Pulse and glide experiment

[jim-frank]

I bet it is the front crank seal. I'll have to look in the manual to see how to fix that.

By the way, I upgraded from the soundcard MPG gauge to the Mpguino some time ago. It's quite a bit more accurate, and easier than hauling a laptop around with me.

[janvos39]

Very nice and interesting Jim-frank. Do you also have data on the pulse time and the glide time?
Interesting case to do some calculations if you also can give estimates for total weight and CdA of your car. What is the additional fuel to make the pulse? Meaning typical MPG without pulsing vs your 41-52 MPG during pulsing?

[MadisonMPG]

I thought pulse and gliding was meant for sub 40mph speeds.

[jim-frank]

Madison-P&G works at higher speeds also.

If I watch the instantaneous mileage while I accelerate, it drops to about 30-35 (fifth gear, about 55 mph). The glide portion is getting 160-200+ mpg. The steady state mpg is a little harder to read, as the instant mpg changes sharply with very small changes in throttle position.

If I look at the 'current mpg' setting on the mpguino, the average will gradually stabilize at around 42 mpg, (60 mph, flat roads, air temp about 80-90 degrees F)

The duty cycle is about 10 sec accelerate, 8-10 coast. It depends, I try to use the terrain to extend the coast as much as possible.

When I use P&G between 30 and 40 mph, to average 35 mph, I get about 61 mpg after the engine is warmed up.

[janvos39]

What would happen if you do the pulse in say 5 sec. The glide will stay at the 8-10 secs.
Will the better glide to pulse ratio compensate for the additional fuel used ?

[woodsmith]

I've been driving in this way for about 8 years now.
I drive an unmodified 2001 Skoda Octavia 1.9TDi estate doing around 20,000 miles pa.

I started driving this way after watching a nature programme on tv showing how small birds save energy when flying. They flap a few beats and then fold their wings for a while and then flap a few beats again. I thought I would try that with the car. I have been happily running at between 60-70mpg on my commutes. My best was 84mpg.

I also use the display's mpg figures to dictate how I drive on motorways. If the reading falls below 50mpg I stop accelerating, if it reads above 65mpg I keep accelerating as fast as I can get away with, especially down hill in readiness for the next up hill.

However, since I decided to keep to the speed limit (too many speed cameras here) it is a lot harder to get better then 67mpg.

When car sharing my passengers often offer to share the cost of the fuel. If I can get better then 60mpg on the journey I don't take their money on the basis it didn't cost me any more then I would have used on my own.

[MadisonMPG]

I understand it works at faster speeds, but isn't it more efficient to do slower?

[woodsmith]

What I did was to experiment a few years back.

I tried driving at a steady 70mph, then 60mph, then 50mph for my long weekend commutes. I was driving 115 miles on the motorway each way then. I found that steady speed only worked if nothing else varied. When I used the mpg computer on the dash I got huge improvements by driving to use less fuel rather then driving to remain legal. It meant that sometimes I was down to 50mph on a long up hill but then got to 90+mph for no fuel at all on the next down hill. When I timed it right it was like riding a roller coaster. All I did was blip the throttle at the crest of the hill to encourage it on a bit. It did mean keeping a good look out for the speeds and positions of other traffic and the police.

When I kept the speeds legal I had to lose a lot of momentum by braking on the downhills and then using fuel to make the next climb. That lost a lot of efficiency.

On the flat though, speed is a big issue and the best economy was when there were road works on the motorway with long, flat sections at 40mph with average speed cameras. If it all ran that way there would be a huge saving for everyone. I would get over 100mpg for those sections in isolation. On other 40mph roads the speeds varied too much without the cameras and other drivers would be speeding up and slowing down all the time.

For fuel consumption I also found an open window was +10%, a roof rack left on was +15%, low tyre pressures was +5%, high tyre pressures was -7%, excess weight in the boot (200lbs of tools) +0% on motorway and +2% urban, climate control on or off made no difference as I think the compressor stays on regardless.

Interesting one was driving around with a damaged front wing, after another driver hit me, added about 6% to the fuel used. I tried to put in a claim for that but the insurance company would play ball.

[jim-frank]

janvos- I do the pulse portion in the minimum amount of time it takes to get to my target speed, which is the speed limit plus 5 mph. I then glide however long it takes to get to speed limit minus 5 mph.

Woodsmith-very interesting, thanks. Interestingly, my car shows no measurable difference in mpg with the driver's window down up to halfway. If I open it more than that, I get a very small reduction in mpg. The tire pressure makes a great difference, but I didn't see any reduction at excess overpressure. I run the tires at 45 psi; the rating on the sidewall is for 40psi.

MadisonMPG- slower will always lose less energy to aero losses, so it works better at lower speeds. Up tp a point, that is... I can't go much slower than 30 mph in fifth gear, for example. The best steady state mileage in fifth seems to be at about 40 mph, which might be some kind of efficiency peak vs RPM for the engine.

[blownb310]

Jim,

Do you have an underhood pic of the hot air setup you built?

Mike