Theoretical gains from weight reduction and aero improvements

[RobertSmalls]

Originally Posted by PaleMelanesian

Why reinvent the wheel? We already have a tool that lets you quickly and easily calculate the impact of aero and weight (and many other) improvements.

Aerodynamic & rolling resistance, power & MPG calculator - EcoModder.com

The calculator is only for steady state (constant speed, constant elevation) cruising. It doesn't capture the benefits from reduced braking.

I'd like to know what percentage of one's energy one spends on braking, rolling, and aero. Maybe Bob Wilson knows. Or maybe I'll buy a datalogger for my car, after my mpguino arrives.

[saand]

cr45 i agree the influence on weight for P&G would be interesting to find out. If your particularly interested there is a thread on the calculator so you could either ask that the function you mention be included in the calculator or you could work it out yourself using the equations.

robert, i haven't seen any posts on any threads mentioning percentage of braking however as a general estimate for myself i rarely get to a stop light without having to use the brakes at around 40kph mostly because other drivers get annoyed if you slowly coast down to a stop light and some other reasons.
I have the ability to log my speed and instantanious fuel usage, if your after some data i can log that info on my standard trip to work and hopefully will be able to spot where braking is occuring. Let me know if you want me to post this info and will

[RobertSmalls]

Originally Posted by saand

I have the ability to log my speed and instantanious fuel usage, if your after some data i can log that info on my standard trip to work and hopefully will be able to spot where braking is occuring. Let me know if you want me to post this info and will

Please do. What's the highest sample rate you can achieve, btw?

[euromodder]

Originally Posted by saand

as a general estimate for myself i rarely get to a stop light without having to use the brakes at around 40kph mostly because other drivers get annoyed if you slowly coast down to a stop light and some other reasons.

They'll get the point when they don't have to stop for the light.

[saand]

my sampling rate is once a second, i shall get the data and post hopefully in a day or 2.

[saand]

Hi,
Sorry it has taken so long but i have the data requested
Here is a log from my drive home, its attached

I have numbered some interesting locations so that i can point out what actions were happening. They are as follows
1: Coasting down in speed in neutral (no break)
2: Breaking for lights from about 40kph to 0 kph
3: Coasting down in speed in neutral (no break), at the end of this coast down i went back into drive and accelerated
4: in neutral, going down a slight hill
5: Coasting down in speed in neutral (no break)
6: Breaking for lights from about 55kph to 0 kph
7: Stopped at lights for a while
8: Coasting down in speed in neutral (no break)
9: in gear, cornering maybe a little breaking but not sure
10: Coasting down in speed in neutral (no break)
11: Breaking for lights from about 60kph to 20 kph, lights changed then i went back into gear and kept going
12: slowing down in gear, no acceleration (i think, not too sure)
13: breaking for my drive way, 52 kph down to 5 kph

So that is it, my trip home from work.
Note: this was actually my most efficient trip home so usually there are more stops or just full stops rather than slowing down then the light changes and i keep going.

hope you get something from this.

[dennyt]

Cool plot! I can see your engine warming up, the idle fuel consumption goes down over time. It looks like an electric fan or AC is kicking on just after point 7.

Post a CSV so we can calculate an energy balance, or do it yourself. It would be interesting to plot energy-in (fuel ml/s * energy of combustion * some efficiency knockdown, make sure units are correct, multiply by the length of the time step to integrate), stored energy (mass of car * speed squared / 2, make sure units are correct; metric or slug-ft/s^2).

Then you can play around with "loss factors" to balance out the equation; Where is the energy going if it's not being stored in kinetic energy? Fit constant, linear vs. car speed, linear vs. engine speed, linear vs. fuel consumption rate (similar to BSFC), and quadratic vs. vehicle speed losses until the balance comes out to zero. This will be difficult to do, but educational I'm sure

[RobertSmalls]

Excellent plot.

Yes, I also wish to play with the raw data in .xls or .csv format. Also, what kind of tires do you have? What I really want to know is your CdA and CRR. Also, what's the total amount of distance covered and fuel used in the trip? It would be good to compare measurements from your odometer to your datalogger.

Btw, you can also calculate the amount of fuel you'd save with a kill switch.

Yep, this is worth firing up MATLAB for.

[busypaws]

Excel and Matlab are fun and if I didn't just spend all day in excel sheets I'd join in the fun.
Let's go back to the original question - "What will my fuel economy improve if I remove xxx weight?"

I would answer this way: Get enough milk jugs/soda bottles to equal the weight you are trying to remove. Removing 30 lbs -- get enough milk jugs to add 30 lbs. Over a week or two do your commute with and without the 30 extra lbs. Keep careful records, recording weather differences and unusual traffic differences. Now that you have many days of data average the days with and the days without the extra weight. Remove the unusual traffic days, remove commutes where engine was already up to temp because you ran an errand, remove days where you stopped at the store, etc. You want to be comparing average commute days with and without the extra weight.

Did you see a change? If so then you're most likely going to see a change if you remove the weight.

Only something above will account for that specific car and that specific commute and that specific driving habit.

P.S. It would be better if you could do a double blind study. Have your wife/significant other put the weight in the back seat with a towel over it. Then you don't know if you have a bunch of full milk jugs or empty ones and you won't subtly change your driving habits to get the answer you want.

[saand]

ok, raw data attached,
Note: i am not sure the injector time to fuel conversion is accurate i haven't looked into this in detail

feel free to play with the info as you see fit, i mostly use it to see where i can find the best gains, i have not tried to analyze in great detail.
Also if your all interested in getting your own data logged from your gauges there might be some ways to do it most likely with the mpguino as its open source software.

Robert, regarding my tires i just have my stock standard tires, they are not low rolling resistance or anything like that however they are pumped up to 45 psi (pressure has likely gone down since they were pumped up)
the total distance covered is according to the log 5.77km which is fairly accurate, the speedo and the speed logged are only out by a few kph.

Regarding kill switch, i would love to put one in but i do not have an manual so i cant bump start and i dont want to ever get in the situation where my car wont restart, i have already lowered my idle as low as it can go because i get gains at traffic lights and while coasting but i would love to turn my engine off if i could.
enjoy matlab, i try to avoid matlab at all costs unless i am doing specialized engineering calcs or want 3d graphs

busypaws, regarding your test suggestion its a good idea however i am fairly sure that the efficiency increase is so low that it will be within the noise of normal day to day driving. From my attempts at testing improvements seems like anything below 1% change is very hard to accurately test. So this is why i did the theoretical calcs