Fuel Monitoring

[Marco69]

Many thanks for all the replies re fuel sender. I have another topic, I have many years experience with industrial instrumentation and have at little cost 2 flow sensors that provide a pulse output. I also have 2 digital counters that will read the pulses as litres. The counters are totalisers and therefor do not give a per hour reading. After much research I have found it difficult to ascertain at what revs the boat be the most economical. My idea is to set the engine at different speeds for a given period and then check the ground covered over that period. I understand other factors such as weather, tides etc. could effect the readings but at least I would have a good idea.
I have very little experience of engines so I though I would ask the question to see if this is a good idea. I can do all the work myself.

Regards

Mark

 

[nigelmercier]

I ... have at little cost 2 flow sensors that provide a pulse output...

That sounds interesting, I once planned to get a pair to make a fuel rate gauge, using a microcontroller. Can you get more than two?

 

[Marco69]

Hi Nigel

I had the counters from an old project so just bought the sensors from ebay approx. €35 each (Micro Stream model OF200).
I also had the idea of using a small plc with 2 analogue and 2 digital inputs. With this you could use 2 external potentiometers and scale these to the rev counter. If you then set the read out on the PLC to the same as the rev counter you could easily get a total and rate.
Furthermore, if there was a way to read the info from the plotter/GPS via Nema you could have a very economical fuel monitoring system for 2 engines. I see they can cost thousands. My real question, am I missing something. By measuring the distance covered over a period of time and fuel used at a given rev is this all you require?

 

[lpdsn]

If it's a diesel engine, don't forget to take account of the return pipe.

 

[coopec]

Marco

Surely what you are doing will only provide an approximate answer so wouldn't it be better to use the manufacturer's data?
If I am wrong please explain why.

If your motor is a Caterpillar 3208 these figures would be relevant. (I've enlarged the picture as much as I can but I suppose you'll have to use a magnifying glass)

http://www.3208.fr/download/spec-sheets-cat-3208-propulsion.pdf

View attachment 41022

 

[William_H]

Interesting Coopec"s chart showing that best power per gram of fuel is produced at mid revs and mid power. This does not relate however to actual boat speed or distance per gram of fuel. So if the boat is going quite slow then one would imagine max distance per gram of fuel. However as speed is increased the added waste of power trying to overcome hull speed restrictions would reduce miles per gram. I would imagine again that going really slow would probably be inefficient also.
So my guess is that if you motor cruise at about ( square root water line length in feet as expressed in knots) or a little less and if your prop pitch is set for an appropriate engine RPM at that speed ie from Coopec's chart about 1800 RPM then you would be close to max distance per gram of fuel.
I am assuming that it is not a very light weight planing hull which may give economy on the plane. (but I doubt it)
Use of 2 fuel flow sensors one for supply and one for return feeding a microprocessor along with GPS speed data with some appropriate algorythms would show best economical cruise speed. good luck olewill

 

[boatmike]

I have a "Floscan" metering system on my boat. I have two 200HP Volvo TAMD41A engines so the rate of fuel burn is of more than passing interest! It cost me about £1700 to buy but I see no reason why you couldn't do the same if you have the components and you can look it up on the internet I guess.
The basic system has a flowmeter on the delivery and return pipes. There are some quite large pressure dampers fitted before each without which the fluctuations in readings cause errors. The electronics deduct the return rate from the delivery rate to give net burn which is the basic system. On top of that because mine is a twin engine setup there are two gauge heads which give the burn in both engines per hour and add them together. There is also a connect to the Chartplotter which gives distance run so I get either litres pur hour or litres per Nm. Many would think what I spent to fit this was unjustified but when you have one fitted it allows you to adjust to best burn conditions which vary with wind, tide and sea state to a very surprising degree. Very often going too slow gives a higher burn rate than speeding up a bit. As an ex raggie I am very used to planning for best wind and tide passages and a lot of MoBo owners don't seem to do this. They just open the throttle and go! I think my Floscan is already well on the way to paying for itself and if you can rig something up yourself for less money you will be well pleased with the result even if you do the calculations manually...... Look at the Floscan system and if you are ever around in the Solent come and see mine for inspiration! Good luck!

 

[nigelmercier]

If it's a diesel engine, don't forget to take account of the return pipe.

If figured that's why he needed two sensors, I may be wrong.

An alternative is to use a Mass Air Flow sensor in the air intake, as the airflow is directly related to the fuel intake. I went as far as buying one, but like many projects, it is waiting in my box of bits.

 

[Trundlebug]

An alternative is to use a Mass Air Flow sensor in the air intake, as the airflow is directly related to the fuel intake.

Hmm not sure that's correct.

In a diesel engine MAF is directly proportional to revs.
Fuel flow varies enormously for a given revs depending upon engine load.

 

[Marco69]

Many thanks for the help, this is why a forum is so good. I would never have thought about the fuel return. I think for this year I might do one engine and see what the figures are like.