Pulse and Glide Fuel Economy Calculator 4 valve / Cylinder

[newtonsfirstlaw]

Originally Posted by MetroMPG

I'm OK with the kludge, too. Will report in later.

For "rpm at actual speed" of 3000 or less, adding 0.03 would probably work ok.

[MetroMPG]

Here's a question: it looks like the calcs are based solely on top gear, correct?

According to the spreadsheet, with all my vehicle's data plugged in, I can theoretically get 132 mpg (US) / 1.78 L/100km at an average P&G speed of 40 km/h, with a total 30 km/h speed delta.

And you know what? That's almost bang on what I observed in those conditions. I did just that one day this summer in my car on an ideal route (a ring road) and after several loops, was averaging 129 mpg (US).

The major difference was that I was pulsing in 2nd and 3rd gears, not 5th.

Cool stuff.

[Lazarus]

Does it matter if the car has a automatic transmission for the worksheet?

[newtonsfirstlaw]

Originally Posted by Lazarus

Does it matter if the car has a automatic transmission for the worksheet?

Shouldn't think so provided that the rolling resistance is similar to a manual (i.e. a function of tires and wheel bearings only, and not the trans).

[newtonsfirstlaw]

Originally Posted by MetroMPG

Here's a question: it looks like the calcs are based solely on top gear, correct?

In devising the spreadsheet, I assume that you can hit BSFC(minimum) if you are below the speed at which you will hit BSFC(minimum) in top gear. You have 4 gears to do this with, so it's not a bad assumption. It'll be near enough.

Above that speed, the BSFC is the best you can do for that rpm in top gear.

The major difference was that I was pulsing in 2nd and 3rd gears, not 5th.

As explained above, it should work at all reasonable speeds you'd pulse and glide with, assuming you accelerate at 62% of BMEP available at that rpm, that you choose the gear that will enable you to get closest to BSFC(minimum), and that the glide speed drop is not too large (it uses air resistance calculated at the average speed, so if you give it a pulse to take you up to a high speed, most of that energy is wasted in pushing wind). It also assumes that most cars don't deviate much from these maps.

You can't achieve peak FE without P&G, and current instantaneous FE meters will not teach you how to P&G properly. Instead, you learn to accelerate anemically in all circumstances.

That's where this spreadsheet comes in - you can fiddle with variables and see what is theoretically achievable with your car, before you spend money and time on building something, and also how you will have to drive to get those benefits. Then you go do it, and confirm it.

Cool stuff.

I thought so, just needed some people to play with it. It appears to be in the ballpark for my car, but I wanted some confirmation. Thanks for providing some! It's gratifying that it appears to be working so well. Provided I've got the equations right, it should work. Newtonian mechanics works just dandy at those speeds, and all we are doing is calculating fuel used in a pulse, fuel used in a glide, and the distances traveled in each to come up with a distance/fuel figure.

After that, we are relying on the particular engine maps (which were an average of several manufacturers' cars) being applicable to our cars, my assumptions as listed in the first paragraph, and that my line of best fit is good. I double checked things as I went.

I'd love to get ahold of all the coordinates of the original engine maps, then I could have it instantly calculate steady state FE for a comparison. One thing at a time.

[RH77]

Excellent system of algorithms. As a un-educated American, it takes a little longer to convert from darn English system. Enter Metric rant here -- we should have it as the everyday standard here. Now, to convert how many KW the 'Teg has.... I'll get it eventually...

Excellent work, however!

Cheers.

RH77

[newtonsfirstlaw]

Originally Posted by RH77

Excellent system of algorithms. As a un-educated American, it takes a little longer to convert from darn English system. Enter Metric rant here -- we should have it as the everyday standard here. Now, to convert how many KW the 'Teg has.... I'll get it eventually...

Thanks, I should really have added the conversions to the spreadsheets, considering my audience. I was just so glad to get it working and get others to share in the joy of seeing where the gains can be had.

One thing I have to wonder though is if I am forgetting accessories (alternator etc) in the equations.

[Lazarus]

Originally Posted by RH77

Excellent system of algorithms. As a un-educated American, it takes a little longer to convert from darn English system. Enter Metric rant here -- we should have it as the everyday standard here. Now, to convert how many KW the 'Teg has.... I'll get it eventually...

Excellent work, however!

Cheers.

RH77

I think it's outstanding also. I'm struggling with the conversions too. Dang American System. Rick try here. I think your 106KW.
What's a frontal area of 20 sq ft = to

[MetroMPG]

Google does conversions. Just enter "N hp to kW" in the search box. (Or any other units.)

Originally Posted by newtonsfirstlaw

One thing I have to wonder though is if I am forgetting accessories (alternator etc) in the equations.

Good point - for the figures I quoted comparing the spreadsheet output vs. real life, the alternator was in fact disconnected at the time.

[newtonsfirstlaw]

Originally Posted by MetroMPG

Good point - for the figures I quoted comparing the spreadsheet output vs. real life, the alternator was in fact disconnected at the time.

You know what... I suspect that the default on parasitic loads may not really matter that much, depending on how long your respective pulse and glide times are. The idle fuel burn rate incorporates those loads, so if your pulse time is short, you could effectively ignore calculating them during the pulse. But it would be simple to include an alternator load in there.

Obviously A/C makes a big difference and you can expect your FE to suck (technical term) with the use of such a device.

Another thing is if claims of companies like Synlube are to be believed, you can improve BSFC some small fraction, possibly dependent on rpm and perhaps load. It can also be added to wheel bearings etc, which would decrease Crr.

I made a mistake I think when I said automatics would have no issues, there are transmission losses to contend with. From what I remember, 8% is the figure generally given. So your BSFC would be reduced by 8% during the pulse. It would be helpful for someone more familiar with transmissions to comment here.

BTW I wrote the authors of that paper asking if they had the original data for those graphs. We'll see if I get a response.