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Old 07-04-2007, 07:46 AM   #1
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burn and glide @ 70mph

I've got a scangauge II and it has me mesmerized. I try different things to see what effect they have on Fuel Economy (FE). My latest test was burn and glide at 70 mph. I was on a trip with about 200 miles on the tank of gas looking at a trip average MPG of 34 when I started accelerating as fast as I could every time the speed dropped to 65mph till I got to 75mph then I shifted (standard transmission - 5sp) into neutral (left the engine running). within a short time the trip MPG moved up to 36 mpg.
To get a reading exclusively of this new environment, I reset my trip data on the scangauge and used the burn and glide exclusively. I immediately started to get between 49 and 53 MPG. For me this is an immediate 50% improvement.
My idea of what is going on here:
At 70mph there is a given power requirement needed, I'm not reducing the amount of power needed. What I'm doing is using the engine more efficiently. I've heard that gasoline engines are most efficient when running at wide open throttle ... the power output versus operating losses is maximized. So, with burn and glide I'm getting maximum efficiency for say a quarter of the time (running wide open throttle) and then using a minimal amount of fuel (idling) for the other three quarters of the time (gliding). I'm sure I could get even better mileage if I turned the engine off during the glide ... but the Scangauge doesn't continue to work when I turn off the engine.
Now all this has me thinking about how to make a more FE car. If an energy storer (like a 12 volt battery) existed that could take blasts of high energy then dribble it out more slowly to keep the car moving exixted this idea could fly. But I can't imagine an electric battery doing this which got me wondering what could take in large amounts of power and then give them back at a still pretty rapid rate and I came up with a flywheel. Take a 50 pound flywheel and spin the hell out of it and then start taking the energy out of it to keep the car going. If the duty cycle were in the order of two minutes, the engine running for say 30 seconds and the "glide" taking the other 1.5 minutes I think there could be equivalent gains seen (50%).
Of course this scenario ignores the technology required to access the flywheel potential eg. what transmission methodology to the wheels would be used? I guess I envision an electric motor driving the wheels that is large enough to sustain the car at a reasonable speed in the most power required environment (say up the steepest hill doing 80mph) with the flywheel driving an electric generator. The engine would then exclusively drive the flywheel and of course the "giving" and "taking" from the flywheel could be done concurently. This would also as a byproduct allow the hybrid effect of allowing slowing down to "give" to the flywheel and it would be highly efficient in vehicle stopped state. What do you think?
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Old 07-04-2007, 08:06 AM   #2
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Very interesting experiment. I'm not sure what kind of traffic patterns you have for this to work but, try the same experiment by turning the engine off during the glide. I think the FE results would be shocking.
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Old 07-04-2007, 08:27 AM   #3
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An efficient way of storing and releasing energy is the million dollar question. Whoever comes up with an efficiency breakthrough on that will be a hero.

Good experiment.

Right now the best application of the concept that I can think of completely bypasses the storage part. Instead, it seems to me that a car could have 2 engines. One to run WOT (or nearly so) at cruise, and another one for rapid acceleration. But that has lots of drawbacks as well...
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Old 07-04-2007, 08:49 AM   #4
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Hondaaccord98, do you have your ScanGauge set to HYBRID? You should. That fixes most cars SG shutoff problems. Coasting. If you are turning off the ignition key, you need to turn it back to run after the engine dies to keep SG on. You definitely should be engine-off neutral coasting.

Heavy flywheels consume considerable power when accelerating, I would not expect to see enough recovery to justify the loss.

To test your inertia theory, rather than change an engine flywheel, you could liquid fill 2 tires. That would add more weight than the heaviest flywheel you could fit to your car.

I love to see people thinking and testing. Keep it going. CO ZX2
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Old 07-04-2007, 08:55 AM   #5
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Originally Posted by Bill in Houston View Post
An efficient way of storing and releasing energy is the million dollar question. Whoever comes up with an efficiency breakthrough on that will be a hero.
If anybody invents one, they need to put it in laptops as well.

m
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Old 07-04-2007, 09:48 AM   #6
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What's more FE on the highway and in the city, sustaining speed using cruise control or doing the burn and glide method? What speeds would be the best? For example on highway 60mph coast to 50mph, back to 60? I can't do engine off coasting due to an auto tranny.
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Old 07-04-2007, 09:54 AM   #7
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Which is better largely depends on the terrain ,traffic patterns and how sensitive the cruise unit is . I've found that the cruise is too abrupt at dealing with terrain changes .I can actually get better FE using my foot than the cc unit does. The Focus seems to like a full coast down to min legal speed of 40 from 53-55 mph . ymmv .
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Old 07-04-2007, 10:07 AM   #8
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Originally Posted by popimp View Post
What's more FE on the highway and in the city, sustaining speed using cruise control or doing the burn and glide method? What speeds would be the best? For example on highway 60mph coast to 50mph, back to 60? I can't do engine off coasting due to an auto tranny.
I used a 10-15 mph difference out on the highway and sometimes even more in the country. The idea is to get the maximum amount of glide time with respect to the burn time.
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Old 07-04-2007, 10:13 AM   #9
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Quote:
Originally Posted by Hondaaccord98 View Post
I've got a scangauge II and it has me mesmerized. I try different things to see what effect they have on Fuel Economy (FE). My latest test was burn and glide at 70 mph. I was on a trip with about 200 miles on the tank of gas looking at a trip average MPG of 34 when I started accelerating as fast as I could every time the speed dropped to 65mph till I got to 75mph then I shifted (standard transmission - 5sp) into neutral (left the engine running). within a short time the trip MPG moved up to 36 mpg.
To get a reading exclusively of this new environment, I reset my trip data on the scangauge and used the burn and glide exclusively. I immediately started to get between 49 and 53 MPG. For me this is an immediate 50% improvement.
How long or miles did you do the pluse and glide? Did the 34 MPG for the 200 miles all highway or was there mixed driving on the tank before you got on the highway? Did you see what the FE was with just the cruise control and the SG reset once on the highway to get a base?
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Old 07-04-2007, 10:39 AM   #10
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I thought it took more fuel to return the vehicle to a speed than it does to keep it at a constant speed?
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