Post by thread:[OT] ?: fluid measurement

Sorry, I accidentally deleted the original message. Pasi has been asking for a "new" way to measure fuel flow in his car. OK, so how about this? A while ago we were discussing a non-invasive fluid flow measuring technique here on the PICLIST. The idea was that ultrasonic sound was injected into a pipe or hose, and upline and downline sensors measured the intensity of that signal a short distance from the source. By comparing the relative intensities from the two pickup sensors, the flow direction and speed can be accurately determined since sound transfer will improve in the direction of the flow, and decrease in the opposite direction. Even though you are only interested in unidirectional flow, you would still probably need two pickup sensors since the calculations are done with relative values, not absolute ones. Different enough for you? Martin R. Green spam_OUTelimarTakeThisOuTbigfoot.com

> OK, so how about this? A while ago we were discussing a non-invasive fluid > flow measuring technique here on the PICLIST. The idea was that ultrasonic > sound was injected into a pipe or hose, and upline and downline sensors > measured the intensity of that signal a short distance from the source. By > comparing the relative intensities from the two pickup sensors, the flow > direction and speed can be accurately determined since sound transfer will > improve in the direction of the flow, and decrease in the opposite > direction. I would think accurate correlation between signal strength and fluid velocity would be difficult. Would it not be better to measure travel time through the liquid? The difference between upstream and downstream travel times should be easily detectable and should easily correlate with the speed of the liquid.

Maybe not digital, but what about the analog MPG meters that BMW's have had just below the speedometer for as long as can remember. I'm pretty sure these existed before FI replaced carburation on BMW's, maybe not. Anyway, these meters respond very quickly to driving conditions. Any idea if these used a flow gauge? Martin R. Green .....elimarKILLspam@spam@bigfoot.com ---------- From: Andrew Warren[SMTP:fastfwdKILLspamIX.NETCOM.COM] Sent: Saturday, September 27, 1997 6:53 AM To: .....PICLISTKILLspam.....mitvma.mit.edu Subject: Re: ?: fluid measurement <SNIP> > - not all emission-controlled cars are injected - some are > conventional carburettors. True... And if you can find a carbed car with a digital fuel-consumption display, I'll buy a beer at the Embedded Systems Conference and MAIL it to you. > For a mass-produced item like a car, is a flow-meter really > expensive? (lets ignore rip-off spare parts prices, I'm thinking > cost) <SNIP> I didn't mean to imply that injector-pulse measurement was the ONLY way (or even necessarily the best way); I was just saying that I don't believe that EXISTING fuel-consumption displays use anything more complicated than that pulse-measurement... It doesn't seem reasonable to me that an auto manufacturer would burden its cars with the cost of ANY extra hardware just to provide a function as minor as a fuel-consumption display. The fact that fuel-consumption displays seemed to appear right around the same time that microprocessor-controlled fuel injection became commonly available, AND the fact that I've never seen a fuel-flow meter on an automobile engine, AND the fact that I know of no carbureted cars that provide a digital fuel-consumption display, would seem to bear out my hypothesis that the fuel-consumption "measurement" is handled indirectly by a software-only process that just looks at injector pulse-widths. Just my opinion, of course... I could be wrong. -Andy === Meet other PICLIST members at the Embedded Systems Conference: === 6:30 pm on Wednesday, 1 October, at Bytecraft Limited's booth. === === For more information on the Embedded Systems Conference, === see: http://www.embedsyscon.com/ === Andrew Warren - EraseMEfastfwdspam_OUTTakeThisOuTix.netcom.com === Fast Forward Engineering - Vista, California === http://www.geocities.com/SiliconValley/2499

> Maybe not digital, but what about the analog MPG meters that BMW's have had > just below the speedometer for as long as can remember. I'm pretty sure > these existed before FI replaced carburation on BMW's, maybe not. Anyway, > these meters respond very quickly to driving conditions. Any idea if these > used a flow gauge? > These, as do most "economy guages" use a pressure sensor on the vacuum line of the engine. The harder the engine work the higher the vacuum. Very imperic. Nic

Martin R. Green wrote: > Maybe not digital, but what about the analog MPG meters that BMW's have had > just below the speedometer for as long as can remember. I'm pretty sure > these existed before FI replaced carburation on BMW's, maybe not. Anyway, > these meters respond very quickly to driving conditions. Any idea if these > used a flow gauge? All the BMW MPG gauges I've seen (I don't personally own one, and wouldn't) were just variations of the old manifold vacuum gauges. Not too exciting, really. Tom Rogers VP-R&D Time Tech Inc.

>> Maybe not digital, but what about the analog MPG meters that BMW's have had >> just below the speedometer for as long as can remember. I'm pretty sure >> these existed before FI replaced carburation on BMW's, maybe not. Anyway, >> these meters respond very quickly to driving conditions. Any idea if these >> used a flow gauge? >These, as do most "economy guages" use a pressure sensor on the >vacuum line of the engine. The harder the engine work the higher the >vacuum. Very imperic. Do you mean "less pressure" when you say "higher vacuum"? If so, you are mistaken. If the engine works harder you get MORE pressure in the intake manifold. Just think of it, when you step on the loud pedal you open the air intake valve to allow more air into the engine. More air -> Higher pressure. On a regular suction engine this pressure will be approx 1 bar, equal to the pressure of the outside air. The above is not true when it comes to turbo or compressor charged engines. -Oyvind

I wrote: > >These, as do most "economy gauges" use a pressure sensor on the > >vacuum line of the engine. The harder the engine work the higher the > >vacuum. Very imperic. -Oyvind replied > > Do you mean "less pressure" when you say "higher vacuum"? > If so, you are mistaken. > > If the engine works harder you get MORE pressure in the intake > manifold. > > Just think of it, when you step on the loud pedal you open the air > intake valve to allow more air into the engine. More air -> Higher pressure. Faster airflow -> lower pressure ! In the manifold that is. > On a regular suction engine this pressure will be approx 1 bar, equal to > the pressure of the outside air. > > The above is not true when it comes to turbo or compressor charged engines. y

At 01:41 PM 9/30/97 +0000, you wrote: >I wrote: >> >These, as do most "economy gauges" use a pressure sensor on the >> >vacuum line of the engine. The harder the engine work the higher the >> >vacuum. Very imperic. > > -Oyvind replied > > >> Do you mean "less pressure" when you say "higher vacuum"? >> If so, you are mistaken. >> >> If the engine works harder you get MORE pressure in the intake >> manifold. >> >> Just think of it, when you step on the loud pedal you open the air >> intake valve to allow more air into the engine. More air -> Higher pressure. > >Faster airflow -> lower pressure ! In the manifold that is. > >> On a regular suction engine this pressure will be approx 1 bar, equal to >> the pressure of the outside air. >> >> The above is not true when it comes to turbo or compressor charged engines. >y > I don't know the exact reason, but on regular carburated engines, intake manifold pressure increases with throttle setting, but goes to 1 bar(29.92 inHG) when the engine is off. (Obviously, it must return to atmospheric press when engine is not doing anything to the air in the manifold). Sean Sean Breheny,KA3YXM Electrical Engineering Student

> I don't know the exact reason, but on regular carburated engines, intake > manifold pressure increases with throttle setting, but goes to 1 bar(29.92 > inHG) when the engine is off. (Obviously, it must return to atmospheric > press when engine is not doing anything to the air in the manifold). How do they manage that? It would seem to me to violate the Bournoulli (sp?) principle. The faster the piston sucks in air the lower pressure the intake air must be in order to force it to move faster. (No, that isn't a quote of the principle, that is the intuitive affect it would have in this case.) Actually, if you want to answer me feel free to go to direct e-mail. Roger

>> True... And if you can find a carbed car with a digital >> fuel-consumption display, > Maybe not digital, but what about the analog MPG meters that > BMW's have had just below the speedometer for as long as can > remember. I'm pretty sure these existed before FI replaced > carburation on BMW's, maybe not. The Pontiac Grand Prix had a fuel economy gauge back in 1963 (on carburated engines). Possibly earlier too but the gauge I've got in my garage is from a '63 model. It had no connection to the fuel flow per se. It measured manifold vacuum. Lee Jones

>> >These, as do most "economy gauges" use a pressure sensor on the >> >vacuum line of the engine. The harder the engine work the higher the >> >vacuum. Very imperic. > -Oyvind replied > > >> Do you mean "less pressure" when you say "higher vacuum"? >> If so, you are mistaken. >> >> If the engine works harder you get MORE pressure in the intake >> manifold. >> >> Just think of it, when you step on the loud pedal you open the air >> intake valve to allow more air into the engine. More air -> Higher pressure. >Faster airflow -> lower pressure ! In the manifold that is. Consider this situation: A regular carbureted engine is driving uphill at a moderate speed (constant) and with a medium throttle setting. In the intake manifold we have, say 0.7 bar. Then the driver open up the intake valve by applying full throttle. The pressure in the manifold now increase to, say 0.9 bar. Why? This happens because the pistons are moving with the same speed as before the throttle was applied, but the air intake is now wide open. If you have ever looked at a regular vacuum economy gauge, you must have noticed that it will show "good economy" when running at idle, but if you stop the engine it will show "bad economy".. There is no doubt that the pressure in the intake manifold is 1 bar with the engine stopped..? There is also no doubt that the pressure is less than 1 bar when running at idle? Still disagree? -Oyvind

On 2 Oct 97 at 8:21, Oyvind Kaurstad wrote: > >> >These, as do most "economy gauges" use a pressure sensor on the > >> >vacuum line of the engine. The harder the engine work the higher the > >> >vacuum. Very imperic. > > > -Oyvind replied > > > > >> Do you mean "less pressure" when you say "higher vacuum"? > >> If so, you are mistaken. > >> > >> If the engine works harder you get MORE pressure in the intake > >> manifold. > >> > >> Just think of it, when you step on the loud pedal you open the air > >> intake valve to allow more air into the engine. More air -> Higher pressure. {Quote hidden}> > >Faster airflow -> lower pressure ! In the manifold that is. > > Consider this situation: > > A regular carbureted engine is driving uphill at a moderate speed > (constant) and with a medium throttle setting. > > In the intake manifold we have, say 0.7 bar. > > Then the driver open up the intake valve by applying full throttle. > The pressure in the manifold now increase to, say 0.9 bar. > > Why? > > This happens because the pistons are moving with the same speed as > before the throttle was applied, but the air intake is now wide > open. > > If you have ever looked at a regular vacuum economy gauge, you > must have noticed that it will show "good economy" when running at > idle, but if you stop the engine it will show "bad economy".. > > There is no doubt that the pressure in the intake manifold is 1 bar > with the engine stopped..? > > There is also no doubt that the pressure is less than 1 bar when > running at idle? > > Still disagree? > The so called 'Economy Gauges' are a total waste of time - they flop backwards and forwards crazily. The tendency of car makers to omit RPM gauges in favour of theses devices is idiotic - a car computer might make sense of manifold pressure, but its useless info to a person. MikeS <mikesmith_ozNOSP*M.relaymail.net> (remove the you know what before replying)

>> >> >These, as do most "economy gauges" use a pressure sensor on the >> >> >vacuum line of the engine. The harder the engine work the higher the >> >> >vacuum. Very imperic. >> >> > -Oyvind replied >> > > >> >> Do you mean "less pressure" when you say "higher vacuum"? >> >> If so, you are mistaken. >> >> >> >> If the engine works harder you get MORE pressure in the intake >> >> manifold. >> >> >> >> Just think of it, when you step on the loud pedal you open the air >> >> intake valve to allow more air into the engine. More air -> Higher > pressure. >> [Snip] {Quote hidden}>> There is also no doubt that the pressure is less than 1 bar when >> running at idle? >> >> Still disagree? >> >The so called 'Economy Gauges' are a total waste of time - they flop >backwards and forwards crazily. The tendency of car makers to omit >RPM gauges in favour of theses devices is idiotic - a car computer >might make sense of manifold pressure, but its useless info to a >person. Yes, I totally agree with you. The principle is more or less correct, but the output (visual) is not directly proportional to fuel consumption, and it has no relation to mpg. But it does tell you what happens with the pressure in the intake manifold when applying throttle, and that's what I'm discussing. -Oyvind