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Old 05-29-2012, 11:46 AM   #11 (permalink)
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Quote:
Originally Posted by meelis11 View Post
What are your Pulse and glide times in seconds?
I keep engine in neutral and idling while glide. Pulse is 3.5-4 seconds (80-100 kmh) and glide is around 12 seconds (100-80 kmh) in level ground (two persons in car). Onboard computer shows 3.9L/100 after 490km driving. Computer is optimistic about 0.5L, so real number is around 4.4L/100km
Pulse time average is around 4 seconds and glide time around 15-16 seconds. You do have to drive uphills in glide with load to get best results. That lowers your average speed little.

I have made a chart where you can estimate your fuel consumption based on P%G ratio on a 1.2 TDI:

https://www.facebook.com/photo.php?f...type=3&theater

So with 4 seconds pulse and 15 second glide gives:0,266 P&G ratio which means about 2.2 liter fuel consumption.

You can make your own chart by making some assumptations on the engine power and BSFC map...

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Old 05-30-2012, 03:59 AM   #12 (permalink)
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Quote:
Originally Posted by Vekke View Post
Pulse time average is around 4 seconds and glide time around 15-16 seconds. You do have to drive uphills in glide with load to get best results. That lowers your average speed little.

I have made a chart where you can estimate your fuel consumption based on P%G ratio on a 1.2 TDI:

https://www.facebook.com/photo.php?f...type=3&theater

So with 4 seconds pulse and 15 second glide gives:0,266 P&G ratio which means about 2.2 liter fuel consumption.

You can make your own chart by making some assumptations on the engine power and BSFC map...
You estimate there different things, but if you make car lighter, probably glide will be shorter also? I agree that lighter car needs shorter time to accellerate, but probably it also means that there is less inertia and glide is shorter too. Lets expect that aero and motor power are same. Or I am missing something?
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Old 05-30-2012, 11:14 AM   #13 (permalink)
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Only things that effect that chart is BSFC map. On TDI engines the average is around same
200g/kWh
Fuel density
0.85 kg/l
Engine power average estimation
40 kW


200*40 8000 g/h

8/0,85 9,41 l/h 0,002613889 l/s

on idle your fuel consumption is 0.5 l/h =0,000138 l/s

Then just calculate how many percentages you are on flat out near 2000 RPM and how much you are gliding.

Because your 1.9 TDI has 81 Kw vs 40 Kw it consumes double the fuel at same P&G times...

Lighter vehicle is not a big factor in the big picture the Cd value means the most when you are gliding in neutral at 80-90 km/h speeds. Ofcourse the bigger car has more energy storeged in itself but that takes also more energy to accelerate it back in push.

Was I clear enough?

I can send the exel sheet in email if someone wants to use it as well just send me private message...
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Old 05-30-2012, 12:25 PM   #14 (permalink)
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My question in short is: is there a point to make car lighter for pulse and glide type driving? Lighter car means shorter pulse and shorter glide. You are saying that pulse goes shorter but glide is not getting shorter by same amount? So there is still point in weight savings in P&G driving or is it mostly for city driving?
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Old 05-30-2012, 12:47 PM   #15 (permalink)
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Quote:
Originally Posted by meelis11 View Post
My question in short is: is there a point to make car lighter for pulse and glide type driving?
While P&G is already cheating a bit, you're always losing out energy-wise.
During the coasting, you can't win back all the energy you put in while pulsing.

By making the car lighter, you're reducing the amount of energy it takes to pulse it from X to Y , so you're reducing the energy loss by reducing the energy that got put into it in the first place ...

A lighter car will have less inertia, but all else being equal, it'll also have lower rolling resistance.
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Old 05-30-2012, 02:53 PM   #16 (permalink)
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A8 luxury fuel sipper - '97 Audi A8 1.2 TDI 6 speed manual
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Difference is basicly the same as losing 10% of cars weight. In highway that means 2-4% savings in city driving that means 6-8% depending on the source. So when doing pulse and glide that 10% weight saving is at least 6% so yes it helps. Might be even more than 8% because you are accelerating all the time...
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Old 05-31-2012, 06:24 AM   #17 (permalink)
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Don't forget your more economical in general because less weight = less braking so less wear. If youu know what it costs in litres of petroleum to fabricate and transport brake pads, thats also energy you can now consume for transportation. If you factor in all these lil bits your probably the most economical driver on the road
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Old 06-06-2012, 08:26 AM   #18 (permalink)
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Congratulations.

But if you are doing P&G between 80 to 95 kph, your average speed is somewhere near 87.5 kph (it tends to maximum speed becuase average increases when higher acceleration you have and lower the deceleration will be). MAths say average of numbers higher than 80 are higher than 80.

YOur fuel consumption is better than you say because average speed needs to be higher than you say or you are wrong in your numbers.

My car/s fuel consumption at 80 kmh now is 3.89L/100km (using cruise control) 1.9 TDI BXE 105 cv @ 138 cv. http://en.wikipedia.org/wiki/Seat_leon
It seems very difficult to me my car going under 3.5 L/100 km at 80 kmh (sport tires, standard underbody, standard gearing will be changed in near future but i'm not going under 3.5 at that speed). Maybe using push and glide but i only glide downhill.

My goal with my car is 5.5 L/100km at 120 kmh cruise control (standard it was 6.76 L/100km). Current fuel consumption is: 122 km/h cruise control 6.06L/100km (22km highway loop) and 5.9 L/100km (240 km higway loop). I will change tires, underbody and gearing in the future. I was focused on cheap aeromods (wheelcaps, grille, spoiler) and ecu flash because i wanted more power to overtake. 2008 Seat Leon Ecomotive Gearbox it's hard to find (but I have to because my topspeed will increase 15 kmh or 10 mph! and fuel economy improve).

I did some P&G with my year 2000 (310.000 km odometer) 1.9 tdi 110CV AHF and I got 4.5 L/100km at 110 km/h (100 to 120 kph interval) saving 0.5 L/100km, tdi's 5 th gear minimum efficiency it's high enough to show little improvement. The same car with Cd aeromoded from 0.31 to 0.28 gave me a fuel consumption of 3.08 L/100km (82 kmh average, using foot control speed). http://en.wikipedia.org/wiki/%C5%A0koda_Octavia

I use P&G with my car while city driving becase of awful effficiency of 1st to 3th gears at cruise speed compared with engine's maximum. I'm getting with the Skoda Octavia 1.9 TDI 110 cv AHF in the city 6.0 L/100km if I drive it with P&G, and long gears etc. Taxi drivers have fuel consumptioms of 7.6 L/100km with same car.

Diesel Trains doesn't need P&G and they get maximum efficiency at steady speed with correct gearing.
Does not using P&G on a 300 km trip sound crazy to you?
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Old 06-06-2012, 10:25 AM   #19 (permalink)
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Quote:
Originally Posted by ausias View Post
My car/s fuel consumption at 80 kmh now is 3.89L/100km (using cruise control) 1.9 TDI BXE 105 cv @ 138 cv.
Try to have the rpm just above the number given for max torque.

For me, that's about 85kph indicated, and it works wonders in my car when on CC : 2.8L/100km indicated, which would be around 3.3 in real life.

Quote:
My goal with my car is 5.5 L/100km at 120 kmh cruise control (standard it was 6.76 L/100km). Current fuel consumption is: 122 km/h cruise control 6.06L/100km
That seems very high for a 1.9 TDi ...


Quote:
I use P&G with my car while city driving becase of awful effficiency of 1st to 3th gears
Try 4th
With a warm engine I've started to do 30kph / 20mph zones in 4th gear, in my car that's at idle rpm, and CC doesn't work down there !
As long as the road is flat or slightly downhill, it'll give good results.
But uphill - even climbing a speedbump - the FC goes way up !
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Old 06-26-2021, 07:27 PM   #20 (permalink)
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One of the best Ecomodder cars ever built/narrated on this site in my opinion... Vekke scored a 72mpg US lifetime and a 117 mpg US 3-tank average. Kicked US butt. I added it to the 70+ MPG lists:
https://ecomodder.com/forum/showthre...tml#post601190

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