measuring fuel efficiency
in [Design]
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From: Rich Grise on 11 Aug 2010 20:24 On Tue, 10 Aug 2010 16:16:45 -0700, Michael wrote: > Nowadays even economy cars (e.g.: 2010 Sentra) measure gas flow and > whatever may be derived from it (mpg, average mpg, "distance to empty" > etc). How do they do it? My (uneducated)guess is either of the > following : > 1. accurate level meter in the gas tank (accuracy may be affected by > temperature and pressure - the tank is not stiff) > 2. flow meter (how accurate are those things??) > 3. count number of fuel injectors squirts (how accurate/repeatable is > the squirt size?) > Any comments/ideas/suggestions/referrals to articles will be > appreciated 1. Fill up the gas tank at a certain pump at a certain station, just until the nozzle clicks off - don't top it up. Record the mileage from the odometer. 2. Drive. Note driving conditions, if desired for more granularity in your mileage assessment. ;-) 3. Fill up again at the same station and pump, again just until the nozzle clicks off. Note gallons. 4. Subtract previous mileage (see step one) from current mileage. 5. Do the math. ;-) Cheers! Rich
From: Joel Koltner on 11 Aug 2010 21:38 "Rich Grise" <richgrise(a)example.net> wrote in message news:pan.2010.08.12.00.24.08.626089(a)example.net... > 1. Fill up the gas tank at a certain pump at a certain station, just until > the nozzle clicks off - don't top it up. Record the mileage from the > odometer. > 2. Drive. Note driving conditions, if desired for more granularity in your > mileage assessment. ;-) > 3. Fill up again at the same station and pump, again just until the nozzle > clicks off. Note gallons. > 4. Subtract previous mileage (see step one) from current mileage. > 5. Do the math. ;-) The more interesting question is how accurate the results are with a random select of stations and pumps, since this is what the vast majority of people use...
From: Jim Thompson on 11 Aug 2010 23:38 On Wed, 11 Aug 2010 18:38:37 -0700, "Joel Koltner" <zapwireDASHgroups(a)yahoo.com> wrote: >"Rich Grise" <richgrise(a)example.net> wrote in message >news:pan.2010.08.12.00.24.08.626089(a)example.net... >> 1. Fill up the gas tank at a certain pump at a certain station, just until >> the nozzle clicks off - don't top it up. Record the mileage from the >> odometer. >> 2. Drive. Note driving conditions, if desired for more granularity in your >> mileage assessment. ;-) >> 3. Fill up again at the same station and pump, again just until the nozzle >> clicks off. Note gallons. >> 4. Subtract previous mileage (see step one) from current mileage. >> 5. Do the math. ;-) > >The more interesting question is how accurate the results are with a random >select of stations and pumps, since this is what the vast majority of people >use... I think station pumps are quite accurate, at least in those states that penalize heavily for inaccurate delivery... like AZ :-) ...Jim Thompson -- | James E.Thompson, CTO | mens | | Analog Innovations, Inc. | et | | Analog/Mixed-Signal ASIC's and Discrete Systems | manus | | Phoenix, Arizona 85048 Skype: Contacts Only | | | Voice:(480)460-2350 Fax: Available upon request | Brass Rat | | E-mail Icon at http://www.analog-innovations.com | 1962 | Harry Reid says... I don't know how anyone of Hispanic heritage could be a Republican I observe... We don't know how anyone of legitimate parentage can be a Democrat
From: Ken S. Tucker on 11 Aug 2010 23:45 On Aug 10, 4:25 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: > On 08/10/2010 04:16 PM, Michael wrote: > > > Nowadays even economy cars (e.g.: 2010 Sentra) measure gas flow and > > whatever may be derived from it (mpg, average mpg, "distance to empty" > > etc). How do they do it? My (uneducated)guess is either of the > > following : > > 1. accurate level meter in the gas tank (accuracy may be affected by > > temperature and pressure - the tank is not stiff) > > 2. flow meter (how accurate are those things??) > > 3. count number of fuel injectors squirts (how accurate/repeatable is > > the squirt size?) > > Any comments/ideas/suggestions/referrals to articles will be > > appreciated > > P.S.: I understand that this is not automotive group, but it's the one > > I regularly visit. Engineers are engineers after all. > > I would guess 3, because for the EFI to work correctly the squirt size > _must_ be highly repeatable (and easily controllable), and is probably > at least fairly accurate. So the only thing that stands between you and > a fuel consumption estimate is software. We have a tachometer, so would it follow that "squirts" are proportional to rpm, assuming 1 squirt for every two revolutions in a 4 cycle motor. Not sure though. Ken
From: Ken S. Tucker on 12 Aug 2010 00:03
On Aug 11, 8:45 pm, "Ken S. Tucker" <dynam...(a)vianet.on.ca> wrote: > On Aug 10, 4:25 pm, Tim Wescott <t...(a)seemywebsite.com> wrote: > > > > > On 08/10/2010 04:16 PM, Michael wrote: > > > > Nowadays even economy cars (e.g.: 2010 Sentra) measure gas flow and > > > whatever may be derived from it (mpg, average mpg, "distance to empty" > > > etc). How do they do it? My (uneducated)guess is either of the > > > following : > > > 1. accurate level meter in the gas tank (accuracy may be affected by > > > temperature and pressure - the tank is not stiff) > > > 2. flow meter (how accurate are those things??) > > > 3. count number of fuel injectors squirts (how accurate/repeatable is > > > the squirt size?) > > > Any comments/ideas/suggestions/referrals to articles will be > > > appreciated > > > P.S.: I understand that this is not automotive group, but it's the one > > > I regularly visit. Engineers are engineers after all. > > > I would guess 3, because for the EFI to work correctly the squirt size > > _must_ be highly repeatable (and easily controllable), and is probably > > at least fairly accurate. So the only thing that stands between you and > > a fuel consumption estimate is software. > > We have a tachometer, so would it follow that "squirts" are > proportional > to rpm, assuming 1 squirt for every two revolutions in a 4 cycle > motor. > Not sure though. > Ken Here's something that might help, http://en.wikipedia.org/wiki/Fuel_injection#Calculate_fuel-flow_rate_from_pulsewidth Ken |