Tips for flat highway driving?

[machoman1337]

I just came back from a road trip to Seattle. I figured that the "eco cruise control" would give me amazing mileage on the highways (I went at early hours with almost no traffic), and I had the A/C set to minimum fan speed at 21.5 degrees. Unfortunately, my trip computer showed 6.0 L/100 km (39.2 mpg) for both ways :(

 

I've gotten 5 and below (in line with the original EPA rating - 5 L/100 km = 47 mpg) with a mix of city and highway in the past, and I figured the highway part was helping. I guess the somewhat hilly nature of Vancouver is what helps me get amazing mileage on the highways here (as good as 3.6 L/100 km once), whereas the drive to Seattle was totally flat which meant the engine stayed on longer than I'd like.

 

I set my cruise control to 110 or 120 km/h depending on the speed limit of the present stretch (it fluctuated between 60 mph and 70 mph, so I'd be exceeding by about 5 mph each time). I know the FFH is capable of coasting on electric at 120 (my own observations). But perhaps 120 sucks the battery too quickly.

 

Any thoughts on how I could do better next time? Should I limit the cruise control to 110 instead? Any advice is appreciated!

[acdii]

Minimize EV use on the highway, use all ICE, and keep it 65 or under. When you keep the SOC of the pack at or above 80% of the graph, you use the ICE for propelling and very little charging. You can see the instant between 40 and 50 MPG when driving like this, but it takes a lot of practice to get the pedal just right.

[jeffo65]

Drafting with ACC helps as well.

[corncobs]

Set the ECC to speed limit and enjoy the ride.

 

Yes you can make better MPGs when playing the manual game but I personally don't believe it's worth the effort in savings return.

 

39 isn't bad I have had lower results but overall that's average in this speed range.

[machoman1337]

Thanks for the advice guys. I really should learn to be patient and actually obey the speed limit :P I set my cruise control to exceed it (up to the max that most cops tolerate) because I just have to get to my destination faster... in the end it doesn't really matter and all I accomplish is wasted gas.

 

Acidii's method is interesting - how would I "ensure" that it's all-ICE though? Doesn't seem to be any kind of setting for this. All I know is that hard acceleration is guaranteed to turn on the engine.

[hybridbear]

Thanks for the advice guys. I really should learn to be patient and actually obey the speed limit :P I set my cruise control to exceed it (up to the max that most cops tolerate) because I just have to get to my destination faster... in the end it doesn't really matter and all I accomplish is wasted gas.

 

Acidii's method is interesting - how would I "ensure" that it's all-ICE though? Doesn't seem to be any kind of setting for this. All I know is that hard acceleration is guaranteed to turn on the engine.

What I often do is set my cruise control for the minimum speed I want to drive and then I use my right foot to keep the pressure on the accelerator so that the ICE won't turn off. That way when I go down hills I pick up speed (often 5-10 MPH) and then as I go up hills the car gradually slows down back to my cruise control speed. Using the Empower screen you can see the threshold and then set your pedal pressure to be right above that. On routes I drive fairly often I've learned which hills are long enough to let the car go into EV and which are short enough that I should keep the ICE on and pick up speed. When you keep the ICE just barely above the threshold it will send lots of electricity into the HVB which is then used as assist when going up a hill.

[talmy]

"Speed Kills" gas mileage. Just finished 800 mile trip to and around Oregon coast. Entire trip but last 50 miles was two lane roads, 55 or less speed limits. (All driving done at speed limit or less, with smooth starts, stops, and speed changes when possible) Until that last 50 miles car was indicating >50.0 mpg the whole time. The last 50 miles was all Interstate with speed limits 55-70 mph. That pulled the trip mileage down to 49.4. That works out to about 42mpg for the Interstate stretch. Flat stretches versus hilly didn't seem to matter.

[Waldo]

I figured that the "eco cruise control" would give me amazing mileage on the highways

 

That's not how a hybrid works. Driving on a flat highway requires a certain amount of power - it's all based on wind and rolling resistance. The hybrid doesn't really have much better wind or rolling resistance than the non-hybrid Fusion, so the only way to get better mileage is to produce the power more efficiently. But cars with small engines all tend to produce power efficiently at highway speeds (look up BSFC to understand that better) so there isn't much room for a hybrid to gain on a similar small engined vehicle. If your engine is operating in it's optimal BSFC range (as they tend to be at highway speeds), the electric mode really doesn't do anything to help you.

[machoman1337]

What I often do is set my cruise control for the minimum speed I want to drive and then I use my right foot to keep the pressure on the accelerator so that the ICE won't turn off. That way when I go down hills I pick up speed (often 5-10 MPH) and then as I go up hills the car gradually slows down back to my cruise control speed. Using the Empower screen you can see the threshold and then set your pedal pressure to be right above that. On routes I drive fairly often I've learned which hills are long enough to let the car go into EV and which are short enough that I should keep the ICE on and pick up speed. When you keep the ICE just barely above the threshold it will send lots of electricity into the HVB which is then used as assist when going up a hill.

 

Ah makes sense. I usually drive in such a way that EV mode kicks in as often as possible (I just LOVE the Lexus-like silence that follows). From what I understand now, sometimes it's best to just let the ICE run as it can help the car to go into EV (by having more charge) in situations where the ICE would probably turn on, i.e. uphill?

[DeeCee]

Just set the cruise at the posted speed limit, sit back, and enjoy the ride. Getting all stressed out for a few more tenths of mpg is not worth it IMHO.

[lolder]

 

That's not how a hybrid works. Driving on a flat highway requires a certain amount of power - it's all based on wind and rolling resistance. The hybrid doesn't really have much better wind or rolling resistance than the non-hybrid Fusion, so the only way to get better mileage is to produce the power more efficiently. But cars with small engines all tend to produce power efficiently at highway speeds (look up BSFC to understand that better) so there isn't much room for a hybrid to gain on a similar small engined vehicle. If your engine is operating in it's optimal BSFC range (as they tend to be at highway speeds), the electric mode really doesn't do anything to help you.

All true. The hybrid's sole advantage at highway speeds is the Atkinson cycle ICE which might have about 10% lower BSFC zones and be operating in the best ( lowest BSFC ) zone and at a lower RPM. Here's a "Fuel Map" for a Prius, http://ecomodder.com/wiki/index.php/File:Toyota_2zrfxe_1.8l_prius_bsfc1.jpg

Fords have a similar shape. The BSFC Zones are within the contour lines. The chart is a little confusing as it is for two different generations of Prii ICE's. The current model 2ZR-FXE 1.8 L ICE operates on the top heavy solid line and the intent is to operate it within the 220 g/ KWh. The next best contour is 230 g/KWh. That area is much bigger for the bigger ICE in the 2010+ Gen III Prii. That's why it gets better mileage than the smaller 1.5 L. GenII. I sure wish we could find a fuel map for the Ford hybrids. They probably have a 220 and good sized 230 contour also. The main Ford-Toyota differences are higher weight and drag Cd for Ford.

 

BSFC is Brake Specific Fuel Consumption. It is in weight of fuel per energy produced. Examples are pounds per horsepower-hour or grams per kilowatt-hour. 220 g/KWh = 0.36 lbs/ Hp h. That is very low. The engineering rule of thumb for gasoline engines for almost a century has been 0.5 lb/ Hp h. An old exception was the Wright 3350 cu in. 18 cylinder twin-row radial turbo-compound aircraft engine of the late '40s and '50's used mostly in 4 engine Douglas DC-7s and Lockheed Super Constellation propeller airliners. They were able to achieve 0.4 lbs / Hp h. They had three exhaust energy power recovery turbines ( PRTs ) that upped the power from about 2800 to 3300 HP. The turbines were connected to the crankshaft with a fluid coupling and added the power that way at no additional fuel consumption. These engines had some things in common with our Atkinsons; they were fuel injected, they operated at almost wide open throttle settings at lower RPMs and because of the radial design with the air intake in the rear center of the engine, they had very even air flows to each cylinder for very uniform mixtures which were manually adjusted in cruise.

They were very finicky engines and required a flight engineer's constant attention.

 

Watch this clip of a restored Qantas "Connie" taking off at dusk.

 

 

The exhaust flames come out at only three equally spaced points around the engine nacelles. Those are the outlets of the PRTs.

Edited September 23, 2014 by lolder

[GrySql]

You used to be a pilot in those, didn't you?

[lolder]

No but my company still had them while I flew Convair 440s which had Pratt and Whitney R 2800 2500 hp twin-row 18 cylinder non fuel injected radials. The R 2800 did not have PRTs and was less efficient with probably a 0.5 lb / Hp h BSFC but it was a much more reliable engine. The Douglas DC 6 had R 2800s and the DC 7 had Wright R 3350s. The DC 7 has a heavier, stretched ( 3 ft. ), faster version of the DC 6 but it burned less fuel because of the PRTs and fuel injection. Both the engines first ran in 1937 and were widely used in WW II. The R 3350 non PRT version in B 29s. It was very unreliable. The PRT version was used in 1953 in Lockheed L-1049C Constellations and Douglas DC-7s. It was fairly reliable by then but mechanics sometimes called the PRTs "parts recovery turbines" because they "swallowed" a lot of exhaust valves. If you were very careful with them they had pretty long lives. They were fine for 4 engine aircraft where it wasn't a big deal if you had to shut one down.

 

Here's a Super Constellation publicity clip with 3 engines shut down at the 7:30 point. It could probably maintain altitude at very light weights and power levels you didn't want to use for very long.

 

[acdii]

I love the sound of radials. I so want to get one for one of my planes, but the cost and low output are a huge deterrence.

[GrySql]

No but my company still had them while I flew Convair 440s which had Pratt and Whitney R 2800 2500 hp twin-row 18 cylinder non fuel injected radials.

Here's a Super Constellation publicity clip with 3 engines shut down

Awesome.... Thank you.

[lolder]

I love the sound of radials. I so want to get one for one of my planes, but the cost and low output are a huge deterrence.

Get one of the audio sound kits with loud speakers if it's an electric. A lot of extra weight and battery drain though.

[acdii]

Electric? Yeah right! LOL Glow or gas, unless given to me like my Twin Otter. I just spent $200 for 2 batteries so I can fly it more than a few minutes. I think I will stick with my glow/gas engines from now on. I bought a used, nearly new Saito 125 for $180, less than I paid for 2 8000mah 3S packs.

[lolder]

I haven't gone to big electrics yet. One calm morning I got 20 minutes in the Hobbyzone micro Champ with the gear removed at slow speed and little need for control except to keep it in sight. 14 minutes is usually achievable with the !S 150 mahr.

[acdii]

OTOH my new T-Clips with the Saito 11cc gas motor flew 40 minutes on 6 ounces of gas. Landed with over half a tank left. Really has nothing to do with flat highway driving, so this thread has strayed so far off topic that we need a plane to get it back on course.

 

One good tip, use the Adaptive cruise behind a flat bed semi at 2 bars. Set the cruise higher than the average speed the truck is moving at, and you will gain at least 2-3 MPG than if you were to just cruise normally.

 

There, that should put it back on topic.....for now.

[lolder]

This got 853 mpg: http://www.barnardmicrosystems.com/UAV/milestones/atlantic_crossing_2.html#Technical

[Cooling Tower Guy]

Staying right on topic...in the late 60's the Blue Angles had a super Connie painted up in the BA colors and used it to fly crew and support stuff to the air shows. While stationed at Roosey Roads I remember that the BA Connie came in and the load master began unloading. He made 2 errors that cost him his career. 1.He unloaded the plane from the front. 2.He forgot to put the tripod in place at the rear. Connie rocked back on her tail and damaged it as well as load master's ego. What a beautiful bird she was.