronts completely zipped up because their stop-and-go operational pattern precludes them from ever really getting warm. Truly long-haul trucks always unbutton their cold fronts on long runs because the trucks get plenty warm due to road load. Class 7 and 8 trucks have staggeringly powerful (in terms of BTU/HP) cooling systems because of the prolonged high-load operation they face, so they do keep the front partially closed until the weather warms up. I think thermodynamic losses are important if you are making runs of less than 5 miles but beyond that the engines and fuel warms up to the point this factor recedes in importance as the trip gets longer.

Aerodynamic Drag
This factor affects everyone to varying degrees. A vehicle becomes a crude propeller because it pushes air out of the way as it moves along. The vehicle moves cubic feet of air, but the work necessary to move air depends on the weight of the air moved. A cubic foot of air at 18,000 feet MSL weighs half of what air does at sea level, so an airplane get better MPG at higher altitudes. Air at 85 degrees and 40% humidity (common Midwestern summer conditions) weighs roughly 0.055 lb per cubic foot. Air at 20 degrees and 50% relative humidity weighs roughly 0.063 lb/cubic foot. That is a 14.5% difference. Your 18 MPG truck (summer) should have its winter mileage reduced to 15.4 MPG if you do a lot of Interstate cruising.

Snow and Ice
Snow, in particular, imposes rolling resistance. How much varies according to the depth and type snow. Western powder and eastern slush would have different effects on MPG. Probably more important is how many days of it you get. Denver can get heroic amounts of snow in short periods, but it usually melts off in a few days. Buffalo gets hammered day after day for months on end, so the guy in Buffalo pays a heavier MPG price than the guy in Denver while the guy in Houston doesn’t understand. Deeper snow also may require use of four-wheel drive which imposes more mechanical friction.


EBPV
These trucks have a back pressure valve to enhance engine warm up. It imposes a heavy load on the engine. I noticed that no matter how clean I got my setup, the darned thing blew from October to May, so it got electrically disconnected. Bingo! I regained 1.5 MPG although the truck takes three times farther to warm up. Maybe a compromise would be to control the valve with a manual switch.

The Perfect Storm
All these factors can add up. My “Perfect Storm” scenario is a truck used for short runs in the Upper Peninsula of Michigan with a sticky EBPV. Very cold temperatures and strong winter blend at relatively low altitude and lots of snow. Such a truck may see it winter MPG drop to half or less of its summer value. The converse is also true. The guy in Houston (is it ever truly winter in Houston?) may only see a 13% drop due to cool temperature air.

[/ QUOTE ]

Another BIG factor is that many people spend a lot of time warming up engines and letting them idle to keep them warm. This uses a lot of fuel.