measuring fuel efficiency
in [Design]
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From: Jim Thompson on 10 Aug 2010 20:02 On Tue, 10 Aug 2010 16:25:35 -0700, Tim Wescott <tim(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. > >"Distance to empty" would require an accurate fuel sensor, but the other >two could just come from the odometer and the fuel flow. I doubt (3), probably (1) because... Take as rough guesstimates: 40MPG, 40MPH, 2000RPM... 4000 "squirts" per minute, each only 0.016mL in volume. Injector isn't that precise, but is tweaked via PWM using O2 sensor to maintain stoichiometric mix. The first "miles-to-go" stuff I worked on (probably ~40 years ago) used a calibrated tank float. My 2� worth :-) ...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 | Spice is like a sports car... Performance only as good as the person behind the wheel.
From: tm on 10 Aug 2010 20:32 "Jim Thompson" <To-Email-Use-The-Envelope-Icon(a)On-My-Web-Site.com> wrote in message news:9np366hmld66o0ailu87lv23n1kctvqj57(a)4ax.com... > On Tue, 10 Aug 2010 16:25:35 -0700, Tim Wescott <tim(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. >> >>"Distance to empty" would require an accurate fuel sensor, but the other >>two could just come from the odometer and the fuel flow. > > I doubt (3), probably (1) because... > > Take as rough guesstimates: 40MPG, 40MPH, 2000RPM... 4000 "squirts" > per minute, each only 0.016mL in volume. Injector isn't that precise, > but is tweaked via PWM using O2 sensor to maintain stoichiometric mix. > > The first "miles-to-go" stuff I worked on (probably ~40 years ago) > used a calibrated tank float. > > My 2� worth :-) > > ...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 | > > Spice is like a sports car... > Performance only as good as the person behind the wheel. It uses #3 by using the injector pulse width and the rate (from the RPM). I have one of the Scan Gauge units that connects to the ODB port and that is how it works. You get instantaneous and average MPG readings. tm --- news://freenews.netfront.net/ - complaints: news(a)netfront.net ---
From: Michael on 10 Aug 2010 21:53 On Aug 10, 8:32 pm, "tm" <the_obamun...(a)whitehouse.gov> wrote: > "Jim Thompson" <To-Email-Use-The-Envelope-I...(a)On-My-Web-Site.com> wrote in > messagenews:9np366hmld66o0ailu87lv23n1kctvqj57(a)4ax.com... > > > > > On Tue, 10 Aug 2010 16:25:35 -0700, 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. > > >>"Distance to empty" would require an accurate fuel sensor, but the other > >>two could just come from the odometer and the fuel flow. > > > I doubt (3), probably (1) because... > > > Take as rough guesstimates: 40MPG, 40MPH, 2000RPM... 4000 "squirts" > > per minute, each only 0.016mL in volume. Injector isn't that precise, > > but is tweaked via PWM using O2 sensor to maintain stoichiometric mix. > > > The first "miles-to-go" stuff I worked on (probably ~40 years ago) > > used a calibrated tank float. > > > My 2¢ worth :-) > > > ...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 athttp://www.analog-innovations.com| 1962 | > > > Spice is like a sports car... > > Performance only as good as the person behind the wheel. > > It uses #3 by using the injector pulse width and the rate (from the RPM). I > have > one of the Scan Gauge units that connects to the ODB port and that is how it > works. > You get instantaneous and average MPG readings. > > tm > > --- news://freenews.netfront.net/ - complaints: n...(a)netfront.net --- ODB reading is probably coming from car computer. There is no accuracy to talk about unless "squirt" volume is known. The car has mpg gauge that is very (overly) sensitive to gas pedal, road incline, etc. It makes me think that they measure flow, not gas level in the tank (it is needed as "reference point"). I just learned that there are so many ways to measure the flow: http://www.engineeringtoolbox.com/flow-meters-d_493.html ... The turbine flow meter seems to be the most accurate. I would think that this is the way to go. BUT... How does gasoline viscosity depend on temperature? Diesel (and vodka) get really viscous when cold. Is it another engineering challenge?
From: linnix on 11 Aug 2010 00:52 On Aug 10, 6:53 pm, Michael <mk5...(a)yahoo.com> wrote: > On Aug 10, 8:32 pm, "tm" <the_obamun...(a)whitehouse.gov> wrote: > > > > > "Jim Thompson" <To-Email-Use-The-Envelope-I...(a)On-My-Web-Site.com> wrote in > > messagenews:9np366hmld66o0ailu87lv23n1kctvqj57(a)4ax.com... > > > > On Tue, 10 Aug 2010 16:25:35 -0700, 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. > > > >>"Distance to empty" would require an accurate fuel sensor, but the other > > >>two could just come from the odometer and the fuel flow. > > > > I doubt (3), probably (1) because... > > > > Take as rough guesstimates: 40MPG, 40MPH, 2000RPM... 4000 "squirts" > > > per minute, each only 0.016mL in volume. Injector isn't that precise, > > > but is tweaked via PWM using O2 sensor to maintain stoichiometric mix.. > > > > The first "miles-to-go" stuff I worked on (probably ~40 years ago) > > > used a calibrated tank float. > > > > My 2¢ worth :-) > > > > ...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 athttp://www.analog-innovations.com| 1962 | > > > > Spice is like a sports car... > > > Performance only as good as the person behind the wheel. > > > It uses #3 by using the injector pulse width and the rate (from the RPM). I > > have > > one of the Scan Gauge units that connects to the ODB port and that is how it > > works. > > You get instantaneous and average MPG readings. > > > tm > > > --- news://freenews.netfront.net/ - complaints: n...(a)netfront.net --- > > ODB reading is probably coming from car computer. There is no accuracy > to talk about unless "squirt" volume is known. > The car has mpg gauge that is very (overly) sensitive to gas pedal, > road incline, etc. It makes me think that they measure flow, not gas > level in the tank (it is needed as "reference point"). > I just learned that there are so many ways to measure the flow:http://www..engineeringtoolbox.com/flow-meters-d_493.html... The > turbine flow meter seems to be the most accurate. > I would think that this is the way to go. BUT... How does gasoline > viscosity depend on temperature? Diesel (and vodka) get really viscous > when cold. Is it another engineering challenge? From floscan.com, at least that many are in use: International leaders in fuel flow technology We've been connected to some well-known engines. FloScan is the world's #1 producer of fuel flow sensor systems - over 500,000 used on cars, trucks, boats, and airplanes. (As a matter of fact, we invented them for each of these industries). Mercury Marine uses our fuel flow instruments to test engines. So does Power and Motoryacht Magazine for their boat test reports. Over the road, in the air There are more than 100,000 FloScan sensors aboard such aircraft as Cessna, Piper, and Beechcraft, and such trucks as Kenworth, Peterbilt, Freightliner, and International. Remember in 1986, the record- breaking, non-stop, around-the-world flight of the "Voyager'" in which error-free fuel monitoring was absolutely paramount to the mission? Pilots Yeager and Rutan were guided by FloScan fuel flow meters. We'll give you the same security at sea. Whether you're fishing the Canyons, the Keys, Cabo, Catalina, or the Kenai, FloScan can extend your range and give you peace of mind - with an instrument that pays for itself.
From: Nial Stewart on 11 Aug 2010 06:50
> Over the road, in the air > There are more than 100,000 FloScan sensors aboard such aircraft as > Cessna, Piper, and Beechcraft, and such trucks as Kenworth, Peterbilt, > Freightliner, and International. 'High end' and safety critical vehicles probably use flow meters, but normal consumer cars mostly use injector on times. Nial. |