Poor Highway fuel economy in cold weather
#21
Re: Poor Highway fuel economy in cold weather
While I don't agree with Willard, I certainly don't agree that the ICE is most efficient under a heavy load.
An example I'll use is it requires my FEH to use a higher load to run my A/C than my V8 Explorer. I use more fuel percentage wise in My FEH than my Explorer. I may lose 3% FE on my FEH, but I may only lose 1% on my V8 Explorer. The smaller engine has more of a load driving the compressor, and becomes less efficient. The load on the V8 is much less and becomes more efficient to run the compressor than the FEH.
Same thing with speed, the wind resistance has less of an effect on the load of the V8 than an I4 or V6 in most cases. This is one of the reasons why the FEH is more efficient in city driving than highway driving. If the A/C in the FEH is on max in the city with no shutdown or EV, it most likely will be of little advantage to a non hybrid Escape I4.
For this reason, I look at both vehicles when I choose to determine which one to drive. When I need to drive up to 70mph plus with the A/C running 100% in stop and go driving, I take the Explorer. I may only get 23mpg hypermiling the Explorer, because I'm not going to do that much better driving the FEH with much harder work.
I think your confusing HP and load with efficiency when most here look how load effects efficiency.
GaryG
An example I'll use is it requires my FEH to use a higher load to run my A/C than my V8 Explorer. I use more fuel percentage wise in My FEH than my Explorer. I may lose 3% FE on my FEH, but I may only lose 1% on my V8 Explorer. The smaller engine has more of a load driving the compressor, and becomes less efficient. The load on the V8 is much less and becomes more efficient to run the compressor than the FEH.
Same thing with speed, the wind resistance has less of an effect on the load of the V8 than an I4 or V6 in most cases. This is one of the reasons why the FEH is more efficient in city driving than highway driving. If the A/C in the FEH is on max in the city with no shutdown or EV, it most likely will be of little advantage to a non hybrid Escape I4.
For this reason, I look at both vehicles when I choose to determine which one to drive. When I need to drive up to 70mph plus with the A/C running 100% in stop and go driving, I take the Explorer. I may only get 23mpg hypermiling the Explorer, because I'm not going to do that much better driving the FEH with much harder work.
I think your confusing HP and load with efficiency when most here look how load effects efficiency.
GaryG
This is one of the many reasons the FEH highway FE is more affected by winter than an over powered Otto cycle vehicle. The increased load of the cold, dense air has the above affect. Also, the large expansion ratio of the Atkinson/Miller results in cooler combustion temps, exascerbating the effects of the cooler atmosphere. Winter blend gas also effects the low DCR Atkinson/Miller more than the Otto.
#22
Re: Poor Highway fuel economy in cold weather
The increased load of the cold, dense air has the above affect. Also, the large expansion ratio of the Atkinson/Miller results in cooler combustion temps, exascerbating the effects of the cooler atmosphere. Winter blend gas also effects the low DCR Atkinson/Miller more than the Otto.
#24
Re: Poor Highway fuel economy in cold weather
I'm being picky on this statement. The statement "if there is little opportunity or no opportunity, to use regenerative braking to recharge the hybrid battery".
During highway travel, my Ford Escape Hybrid does not display a slowly degenerating hybrid battery state of charge. This vehicle is designed to maintain hybrid battery state of charge in more than one way. I will let the well known posters accurately describe this.
Yes, when regenerative braking cannot be used, say OAT below freezing and a reasonably flat 200 mile trip, the ICE will be used to maintain a reasonable state of charge.
In our Prius Toyota apparently recognized that to be a fairly "lossy" path and so using the ICE to recharge the battery is done only as a last resort. On a trip from Seattle to Portland it seems to use about three discharge/recharge cycles. Hybrid battery is allowed to get down to about 30% before the system will begine using the ICE to bring it back up to close to a full charge.
As for the cold weather effect on highway mileage. Yesterday I averaged 30 mpg (almost 200 miles) on E90 and today I got 32.1 for 210 miles on straight gasoline. Yesterday's temperature was in the mid to upper 20's and today was in the low 30's. Both days involved speeds between 50-60 mph on two and four lane highways. Mileage is less than what I experienced last summer but not the 18% drop others are reporting.
During highway travel, my Ford Escape Hybrid does not display a slowly degenerating hybrid battery state of charge. This vehicle is designed to maintain hybrid battery state of charge in more than one way. I will let the well known posters accurately describe this.
Yes, when regenerative braking cannot be used, say OAT below freezing and a reasonably flat 200 mile trip, the ICE will be used to maintain a reasonable state of charge.
In our Prius Toyota apparently recognized that to be a fairly "lossy" path and so using the ICE to recharge the battery is done only as a last resort. On a trip from Seattle to Portland it seems to use about three discharge/recharge cycles. Hybrid battery is allowed to get down to about 30% before the system will begine using the ICE to bring it back up to close to a full charge.
As for the cold weather effect on highway mileage. Yesterday I averaged 30 mpg (almost 200 miles) on E90 and today I got 32.1 for 210 miles on straight gasoline. Yesterday's temperature was in the mid to upper 20's and today was in the low 30's. Both days involved speeds between 50-60 mph on two and four lane highways. Mileage is less than what I experienced last summer but not the 18% drop others are reporting.
#25
Re: Poor Highway fuel economy in cold weather
That may be what's in a book, but in real life I see how load effects the efficiency of every thing I drive. Efficiency means to me getting more miles to the gallon. If I'm pulling my boat and putting more of a load on any engine, fuel consumption goes up not down.
Drafting is another good example of how taking away load (wind) will increase MPG. In my Explorer pulling my boat at 65mph in a steady state speed and RPM, I was getting 12-13mpg. Picking up a draft, MPG went up to 18mpg at the same speed and RPM. Same thing without the boat with less load I get around 19-20mpg without a draft, and about 23-26mpg with a draft. The RPM doesn't drop while drafting like the FEH because of fixed gearing, but load always reduces MPG which decreases efficiency.
Your examples have to do with HP, my example is how increasing load decreases MPG when we are talking vehicles. With regard to the Atkinson having a cooler combustion temp, how is that possible with the air and fuel mixture staying in the engine longer? It would appear to me that having the intake valve open on the compression stroke would allow for a warmer combustion temp. This is why WOT is not more efficient than a lower RPM. The slower cold air moves threw the intake system, the more time it has to warm for final combustion. I guess what I saying is HP and efficiency split off when higher HP is no longer needed to accelerate.
GaryG
Drafting is another good example of how taking away load (wind) will increase MPG. In my Explorer pulling my boat at 65mph in a steady state speed and RPM, I was getting 12-13mpg. Picking up a draft, MPG went up to 18mpg at the same speed and RPM. Same thing without the boat with less load I get around 19-20mpg without a draft, and about 23-26mpg with a draft. The RPM doesn't drop while drafting like the FEH because of fixed gearing, but load always reduces MPG which decreases efficiency.
Your examples have to do with HP, my example is how increasing load decreases MPG when we are talking vehicles. With regard to the Atkinson having a cooler combustion temp, how is that possible with the air and fuel mixture staying in the engine longer? It would appear to me that having the intake valve open on the compression stroke would allow for a warmer combustion temp. This is why WOT is not more efficient than a lower RPM. The slower cold air moves threw the intake system, the more time it has to warm for final combustion. I guess what I saying is HP and efficiency split off when higher HP is no longer needed to accelerate.
GaryG
Why the temperature of the combustion gasses decreases with a larger expansion ratio is basic thermodynamics. It has been nearly 30 years since I took thermodynamics, fluid mechanics and flight dynamics, but I still have my books and I still can run through the numbers, and I doubt the laws of physics have changed much since then....
The graph I referred to was measured data of a real Ford Otto cycle engine. It wasn't an academic exercise, and it does reflect what happens in the real world. Lugging an engine is always better for FE, but Ford won't let us do that in the FEH due to the eCVT and throttle-by-wire. Lugging gives better FE but is harder on the engine. Ford has always been very conservative with respect to engine performance, and the FEH is certainly no exception. I have had IC's I designed put into both Ford and GM vehicles, and Ford was definitely the more **** of the two during qual.
If loading an ICE didn't give better efficiency, then pushing EV would give you substantially worse FE. It doesn't.
#26
Re: Poor Highway fuel economy in cold weather
Carl (Desert Dog) thanks for the free education. We learn a lot in this forum. Maybe we should feature "on-line classes" to further our knowledge.
Wwest--thanks for detailing basic differences between the Prius and Ford Escape Hybrid. Both are parallel design hybrids. Does the Prius normally allow the operator to discharge the hybrid battery down to 30%? What is the normal upper charge limit for the hybrid battery in the Prius? There was a recent thread in consumer report website on the Prius's deficiencies on the highway in regards to a degenerating hybrid battery state of charge. Most posters were then thrashing hybrid vehicles (all makes) in environments where regenerative braking would not occur.
Wwest--thanks for detailing basic differences between the Prius and Ford Escape Hybrid. Both are parallel design hybrids. Does the Prius normally allow the operator to discharge the hybrid battery down to 30%? What is the normal upper charge limit for the hybrid battery in the Prius? There was a recent thread in consumer report website on the Prius's deficiencies on the highway in regards to a degenerating hybrid battery state of charge. Most posters were then thrashing hybrid vehicles (all makes) in environments where regenerative braking would not occur.
#27
Re: Poor Highway fuel economy in cold weather
Put another way, gaining elevation under heavy load gets you up that hill with the least amount of gasoline.
Taking the gentle route up the hill would take more gas total, even if your Instant MPG looked better.
Yes you would have. Disagreeing is your hobby.
Last edited by gpsman1; 01-07-2008 at 09:36 AM.
Thread
Topic Starter
Forum
Replies
Last Post
prpetersen
GM Hybrid Trucks, Cadillac Escalade Hybrid, Chevrolet Tahoe Hybrid & GMC Yukon Hybrid
7
09-12-2011 10:15 PM
clett
Fuel Economy & Emissions
12
05-25-2006 12:22 AM