Fuel Flow Meter

[dubbleUJay]

This is a 2-part question, 1 mechanical, but I thought to place both here:

1st) I've connected a clear piece of PVC pipe on a retort stand to measure WVO usage over time. I noticed then that there is a huge pulsating effect coming from the Lister CS fuel pump, squirting fuel back in the opposite direction while running. Is this normal and would a check valve in line to prevent this be a problem? In other words, where would the excess fuel go if it cannot go back the pipe I'll hate to try and read the flow rate on the High Pressure fuel line side!

2ndly) I ask this 'cos I want to measure fuel flow with some type of sensor and I think this might affect it or more accurately, make the sensor that compensate for this, more expensive!
To the question, does anyone know of a production vehicle that might have a fuel flow meter installed? I presume some fuel injection units might have them, so that I can look at the junkyards for one to use

Thanks guys,
dubbleUJay

[mobile_bob]

good luck with measureing fuel flow on your engine, you have the return line coming
off the injector to contend with and between all the interactions and the fact that
the flow rate is so low,, i just don't see it happening with any degree of accuracy

now if you are using a day tank, perhaps you can measure fuel rate of consumption by
weight, which would be far more accurate in my opinion anyway.

measureing by weight and not by volume is the great equalizer of fuels, and where the rubber
meets the road in getting really good test results,

so if you are going to go to the trouble, and given the fact that this is a stationary application
it seems to me that logging by weight would be not only easier but more accurate.

thats the way i see it, ymmv of course

bob g

[dubbleUJay]

BobG, I want to measure short runs, so I've got to see if I can measure it accurately electronically. I can probably use 2 sensors (Supply & Spill) and subtract the 2 values from each other, but the big problem will be the cost of such accurate sensors. (800ml of diesel for a hour = approx. a flow rate of 10ml/min) Before you say anything about the figure, its just a ball park I've got in mind!
Weighing the fuel like you said will be the answer, but how to implement it electronically in real time

dubbleUJay

[mobile_bob]

why not sample the weight, and log the value
sample again in perhaps 6 sec, and log that value
subtract one from the other and multiply x 10 or whatever
to get the value used over time?
that of course could be factored by the amount of power generated to get
a bsfc in gr/kw/hr.

or so it would seem to me, especially for you fella's that are intent on automating these things
and programming far above my ability or desire to learn.

in reality something like that would have to happen if you were to do it with a flowmeter anyway
a flowmeter telling you the amount of fuel passing the line is useless without being factored against
time and load, would it not?

a flow meter that simply states 5 gallons have passed doen't really tell me much, without knowing
how long it took to pass, and under what load the engine was under.

so even if you use load you still have to have a start value, a timed event, and end value, and computation
made to determine the volume that has passed, then factor that against load and some sort of time multiplier to
make it work out in some meaningful value.

or so it would seem to me.

it just seems to me if i were to go to all the trouble to work out all the programming and hardware, i would at least
look into using weight instead of volume because weight of the fuel is much more useful than volume, volume changes with
temperature and the btu content is largely unaccounted for.

weight seems to account for temp and btu fluctuations of the fuel to a large extent.

thoughts?

bob g

[billswan]

dubbleUJay

I doubt you will find a fuel flow meter in any junk vehicle. The cars that have mileage computers use the pulse width signal off the fuel injectors to calculate fuel use against time and miles driven. Anyway that is how I understand the system, could be wrong though.

I voter with bob, balance your fuel tank on a weigh bar and go with that.

Billswan

[dubbleUJay]

a flow meter that simply states 5 gallons have passed doen't really tell me much, without knowing
how long it took to pass, and under what load the engine was under.

thoughts?

Yes Bob, your right on, the time and load will be available with the other sensors in my setup and from there the calculation will be made.
I have to way up the cost against accuracy though, I can buy a commercial one for more than the whole system is worth, but on the other hand I need acceptable accuracy. A difficult one, but maybe a crude meter can be calibrated with a few test runs by entering a constant into the computed formula. I just dont know at this stage.

Your weighing idea will still be the best I think, but one would have to make some sort of inline device that would hold say 1kg of fuel and then auto-fill itself when empty for long runs or just have a separate container on an electronic scale type setup, probably a strain gauge to interface to the rest of the system.
Its probably impractical to way a large amount of fuel.
Still, if a VW Jetta or BMW315i had something like a fuel flow sensor in them, it could be calibrated with software to give very close reading I would think.
I just don't have any knowledge if any oldish vehicles had them in

dubbleUJay

[dubbleUJay]

dubbleUJay

I doubt you will find a fuel flow meter in any junk vehicle. The cars that have mileage computers use the pulse width signal off the fuel injectors to calculate fuel use against time and miles driven. Anyway that is how I understand the system, could be wrong though.
Billswan

Billswan, thanks, I'm also not sure how they do it, but then they must know how much fuel are being released with a given pulse duration or "voltage", again a set number they must put into the calculations.
Well there goes the easy way out
Weighing will involve quite a bit of hardware, not the electronic type, but the scale mechanism. 
I'll probably leave this for one of the last things to impliment for my project.
Thanks for all the input guys.
dubbleUJay

[dubbleUJay]

Jens, would using a very small ID supply pipe not give more "detectable" flow
Obviously up to the point that the fuel will actually gravity feed.

dubbleUJay

[dubbleUJay]

I did the same as you this morning, looked all over for meters and came up with nothing! 

I did get DIY circuits for ultrasonic and magnetic sensors, I'll look at them again. From there the 1st question about the pulsating fuel in the line going back and forth! I doubt that they would be accurate though.

[mobile_bob]

here is a possible solution to the problem/project

use a small tank, that can either be weighed or of suitable volume

decide which you would rather measure, volume or weight

we will call this small fuel tank a day tank

and i will illustrate how i would do a weight based solution
set the tank up on some sort of balance beam with limit switches at the high
and low mark, these switches will be used to do two things, one is to control a small pulse
electric fuel pump to fill the tank to the upper limit and also provide a reference signal to your puter
to tell it that the fill cycle is complete.  the lower limit will turn on the pump and send a reference signal
that a fill cycle has started.

the fill weight can be calibrated easy enough to determine exactly how many grams it takes to function both
limit switches, and the puter can keep track of time, load levels and do the calculations, and post a total
bsfc for each cycle,

if the cycles are short in duration one should be able to get a chart that would be useful in determining bsfc
at various load levels on the engine.

as for doing in in volume, you simply could use a brass toilet float to control the limit switches and calibrate by volume
between on and off cycles.

the key is to log only full cycles, and forget the part cycles and not being relavent.

it appears you want to do logging over the long run and not short run tests anyway, so this looks to me like a possible solution
that could be done fairly inexpensively and will be as accurate as your attention to detail.

bob g

[dubbleUJay]

it appears you want to do logging over the long run and not short run tests anyway, so this looks to me like a possible solution
that could be done fairly inexpensively and will be as accurate as your attention to detail.

bob g

Thanx again Bob,
Actually, I wanted the measuring to be for both, long & short runs, so that anyone can use it, depending on their setup. I'm not just thinking of my specific setup.
Come high or low water, I'm going to build this thing if I can, I'm just trying to make it universal and easy as far as possible from the beginning.
Obviously if it cannot be done a simple way, it cant and I'll have to look at something else. 

[ndavid79]

WildA$$IdeaTime

What about a drip meter like an IV?
Murphy Drip Meter (pic) + a LED/photodetecter setup to count the drops.
Don't know the max flow rate or if they can be paralleled. Though IIRC my old food pump that used a drip chamber, was at least capable of 400ml/hr.
Viscosity will prolly affect drop volume, so thinking it would require a one time calibration against weight for different fuels.

Murphy drip meter - retail

[dubbleUJay]

WildA$$IdeaTime

What about a drip meter like an IV?
Murphy Drip Meter (pic) + a LED/photodetecter setup to count the drops.
Don't know the max flow rate or if they can be paralleled. Though IIRC my old food pump that used a drip chamber, was at least capable of 400ml/hr.
Viscosity will prolly affect drop volume, so thinking it would require a one time calibration against weight for different fuels.

Murphy drip meter - retail

Not such a "WildA$$Idea" David as I also thought about something to that effect,
well maybe the others would say 2x WildA$$'s makes a whole @$$!


Anyway, I just don't know how one would automatically increase/decrease the flow-rate when the fuel demand varies without making it very difficult

dubbleUJay

[ndavid79]

These are passive devices actually, the natural flow to the fuel pump causes the drip rate. Being sealed, fuel flow stops = drips stop, low flow = slow drips, high flow = fast drips. But at some point drips can't keep up and it become a stream.

[dubbleUJay]

These are passive devices actually, the natural flow to the fuel pump causes the drip rate.

Well that solves that problem, I didn't think of it that way. I'm still reading up on the links you provided, but I presume there's some sort of vacuum involved then or the air gets trapped.
Funny thing is I had a lot of IV's in me during my life and never thought about how they actually work! I suppose when your lying in hospital one's got other things to worry about though!

I'll check it out some more and I don't think counting the drops would be a big problem electronically, my Lister on an IV would look cool though

You've modified your post while I was typing hey! 
That answers my assumption.
I think the maximum flow-rate would be:
1 liter per hour (Just taking an approx. figure of a Lister CS single for argument sake)
thats 1000ml/60min=16.7ml/min we need to get droplets for and not a stream. Lets call it 20ml/min to be on the safe side as the Changfa's uses a lot more fuel. 
I dont even know if that will be enough for them, I'll ask Bob