Fuel flow measurement on small diesel engines

Rogershaw said:
Regarding the relationship of fuel flow to air flow. A constant speed diesel generator will tend to have a constant air flow as the speed there for the air sucked in at each cycle would be the same but as the load increases from the alternator the governor moves the injector pump rack to allow more fuel in to maintain the set speed. So in this case the fuel flow to air intake flow cannot be constant.
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+1
 
I had a bit of a look on the web just to see if there was anything interesting. Obviously considered a fishing safety issue as Seafish conducted a study a few years ago.

http://www.seafish.org/media/Publications/FS25_03_09_Fuel_Flow_Meters_incl_Turnkey.pdf

Interesting information. They think it is important that you have a bypass, in case a meter fault stops the flow (bit of a bugger in a F10 with the nets down). They've also compared different flow detection methods. The suppliers of the meters tested are listed, so that might be handy if looking for a supplier.
 
A fuel flow meter in the line from the tank would be of little use as only a small amount of the flow goes to the injectors the reminder returns to tank on most marine engines.
I remember a similar thread some time ago where it was suggested two meters would be required. One in the supply pipe and one in the return pipe with a difference calculator used to feed a display.
 
Yes that is interesting but looking at page 6 where it compares the various meters tested tend to be for higher hp engines so we would be working at the lower , less accurate end of the range. I am looking for some meter with a max fuel flow in the 15-20 litres / hr range. The closest is the flowscan which I know about and will look at again.

Thks for the info.
 
theoldsalt said:
A fuel flow meter in the line from the tank would be of little use as only a small amount of the flow goes to the injectors the reminder returns to tank on most marine engines.
I remember a similar thread some time ago where it was suggested two meters would be required. One in the supply pipe and one in the return pipe with a difference calculator used to feed a display.
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Well yes so if you have a set up like this then 2 of the pulse turbine type flow transducers would be OK as the flow and returns would be closer to the maximum rated flow of the transducers and the difference calculated being below the accurate working range of any available transducer. My engines have a very low if any return so I need to transducer where the max flow of the transducer is closer to the consumption of the engine.

Thks for the info
 
I'm interested in what you are trying to achieve with the flow meter. Is it to find the most economical revs, or is it a means of estimating fuel used? With the generator, the revs will be fixed, but of course the amount of fuel used will depend on the demand. I wouldn't like to think that you were going to go to the trouble of installing multiple fuel flow meters, to give an idea of fuel remaining in the tank(s), for which there are much simpler and cheaper solutions.

I know that with the system installed in my car, it gives an indication of the mpg, and therefore probably encourages me to drive economically, but I'm not sure how that translates to boat use.

Just interested.
 
Its not may generator I am interested it is my main engine. If I can find a way to determine fuel usage accurately I can then feed it into my boat computer and determine the most economical cruising speed. Its also an interesting retirement project when I am stuck at home and not on my boat sailing.
 
Rogershaw said:
My engines have a very low if any return so I need to transducer where the max flow of the transducer is closer to the consumption of the engine.
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I did wonder that if you had a sealed day tank and fed the return to that, you could measure flow from the main tank to day tank by putting the meter in that link. Tank would need to be sealed and reasonably thick-walled so that flow into it equates to nett flow out.

Not sure I'd want that as a permanent arrangement on my boat, but if you're just planning to carry out a series of experimental measurements to determine fuel consumption under various conditions it might be OK.
 
Rogershaw said:
Ford Falcon by any chance, mine was an XR6 4l straight 6.
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Yes good guess Roger. A Ford Territory. Falcon gear in a SUV body. Did you know by the end of next year all Oz car manufacture will cease. Outdone by the Japanese Koreans Chines etc. Thats Ford, GM and Toyota all closing down. sad olewill
 
Have you thought of a home built ultra sonic system? Commercial solutions seem to have a slow (0.2 second) response time, so might either account for pulsed flow or fail because of it. A home built system with PIC might well be able to measure the pulses, particularly with the doppler set up.

edit add:

One big bonus with ultra sonic flow measurement is that it can be non-invasive, so zero problems with the detector restricting/blocking fuel flow.
 
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Dougal Tolan said:
Have you thought of a home built ultra sonic system? Commercial solutions seem to have a slow (0.2 second) response time, so might either account for pulsed flow or fail because of it. A home built system with PIC might well be able to measure the pulses, particularly with the doppler set up.

edit add:

One big bonus with ultra sonic flow measurement is that it can be non-invasive, so zero problems with the detector restricting/blocking fuel flow.
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I came across these while looking for suppliers of very small venturis but not investigated further. I also came across vortex low measuring systems and again not looked at that type yet.

My interest n venturis gos back to my fluid mechanics days and the fact that it is very easy to prove the concept using a U tube manometer and it it look OK to go for one of those differential pressure chips connected to a PIC or the like

Not found any off the shelf small venturis vet so may have a go at making one from perspex rod just to prove concept.
 
If you have quite a high return flow you will be subtracting two numbers that are close to being the same, you will need very accurate flow measurement to get any sort of accuracy with that.
 
gordmac said:
If you have quite a high return flow you will be subtracting two numbers that are close to being the same, you will need very accurate flow measurement to get any sort of accuracy with that.
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Thats why you need a transducer where the maximum capacity of the transducer is close to the maximum flow rate of the engine as accuracy is always quoter as a percentage of the maximum transducer flow rate.

If you have a transducer capable of measuring 100 lt/hour at 0.5% accuracy the error would be +- 0.5 of a litre but the same transducer measuring 1 lt/hr the 0.5 litre error would now be 50% which is totally unacceptable.

This is the problem in a nutshell and together with some of the transducer types do not measure very low flow rates or are too expensive fore small engined pleasure boat use.

The ultrasonic flow meters to seem to be able measure down to zero flow rate but are quite expensive to just try out without any confidence that it will work.
 
Having followed this thread and searching from others I have found the following items which may be of use in measuring the fuel flow.

It appears that two the sensors can be attached to the meter which can then be set up to add one of the flows and subtract the second to give the overall flow rate so ideal for a diesel engine with a spill back to tank.

The sensors measure from 0.01 l/min to 3.5 l/min which I think should cover most smallish diesel engines and the meter can be set up to display a range of fuel consumptions in l/min/hr or gallons etc.

And it is not too pricey either at about £175 for the sensors and display.

Sensors:

http://www.conrad-electronic.co.uk/...-Flow-Meter-FCH-m-POM-LC-001-35-Lmin?ref=list

Display:

http://www.conrad-electronic.co.uk/...-Flow-Controller/?ref=bundles&rt=bundles&rb=1

The user manuals for the items are however in German which I haven't been able to read to see if it would work well for this application but from the description of the items I do not see why not.
 
Thks guys the small Conrad flow transducer is a possibility but the lower limit and published accuracy is still a problem.

If you consider the 0.01 lit/min is 0.6 lit/hr and at 1lit/hr per 5 hp rule of thumb that is 3 hp. and if you consider the published accuracy of +- 2% which is normally at max flow that would be +- 0.02 lit/min so that does not show good accuracy of low flow rates and as there is no accuracy v flow rate chart how accurate would the reading be.

This is the one posted with the 1mm nozzle max flow 1 lit/min 60 lit/hr which is 300 hp. So my 63 max hp say cruising at 40hp this is less than 15% of the flow meter capacity where the accuracy would be questionable IMHO

Any one disagree with my assumptions please correct me.
 
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I suspect one issue will be that the flows, particularly the return, are pulsed, not steady.
An analogue sensor might need quite a lot of bandwidth to capture the detail of the waveform.
You may also find issues with turbulence in the pipes affecting the local pressure at some flow rates/engine speeds.
You might need a lot of calibration factors.
 
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