24th Grade Science Fair

[grayden]

Experiment 1
Observation

Vehicle fuel efficiency is usually listed in two parts: highway average mileage and city average mileage. Two numbers are listed because each driving style involves very different acceleration and braking profiles. Highway miles are usually driven at a reasonably constant speed with only occasional need for acceleration

Comments

[green_jedi]

That is very cool :) I have been keeping fuel records as well, should take a look to see what they say.

How do you think the mileage you get out of your car compares to other cars being driven by your friends (and/or people in similar circumstances; I'm not trying to compare you with a Hummer!)? Is your car particularly fuel-efficient, particularly inefficient, or somewhat average?

[grayden]

I think my car is quite normal for its vehicle class, year, and power. Newer and smaller cars will get maybe another 5-10mpg.

[thpeech]

You could start a car-mileage-fuel-efficiency graph maker service. I also have data points over the life of 2 cars (in kilometres and litres, mind you). I'm sure it's not all that difficult to calculate the mileage per tank and amount of gas for each point, but I haven't been able to bring myself to sit down and do it.

How did that guy calculate instantaneous mileage? (Drove constantly at one speed, for half an hour, refilled and calculated?)

[grayden]

Many new cars can give you a readout of instantaneous mileage, because the car computer knows how fast you are going and exactly how much fuel the injectors are putting into the cylinders at any time. His method was to cruise at a constant speed, reset his average economy counter, and then drive for a while at that speed to smooth out blips.

[lynevere]

Ha. I totally made that first graph a year or two ago. The "time between fill ups" is a little skewed by work trips made via airplane, but the overall trend is seen.

Other things I like tracking via that data:
- I attempted to drive better after the fuel price increased, and I was able to average 35 mpg vs. 33 mpg on my commute.
- The depressing figure of total money spent on gas.

MPG going away soon?

[djohn89]

I used miles/gallon (MPG) measurements to diagnose problems with the exhaust system in a car I used to own. It was failing e-checks because it was emitting too much NOx, but its fuel efficiency was really good. After I replaced the cat, the NOx was acceptable but MPG was lower. :( I replaced an oxygen sensor and the MPG was acceptable.

PS - Congress has tried to pass bills that would tax miles driven instead of gallons of fuel purchased because hybrid and electric cars will become the norm, and current fuel taxes are inadequate to keep the roads repaired[1]. So would you rather pay tolls on every mile you drive (tracked by your own vehicle), every road you enter/exit (fares on privatized highways), or double the fuel taxes?

[1] Gasoline tax unable to fill federal highway fund's tank. Sunday, January 25, 2009. By Jon Schmitz, Pittsburgh Post-Gazette.